Atom lithography

Abstract

A method of performing atom lithography, the method comprises: forming a self-assembled monolayer comprising a plurality of SAM molecules by exposing a substrate surface to a plurality of SAM precursors, wherein the plurality of SAM precursors comprise a backbone having: a surface attachment moiety (SM) at or proximate to an end of the backbone and configured to attach the SAM precursor to a substrate when forming a self-assembled monolayer; a cleavage moiety (CM); and an electron directing moiety (EDM) comprising a dipole; and directing a source of metastable atoms (100) at the self-assembled monolayer (Figure 1b), transferring energy from the metastable atoms to the self-assembled monolayer (Figure 1c) to break a bond within the cleavage moiety of at least one of said one or more SAM molecules such that part of the one or more SAM molecules is removed to provide a modified self-assembled monolayer (Figure 1d), wherein the modified self-assembled monolayer comprises one or more broken SAM molecules attached to the substrate surface, and wherein preferably one of the following conditions may be satisfied, either wherein the cleavage moiety (CM) comprises the electron directing moiety (EDM) or wherein the electron directing moiety (EDM) and the cleavage moiety (CM) are distinct.

Description

[0001] Att. Ref.: P382016WO

[0002] ATOM LITHOGRAPHY

[0003] Technical Field

[0004] This invention relates to atom lithography. More specifically, although not exclusively, this invention relates to a method for atom lithography on a substrate comprising a selfassembled monolayer. The invention also relates to a SAM precursor and a substrate comprising a self-assembled monolayer formed from one or more SAM molecules (e.g. provided by exposing the SAM precursors to a substrate).

[0005] Background

[0006] Manufacturing semiconductor devices, such as complementary metal-oxide semiconductor (CMOS) devices, typically requires the use of lithography techniques, usually photolithography. Photolithography typically uses light to transfer a pattern from a patterning mask to a chemical layer coated on a substrate (e.g. a semiconductor substrate). This chemical layer is often referred to as the resist layer. The targeted interaction between the electromagnetic radiation and the resist layer causes a chemical change in the exposed areas of the resist layer which then alters how the resist layer behaves compared to unexposed areas in subsequent steps in the manufacturing process. For example, the unexposed areas may be more or less sensitive to a chemical etchant leading to the selective removal of the unexposed areas vs the exposed areas, or vice versa. For example, the unexposed areas may be more or less sensitive to further reactants or exposed to the substrate such that layers of the further reactants may be selectively deposited on parts of the substrate and not others. Lithography techniques therefore allow patterning of a substrate.

[0007] Photolithography has been favoured in recent years for such applications because it enables high throughput fabrication compared to direct write methods such as electron beam lithography which has a low throughput and, as such, is considered unsuitable for large-scale industrial fabrication. However, the pattern resolution achievable by electron beam lithography far exceeds that of photolithography. Accordingly, there currently exists a compromise between throughput and resolution. However, as the size of discrete transitions decreases to keep up with Moore’s law, the need for techniques with higher resolution are becoming more pressing, requiring further advancements in lithography techniques.One way to address the resolution issue is to change the wavelength of the incidental light. In doing so the wavelength of incident light has been increasingly reduced towards extreme ultraviolet (EUV) wavelengths. This can improve the theoretical critical dimension size and resolution of a nanostructure or pattern, whilst retaining high throughputs suitable for industrial process. However, it is extremely expensive to implement due to the equipment required. Furthermore, yet further reductions in wavelength towards the X-ray region to keep up with Moore’s law is anticipated to cause various problems such as increased substate damage (due to the higher energy of low wavelength light). Moreover, eventually the wavelength of light will reach and exceed the ionisation threshold of the resist material such that any improvements in resolution will be negated by increased photoelectron blur which is evidenced to occur around 6 nm. Thus, current techniques are considered to have a theoretical limitation to around 6-7 nm half-pitch.

[0008] Alongside developments in the radiation used in photolithography, there has also been a focus on developing improved resist materials which provide suitable photochemistry at desirable photon energies. Furthermore, the need to develop very thin resist films (e.g. sub 30 nm) is increasingly desirable. However, this has led to challenges in controlling resist layer uniformity (in both thickness and composition) which, in turn, can lead to patterning edge roughness and loss of pattern control.

[0009] Recently, self-assembled monolayers (SAMs) comprising a plurality of SAM molecules derived from SAM precursors have been explored as resist materials to seek to provide improvements in at least some of the aforementioned problems. However, it has been difficult to find SAM precursors / molecules that are selective to EUV photon energies and that can be used for both positive and negative tone photolithography techniques.

[0010] It would therefore be advantageous to provide a lithography technique which allows the semiconductor industry to keep pace with Moore’s law.

[0011] The objective of the present invention to address at least some, if not all, of the above-mentioned problems.

[0012] Summary of Invention

[0013] Accordingly, a first aspect of the invention provides a method for atom lithography (e.g. for the manufacture of semiconductor devices), the method comprising:directing a source of metastable atoms at a self-assembled monolayer arranged on a substrate surface, wherein the self-assembled monolayer comprises a plurality of one or more SAM molecules, wherein each SAM molecule comprises a backbone having:

[0014] i. a surface attachment moiety (SM) at or proximate an end of the backbone and configured to attach the SAM molecule to a substrate when forming a selfassembled monolayer;

[0015] ii. a cleavage moiety (CM); and

[0016] iii. an electron directing moiety (EDM) comprising a {e.g. permanent) dipole; and

[0017] transferring energy from the metastable atoms to the self-assembled monolayer to break a bond within the cleavage moiety of one or more SAM molecules such that at least part of the self-assembled monolayer is removed.

[0018] In a second aspect, the method of performing atom lithography may comprise:

[0019] forming a self-assembled monolayer comprising a plurality of SAM molecules by exposing a substrate surface to a plurality of SAM molecules, wherein the plurality of SAM molecules comprise a backbone having:

[0020] i. a surface attachment moiety (SM) at or proximate to an end of the backbone and configured to attach the SAM molecule to a substrate when forming a selfassembled monolayer;

[0021] ii. a cleavage moiety (CM); and

[0022] iii. an electron directing moiety (EDM) comprising a dipole; and

[0023] directing a source of metastable atoms at the self-assembled monolayer, transferring energy from the metastable atoms to the self-assembled monolayer to break a bond within the cleavage moiety of at least one of said one or more SAM molecules such that part of the one or more SAM molecules is removed to provide a modified selfassembled monolayer,

[0024] wherein the modified self-assembled monolayer comprises one or more broken SAM molecules attached to the substrate surface, and

[0025] wherein preferably one of the following conditions may be satisfied, either wherein the cleavage moiety (CM) comprises the electron directing moiety (EDM) or wherein the electron directing moiety (EDM) and the cleavage moiety (CM) are distinct.Atom lithography utilises neutral atoms (e.g. noble gas atoms such as helium or argon) provided in a metastable excited state ( / .e. metastable atoms). As such, interaction between the metastable atom and the substrate surface results in energy being transferred from the metastable atom (and its simultaneous deexcitation) to the substrate surface and / or a resist layer provided thereon. As the metastable atoms have sufficient energy to react with a resist layer, the present inventors have thus appreciated that there are multiple advantages associated with the application of atom lithography, especially with respect to semiconductor device manufacture.

[0026] Most notably, the methods of the first and second aspects both provides at least the following advantages:

[0027] 1. it may be used with a patterning mask such that high throughput patterning is attainable;

[0028] 2. the energy of the metastable state is sufficient to react with the resist layer but has low penetration depth when compared to EUV lithography, thus reducing the likelihood of substrate damage; and

[0029] 3. the metastable atoms have a negligible wavelength which results in minimal diffraction when passing through a mask. Accordingly, improved resolution is possible. Indeed, the inventors have hypothesised that nanofabrication towards the single nanometre resolution may be attainable.

[0030] However, a limitation of the application of atom-based lithography is the identification of suitable resist materials. Typical applications of atom lithography use simple resist materials that can undergo the lithographic process but yield poor sensitivity, poor patterning resolution and are limited in terms of reactivity to post lithographic steps required to obtain substrate patterning.

[0031] The present inventors have surprisingly found a novel family of self-assembled monolayer precursor molecules ( / .e. SAM precursors) that may be used to provide a self-assembled monolayer as a resist layer for atom lithography. This allows the present invention to also take advantage of the benefits offered by self-assembled monolayers as resist layers such as improved uniformity in both composition and thickness, ultimately providing an improved patterning process.Thus, in a third aspect of the present invention, a SAM precursor is provided (e.g. for forming the self-assembled monolayer on the substrate in the first or second aspects) comprising a backbone having the following moieties:

[0032] i. a surface attachment moiety (SM) at or proximate a first end of the backbone and configured to attach the SAM molecule to a substrate when forming a self-assembled monolayer;

[0033] ii. a cleavage moiety (CM); and

[0034] iii. an electron directing moiety (EDM) comprising a {e.g. permanent) dipole.

[0035] In a fourth aspect of the present invention, a bridged group {e.g. pair) of SAM precursors is provided e.g. for forming the self-assembled monolayer on the substrate in the first or second aspects) comprising two or more SAM precursors {e.g. of the third aspect) and a bridging moiety, wherein the bridged group comprises:

[0036] i. two or more surface attachment moieties (SM), wherein each of the two or more surface attachment moieties are configured to attach the bridged group to a substrate when forming a self-assembled monolayer;

[0037] ii. two or more cleavage moieties (CM); and

[0038] iii. one or more electron directing moieties (EDM) comprising a {e.g. permanent) dipole.

[0039] It will be appreciated that by exposing a substrate to a plurality of the SAM precursors of the third aspect and / or a plurality of the bridged group of SAM precursors of the fourth aspect, a self-assembled monolayer will be formed comprising a plurality of SAM molecules ( / .e. the SAM precursors when attached to the substrate) and / or a plurality of bridged groups of SAM molecules ( / .e. the bridged group of SAM precursors when attached to the substrate). Without wishing to be limited by theory, the present inventors have surprisingly found that a self-assembled monolayer formed of the SAM precursors and / or bridged groups of the second and / or third aspects, upon interaction with a metastable atom, results in selective cleavage of a bond within the cleavage moiety (CM) to provide two well defined and reliably formed portions of the SAM molecule, i.e. a removable portion and a portion that remains attached to the substrate surface. This allows the method described herein to provide a patterned self-assembled monolayer with well-defined characteristics and molecular heights.

[0040] It will be appreciated that in some embodiments, the SAM precursors of the third aspect may be a precursor to the formation of the bridged group of SAM precursors of the fourthaspect. For example, the bridged group of the fourth aspect may be formed by reacting two or more SAM precursors of the third aspect with a bridging molecule comprising two or more functional groups configured to react with a group {e.g. the EDM group) on each of the SAM precursors to join them. For example, to provide a bridged pair of SAM precursors, two SAM precursors may be reacted with a difunctional bridging molecule comprising two functional groups each configured to react with a group of different SAM precursors to functionally join two SAM precursors together.

[0041] For example, before the substrate surface is exposed to the plurality of SAM precursors, the plurality of SAM precursors are reacted with a bridging molecule comprising multiple functional groups to provide one or more bridged pairs of SAM precursors, wherein the substrate surface are exposed to the one or more bridged pairs of SAM precursors;

[0042] wherein each of the functional groups is configured to react with a functional group present on each of the two SAM precursors to provide a bridged group,

[0043] wherein the bridged group comprises two or more cleavage moieties and one or more electron directing moieties,

[0044] optionally, wherein the bridging molecule provides one or more of said one or more electron directing moieties.

[0045] Furthermore, the present inventors have surprisingly and advantageously found that the presence of the electron directing moiety (EDM) improves the efficiency and the selectivity of the atom lithography process. Again, without wishing to be bound by theory, it is thought that the (e.g. strength and / or direction of the) dipole of the electron directing moiety encourages the Penning ionisation reaction and acts as a harpooning moiety to generate an electron and / or direct the electron generated by interaction with the metastable atom in a desired direction along the SAM molecule to induce breakage of the bone in the cleavage moiety. In addition, the electron directing moiety may be also considered to be a “sensitiser moiety” that increases the emitted electron yield of the Penning ionisation reaction.

[0046] Within the meaning of the present invention, a dipole is any dipole moment of 0.1D or greater, preferably 0.5D or greater, more preferably 1 D or greater. The dipole moment may be across a single bond (e.g. an -OH bond) or may be a net dipole moment across all or part of a moiety or functional group. The dipole moment is preferably a permanent dipole moment having a permanent charge separation, e.g. across at least one bond of a molecule.In a fifth aspect of the present invention, a substrate comprising a self-assembled monolayer is provided {e.g. suitable for use in the method of the first or second aspects), wherein the self-assembled monolayer comprises a plurality of one or more distinct SAM molecules {e.g. originating from the third aspect), wherein each SAM molecule comprises a backbone having:

[0047] i. a surface attachment moiety (SM) at or proximate an end of the backbone and configured to attach the SAM molecule to a substrate when forming a self-assembled monolayer;

[0048] ii. a cleavage moiety (CM); and

[0049] iii. an electron directing moiety (EDM) comprising a e.g. permanent) dipole; preferably, wherein the backbone has one of the following linear arrangements of moieties: SM-R1-CM-R2-EDM-X or SM-R1-EDM-R2-CM-X;

[0050] wherein R1 comprises an aliphatic and / or aromatic group having between 1 and 20 carbon atoms;

[0051] wherein R2 comprises an aliphatic and / or aromatic group having between 1 and 20 carbon atoms; and

[0052] wherein X is optional such that when X is not present the electron directing moiety (EDM) or the cleavage moiety (CM) terminate the backbone, wherein, when X is present, X is selected to be one of the following groups:

[0053] a group R3 comprising an aliphatic group and / or aromatic group having between 1 and 20 carbon atoms ;

[0054] a group R3’ comprising an aromatic group; or

[0055] a hydrogen atom or a deuterium atom

[0056] wherein each group R3 or R3’ may each optionally comprise a terminal reactive group Y, wherein Y is selected from a carboxylic acid group, amine group, amide group, ester group, alkene group, alkyne group or azide group;

[0057] and optionally, wherein the backbone comprises a fluorophore, more optionally, wherein one of R1, R2, R3, R3’, Y or EDM comprises the fluorophore.

[0058] In a sixth aspect of the present invention, a substrate comprising a self-assembled monolayer is provided {e.g. suitable for use in the method of the first or second aspects), wherein the self-assembled monolayer comprises one or more bridged groups {e.g. pairs) of SAM molecules {e.g. originating from the fourth aspect), wherein each bridged group(e.g. pair) comprises two or more (e.g. two for a bridged pair) SAM molecules and a bridging moiety, and wherein the bridged group (e.g. pair) comprises:

[0059] i. two or more surface attachment moieties (SM), wherein each of the two or more surface attachment moieties is configured to attach each of the two SAM molecules to the substrate;

[0060] ii. two or more cleavage moieties (CM); and

[0061] iii. one or more electron directing moieties (EDM) (e.g. each) comprising a (e.g.

[0062] permanent) dipole;

[0063] preferably, wherein the backbone has one of the following linear arrangements of moieties: SM-R1-CM-R2-EDM-X or SM-R1-EDM-R2-CM-X;

[0064] wherein R1 comprises an aliphatic and / or aromatic group having between 1 and 20 carbon atoms;

[0065] wherein R2 comprises an aliphatic and / or aromatic group having between 1 and 20 carbon atoms; and

[0066] wherein X is optional such that when X is not present the electron directing moiety (EDM) or the cleavage moiety (CM) terminate the backbone, wherein, when X is present, X is selected to be one of the following groups:

[0067] a group R3 comprising an aliphatic group and / or aromatic group having between 1 and 20 carbon atoms ;

[0068] a group R3’ comprising an aromatic group; or

[0069] a hydrogen atom or a deuterium atom

[0070] wherein each group R3 or R3’ may each optionally comprise a terminal reactive group Y, wherein Y is selected from a carboxylic acid group, amine group, amide group, ester group, alkene group, alkyne group or azide group;

[0071] and optionally, wherein the backbone comprises a fluorophore, more optionally, wherein one of R1, R2, R3, R3’, Y or EDM comprises the fluorophore.

[0072] Optionally, the bridged group of SAM molecules comprises two SAM molecules, thus forming a bridged pair, wherein the bridged pair comprises:

[0073] i. two surface attachment moieties (SM), at each end of the bridged pair, wherein each of the two surface attachment moieties (SM) is configured to attach one of the two SAM molecules to the substrate;

[0074] ii. two cleavage moieties (CM); and

[0075] iii. one or more electron directing moieties (EDM), (e.g. each) comprising a (e.g.

[0076] permanent) dipole;preferably, wherein the backbone has one of the following linear arrangements of moieties: SM-R1-CM-R2-EDM-X or SM-R1-EDM-R2-CM-X;

[0077] wherein R1 comprises an aliphatic and / or aromatic group having between 1 and 20 carbon atoms;

[0078] wherein R2 comprises an aliphatic and / or aromatic group having between 1 and 20 carbon atoms; and

[0079] wherein X is optional such that when X is not present the electron directing moiety (EDM) or the cleavage moiety (CM) terminate the backbone, wherein, when X is present, X is selected to be one of the following groups:

[0080] a group R3 comprising an aliphatic group and / or aromatic group having between 1 and 20 carbon atoms ;

[0081] a group R3’ comprising an aromatic group; or

[0082] a hydrogen atom or a deuterium atom

[0083] wherein each group R3 or R3’ may each optionally comprise a terminal reactive group Y, wherein Y is selected from a carboxylic acid group, amine group, amide group, ester group, alkene group, alkyne group or azide group;

[0084] and optionally, wherein the backbone comprises a fluorophore, more optionally, wherein one of R1, R2, R3, R3’, Y or EDM comprises the fluorophore.

[0085] The bridged group may comprise three or more SAM molecules, e.g. from three to six SAM molecules.

[0086] In a seventh aspect of the present invention, a substrate comprising a self-assembled monolayer is provided, wherein the self-assembled monolayer comprises one or more distinct SAM molecules and one or more bridged groups of SAM molecules, wherein: the one or more distinct SAM molecules (e.g. originating from the third aspect), wherein each SAM molecule comprises a backbone having:

[0087] i. a surface attachment moiety (SM) at or proximate an end of the backbone and configured to attach the SAM molecule to a substrate when forming a selfassembled monolayer;

[0088] ii. a cleavage moiety (CM); and

[0089] iii. an electron directing moiety (EDM) comprising a (e.g. permanent) dipole; and the one or more one or more bridged groups (e.g. pairs) of SAM molecules (e.g. originating from the fourth aspect), wherein each bridged group (e.g. pair) comprises twoor more (e.g. two for a bridged pair) SAM molecules and a bridging moiety, and wherein the bridged group {e.g. pair) comprises:

[0090] i. two surface attachment moieties (SM), at each end of the bridged pair, wherein each of the two surface attachment moieties (SM) is configured to attach one of the two SAM molecules to the substrate;

[0091] ii. two cleavage moieties (CM); and

[0092] iii. one or more electron directing moieties (EDM), {e.g. each) comprising a e.g.

[0093] permanent) dipole.

[0094] In an eighth aspect of the present invention, a method of forming a self-assembled monolayer comprising a bridged group (e.g. pair) of SAM molecules on a substrate is provided, wherein the method comprises:

[0095] A. forming a self-assembled monolayer on a substrate from a plurality of SAM molecules (e.g. as defined in the third aspect); and

[0096] B. bridging two or more of the plurality of SAM molecule molecules assembled on the substrate with a bridging moiety to form a bridged group (e.g. pair) of SAM molecules {e.g. as defined in the fourth aspect) by reacting the two or more of the plurality of SAM molecules with one or more bridging molecules.

[0097] It will therefore be appreciated that the method of the eighth aspect may form part of the method of the first or second aspects. For example, the first or second aspects of the invention may comprise the step of bridging two or more of the plurality of SAM molecule molecules before the step of transferring energy from the metastable atoms to the selfassembled monolayer is performed.

[0098] In a ninth aspect of the present invention, a method of forming a self-assembled monolayer comprising a bridged group (e.g. pair) of SAM molecules on a substrate is provided, wherein the method comprises:

[0099] A. providing a bridged group (e.g. pair) of SAM precursors by reacting two or more SAM precursors with a bridging molecule, wherein the bridged group (e.g. pair) comprises:

[0100] i. two or more surface attachment moieties (SM), wherein each of the two or more surface attachment moieties is configured to attach the bridged group to the substrate;

[0101] ii. two or more cleavage moieties (CM); andiii. one or more electron directing moieties (EDM) (e.g. each) comprising a (e.g. permanent) dipole;

[0102] B. forming a self-assembled monolayer on a substrate by exposing the substrate to a plurality of the bridged groups of SAM precursors.

[0103] In other words, the eighth aspect of the present invention provides a method whereby the step of bridging two or more SAM molecules with a bridging molecule arises after the substrate has been exposed to the plurality of SAM precursors to provide a plurality of SAM molecules assembled on the substrate, i.e. the bridged group of SAM molecules is formed in situ. In contrast, the ninth aspect of the present invention provides a method whereby the self-assembled monolayer is formed directly from bridged groups of SAM precursors, i.e. the bridged group of SAM precursors is formed ex situ.

[0104] For the avoidance of doubt, any of the following optional features described herein apply equally to all aspects of the invention described above. For example, the substrates of the fifth, sixth and seventh aspects may comprise any one or more features of the SAM precursors of the third aspect and / or the features of the bridged group of SAM precursors of the fourth aspect. Similarly, the bridged group of SAM precursors of the fourth aspect may include one or more SAM precursors of the third aspect and thus the features related thereto. Moreover, the method of the first, second, eighth and ninth aspects may comprise any one or more features or steps relevant to one or more features of the SAM molecule of the second aspect, the bridged group of SAM molecules of the seventh aspect or the substrates of the third and fourth aspect which are suitable for use as part of the method. The following optional features are combinable in any suitable and / or desirable combination to provide various embodiments falling within the scope of the present invention.

[0105] Optionally, the cleavage moiety comprises at least one bond configured to break when energy is transferred from one or more metastable atoms directed at a self-assembled monolayer comprising the SAM molecule. Optionally, the cleavage moiety comprises plural bonds configured to break when energy is transferred from one or more metastable atoms directed at the self-assembled monolayer comprising the SAM molecule. Optionally, the cleavage moiety comprises one bond that is configured to break when energy is transferred from one metastable atom directed at a self-assembled monolayer comprising the SAM molecule. Optionally, the cleavage moiety comprises two or more bonds that are configuredto break when energy is transferred from a single metastable atom directed at a selfassembled monolayer comprising the SAM molecule. Optionally, the cleavage moiety comprises two or more bonds that are configured to break, wherein each of the two or more bonds are configured to break when energy is transferred from a single metastable atom directed at a self-assembled monolayer comprising the SAM molecule.

[0106] Optionally, the cleavage moiety (e.g. of each of the one or more SAM molecules) is or comprises one or more of: a disulfide bond, a sulfonamide moiety (e.g. a N-tosyl carboxamide moiety) or a diazene moiety. Optionally, the cleavage moiety (e.g. of each of the one or more SAM molecules) is configured such that, when sufficient energy is transferred to the SAM molecule (e.g. by directing a metastable atom at the self-assembled monolayer), a bond in the cleavage moiety breaks to provide a portion of a SAM molecule that remains attached to the substrate and a portion of the SAM molecule that is removable or is removed. Optionally, the portion that remains attached to the substrate terminates in a sulfhydryl (-SH) group.

[0107] Optionally, the cleavage moiety comprises the electron directing moiety. For example, the cleavage moiety may comprise the dipole ( / .e. of the electron directing moiety) proximate (e.g. adjacent to, e.g. directly connected to) the bond configured to break. In some examples, the bond(s) configured to break within the cleavage moiety may have a dipole moment extending thereacross.

[0108] Optionally, the electron directing moiety is distinct from the cleavage moiety. In other words, the electron directing moiety and the cleavage moiety may be spatially separated along the backbone. In some examples, spatially separated may mean that there are 2 or more (e.g. carbon-carbon) bonds located between the electron directing moiety (e.g. the dipole containing functional group) and the cleavage moiety (e.g. the bond configured to break). For example, the electron directing moiety may be connected to the cleavage moiety by a linker group (e.g. a group comprising or consisting of an aliphatic group (e.g. a hydrocarbon chain) or an aromatic group). Optionally the linker group comprises a (e.g. linear) chain of at least 3 atoms such that there are at least two bonds between the electron directing moiety (e.g. the dipole containing functional group) and the cleavage moiety (e.g. the bond configured to break). Optionally the linker group comprises a linear chain of at least 4 (e.g.

[0109] 5, e.g. 6, e.g. 7, e.g. 8, e.g. 9, e.g. 10, e.g. from 4 to 20) atoms such that there is at least 3 (e.g. 4, e.g. 5, e.g. 6, e.g. 7, e.g. 8, e.g. 9, e.g. from 3 to 19) bonds between the electrondirecting moiety (e.g. the dipole containing functional group) and the cleavage moiety (e.g. the bond configured to break). The bonds may be single bonds, double bonds, conjugated bonds or triple bonds.

[0110] Optionally, following removal of at least part of the self-assembled monolayer the selfassembled monolayer comprises one or more unbroken SAM molecules comprising the surface attachment moiety, the cleavage moiety and the electron directing moiety; and one or more broken SAM molecules comprising the surface attachment moiety and an exposed moiety resulting from breaking the bond in the cleavage moiety. Optionally, the broken SAM molecules comprise the electron directing moiety ( / .e. the electron directing moiety and / or dipole was unaffected by scission of the bond in the cleavage moiety). Optionally, the broken SAM molecules do not include the electron directing moiety.

[0111] Optionally, the method may further comprise reacting the exposed moiety with a reactant or deposit (e.g. nanoparticles, e.g. metals, e.g. metal nanoparticles, e.g. a gold nanoparticle, e.g. alkenes, e.g. maleimides, e.g. polymer brushes, e.g. functionalised silsesquixoanes, e.g. thiols, e.g. oxides, e.g. inorganic oxides such as silicon oxide, aluminium oxide or titanium oxide) to modify the reactivity or functionality of the one or more broken SAM molecules. In so doing, the contrast of the pattern following a subsequent etching step may be enhanced. For example, the method may comprise a negative tone post-patterning deposition step.

[0112] Optionally, the SAM molecules comprise a terminal functional group or exposed moiety at or proximate to the surface of the self-assembled monolayer. In such a scenario, following removal of at least part of the self-assembled monolayer the self-assembled monolayer comprises one or more unbroken SAM molecules comprising the surface attachment moiety, the cleavage moiety, the electron directing moiety and the terminal functional group or exposed moiety; and one or more broken SAM molecules comprising the surface attachment moiety and a moiety resulting from breaking the bond in the cleavage moiety. Optionally, the broken SAM molecules comprise the electron directing moiety ( / .e. the electron directing moiety and / or dipole was unaffected by scission of the bond in the cleavage moiety). Optionally, the broken SAM molecules do not include the electron directing moiety.

[0113] Optionally, the method may further comprise reacting the terminal functional group or exposed moiety with a reactant or deposit (e.g. metals, e.g. metal nanoparticles, e.g. a goldnanoparticle, e.g. alkenes, e.g. maleimides, e.g. polymer brushes, e.g. functionalised silsesquixoanes, e.g. thiols, e.g. oxides, e.g. inorganic oxides such as silicon oxide, aluminium oxide or titanium oxide) to modify the reactivity or functionality of the one or more unbroken SAM molecules. In so doing, the contrast of the pattern following a subsequent etching step may be enhanced. For example, the method may comprise a positive tone post-patterning deposition step.

[0114] Optionally, the one or more broken SAM molecules each comprise the surface attachment moiety and an exposed moiety resulting from breaking the bond in the cleavage moiety. In such examples, the method may further comprise reacting the one or more exposed moieties of the one or more broken SAM molecules with a reactant to modify the reactivity or functionality of the one or more broken SAM molecules. For example, the reactant may be one or more of: a (e.g. metal) nanoparticle such as a gold nanoparticle, alkenes, maleimides, polymer brushes, functionalised silsesquixoanes, thiols, oxides, or inorganic oxides such as silicon oxide, aluminium oxide or titanium oxide. The reactant may thus modify the reactivity such that the broken SAM molecules are more resistant to a chemical etch compared to the unbroken SAM molecules.

[0115] Optionally, after reacting the exposed moieties with the reactant, the method may further comprise exposing the self-assembled monolayer to a chemical etchant and selectively removing one or more of the unbroken SAM molecules.

[0116] Optionally, the method may further comprise forming a deposition layer on top of (at least part of) the self-assembled monolayer. For example, the exposed moieties of the broken SAM molecules may be used to indue or seed deposition of further layers, such as metal (e.g. copper) layers whereas the unbroken SAM molecules are more resistant to said deposition. For example, the unbroken SAM molecules may comprise a terminal functional group or exposed moiety that indues or seeds deposition of further layers, such as metal (e.g. copper) layers, whereas the broken SAM molecules (which do not contain said moieties) are more resistant to said deposition.

[0117] Optionally, the reactant modifies the reactivity such that the broken SAM molecules are more resistant to a chemical etch compared to the unbroken SAM molecules. Optionally, the reactant modifies the reactivity such that the broken SAM molecules are less resistant to a chemical etch compared to the unbroken SAM molecules.Optionally, the reactant comprises an alkene group. Optionally, the reactant is configured to undergo a thiol-ene reaction with a terminating thiol group of the broken SAM molecules. Optionally, the reactant is configured to undergo a Michael addition reaction with the terminating group (e.g. thiol group) of the broken SAM molecules.

[0118] Optionally, the method further comprises exposing the self-assembled monolayer to a chemical etchant and selectively removing one or more of the unbroken SAM molecules. Optionally, the method further comprises exposing the self-assembled monolayer to a chemical etchant and selectively removing one or more of the broken SAM molecules.

[0119] The surface attachment moiety may be a hydrolysable moiety. Optionally, the surface attachment moiety is or comprises: sulphur (e.g. a thiol group), silicon (e.g. a silane, e.g. trichlorosilane (-SiC ), methoxysilane (-Si(OMe)H2), dimethoxylsilane (-Si(OMe)2H), trimethoxysilane (-Si(OMe)s), ethoxysilane (-Si(OEt)H2), diethoxylsilane (-Si(OEt)2H) or triethoxysilane (-Si(OEt)s)) or phosphor (e.g. a phosphonate group) or a carboxyl moiety (e.g. a carboxylic acid moiety).

[0120] The surface attachment moiety, the cleavage moiety and the electron directing moiety may be directly attached. Within the meaning of the present invention, “directly” attached means that an atom of one moiety is bonded to an atom of another moiety. In other embodiments, at least one of moieties may be bound to at least one of the other moieties by a connecting or linker group. For example, the surface attachment moiety may be connected to the cleavage moiety or the electron directing moiety via a connecting or linker group. For example, the cleavage moiety may be connected to the electron directing moiety via a connecting or linker group. The connecting or linker group may be any suitable and / or desirable group. Optionally, the connecting or linker group may be or comprise an aliphatic group (R) or an aromatic group. Optionally, the aliphatic group comprises or consists of a (e.g. linear) hydrocarbon chain.

[0121] The SAM molecule may comprise two or more linker groups. Optionally, each of the moieties ( / .e. the cleavage moiety, the electron directing moiety and the surface attachment moiety) are connected to at least one of the other moieties by at least one of the two linker groups. For example, the cleavage moiety may be connected to the surface attachment moiety by a first linker group and connected to the electron directing moiety by a second linker group. In other words, the cleavage moiety may be located between the electrondirecting moiety and the surface attachment moiety. For example, the electron directing moiety may be connected to the surface attachment moiety by a first linker group and connected to the cleavage moiety by a second linker group. In other words, the electron directing moiety may be located between the cleavage moiety and the surface attachment moiety. Optionally, the linker group may be an aliphatic group (R) or an aromatic group. Optionally, the aliphatic group comprises or consists of a (e.g. linear) hydrocarbon chain.

[0122] In the present invention, an aliphatic hydrocarbon group or chain may comprise or consist of an unsaturated hydrocarbon chain (e.g. a -CnH2n- group or a -CnH2n+i group), a saturated hydrocarbon chain (e.g. a -C2nH2n- group or a -C2nH2n+i group) or a partially saturated hydrocarbon chain (e.g. a chain comprising one or more C=C bonds). The aliphatic hydrocarbon group or chain may be a linear chain or a branched chain. The aliphatic hydrocarbon group may comprise a substituent group (e.g. substituting one or more hydrogens). Preferably, the aliphatic hydrocarbon group comprises only carbon and hydrogen atoms. Optionally, the aliphatic hydrocarbon group comprises from 1 to 12 carbon atoms, e.g. from 1 to 10 carbon atoms, e.g. from 1 to 8 carbon atoms, e.g. from 1 to 6 carbon atoms, e.g. from 1 to 4 carbon atoms, e.g. from 1 to 3 carbon atoms, e.g. from 1 to 2 carbon atoms. Optionally, the aliphatic hydrocarbon group comprises a linear chain of from 1 to 12 carbon atoms, e.g. from 1 to 10 carbon atoms, e.g. from 1 to 8 carbon atoms, e.g. from 1 to 6 carbon atoms, e.g. from 1 to 4 carbon atoms, e.g. from 1 to 3 carbon atoms, e.g. from 1 to 2 carbon atoms.

[0123] The backbone may be terminated by a terminal moiety. Optionally the terminal moiety may comprise or be the cleavage moiety or the electron directing moiety. Optionally, the terminal moiety comprises or consists of an aliphatic group (e.g. a hydrocarbon moiety or chain). For example, the backbone may have the surface attachment moiety at or proximate the first end of the backbone and an aliphatic group at or proximate the second end of the backbone. Optionally, the aliphatic group of the terminal moiety may comprise from 1 and 10 carbon atoms, e.g. from 1 to 8 carbon atoms, e.g. from 1 to 6 carbon atoms, e.g. from 1 to 4 carbon atoms, e.g. from 1 to 3 carbon atoms, e.g. from 1 to 2 carbon atoms. Optionally, the aliphatic group of the terminal moiety may comprise a linear chain of from 1 and 10 carbon atoms, e.g. from 1 to 8 carbon atoms, e.g. from 1 to 6 carbon atoms, e.g. from 1 to 4 carbon atoms, e.g. from 1 to 3 carbon atoms, e.g. from 1 to 2 carbon atoms.The terminal moiety may functionalise the self-assembled monolayer surface. This may allow the SAM molecules to be further functionalised {e.g. react) after formation of the selfassembled monolayer. For example, the SAM molecules may react with protecting groups or bridging molecules as discussed further below. For example, the terminal moiety may comprise a terminal carboxylic acid group, amine group, amide group, ester group, alkene group, alkyne group or azide group.

[0124] The second end of the SAM molecule backbone may be terminated by a terminal aliphatic group (R) attached to the electron directing moiety (EDM), e.g. the backbone is terminated by the group -EDM-R. Optionally, R comprises from 1 to 20 carbon atoms, e.g. from 1 to 18 carbon atoms, e.g. from 1 to 16 carbon atoms, e.g. from 1 to 14 carbon atoms, e.g. from 1 to 12 carbon atoms, e.g. from 1 to 10 carbon atoms, e.g. from 1 to 9 carbon atoms, e.g. from 1 to 8 carbon atoms, e.g. from 1 to 7 carbon atoms, e.g. from 1 to 6 carbon atoms, e.g. from 1 to 5 carbon atoms, e.g. from 1 to 4 carbon atoms, e.g. from 1 to 3 carbon atoms, e.g. from 1 to 2 carbon atoms. Optionally, R is a methyl, ethyl, propanyl, butanyl, pentanyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl group. R may be linear or branched. Optionally, R is linear.

[0125] The inventors have appreciated that modifying the number of carbons (or other atoms and / or moieties) provided between the exposed surface of the self-assembled monolayer (e.g. formed by the terminal moieties of the SAM molecules) and the electron directing moiety advantageously allows the selectivity and / or efficiency of removal of part of the selfassembled monolayer ( / .e. by cleavage of a bond in the cleavage moiety) to be tuned. This provides improved flexibility of the atom lithography process.

[0126] The second end of the SAM molecule backbone may be terminated by a terminal aliphatic group (R) attached to the cleavage moiety (CM), e.g. the backbone is terminated by the group -CM-R. Optionally, R comprises from 1 to 20 carbon atoms, e.g. from 1 to 18 carbon atoms, e.g. from 1 to 16 carbon atoms, e.g. from 1 to 14 carbon atoms, e.g. from 1 to 12 carbon atoms, e.g. from 1 to 10 carbon atoms, e.g. from 1 to 9 carbon atoms, e.g. from 1 to 8 carbon atoms, e.g. from 1 to 7 carbon atoms, e.g. from 1 to 6 carbon atoms, e.g. from 1 to 5 carbon atoms, e.g. from 1 to 4 carbon atoms, e.g. from 1 to 3 carbon atoms, e.g. from 1 to 2 carbon atoms. Optionally, R is a methyl, ethyl, propanyl, butanyl, pentanyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or dodecyl group. R may be linear or branched. Optionally, R is linear.The SAM molecule backbone may comprise a linear backbone chain of from 1 to 30 atoms, e.g. from 1 to 25 atoms, e.g. from 1 to 20 atoms, e.g. from 1 to 18 atoms, e.g. from 1 to 16 atoms, e.g. from 1 to 15 atoms, e.g. from 1 to 14 atoms, e.g. from 1 to 13 atoms, e.g. from 1 to 12 atoms, e.g. from 1 to 11 atoms, e.g. from 1 to 11 atoms, e.g. from 1 to 10 atoms, e.g. from 1 to 9 atoms, e.g. from 1 to 8 atoms, e.g. from 1 to 7 atoms, e.g. from 1 to 6 atoms, e.g. from 1 to 5 atoms. Optionally, the linear backbone chain may comprise further atoms as part of pendant groups, branched groups or side chains. Optionally, the linear backbone chain includes at least one atom (e.g. two or more, e.g. all of the atoms) of the cleavage moiety, at least one atom (e.g. two or more, e.g. all of the atoms) of the electron directing moiety and at least one atom of the surface attachment moiety.

[0127] The cleavage moiety may be arranged between the electron directing moiety and the surface attachment moiety. Optionally, the electron directing moiety is arranged between the cleavage moiety and the surface attachment moiety.

[0128] The SAM molecule backbone has a linear arrangement of moieties. Preferably, the backbone has a linear arrangement of the following moieties: SM-R1-CM-R2-EDM-X or SM-R1-EDM-R2-CM-X;

[0129] wherein R1 comprises an aliphatic and / or aromatic group, wherein R1 may have from 1 to 20 carbon atoms, e.g. from 1 to 18 carbon atoms, e.g. from 1 to 16 carbon atoms, e.g. from 1 to 14 carbon atoms, e.g. from 1 to 12 carbon atoms, e.g. from 1 to 10 carbon atoms, e.g. from 1 to 9 carbon atoms, e.g. 1 to 8 carbon atoms, e.g. from 1 to 7 carbon atoms, e.g. from 1 to 6 carbon atoms, e.g. from 1 to 5 carbon atoms, e.g. from 1 to 4 carbon atoms, e.g. from 1 to 2 carbon atoms, e.g. from 1 to 2 carbon atoms;

[0130] wherein R2 comprises an aliphatic and / or aromatic group, wherein R2 may have from 1 to 20 carbon atoms, e.g. from 1 to 18 carbon atoms, e.g. from 1 to 16 carbon atoms, e.g. from 1 to 14 carbon atoms, e.g. from 1 to 12 carbon atoms, 1 and 10 carbon atoms, e.g. from 1 to 9 carbon atoms, e.g. from 1 to 8 carbon atoms, e.g. from 1 to 7 carbon atoms, e.g. from 1 to 6 carbon atoms, e.g. from 1 to 5 carbon atoms, e.g. from 1 to 4 carbon atoms, e.g. from 1 to 2 carbon atoms, e.g. from 1 to 2 carbon atoms; and

[0131] wherein X is optional such that when X is not present ( / .e. absent), the electron directing moiety or the cleavage moiety terminate the backbone, and when X is present, X is selected to be one of the following groups:Rs comprising an aliphatic and / or aromatic group, wherein Rs may have from 1 to 20 carbon atoms, e.g. from 1 to 18 carbon atoms, e.g. from 1 to 16 carbon atoms, e.g. from 1 to 14 carbon atoms, e.g. from 1 to 12 carbon atoms, 1 to 10 carbon atoms, e.g. from 1 to 9 carbon atoms, e.g. from 1 to 8 carbon atoms, e.g. from 1 to 7 carbon atoms, e.g. from 1 to 6 carbon atoms, e.g. from 1 to 5 carbon atoms, e.g. from 1 to 4 carbon atoms, e.g. from 1 to 3 carbon atoms, e.g. from 1 to 2 carbon atoms; or

[0132] a hydrogen or deuterium atom.

[0133] Optionally, Rs may comprise a terminal reactive group Y, wherein Y is selected from a carboxylic acid group, amine group, amide group, ester group, alkene group, alkyne group or azide group.

[0134] Optionally, the electron directing moiety (EDM) and the cleavage moiety (CM) are separated by more than 1 carbon atom, e.g. more than 2 carbon atoms, e.g. more than 3 carbon atoms. In other words, the electron directing moiety (EDM) and the cleavage moiety (CM) are optionally separated from each other by at least 2 bonds, e.g. at least 3 bonds, e.g. at least 4 bonds. For example, the electron directing moiety (EDM) and the cleavage moiety (CM) may be coupled (e.g. linked) by an aliphatic and / or aromatic group (e.g. R2) comprising a chain with more than 2 atoms disposed between the electron directing moiety (EDM) and the cleavage moiety (CM). For example, the electron directing moiety (EDM) and the cleavage moiety (CM) may be separated by (e.g. be located at either ends of) a group (e.g. R2 comprising an aliphatic and / or aromatic group) consisting of or comprising an ethyl, propyl, butyl or pentyl linear carbon chain.

[0135] Optionally, the electron directing moiety (EDM) is located at or proximate a second end (e.g. an end opposite to the end comprising the surface attachment moiety) of the backbone. Optionally, the electron directing moiety (EDM) is provided at a terminus of the backbone (e.g. it forms or comprises part of the terminal moiety). For example, the electron directing moiety (EDM) is configured to be at or near the surface of the self-assembled monolayer on the substrate. Without wishing to be bound by theory, the inventors have appreciated that the electron directing moiety (EDM) improves the interaction with metastable atoms directed at the self-assembled monolayer. The interaction may be or include an interaction via resonant ionization followed by Auger neutralisation (RI+AN); or an interaction via Auger Deexcitation (AD) which can also be referred to as Penning Ionization (PI) or Surface Penning Ionization (SPI) or any other such mechanism. Herein, all of these mechanisms are grouped under the term Penning Ionization. As such, theinventors have surprisingly observed that by providing an electron directing moiety at or near the surface of the self-assembled monolayer, an improvement in the rate of energy transfer between the metastable atoms and the SAM molecule(s) is increased.

[0136] The electron directing moiety comprises a dipole and thus, following the Penning ionisation reaction, the electron directing moiety is thought to generate the electron which is then directed along the backbone of the SAM molecule {e.g. towards or away from the cleavage moiety). In other words, without wishing to be bound by theory, it is currently believed that the electron directing moiety acts as a harpooning moiety which improves selectivity of the cleavage of part of the self-assembled monolayer. It has been further observed that the direction of the dipole may further improve or modulate the selectivity and / or efficiency of the Penning ionisation reaction and / or subsequent cleavage of the cleavage moiety.

[0137] The electron directing moiety (e.g. of each of the one or more SAM molecules) may comprise a permanent dipole moment. Optionally, the permanent dipole moment is arranged such that the dipole vector ( / .e. defined from positive to negative) of the dipole moment points substantially towards the cleavage moiety. Optionally, when the cleavage moiety is provided between the electron directing moiety and the surface attachment moiety, the dipole vector may point substantially towards the substrate on which the selfassembled monolayer is assembled. Optionally, when the electron directing moiety is provided between the cleavage moiety and the surface attachment moiety, the dipole vector may point substantially away from the substrate on which the self-assembled monolayer is assembled. Without wishing to be bound by theory, it is thought that the dipole moment acts as a harpooning directional moiety such that the electron generated in the Penning ionisation reaction with a metastable atom is preferentially emitted or directed alone the backbone from the electron directing moiety (EDM) to the cleavage moiety which improves the energy transfer efficiency to the cleavage moiety resulting in cleavage of the bond and thus removal of part of the SAM molecule from the self-assembled monolayer.

[0138] Optionally, the permanent dipole moment is arranged such that the dipole vector (e.g. from positive to negative) of the dipole moment points substantially away from the cleavage moiety. Optionally, when the cleavage moiety is provided between the electron directing moiety and the surface attachment moiety, the dipole vector may point substantially away from the substrate on which the self-assembled monolayer is assembled. Optionally, when the electron directing moiety is provided between the cleavage moiety and the surfaceattachment moiety, the dipole vector may point substantially towards the substrate on which the self-assembled monolayer is assembled. As such, the direction of the dipole along the SAM molecule backbone can allow the energy transfer efficiency and / or cleavage of a bond in the cleavage moiety to be modified.

[0139] Optionally, the electron directing moiety comprises one or more of: an O-H bond, a C-0 bond, a C=O bond, an N-H bond, a C-N bond, a C=N bond, a CHN bond, a C-S bond, and / or a C-X bond (wherein X is a halogen, e.g. F, Cl, Br, I). Optionally, the electron directing moiety is or comprises one or more of the following: an ester moiety, a thioester moiety, a carboxylic acid moiety, an amide moiety, a phenyl moiety (e.g. a substituted phenyl group, e.g. a phenol group, e.g. comprising one or more substituent groups providing one or more dipoles, e.g. a net dipole across the group), a naphthalene-based moiety (e.g. a substituted naphthalene, e.g. comprising one or more substituent groups providing one or more dipoles, e.g. a net dipole across the group), an azulene based moiety (e.g. a substituted azulene, e.g. comprising one or more substituent groups providing one or more dipoles, e.g. a net dipole across the group), a pyrimidine moiety, a pyrimidine-based moiety (e.g. a substituted pyrimidine moiety, e.g. comprising one or more substituent groups providing one or more dipoles, e.g. a net dipole across the group), a naphthalene moiety or derivatives thereof, an azulene moiety or derivatives thereof or a zwitterionic moiety such as sulfobetaine or carboxybetaine.

[0140] The SAM molecule may comprise a moiety capable of luminescing, for example fluorescing (e.g. a luminescent or fluorescent moiety, e.g. a fluorophore). Optionally, the electron directing moiety comprises a substituent capable of luminescing, e.g. fluorescing. Optionally, the electron directing moiety comprises or consists of a luminescent or fluorescent moiety, e.g. the electron directing moiety may comprise or provide the fluorophore. Optionally, the fluorophore or fluorescent moiety may be a distinct moiety, e.g. distinct from the electron directing moiety, the surface attachment moiety and the cleavage moiety. Preferably, the luminescent or fluorescent moiety is provided in the part of the SAM molecule that is removed upon interaction with a metastable atom, e.g. the broken SAM molecules that remain attached to the substate surface do not comprise the luminescent or fluorescent moiety. As such, the parts of the self-assembled monolayer that are removed during the atomic lithography process do not luminesce or fluoresce when exposed to an appropriate wavelength of electromagnetic radiation whereas the parts of the selfassembled monolayer that have not been removed ( / .e. formed from unbroken SAMmolecules) do luminesce or fluoresce. This then allows optical imaging of the monolayer patterned film using e.g. fluorescence microscopy, e.g. to characterise the quality and / or resolution of the patterning.

[0141] Optionally, the part of the one or more SAM molecules that is removed comprises the fluorophore such that the one or more unbroken SAM molecules each comprise the fluorophore but the one or more broken SAM molecules do not comprise the fluorophore. Optionally, the self-assembled monolayer comprises: one or more broken SAM molecules attached to the substrate surface; and one or more unbroken SAM molecules attached to the substrate surface.

[0142] Optionally, the one or more unbroken SAM molecules comprise a fluorophore and the one or more broken SAM molecules does not comprise a fluorophore. This allows the method of the first or second aspect to be used in conjunction with a fluorescence monitoring method (e.g. fluorescence microscopy) to quantitatively analyse the progression of the lithography process.

[0143] Optionally, each of the broken SAM molecules comprise the surface attachment moiety and an exposed moiety resulting from breaking the bond in the cleavage moiety; and the exposed moiety is attached to a reactant to modify the reactivity or functionality of the one or more broken SAM molecules. The reactant may be one or more of: a (e.g. metal) nanoparticle such as a gold nanoparticle, alkenes, maleimides, polymer brushes, functionalised silsesquixoanes, thiols, oxides, or inorganic oxides such as silicon oxide, aluminium oxide or titanium oxide. Additionally or alternatively, the reactant may modify the reactivity such that the broken SAM molecules are more resistant to a chemical etch compared to the unbroken SAM molecules.

[0144] The fluorescing moiety (and / or the electron directing moiety fluorophore) may be a derived from naphthalene or azulene, e.g. a naphthalene-based moiety comprising one or more substituents, e.g. an azulene-based moiety comprising one or more substituents. For example, it is known that naphthalene undergoes an excitation to the Si state at or around 4 eV to 5.5 eV. As such, a substituted naphthalene group (e.g. substituted to have a dipole moment) may participate in a Penning ionisation reaction with a metastable (e.g. helium) atom such that the naphthalene is electronically excited to an excited state substantially congruent with generation of an electron.Optionally, the method comprises detecting (e.g. a change in) luminescence or fluorescence emitted from the self-assembled monolayer concurrent with, or following the step of, directing the metastable atoms at the self-assembled monolayer.

[0145] Optionally, the self-assembled monolayer forms a layer having a thickness of less than 10 nm, e.g. less than 5 nm, e.g. less than 4 nm, e.g. less than 3 nm, e.g. less than 2 nm, e.g. less than 1 nm. Optionally, the self-assembled monolayer forms a layer with a thickness from 0.5 nm to 5 nm, e.g. from 1 nm to 4 nm, e.g. from 1 nm to 3 nm.

[0146] Optionally, the method comprises directing the source of metastable atoms through a patterning mask applied on or proximate the self-assembled monolayer.

[0147] Optionally, before the substrate surface is exposed to the plurality of SAM precursors, the plurality of SAM precursors are reacted with a bridging molecule comprising multiple functional groups to provide one or more bridged pairs of SAM precursors, wherein the substrate surface are exposed to the one or more bridged pairs of SAM precursors, wherein each of the functional groups is configured to react with a functional group present on each of the two SAM precursors to provide a bridged group, wherein the bridged group comprises two or more cleavage moieties and one or more electron directing moieties, and more optionally, wherein the bridging molecule provides one or more of said one or more electron directing moieties. In some such examples, the method further comprises directing at least two metastable atoms at the bridged group to break the two or more cleavage moieties in the bridge pair and thus remove at least part the bridge pair from the self-assembled monolayer.

[0148] Optionally, the method further comprises exposing at least part of the self-assembled monolayer to a protecting group before the source of metastable atoms is directed at the self-assembled monolayer such that one or more of the SAM molecules comprise the protecting group. This may be advantageous as the protecting group can introduce part of the self-assembled monolayer with chemoselectivity to further reactants. For example, when the protecting group is more reactive than the terminal group to a subsequent reactant (e.g. bridging molecule, e.g. chemical etchant), SAM molecules comprising the protecting group may be preferentially reacted with said reactants over SAM molecules that do notcomprise the protecting group. Alternatively, when the protecting group is less reactive that the terminal group to subsequent reactants, the reverse would be true.

[0149] Optionally, the protecting group is configured to modify removal of at least part of the selfassembled monolayer. For example, the protecting group may be configured to improve or reduce the removal of SAM pre-cursors comprising the protecting group with respect to SAM molecules that do not comprise the protecting group. The modification effected by the protecting group may be to introduce chemoselectivity to subsequent reactants (as described above). Additionally or alternatively, the protecting group may modify or change the effectiveness of the energy transfer between the metastable atom and the SAM molecule comprising the metastable atom. For example, if the protecting group comprises an electron directing moiety having a dipole, the dipole of the protecting group may modify the energy transfer of the metastable atoms. For example, if the dipole of the protecting group improves the energy transfer compared to the terminal group, it may be appreciated that SAM molecules comprising the protecting group are preferentially removed due to scission of the bond in the cleavage moiety.

[0150] For example, without wishing to be bound by theory, it is thought that a protecting group having a stronger dipole moment than the electron directing moieties in the SAM molecules without the protecting group may increase the effectiveness of the energy transfer. For example, without wishing to be bound by theory, it is thought that when the protecting group comprises a dipole that has a vector in substantially the same direction as the electron directing moiety of the SAM molecules, the dipoles may compound to further enhance the harpooning reaction. Conversely, if the protecting group has a dipole moment with a vector that points in the opposite direction to the vector of the electron directing moiety, the energy transfer may be reduced such that SAM molecules not comprising the protecting group are more selectively removed.

[0151] The protecting group may be any suitable and / or desirable protecting group known in the art. The protecting group may comprise a dipole such that the protecting group forms a further electron directing moiety. The protecting group may be derived from N-hydroxysuccinimide.

[0152] Optionally, the method further comprises bridging two or more SAM molecule molecules with a bridging moiety to form a bridged group of SAM molecules by reacting two or moreSAM molecules with one or more bridging molecules. Optionally, the method comprises reacting the two or more SAM molecules with a single bridging molecule. Optionally, the method comprises reacting the two or more SAM molecules with a plurality of bridging molecules. For example, each bridging molecule may function to react (e.g. bridge) two or more SAM molecules, wherein the plurality of bridging molecules may then be subsequently or contemporaneously linked or reacted together.

[0153] For example, the method may comprise bridging two or more SAM molecules with a bridging moiety by reacting two or more SAM molecules with a bridging molecule comprising multiple functional groups, wherein each of the functional groups is configured to react with a functional group present on each of the two SAM molecules to provide a bridged group, wherein the bridged group comprises two or more cleavage moieties and one or more electron directing moieties, and optionally, wherein the bridging molecule provides one or more of said one or more electron directing moieties. In some such examples, the method further comprises directing at least two metastable atoms at the bridged group to break the two or more cleavage moieties in the bridge pair and thus remove at least part the bridge pair from the self-assembled monolayer.

[0154] Optionally, the bridging molecule comprises the same number of functional groups as the number of SAM molecules it is to be reacted with to form the bridged group. For example, the bridging molecule may be a polyfunctional molecule. Optionally, the bridging molecule comprises two or more functional groups, wherein each of the two or more (e.g. two) functional groups are configured to react with a functional group (e.g. provided by the terminal moiety, e.g. provided by a protecting group) present on each of the two or more (e.g. two) SAM molecules to provide the bridged group (e.g. pair). Optionally, the bridging molecule and the SAM molecules are connected by a linking functional group resulting from the reaction therebetween.

[0155] It will be appreciated that the bridging moiety is a polyfunctional (e.g. difunctional) protecting group that effectively protects and modifies the removal of two or more (e.g. two) SAM molecules. The bridging molecule may be a symmetrically difunctional molecule (e.g. comprising the same functional group at two ends of the molecule) or an asymmetrically difunctional molecule (e.g. comprising different functional groups at two ends of the molecule).Optionally, the bridged group comprises two or more (e.g. two, e.g. three, e.g. four) cleavage moieties and one or more (e.g. two, e.g. three, e.g. four) electron directing moieties. Optionally, the bridged group comprises a 1:1:1 ratio of SAM molecules to cleavage moieties to electron directing moieties. For example, if the bridged group comprises three SAM molecules, there may be three cleavage moieties and three electron directing moieties in the bridged group. Optionally, the bridged group comprises a 1:1:1 ratio of SAM molecules to cleavage moieties to electron directing moieties. For example, the bridged group may comprise three SAM molecules, three cleavage moieties and six electron directing moieties (e.g. two per cleavage moiety). Optionally, the linkergroup (e.g. the group connecting the cleavage moiety to the surface attachment moiety) may provide one or more of the one or more electron directing moieties.

[0156] Optionally, the bridged pair comprises one or more (e.g. two) cleavage moieties and one or more (e.g. two) electron directing moieties. Optionally, the bridged pair comprises two cleavage moieties and two electron directing moieties. Optionally, the bridged pair comprises two cleavage moieties and four electron directing moieties. Optionally, the linking functional group provides one or more of the one or more electron directing moieties.

[0157] Optionally, the bridging molecule reacts with a functional group (e.g. provided by an electron directing moiety, e.g. provided by the terminal moiety) on each of the two SAM molecules (e.g. via a nucleophilic or electrophilic substitution reaction). Optionally, the linking functional group provides two of the electron directing moieties in the bridged pair.

[0158] Optionally, the bridged pair comprises four electron directing moieties. Optionally, two of the four electron directing moieties are provided by the linking functional group and the other two of the four electron directing moieties are provided solely by the SAM molecules (e.g. one from each SAM molecule).

[0159] Optionally, the bridging molecule is di-functional. Optionally, the bridging molecule is configured to undergo nucleophilic or electrophilic substitution with two SAM molecules. Optionally, the bridging molecule is configured to undergo a ring opening reaction. Optionally, the bridging molecule is configured to undergo a ring opening reaction with an electron directing moiety of one or both of the two SAM molecules.Optionally, the bridging molecule is, or is derived from, a polyfunctional carboxylic acid ( / .e. poly-carboxylic acid), a polyfunctional ester ( / .e. a poly-ester), a polyfunctional amine ( / .e. a poly-amine) ora polyfunctional amide ( / .e. a poly-amide). Optionally, the bridging molecule is, or is derived from, a difunctional carboxylic acid ( / .e. a dicarboxylic acid), a difunctional ester {e.g. a diester), a difunctional amine e.g. a diamine) or a difunctional amide {e.g. a diamide). Optionally, the bridging molecule comprises or is derived from pyrrolidine, e.g. derived from N-hydroxysuccinimide. Optionally, the bridging molecule comprises a difunctional ester. Optionally, the bridging molecule comprises a difunctional ester formed by reacting a difunctional carboxylic acid with a N-hydroxysuccinimide. Optionally, the bridging molecule is configured to react with (e.g. part of) the SAM molecule (e.g. the electron directing moiety, e.g. the terminal functional group of the terminal moiety) such that the linking functional group is an ester moiety.

[0160] Optionally, the linking functional group is an ester group, a thioester group, an amide group, an anhydride group, a double bond (e.g. alkenyl moiety), a triple bond (e.g. an alkynyl moiety), or an azide moiety ( / .e. -N3).

[0161] Optionally, the method further comprises directing at least two metastable atoms at the bridged pair to break the cleavage moieties in the bridge pair and thus remove at least part the bridge pair from the self-assembled monolayer. This advantageously makes the atom lithography process a two-electron process.

[0162] Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. For the avoidance of doubt, the terms “may”, “and / or”, “e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

[0163] Figure 1 is a schematic representation of an atom lithography method in accordance with an embodiment the invention;

[0164] Figure 2 show methods of manufacturing SAM precursor molecules in accordance with embodiments of the invention;

[0165] Figure 3 shows electron directing moieties in accordance with embodiments of the invention;

[0166] Figure 4 schematically represents a method of modifying the reactivity of a selfassembled monolayer in accordance with an embodiment of the present invention; Figure 5 schematically represents a method of modifying the reactivity of a selfassembled monolayer in accordance with an embodiment of the present invention; Figure 6 schematically represents a method of modifying the reactivity of parts of a self-assembled monolayer in accordance with an embodiment of the present invention;

[0167] Figure 7 schematically represents a method of modifying the reactivity of parts of a self-assembled monolayer in accordance with an embodiment of the present invention;

[0168] Figure 8 schematically represents a method of modifying the reactivity of a selfassembled monolayer in accordance with an embodiment of the present invention; Figures 9A and 9B shows a synthetic scheme for making (A) mercaptoalcohols and (B) mercaptocarboxylic acids which may be used as a precursors for providing SAM precursors in accordance with the present invention;

[0169] Figures 10A and 10B show the products of method steps shown in Figures 9A and 9B respectively with the carbon and hydrogen atoms labelled for assignment in corresponding NMR data;

[0170] Figure 11 shows two Steglich esterification schemes for esterifying the products of Figures 9A and 9B;

[0171] Figures 12A and 12B show the products of the two Steglich esterification steps shown in Figure 11 with the carbon and hydrogen atoms labelled for assignment in corresponding NMR data;

[0172] Figures 13 shows two schematic schemes for sulfenamide formation in the products of Figure 11;Figures 14A and 14B shows the products of the sulfenamide formation steps shown in Figure 13 with the carbon and hydrogen atoms labelled for assignment in corresponding NMR data;

[0173] Figure 15 shows an synthetic scheme for making a SAM precursor in accordance with an embodiment of the present invention;

[0174] Figure 16 shows the products of the method steps shown in Figure 15 with the carbon and hydrogen atoms labelled for assignment in corresponding NMR data;

[0175] Figure 17 shows a schematic methodology for obtaining metastable de-excitation spectroscopy data of a self-assembled monolayer according to the present invention as well as X-ray photoelectron spectroscopy data of said self assembled monolayer following exposure to metastable atoms;

[0176] Figure 18 shows metastable de-excitation spectroscopy data for self-assembled monolayers formed from different SAM molecule molecules, wherein A) and B) show comparative data for SAM molecules not falling within the scope of the Claims and C) to F) show data for SAM molecules in accordance with embodiments of the present invention;and

[0177] Figure 19 shows other SAM precursor molecules in accordance with embodiments of the present invention.

[0178] Referring now to Figure 1, there is shown a schematic representation of a method 100 according to the first aspect of the invention which utilises a SAM molecule in accordance with the second aspect of the invention. Figure 1 a shows a schematic representation of the SAM molecule having a surface attachment moiety, SM, a cleavage moiety, CM and an electron directing moiety, EDM, all of which are connected in a linear arrangement by intervening linker moieties (here aliphatic chains, Ri, R2) and a third moiety (here aliphatic chain R3).

[0179] Once the SAM molecule has been assembled on a substrate (not shown) by attachment through the surface attachment moiety, electrons emitted by the de-excitation of metastable atoms, MA*, can be selectively directed to the SAM molecule in the self-assembled monolayer, as shown in Figure 1b and 1c. The metastable atom, such as a metastable helium atom, upon interaction with the SAM molecule, transfers energy to the SAM molecule (e.g. via the electron directing moiety, EDM) which induces a Penning ionisation reaction that generates an electron, e; and deexcites the metastable atom to its ground state.Once generated, the electron, e; is then directed towards the cleavage moiety, CM, as shown in Figure 1c where it induces selective breakage of a bond within the cleavage moiety. The breakage of this bond results in the SAM molecule being broken into two portions 110, 120, each comprising part of the cleavage moiety, CM’, CM” as shown in Figure 1d.

[0180] The portion 120 of the SAM molecule that remains affixed to the surface following breakage of the cleavage moiety CM is then able to react with a reacting group, RG, which acts to modify the reactivity of the broken SAM molecule 120. This therefore allows the broken SAM molecules to show different sensitivities compared to unbroken SAM molecules (that have not interacted with metastable atoms) to further reactants, e.g. a chemical etchant, which can therefore improve the etching and pattern resolution.

[0181] In some embodiments, etching may be performed without the addition of a reacting group, RG. For example, some wet etches of silicon have a very high selectivity for silicon over carbon such that the thinness of the self-assembled monolayer does not inhibit the etching process, allowing the substrate to be etched without a reacting group.

[0182] Although Figure 1 shows that the electron directing moiety, EDM, is provided proximate the second end of the backbone of the precursor (the first end comprising the surface attachment moiety, SM, at or near the substrate surface), it will be appreciated that the method may equally be applied to other arrangements of the moieties, including providing the cleavage moiety, CM, closer to the second end that the electron directing moiety, EDM.

[0183] Referring to Figure 2, three exemplary syntheses for providing SAM precursor molecules in accordance with the invention are shown. In all three syntheses shown, the starting material 1 is shown to be 3-mercaptopropionic acid. It will however be appreciated that any suitable and / or desirable bifunctional molecule, for example comprising a carboxylic acid group and a thiol group may be used.

[0184] In step A of the syntheses the thiol group of the starting molecule 1 is protected by forming a symmetrical dithiodicarboxylic acid (HO2R-S2-RO2H) 2. In the examples shown, the dithiodicarboxylic acid 2 is 3,3’-dithiodipropanoic acid.In step B of the syntheses, the electron directing ( / .e. ester, amide and thioester) moieties are formed. In step B’, the dithiodicarboxylic acid 2 is reacted with an alcohol to provide a dithiodiester (R2O2R1-S2-R1C>2R2) 3. In step B”, the dithiodicarboxylic acid 2 is reacted with an amine to provide a dithiodiamide (R2NHOR1-S2-R1OHNR2) 4. In step C”, the dithiodicarboxylic acid 2 is reacted with an amine to provide a dithiodithioester (R2SHOR1-S2-RIOHSR2) 5.

[0185] In steps C and D, the symmetrical disulfide bond is broken to form sulfenamides 6, 7, 8 (step C) before the cleavage moiety is formed by reacting the sulfenamides 6, 7, 8 with a molecule comprising a surface attachment moiety to provide the SAM precursors 9, 10, 11. In the examples shown, the SAM precursors 9, 10, 11 have a triethoxysilane moiety as the surface attachment moiety, a disulfide bond as the cleavage moiety and an ester (SAM precursor 9), amide (SAM precursor 10) and thioester (SAM precursor 11) as the electron directing moieties.

[0186] Figure 2 therefore shows the versatility of the synthesis in producing a vast variety of SAM precursors. Other SAM precursors beyond those shown in Figure 2 are possible. For example, Figures 14A, 14B show SAM precursors 10a-c, 11a-c comprising ester electron donating groups. For example, Figure 19 shows a SAM precursor 30 having an amide electron donating group and a SAM precursor 31 having a thioester electron donating group.

[0187] Figure 3 shows examples of electron directing moieties which may be incorporated into SAM precursors in accordance with the present invention with their associated dipole moments depicted. As shown, the dipole moment vector is defined from positive to negative as is convention.

[0188] Referring to Figure 4, an exemplary method of modifying the reactivity of part of a selfassembled monolayer is provided in accordance with an embodiment of the present invention. The self-assembled monolayer is provided by assembling a plurality of SAM precursors 12 on a substrate S (thus comprising a plurality of SAM molecules 12), wherein each SAM molecule 12 comprises a cleavage moiety, CM, an electron directing moiety, EDM, a terminal group, TG, and a surface attachment moiety (not shown) via which the Sam precursor is attached to the substrate. In the SAM molecules shown the terminal group, TG, is shown as a carboxylic acid group and the cleavage moiety, CM, is shown asa disulfide bond. It will be appreciated that these are exemplary in nature and not intended to be limiting. Indeed, any suitable and / or desirable cleavage moiety, CM, and terminal functional group, TG, may be utilised. The electron directing moiety, EDM, is represented by X.

[0189] In step E, the SAM precursors shown are reacted with N-hydroxysuccinimide 13 in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide 14 to convert the SAM molecules into N-hydroxysuccinimide esters 15, wherein the N-hydroxysuccinimide is provided as a protecting group, PG. It will be appreciated that although both SAM molecules shown in Figure 4 are reacted to provide the N-hydroxysuccinimide esters 15, this is not intended to indicate that the entire self-assembled monolayer is functionalised to include the protecting groups PG. Indeed, it will be appreciated that only part of a self-assembled monolayer may be reacted to include the protecting groups PG such that the reactivity of these SAM molecules are modified with respect to SAM molecules that do not include the protecting groups PG. Furthermore, it will be appreciated that the invention is not limited to use of N-hydroxysuccinimide as the protecting group. Indeed, any suitable and / or desirable protecting group may be used.

[0190] In step F, the N-hydroxysuccinimide ester SAM molecules 15 are reacted with a diamide 16 functioning as a bridging molecule such that a bridging pair 17 is provided comprising two SAM molecules 15 and a bridging moiety, BG, derived from the bridging molecule. In this example the bridging moiety is linked to the SAM molecules by an amide linking group, LG. It will however be appreciated that the invention is not restricted to use of diamides as bridging molecules. Indeed, any symmetrical or unsymmetrical difunctional molecule, providing any corresponding linking group LG, may be used to bridge SAM molecules together and form a bridging pair 17.

[0191] In step G, a metastable helium atom, He*, is directed at the self-assembled monolayer such that energy is transferred from the metastable helium atom He* to the bridging pair 17 resulting in the deexcitation of the metastable helium atom He*. The energy transferred to the bridging pair is then used to break one of the two disulfide bonds of the two cleavage moieties in the bridging pair 17.

[0192] In the example shown, engagement of the metastable helium atom He* with the selfassembled monolayer results in sufficient energy being transferred to break only onedisulfide bond. As such, following interaction with one metastable helium atom He*, a partially detached bridged pair 17’ is provided having a terminating thiol group at one end.

[0193] In step H, a second metastable helium atom He* is directed at the self-assembled surface such that energy is transferred from the metastable helium atom He* to the partially detached bridging pair 17’. This in turn results in scission of the second disulfide bond such that the bridged pair 17’” is removed. This in turn leaves behind a thiol functionalised substrate formed by the part of the SAM precursors 12 that remain affixed to the substrate S by the surface attachment moieties of the SAM precursors 12. Accordingly, it is possible to design SAM molecules with multi-atom scission requirements, thereby potentially improving contrast.

[0194] The inventors have further appreciated that by using bridged groups of SAM precursors / molecules, the effect of stochastic variations in the metastable atom dose may be reduced by increasing the contrast of the SAM resist and eliminating the impact of randomly scattered and / or unwanted metastable atoms (analogous to flare and / or photon shot noise in photolithography).

[0195] Figure 5 shows another method of modifying the reactivity of part of a self-assembled monolayer provided in accordance with an embodiment of the present invention. As with Figure 4, the self-assembled monolayer is provided by assembling a plurality of SAM precursors 18 on a substrate S, wherein each SAM precursor 18 comprises a cleavage moiety, CM, an electron directing moiety, EDM, a terminal group, TG, and a surface attachment moiety (not shown) via which the SAM precursor is attached to the substrate (thus becoming a SAM molecule). In the SAM molecules 18 shown in Figure 4, the terminal group, TG, is a hydroxy group and the cleavage moiety, CM, is shown as a disulfide bond. It will be appreciated that these are exemplary in nature and not intended to be limiting. Indeed, any suitable and / or desirable cleavage moiety, CM, and terminal functional group, TG, may be utilised. The electron directing moiety, EDM, is represented by X.

[0196] In step I, the SAM molecules 18 are reacted with a difunctional bridging molecule 19 to provide the bridged pair 20. In this example the bridging molecule 19 is a symmetrical diester derived from N-hydroxysuccinimide and a difunctional carboxylic acid. In some examples, the bridging molecule 19 may be generated in situ or may be pre-formed prior to interaction with the self-assembled monolayer. Reaction of the SAM molecules 18 withthe bridging molecule 19 results in the formation of an ester linking group LG between the bridging moiety and the SAM molecule. In this example, the bridging moiety, BG, does not comprise the N-hydroxysuccinimide group.

[0197] As with Figure 4, it will be appreciated that only part of a self-assembled monolayer shown in Figure 5 may be reacted to include the bridging moiety BG such that the reactivity of the SAM precursors 18 in the bridged pair 20 are modified with respect to SAM precursors that do not include the bridging moiety BG. Furthermore, it will be appreciated that the invention is not limited to use of N-hydroxysuccinimide difunctional ester as the bridging molecule 19 precursor to the bridging moiety. Indeed, any suitable and / or desirable bridging molecule may be used.

[0198] In step J, a metastable helium atom, He*, is directed at the self-assembled monolayer such that energy is transferred from the metastable helium atom He* to the bridging pair 20 resulting in the deexcitation of the metastable helium atom He*. The energy transferred to the bridging pair is then used to break one of the two disulfide bonds of the two cleavage moieties in the bridging pair 20. As with the example shown in Figure 4, in this example engagement of the metastable helium atom He* with the self-assembled monolayer results in sufficient energy being transferred to break only one disulfide bond. As such, following interaction with one metastable helium atom He*, a partially detached bridged pair 20’ is provided having a terminating thiol group at one end.

[0199] In step K, a second metastable helium atom He* is directed at the self-assembled surface such that energy is transferred from the metastable helium atom He* to the partially detached bridging pair 20’. This in turn results in scission of the second disulfide bond such that the bridged pair 20’” is removed. This in turn leaves behind a thiol functionalised substrate formed by the part of the (broken) SAM molecule 18 that remain affixed to the substrate S by the surface attachment moieties of the SAM molecule 18.

[0200] Although both Figures 4 and Figure 5 show examples where the metastable atoms directed at the surface result in the breakage of one bond in the cleavage moiety of the SAM precursors 12, 18, it will be appreciated that the invention is not so limited. For example, in some embodiments, one metastable atom may provide sufficient energy to fully detach the bridge pair by breaking the requisite bonds in both cleavage moieties. For example, the bonds may require less energy to break or the metastable atom may be exited to a greaterextent such that more energy is transferred to the bridged pair 17, 20. Alternatively, the cleavage moiety may require multiple bonds to be broken to result in detachment of only one side of the bridged pair. For example, multiple metastable atoms may be required to effect scission of the cleavage moiety in just one of the two SAM precursors 12, 18 forming the bridged pair 17, 20. As such, fully detaching the bridged pairs 17, 20 may require more than two metastable atoms.

[0201] Although both Figures 4 and 5 are described with respect to the use of metastable helium atoms, He*, it will be appreciated that any suitable and / or desirable metastable atom may be used without modification of the underlying principles described.

[0202] Referring to Figure 6, a method of modifying the reactivity of parts of a self-assembled monolayer 21 in accordance with an embodiment of the present invention is shown. In this example, a self-assembled monolayer 21 is provided by a plurality of SAM precursors 22 formed on a silicon substrate S. Each of the SAM precursors 22 has a silane surface attachment moiety, SM, a disulfide cleavage moiety, CM, and an electron directing moiety, EDM, represented by X. The SAM precursors 22 are terminated by a linear aliphatic chain.

[0203] In step L, the self-assembled monolayer 21 is selectively exposed to metastable atoms, MA*, using a patterning mask for example. In the regions of the self-assembled monolayer 21 that are exposed to the metastable atoms, energy is transferred from the metastable atoms MA* to the SAM precursors 22 resulting in scission of the disulfide bond, leaving behind a plurality of broken SAM precursors 23 terminating in a thiol moiety. In contrast, the SAM precursors 22 that are present in regions that are not exposed to the metastable atoms MA* remain unbroken.

[0204] As such, in this example, following exposure to metastable atoms, the self-assembled monolayer 2T comprises a thiol functionalised regions due to the broken SAM precursors 23 and regions absent significant functionalisation (e.g. due to the terminal aliphatic chains) arising from the unbroken SAM precursors 22. The inventors have appreciated that this difference in functionalisation between the broken 23 and unbroken 22 SAM precursors can advantageously provide the possibility of introducing increased selectivity in subsequent lithography steps and / or allow the introduction of further functionalisation which can improve the resolution and contrast of the resulting pattern.Although, in this example, the unbroken SAM precursors are terminated in an aliphatic chain, it will be appreciated that the unbroken SAM precursors 22 may also provide a functionalised surface due to a terminal group comprising a functional group such as a hydroxy group or a carboxylic acid group. In these examples, a difference in reactivity of the functional groups provided by the broken 23 and unbroken 22 SAM precursors may provide chemoselectivity of further reaction steps.

[0205] In step M, the self-assembled monolayer surface 2T is exposed to gold nanoparticles which selectively react with the thiol moieties of the broken SAM precursors 23. The gold nanoparticles thus function as an etch mask which increases the etch resistance of the regions of the self-assembled monolayer surface 2T which have been exposed to the metastable atoms MA*.

[0206] As such, upon exposure to an etchant (e.g. plasma etch, e.g. reactive ion etch, e.g. wet chemical etchant) in a subsequent step (not shown), the portions of the surface comprising the unbroken SAM precursors 22 are preferentially etched over the portions comprising the broken SAM precursors 23 and gold nanoparticles. This further improves the resolution and contrast of the resulting patterns provided by the lithography techniques disclosed herein.

[0207] Figures 7 and 8 each schematically show alternative methods of chemically modifying the reactivity of parts of the self-assembled monolayer in a manner analogous to Figure 6.

[0208] In both Figures 7 and 8, a self-assembled monolayer 25 is provided by a plurality of SAM precursors 26. Each of the SAM precursors 26 comprises a silane surface attachment moiety, SM, a disulfide cleavage moiety, CM, an ester electron directing moiety, EDM and a linear aliphatic chain as a terminal group.

[0209] In step N of both Figures 7 and 8, the self-assembled monolayer 25 is selectively exposed to metastable atoms such that a self-assembled monolayer 25’ comprising regions of thiol terminated broken SAM precursors 27 and regions of unbroken SAM precursors 26 are provided. Step N is therefore analogous to step L of Figure 6.

[0210] In steps O’ and O”, the thiol reactivity introduced to the surface by the broken SAM precursors 27 is exploited by using thiol-ene click chemistry to further functionalise the broken SAM precursors 27. For example, alkene or maleimide based reactants may beconjugated to the unbroken SAM precursors 27 to introduce advantageous properties to these areas. For example, the alkene or maleimide based reactants could improve contrast during imaging of the exposed resist. For example, the reactants could fluoresce or comprise a fluorescing moiety. For example, the conjugation may introduce a group with increased etch resistance with respect to the unbroken precursors 26 such that enhanced contrast and resolution of the etched pattern is obtained. For example, vinylogous cyclomethycaine may be used to grow a silica rich layer on the thiol. This may provide a useful method of increasing the etch contrast between exposed and unexposed areas. It may also provide a method to further enhance the difference in contrast when removing the SAM material by using a UV exposure to cleave the remaining disulfide bonds without affecting the thioethers, e.g. using a mild disulfide chemical reduction reaction. Additionally or alternatively, mercaptoethanol solution could be used to cleave remaining unexposed disulfides whilst leaving the thioethers intact after they have formed via a click chemistry reaction.

[0211] In step O’ of Figure 7, the thiol group of the broken SAM precursors 27 is utilised in a thiolene “click” chemistry reaction with an alkene. Similarly, in step O” of Figure 8, Michael addition is used to conjugate the thiol group of the broken SAM precursors 27 to a maleimide terminated compound. In both examples, the alkene comprises a terminal group X that may be used to introduce advantageous properties. For example, group X could be a fluorescing group or could improve the contrast between the different regions of the exposed resist pattern.

[0212] Figure 9A shows a multistep synthetic scheme for making precursor compounds 2a, 2b, 2c, 4a, 4b, and 4c (which may be used to provide SAM precursors in accordance with the invention) from mercaptoalcohols 1a, 1b, 1c. Figure 9A shows a synthetic scheme form making precursor compounds 6a, 6b, 6c, 6d, 8a, 8b, 8c and 8d (which may be used to provide SAM precursors in accordance with the invention) from mercaptocarboxylic acids 5a, 5b, 5c. It will be appreciated that the precursor compounds 4a-4c and 8a-8d provided by the syntheses shown in Figures 9A and 9B respectively differ in the direction of the dipole of the ester moiety group. Thus, precursor compounds 4a-4c may be used to provide SAM precursors having an ester ( / .e. electron directing) moiety dipole ( / .e. from positive to negative) directed away from the sulfide ( / .e. cleavage) moiety as the electron directing moiety (EDM). In contrast, precursor compounds 8a-8d may be used to provide SAM precursors having an ester ( / .e. electron directing) moiety dipole ( / .e. from positive tonegative) directed toward the sulfide ( / .e. cleavage) moiety as the electron directing moiety (EDM).

[0213] For the avoidance of doubt, the compounds shown in Figures 9-14 are provided with an alphanumeric label containing a number {e.g. 1, 2, 3...) and a letter e.g. a, b, c..). It will be appreciated that the different numbers signify a change in functionality due to a synthetic step or reaction, whereas the letters are associated with the value of n or ri arising from the starting materials. As such, step P converts compound 1a into compound 2a which is in turn converted into compound 4a in step Q by virtue of a reaction with compound 3a. In other words, only compounds with the same letter form part of the same synthesis sequence. Table 1 provides the characterising information for the compounds used in the syntheses shown in Figures 9A and 9B.

[0214] Figure 10A shows the atom assignments used in the NMR spectroscopy assignments for the precursor compounds 2a-2c and 4a-4c resulting from steps P and Q shown in Figure 9A, and Figure 10B shows the atom assignments used in the NMR spectroscopy assignments for the precursor compounds 5a-5d and 8a-8d resulting from steps R and S shown in Figure 9B. The associated NMR data is discussed below in conjunction with the synthetic steps used to provide the compound.

[0215] Table 1 shows chemical information of the compounds shown in Figure 9.

[0216]

[0217] Step P: synthesis of compounds 2a-2c from mercaptoalcohols 1a-1c Sodium iodide (1 mol%, 0.0283 mmol, 4.24 mg) is added to ethyl acetate (5.7 mL) along with the mercaptoalcohol 1a (2.83 mmol, 0.5 g) or 1b (2.83 mmol, 0.38 g) or 1c (2.83 mmol, 0.22 g) and stirred at 40°C until the contents of the mixture dissolve. To the solution is added aqueous hydrogen peroxide (30% w / w) (2.83 mmol, 0.31 mL) dropwise over 1 minute. The resulting mixture is stirred until the solution turns from a pale-yellow colour to a deep red-orange colour (0.5h). Afterwards, the contents of thereaction are transferred to a separating funnel along with a saturated aqueous solution of sodium thiosulfate and shaken, causing a colour change from red to colourless of the organic phase. The organic phase is washed with brine (3x 15 mL). The combined organic phases are dried over anhydrous magnesium sulphate and the solvent removed in vacuo to yield the disulfide alcohol.

[0218] Compound 2a: 9,9’-disulfanediylbis(nonan-1-ol)

[0219] 1H NMR (400 MHz, CDCh): 6 ppm: 3.64 (4H, t, Hb,3J = 8 Hz); 2.68 (4H, t, Hk,3J = 8 Hz); 1.67 (4H, p, Hj,3J = 8 Hz); 1.57 (4H, p, Hc,3J = 8 Hz); 1.30 (22H, m, Ha+ Hd-Hi).

[0220] 13C NMR (400 MHz, CDCI3): 5 ppm: 63.06 (Ci); 32.79 (C2); 25.73 (C3); 29.20 (C8); 39.20 (C9); 28.49, 29.16, 19.36, 29.46, (C4-C7).

[0221] ESI-MS: m / z: [M+H]+= 351.24; [M+Na]+= 373.22

[0222] I R:vmax / cm-1: 3311 (br) (O-H stretch); 2921 (w) and 2849 (w) (C-H stretch).

[0223] Yielded a white powdered solid with 62% yield.

[0224] Compound 2b: 6.6’-disulfanediylbis(hexan-1-ol)

[0225] 1H NMR (400 MHz, CDCh): 6 ppm: 1.96 (2H, s, Ha); 3.63 (4H, t,3J = 8 Hz, Hb); 1.58 (4H, p,3J = 8 Hz, Hc); 1.41 (8H, m, Hd& He); 1.70 (4H, p,3J = 8 Hz, Hf); 2.69 (4H, t,3J = 8 Hz, Hg).

[0226] 13C NMR (400 MHz, CDCI3): 5 ppm: 62.75 (Ci); 32.56 (C2); 25.39 (C3); 28.25 (C4); 29.13 (C5); 39.04 (C6).

[0227] ESI-MS: m / z: [M]+= 266.17

[0228] I R:vmax / cm-1: 3310 (br) (O-H stretch); 2925 (w) and 2854 (w) (C-H stretch).

[0229] Yielded as a pale-yellow oil which solidifies to form a white powdered solid at room temperature over approximately three hours with a 93% yield.

[0230] Compound 2c: 2.2’-disulfanediylbis(ethan-1-ol)

[0231] 1H NMR (400 MHz, CDCh): 6 ppm: 2.99 (2H, s, Ha); 3.91 (4H, t,3J = 8 Hz, Hb); 2.89 (4H, t,3J = 8 Hz, Hc).

[0232] 13C NMR (400 MHz, CDCI3): 5 ppm: 60.40 (Ci); 41.25 (C2)

[0233] ESI-MS: m / z: [M+Na]+= 177.00

[0234] IR:vmax / cm’1: 3322 (br) (O-H stretch); 2926 (w) and 2873 (w) (C-H stretch).Yielded as a dark orange oil with an 88% yield.

[0235] Step Q: synthesis of compounds 4a-4c by Steglich esterification

[0236] To dry DCM (20 mL) is added the disulfide alcohol product 2a-2c of step P (see table 2) along with DCC (2.547 mmol, 0.5256 g) and DMAP (10 mol%, 0.0310 g). The resulting mixture is stirred at 25°C under an inert N2 atmosphere until the contents of the mixture are fully dissolved. Carboxylic acid 3a-3c (see table 2) is added to the resulting solution via a syringe. The resulting mixture is stirred at 25°C for 24h. The resulting cloudy suspension is filtered through filter paper to remove the white powdered precipitate (urea by-product). The resulting DCM filtrate is washed with brine (3 x 15 mL) and the combined aqueous phases are extracted with DCM (3 x 15 mL). The combined organic phases are concentrated via rotary evaporation under reduced pressure. The resulting oil-like crude product mixture is purified via column chromatography over silica gel with a DCM eluent.

[0237] Table 2 shows the reagents and compounds used in the synthesis step Q

[0238]

[0239] Compound 4a: Disulfanediylbis(nonane-9, 1-diyl) diacetate

[0240] 1H NMR (400 MHz, CDCI3): 6 ppm: 4.05 (4H, t, Hb,3J = 8 Hz); 2.68 (4H, t, Hj,3J = 8 Hz); 2.05 (6H, s, Ha); 1.64 (8H, m, Hc, Hi); 1.35 (20H, m, Hd-Hh).

[0241] 13C NMR (400 MHz, CDCI3): 5 ppm: 21.03 (Ci); 171.28 (C2); 64.63 (C3); 39.14 (Cn); 26.36. 29.19 (C4 / C10); 29.18, 29.14, 28.59, 28.48, 25.88 (C5-C9).

[0242] ESI-MS: m / z: [M]+= 434.28

[0243] I R:vmax / cm-1: 2925 (w) and 2854 (w) (C-H stretch); 1737 (s) (C=O stretch).

[0244] Yielded as a light-yellow oil with a 55% yield.

[0245] Compound 4b: Disulfanediylbis(hexane-6, 1-diyl) dipentanoate

[0246] 1H NMR (400 MHz, CDCI3): 6 ppm: 0.92 (6H, t, Ha); 2.30 (4H, t, Hd); 4.06 (4H, t, He); 2.68 (4H, t, Hj); 1.63 (12H, m, Hf, Hi, Hc); 1.40 (12H, m, Hb, Hg, Hh).13C NMR (400 MHz, CDCI3): 6 ppm: 13.73 (Ci); 34.10 (C4); 173.96 (C5); 64.17 (C6); 38.91 (C11); 22.28, 25.61, 28.11 (C2, C8, C9); 27.09, 28.54, 29.06 (C3, C7, C10).

[0247] ESI-MS: m / z: [M+H]+= 435.26; [M+Na]+= 457.24

[0248] I R:vmax / cm-1: 2932 (w) and 2857 (w) (C-H stretch); 1732 (s) (C=O stretch).

[0249] Yielded as a light-yellow oil with a 61% yield.

[0250] Compound 4c: Disulfanediylbis(ethane-2.1-diyl) dinonanoate

[0251] 1H NMR (400 MHz, CDCI3): 6 ppm: 0.88 (6H, t, Ha,3J = 8 Hz); 1.27 (20H, m, Hb- Hf); 1.62 (4H, m, Hg,3J = 8 Hz); 2.32 (4H, t, Hh,3J = 8 Hz); 4.33 (4H, t, Hi,3J = 8 Hz); 2.92 (4H, t, Hj,3J = 8 Hz).

[0252] 13C NMR (400 MHz, CDCI3): 5 ppm: 14.10 (Ci); 24.92 (C7); 34.32 (C8); 173.62 (C9); 62.05 (Cw); 37.36 (Cn); 31.81, 29.22, 29.15, 29.13, 22.65 (C2- C6).

[0253] ESI-MS: m / z: [M+ NH4]+= 452.29

[0254] I R:vmax / cm-1: 2924 (w) and 2853 (w) (C-H stretch); 1737 (s) (C=O stretch).

[0255] Yielded as a light-yellow oil with a 69% yield.

[0256] Step R: synthesis of compounds 6a-6d from mercapto carboxylic acids 5a-5d Sodium iodide (1 mol%, 0.0283 mmol, 4.24 mg) is added to ethyl acetate (5.7 mL) along with the mercapto carboxylic acid 5a (2.83 mmol, 0.5 g) or 5b (2.83 mmol, 0.42 g) or 5c (2.83 mmol, 0.26 g) or 5d (2.83 mmol, 0.30 g) and stirred at 40°C until the contents of the mixture dissolve. To the solution is added aqueous hydrogen peroxide (30% w / w) (2.83 mmol, 0.31 mL) dropwise over 1 minute. The resulting mixture is stirred until the solution turns from a pale-yellow colour to a deep red-orange colour (0.5h). Afterwards, the contents of the reaction are transferred to a separating funnel along with a saturated aqueous solution of sodium thiosulfate and shaken, causing a colour change from red to colourless of the organic phase. The organic phase is washed with brine (3 x 15 mL) and the combined aqueous phases are washed with ethyl acetate (3 x 15 mL). The combined organic phases are dried over anhydrous magnesium sulphate and the solvent removed in vacuo to yield the disulfide carboxylic acid.Compound 6a: 8,8’-disulfanediyldioctanoic acid

[0257] 1H N MR (400 MHz, CDCh): 6 ppm: 11.57 (2H, s, Ha); 2.67 (4H, t, Hh,3J = 8 Hz); 2.35 (4H, t, Hb,3J = 8 Hz); 1.66 (8H, hept, Hc, Hg); 1.35 (12H, m, Hd, He, Hf).

[0258] 13C NMR (400 MHz, CDCI3): 5 ppm: 180.48 (Ci); 39.03 (C8); 34.07 (C2); 29.10, 24.56 (C3 / C7); 28.88, 28.83, 38.26 (C Cs / Ce).

[0259] ESI-MS: m / z: [M-H]+= 349.15; [M]+= 350.15.

[0260] IR:vmax / cm’1: 3036 (br) (O-H stretch); 2922 (s) and 2851 (s) (C-H stretch); 1687 (vs) (C=O stretch).

[0261] Yielded as a white powdered solid at a yield of 96%.

[0262] Compound 6b: 6, 6’-disulfanediyldihexanoic acid

[0263] 1H NMR (400 MHz, CDCh): 6 ppm: 2.69 (4H, t, Hf,3J = 8 Hz); 2.38 (4H, t, Hb,3J = 8 Hz); 1.69 (8H, hex, Hc, He); 1.46 (4H, m, Hd).

[0264] 13C NMR (400 MHz, CDCI3): 5 ppm: 179.75 (Ci); 33.85 (C2); 24.25, 28.80 (C3 / C5); 38.84 (C6); 27.83 (C4).

[0265] ESI-MS: m / z: [M+NH4]+= 312.13; [M+Na]+= 317.09.

[0266] IR:vmax / cm’1: 2990 (br) (O-H stretch); 2933 (s) and 2856 (s) (C-H stretch); 1684 (vs) (C=O stretch).

[0267] Yielded as a white powdered solid with a yield of 70%.

[0268] Compound 6c: 3.3’-disulfanediyldipropionic acid

[0269] 1H NMR (400 MHz, CDCh): 6 ppm: 2.83 (4H, t, Hc,3J = 8 Hz); 2.61 (4H, t, Hb,3J = 8 Hz).

[0270] 13C NMR (400 MHz, CDCI3): 5 ppm: 173.94 (Ci); 33.33 (C3); 32.90 (C2).

[0271] ESI-MS: m / z: [M+Na]+= 232.99.

[0272] IR:vmax / crn-1: 2927 (s) (C-H stretch); 2880 (br) (O-H stretch); 1684 (vs) (C=O stretch). Yielded as a white powdered solid with a yield of 85%.Compound 6d: 2,2’-disulfanediyldiacetic acid

[0273] 1H NMR (400 MHz, CDCh): 6 ppm: 3.52 (4H, s, Hb)

[0274] 13C NMR (400 MHz, CDCI3): 5 ppm: 171.63 (Ci); 40.65 (C2).

[0275] ESI-MS: m / z: [M+NH4]+= 200.05.

[0276] IR:vmax / cm’1: 2995 (br) (C-H stretch); 2911 (br) (O-H stretch); 1683 (vs) (C=O stretch).

[0277] Yielded as a white powdered solid with a yield of 85%.

[0278] Step S: synthesis of compounds 8a-8d by Steglich esterification

[0279] To dry DCM (20 mL) is added the disulfide carboxylic acid product 6a-6d of step R (see table 3) along with DCC (2.88 mmol, 0.5941 g) and DMAP (10 mol%, 0.0352 g). The resulting mixture is stirred at25°C under an inert N2atmosphere until the contents of the mixture are fully dissolved. Alcohol 7a-7d (see table 3) is added to the solution via a syringe. The resulting mixture is stirred at 25°C for 24h. The resulting cloudy suspension is filtered through filter paper to remove the white powdered precipitate (urea by-product). The resulting DCM filtrate is washed with brine (3x 15 mL) and the combined aqueous phases are extracted with DCM (3 x 15 mL). The combined organic phases are concentrated via rotary evaporation under reduced pressure. The resulting oil-like crude product mixture is purified via column chromatography over silica gel with a DCM eluent.

[0280] Table 3 shows the reagents and compounds used in the synthesis step S

[0281]

[0282] Compound 8a: dipropyl 8,8’-disulfanediyldioctanoate

[0283] 1H NMR (400 MHz, CDCh): 6 ppm: 4.03 (4H, t, Hc,3J = 8 Hz); 2.67 (4H, t, Hj,3J = 8 Hz); 2.30 (4H, t, Hd,3J = 8 Hz); 1.65 (12H, m, Hb, He, Hi); 1.35 (12H, m, Hf, Hg, Hh); 0.94 (6H, t, Ha,3J = 8 Hz).13C NMR (400 MHz, CDCI3): 5 ppm: 173.84 (C4); 65.82 (C3); 39.04 (Cn); 34.29 (C5); 29.12, 24.91, 22.00 (C2, C6, C10); 28.98, 28.86, 28.30 (C7, C8, C9); 10.40 (Ci).

[0284] ESI-MS: m / z: [M+H]+= 435.26; [M+NH4]+= 452.29; [M+Na]+= 457.24.

[0285] I R:vmax / cm-1: 2926 (s) and 2854 (s) (C-H stretch); 1731 (vs) (C=O stretch).

[0286] Yielded as a pale yellow oil at a yield of 33%.

[0287] Compound 8b: dipentyl 6, 6’ -disulf anediyldihexanoate

[0288] 1H NMR (400 MHz, CDCh): 6 ppm: 4.06 (4H, t, Hc,3J = 8 Hz); 2.67 (4H, t, Hj,3J = 8 Hz); 2.31 (4H, t, Hf,3J = 8 Hz); 1.67 (12H, m, Hi, Hg, Hd); 1.39 (12H, m, Hb, Hh, Hc); 0.91 (6H, t, Ha,3J = 8 Hz).

[0289] 13C NMR (400 MHz, CDCI3): 5 ppm: 173.58 (C6); 64.41 (C5); 38.69 (Cn); 34.12 (C7); 28.80, 28.32, 24.55 (C10, C8, C4); 28.06, 27.94, 22.29 (C2, C3, C9); 13.94 (Ci).

[0290] ESI-MS: m / z: [M+H]+= 435.26; [M+NH4]+= 452.29 ; [M+Na]+= 457.24.

[0291] I R:vmax / cm-1: 2929 (s) and 2856 (s) (C-H stretch); 1732 (vs) (C=O stretch).

[0292] Yielded as a pale yellow oil at a yield of 91%.

[0293] Compound 8c: dioctyl 3,3’-disulfanediyldipropionate

[0294] 1H NMR (400 MHz, CDCh): 5 ppm: 4.02 (4H, t, Hh,3J = 8 Hz); 2.86 (4H, t, Hj,3J = 8 Hz); 2.66 (4H, t, Hi,3J = 8 Hz); 1.56 (4H, p, Hg,3J = 8 Hz); 1.21 (20H, m, Hb-Hf); 0.81 (6H, t, Ha,3J = 8 Hz); 1.56 (4H, p Hg,3J = 8 Hz); 1.21 (20H, m, Hb-Hf); 0.81 (6H, t, Ha,3J = 8 Hz).

[0295] 13C NMR (400 MHz, CDCI3): 5 ppm: 171.62 (C9); 64.90 (C8); 34.11 (C10); 33.21 (Cn); 31.75 (C2-C6); 29.17 (C2-C6); 29.14 (C2-C6); 28.56 (C7); 25.88 (C2-C6); 22.60 (C2-C6); 14.05 (Ci); 31.75 (C2-C6); 29.17 (C2-C6); 29.14 (C2-C6); 28.56 (C7); 25.88 (C2-C6); 22.60 (C2-C6); 14.05 (Ci).

[0296] ESI-MS: m / z: [M+Na]+= 457.24.

[0297] I R:vmax / cm-1: 2925 (s) and 2854 (s) (C-H stretch); 1733 (vs) (C=O stretch).

[0298] Yielded as a pale yellow oil at a yield of 77%.

[0299] Compound 8d: di nonyl 2,2’-disulfanediyldiacetate

[0300] 1H NMR (400 MHz, CDCh): 6 ppm: 4.14 (4H, t, Hj,3J = 8 Hz); 3.58 (4H, s, Hj); 1.66 (4H, p, Hh,3J = 8 Hz), 1.32 (24H, m, Hb-Hg); 0.88 (6H, t, Ha,3J = 8 Hz).

[0301] 13C NMR (400 MHz, CDCI3): 5 ppm: 169.40 (Cw); 65.85 (C9); 14.10 (Ci); 31.85, 29.46, 29.22, 25.83, 22.66 (C2-C7); 41.44 (Cn); 28.53 (C8).ESI-MS: m / z: [M]+= 434.25.

[0302] I R:vmax / cm-1: 2924 (s) and 2854 (C-H stretch); 1732 (vs) (C=O stretch).

[0303] Yielded as a pale yellow oil at a yield of 60%.

[0304] Figure 11 shows a synthetic step for converting the ester disulfide precursor compounds 4a-4c or 8a-8c (which may be provided by the synthesis shown in Figure 9 and described above) into the precursor compounds 9a-9c or 10a-10c respectively (which may in turn be used to provide SAM precursors in accordance with the invention).

[0305] Figures 12A and 12B respectively show the atom assignments for the precursor compounds 9a-9c and 10a-10c which are used in the NMR spectroscopy assignments discussed below.

[0306] Step T: synthesis of compounds 9a-9c and 10a-10c by sulfenamide formation To a stirring mixture of pyridine (2 mL) and acetonitrile (2 mL) at 40°C is added the selected ester disulfide compound 4a-4c, 8a-8c (1.00 g, 2.30 mmol, 1.0 eq) and phthalimide (0.64 g, 4.37 mmol, 1.9 eq.) The mixture is stirred until the contents are fully dissolved. Once the contents are dissolved, the mixture is cooled to 0°C in an ice bath and stirred, whereby bromine (0.48 g, 2.64 mmol, 1.15 eq.) is added dropwise to the solution over a period of 90 minutes. After the bromine is added, the resulting solution is stirred for an additional 30 minutes at25°C. Afterwards, the contents of the reaction mixture are transferred to a separating funnel along with a saturated solution of aqueous sodium thiosulfate (30 mL) and then partitioned with dichloromethane (30 mL). The aqueous phase is washed with dichloromethane (3 x 30 mL) and the combined organic phases are dried over anhydrous magnesium sulfate. The dichloromethane is removed in vaccuo and to the resulting residue is added toluene (50 mL) which forms a white-cream precipitate, which is unreacted phthalimide. The precipitate is removed via filtration and the resulting filtrate is reduced in volume in vacuo and purified over silica via flash column chromatography (eluent system: ethyl acetate: hexane 1:1).Compound 9a: 9-((1 ,3-dioxoisoindolin-2-yl)thio)nonyl acetate

[0307] 1H NMR (400 MHz, CDCh): 6 ppm: 7.91 (2H, m, Hk); 7.78 (2H, m, Hi); 2.04 (3H, s, Ha); 4.04 (2H, t, Hb,3J = 8 Hz); 1.59 (4H, m, Hc+Hi); 2.88 (2H, t, Hj,3J = 8 Hz); 1.42 (2H, m, Hd); 1.27 (8H, m, He-Hh).

[0308] 13C NMR (400 MHz, CDCI3): 5 ppm: 171.27 (C2); 168.56 (C12); 134.58 (C15); 132.09 (C13); 123.87 (C14); 64.62 (C3); 29.28, 29.12, 29.01, 28.85 (C6-C9); 28.57, 28.11 (C4+C10); 28.37 (C5); 21.03 (Ci).

[0309] ESI-MS: m / z [M+H]+= 364.16.

[0310] IR:vmax / cm’1: 2854 (w) and 2927 (w) (C-H stretch); 1733 (s) and 1712 (s) (C=O stretch).

[0311] EA: Calculated for C19H25NO4S (C, 62.79%; H, 6.93%, N, 3.85%; S, 8.82%), found (C, 62.94%, H, 5.76%; N, 4.34%; S, 8.45%)

[0312] Yielded as a pale yellow viscous oil at a yield of 83%.

[0313] Compound 9b: 6-((1,3-dioxoisoindolin-2-yl)thio)hexyl pentanoate

[0314] 1H NMR (400 MHz, CDCh): 6 ppm: 7.92 (2H, m, Hk); 7.78 (2H, m, Hi); 4.03 (2H, t, He,3J = 8 Hz); 2.88 (2H, t, Hj,3J = 8 Hz); 2.28 (2H, t, Hd,3J = 8 Hz); 1.59 (6H, m, Hc, Hi, Hf); 1.47 (2H, m, Hg); 1.34 (4H, m, Hb, Hh); 0.90 (3H, t, Ha),3J = 8 Hz).

[0315] 13C NMR (400 MHz, CDCI3): 5 ppm: 173.91 (C5); 168.49 (C12); 134.59 (C15); 132.05 (C13); 123.86 (C14); 64.08 (C6); 38.58 (Cn); 34.06 (C4); 28.46, 28.04, 27.05 (C3, C7, C10); 28.00 (C8); 25.51, 22.25 (C2, C9); 13.70 (Ci).

[0316] ESI-MS: m / z: [M+Na]+= 386.14.

[0317] IR:vmax / cm’1: 2860 (w) and 2932 (w) (C-H stretch); 1732 (s) and 1712 (s) (C=O stretch).

[0318] EA: Calculated for C19H25NO4S (C, 62.79%; H, 6.93%, N, 3.85%; S, 8.82%), found (C, 63.06%, H, 7.05%; N, 3.85%; S, 8.80%)

[0319] Yielded as a light orange viscous oil at a yield of 66%.

[0320] Compound 9c: 2-((1,3-dioxoisoindolin-2-yl)thio)ethyl nonanoate

[0321] 1H NMR (400 MHz, CDCh): 6 ppm: 7.94 (2H, m, Hk); 7.80 (2H, m, Hi); 4.31 (2H, t, Hi,3J = 8 Hz); 3.10 (2H, t, Hj,3J = 8 Hz); 2.14 (2H, t, Hh,3J = 8 Hz); 1.51 (2H, m, Hg); 1.24 (10H, m, Hb, He, Hd, He, Hf).

[0322] 13C NMR (400 MHz, CDCI3): 5 ppm: 173.32 (C9); 168.14 (C12); 134.71 (C15); 123.04 (C13); 123.95 (C14); 62.74 (C10); 37.29 (Cn); 31.78 (C8); 24.74 (C7); 14.09 (Ci); 29.14, 29.08, 29.06, 22.62, 33.96 (C2, C3, C4, C5, C6).ESI-MS: m / z: [M+Na]+= 386.14.

[0323] IR:vmax / cm’1: 2853 (w) and 2924 (w) (C-H stretch); 1737 (s) and 1713 (s) (C=O stretch).

[0324] EA: Calculated for C19H25NO4S (C, 62.79%; H, 6.93%, N, 3.85%; S, 8.82%), found (C, 62.94%, H, 7.62%; N, 4.01%; S, 8.41%)

[0325] Yielded as a light orange viscous oil at a yield of 63%.

[0326] Compound 10a: propyl 8-((1,3-dioxoisoindolin-2-yl)thio)octanoate

[0327] 1H NMR (400 MHz, CDCI3): 6 ppm: 7.92 (2H, m, Hk); 7.80 (2H, m, Hi); 4.02 (2H, t, Hc,3J = 8 Hz); 2.88 (2H, t, Hc,3J = 8 Hz); 2.28 (2H, t, Hd,3J = 8 Hz); 1.62 (6H, m, Hb+Hi+He); 1.45 (2H, m, Hh); 1.30 (4H, m, Hg+Hf); 0.93 (3H, t, Ha,3J = 8 Hz).

[0328] 13C NMR (400 MHz, CDCI3): 5 ppm: 173.86 (C4); 168.53 (C12); 134.58 (C15); 132.08 (C13); 123.86 (C14); 65.84 (C3); 38.62 (Cn); 34.27 (C5); 28.92, 28.75 (C8+C7); 28.22 (C9); 28.07, 24.87, 22.00 (C2+Cio+C6); 10.40 (Ci).

[0329] ESI-MS: m / z [M+H]+= 364.16.

[0330] IR:vmax / cm’1: 2855 (w) and 2930 (w) (C-H stretch); 1732 (s) and 1713 (s) (C=O stretch).

[0331] EA: Calculated for C19H25NO4S (C, 62.79%; H, 6.93%, N, 3.85%; S, 8.82%), found (C, 62.70%, H, 6.56%; N, 4.11%; S, 8.19%)

[0332] Yielded as a cream coloured wax-like solid at a yield of 63%.

[0333] Compound 10b: pentyl 6-((1.3-dioxoisoindolin-2-yl)thio)hexanoate

[0334] 1H NMR (400 MHz, CDCI3): 6 ppm: 7.93 (2H, m, Hk); 7.81 (2H, m, Hi); 4.05 (2H, t, Hc,3J = 8 Hz); 2.89 (2H, t, Hj,3J = 8 Hz); 2.30 (2H, t, Hf,3J = 8 Hz); 1.61 (6H, m, Hd, Hi, Hg); 1.49 (2H, m, Hc); 1.32 (4H, m, Hb, Hh); 0.90 (3H, t, Ha,3J = 8 Hz).

[0335] 13C NMR (400 MHz, CDCI3): 5 ppm: 173.52 (C6); 168.43 (C12); 134.58 (C15); 132.01 (C13); 123.83 (C14); 64.41 (C10); 38.45 (Cn); 34.03 (C8); 28.28, 22.27 (C2, C9); 28.02, 27.81, 24.42 (C4, C10, C8); 27.86 (C3); 13.93 (Ci).

[0336] ESI-MS: m / z: [M+Na]+= 386.14.

[0337] IR:vmax / cm’1: 2861 (w), 2932 (w) and 2953 (w) (C-H stretch); 1731 (s) and 1714 (s) (C=O stretch).

[0338] EA: Calculated for C19H25NO4S (C, 62.79%; H, 6.93%, N, 3.85%; S, 8.82%), found (C, 62.89%, H, 6.64%; N, 3.95%; S, 8.48%)

[0339] Yielded as a light yellow viscous oil at a yield of 44%.Compound 10c: octyl 3-((1 ,3-dioxoisoindolin-2-yl)thio)propanoate

[0340] 1H NMR (400 MHz, CDC ): 6 ppm: 7.94 (2H, m, Hk); 7.82 (2H, m, Hi); 4.03 (2H, t, Hh,3J = 8 Hz); 3.14 (2H, t, Hj,3J = 8 Hz); 2.75 (2H, t, Hi,3J = 8 Hz); 1.61 (6H, m, Hg); 1.29 (10H, m, Hb-Hf); 0.90 (3H, t, Ha,3J = 8 Hz).

[0341] 13C NMR (400 MHz, CDCI3): 5 ppm: 171.36 (C9); 168.36 (C12); 134.66 (C15); 132.06 (C13); 123.93 (C14); 65.16 (C8); 34.44 (C10); 33.99 (Cn); 31.78, 29.19, 29.16, 25.85, 22.64 (C2-C6); 28.52 (C7); 14.09 (Ci).

[0342] ESI-MS: m / z: [M+Na]+= 386.14.

[0343] IR:vmax / cm’1: 2848 (w), 2920 (w) and 2952 (w) (C-H stretch); 1726 (s) and 1710 (s) (C=O stretch).

[0344] EA: Calculated for C19H25NO4S (C, 62.79%; H, 6.93%, N, 3.85%; S, 8.82%), found (C, 63.93%, H, 6.92%; N, 4.05%; S, 8.73%)

[0345] Yielded as a white wax-like solid at a yield of 61%.

[0346] Figure 13 shows a synthetic step for converting the precursor compounds 9a-9c or 10a-10c (which may be provided by the synthesis shown in Figure 11 and described above) into the SAM precursor compounds 11a-11c or 12a-12c respectively (which are in accordance with the present invention).

[0347] Figures 14A and 14B respectively show the atom assignments for the SAM precursors 11a-11c and 12a-12c which are used in the NMR spectroscopy assignments discussed below.

[0348] Step U: synthesis of SAM precursors 11a-11c and 12a-12c by disulfide silane formation

[0349] To a multi-neck round bottom flask is added the phtlaimide-adduct precursor 9a-9c or 10a-10c (1.0 g, 2.75 mmol, 1.00 eq.) corresponding to the desired final silane. The flask is fitted with a reflex-condenser, sealed with an airtight rubber septum and flushed with nitrogen for 10 minutes. To the flask under a N2 atmosphere is added anhydrous toluene (4 mL), the temperature raised to 110°C and the contents stirred. Once there are no signs of undissolved solid / oil left, mercaptopropyltriethoxysilane (MPTES) (0.36 g, 1.51 mmol, 0.55 eq), is added via a syringe. The resulting mixture is stirred for 48 h at 110°C under N2. After completion, the mixture is cooled to room temperature whereby a white crystalline solid forms in the mixture. The mixture is filtered and the resulting white crystalline solid washed with anhydrous toluene. The collected filtrates are combined and toluene removed in vacuo to form the crudeproduct mixture which is subsequently purified via flash column chromatography over silica using an ethyl acetate and hexane eluent system (1:1)

[0350] Compound 11a: 9-((3-trethoxysilyl)propyl)disulfaneyl) nonyl acetate

[0351] 1H NMR (400 MHz, CDCh): 6 ppm: 4.05 (2H, t, Hb,3J = 8 Hz); 3.83 (6H, q, Hn,3J = 8 Hz); 2.71 (2H, t, Hk,3J = 8 Hz); 2.68 (2H, t, Hj,3J = 8 Hz); 2.05 (3H, s, Ha); 1.81 (2H, p, Hi,3J = 8 Hz); 1.63 (4H, m, Hc+Hi); 1.34 (10H, m, Hd-Hh); 1.23 (9H, t, Ho,3J = 8 Hz); 0.74 (2H, m, Hm).

[0352] 13C NMR (400 MHz, CDCI3): 5 ppm: 171.22 (C2); 64.61 (C3); 54.40 (C15); 41.94 (C12); 39.13 (C11); 29.36, 39.17, 29.14, 28.48, 25.88 (C5-C9); 29.19, 28.59 (C4+C10); 22.67 (C13); 21.01 (Ci); 18.31 (Cie); 9.48 (C14).

[0353] ESI-MS: m / z [M+Na]+= 477.21.

[0354] I R:vmax / cm-1: 2944 (w), 2926 (w) and 2854 (w) (C-H stretch); 1740 (s) (C=O stretch). EA: Calculated for C19H25NO4S (C, 52.82%; H, 9.31%, N, 0.00%; S, 14.10%), found (C, 52.62%, H, 9.03%; N, 0.00%; S, 14.35%)

[0355] Yielded as a pale yellow oil at a yield of 61%.

[0356] Compound 11b: 6-((3-trethoxysilyl)propyl)disulfaneyl)hexyl pentanoate

[0357] 1H NMR (400 MHz, CDCh): 5 ppm: 3.99 (2H, t, He,3J = 8 Hz); 3.76 (6H, q, Hn,3J = 8 Hz); 2.64 (2H, t, Hk,3J = 8 Hz); 2.61 (2H, t, Hj,3J = 8 Hz); 2.23 (2H, t, Hd,3J = 8 Hz); 1.74 (2H, p, Hi,3J = 8 Hz); 1.58 (6H, m, Hf+Hi+Hc); 1.16 (9H, t, H0,3J = 8 Hz); 0.85 (3H, t, Ha,3J = 8 Hz); 0.66 (2H, m, Hm).

[0358] 13C NMR (400 MHz, CDCI3): 5 ppm: 172.94 (C5); 63.16 (C6); 57.40 (C15); 40.90 (C12); 37.90 (C11); 33.08 (C4); 28.05, 27.53, 36.07 (C7, C3, C10); 27.11, 24.60, 21.26 (C2, C8, C9); 21.66 (Ci3); 17.30 (C ); 12.71 (Ci); 8.47 (C14).

[0359] ESI-MS: m / z: [M+Na]+= 477.21.

[0360] I R:vmax / cm-1: 2941 (w) and 2927 (w) (C-H stretch); 1735 (s) (C=O stretch).

[0361] EA: Calculated for C19H25NO4S (C, 52.82%; H, 9.31%, N, 0.00%; S, 14.10%), found (C, 56.27%, H, 9.35%; N, 0.00%; S, 13.96%)

[0362] Yielded as a pale orange oil at a yield of 85%.

[0363] Compound 11c: 2-((3-trethoxysilyl)propyl)disulfaneyl)ethyl nonanoate

[0364] 1H NMR (400 MHz, CDCh): 5 ppm: 4.32 (2H, t, Hi,3J = 8 Hz); 3.82 (6H, q, Hn,3J = 8 Hz); 2.89 (2H, t, Hj,3J = 8 Hz); 2.73 (2H, t, Hk,3J = 8 Hz); 2.31 (2H, t, Hh,3J = 8 Hz);l.81 (2H, p, Hi,3J = 8 Hz); 1.62 (2H, p, Hg,3J = 8 Hz); 0.88 (3H, t, Ha,3J = 8 Hz); 1.25 (19H, m, Ho+Hb-Hf); 0.74 (2H, m, Hm).

[0365] 13C NMR (400 MHz, CDCI3): 5 ppm: 173.65 (C9); 62.31 (C10); 58.43 (C15); 41.98 (C12); 37.19 (C11); 34.23 (C8); 31.81, 29.22, 29.15, 29.12, 22.59 (C2-C6); 24.93 (C7); 22.65 (C13); 18.32 (Cie); 14.10 (Ci); 9.47 (Ci4).

[0366] ESI-MS: m / z: [M+Na]+= 477.21.

[0367] I R:vmax / cm-1: 2924 (w) and 2855 (w) (C-H stretch); 1738 (s) (C=O stretch).

[0368] EA: Calculated for C19H25NO4S (C, 52.82%; H, 9.31%, N, 0.00%; S, 14.10%), found (C, 52.06%, H, 8.29%; N, 0.00%; S, 14.15%)

[0369] Yielded as a pale yellow oil at a yield of 66%.

[0370] Compound 12a: propyl 8-((3-trethoxysilyl)propyl)disulfaneyl)octanoate

[0371] 1H NMR (400 MHz, CDCI3): 6 ppm: 4.03 (2H, t, Hc,3J = 8 Hz); 3.82 (6H, q, Hn,3J = 8 Hz); 2.69 (4H, p, Hj+Hk,3J = 8 Hz); 2.30 (2H, p, Hd,3J = 8 Hz); 1.81 (2H, t, Hi,3J = 8 Hz); 1.64 (6H, m, Hb+He+Hi); 1.37 (6H, m, Hf-Hh); 1.23 (9H, t, Ho,3J = 8 Hz); 0.74 (2H, m, Hm).

[0372] 13C NMR (400 MHz, CDCI3): 5 ppm: 173.90 (C4); 65.86 (C3); 58.41 (C15); 41.95, 39.07 (C11+C12); 34.33 (C5); 29.14, 24.93, 22.02 (C2+C6+Cio); 29.01, 28.88, 28.33 (C7-C9); 22.68 (C13); 18.32 (C ); 10.41 (Ci); 9.49 (Ci4).

[0373] ESI-MS: m / z [M+Na]+= 477.21.

[0374] I R:vmax / cm-1: 2938 (w), 2926 (w) and 2856 (w) (C-H stretch); 1734 (s) (C=O stretch). EA: Calculated for Ci9H25NO4S (C, 52.82%; H, 9.31%, N, 0.00%; S, 14.10%), found (C, 52.80%, H, 8.69%; N, 0.00%; S, 14.67%)

[0375] Yielded as a pale yellow oil at a yield of 80%.

[0376] Compound 12b: pentyl 6-((3-trethoxysilyl)propyl)disulfaneyl) hexanoate

[0377] 1H NMR (400 MHz, CDCI3): 5 ppm: 4.06 (2H, t, He,3J = 8 Hz); 3.82 (6H, q, Hn,3J = 8 Hz); 2.70 (2H, t, Hk,3J = 8 Hz); 2.68 (2H, t, Hj,3J = 8 Hz); 2.31 (2H, t, Hf,3J = 8 Hz); 1.81 (2H, p, Hi,3J = 8 Hz); 1.66 (6H, m, Hg+Hh+Hd); 1.43 (2H, p, Hi,3J = 8 Hz); 1.33 (4H, m, Hb+Hc); 1.23 (9H, t, Ho,3J = 8 Hz); 0.73 (2H, m, Hm).

[0378] 13C NMR (400 MHz, CDCI3): 5 ppm: 173.65 (C6); 64.46 (C5); 58.39 (C15); 41.88 (C12); 38.73 (C11); 34.17 (C7); 28.82, 28.33, 24.59 (C4+C8+C9); 28.08, 22.31 (C2+C3); 22.66 (C13); 18.30 ; 13.96 (Ci); 9.45 (Ci4).

[0379] ESI-MS: m / z

[0380]

[0381] +Na]+= 477.21.I R:vmax / cm-1: 2938 (w) and 2927 (w) (C-H stretch); 1733 (s) (C=O stretch).

[0382] EA: Calculated for C19H25NO4S (C, 52.82%; H, 9.31%, N, 0.00%; S, 14.10%), found (C, 52.77%, H, 9.42%; N, 0.00%; S, 14.64%)

[0383] Yielded as a pale orange oil at a yield of 92%.

[0384] Compound 12c: octyl 3-((3-trethoxysilyl)propyl)disulfaneyl)propanoate

[0385] 1H NMR (400 MHz, CDCI3): 6 ppm: 4.09 (2H, t, Hh,3J = 8 Hz); 3.82 (6H, q, Hn,3J = 8 Hz); 2.91 (2H, t, Hi,3J = 8 Hz); 2.72 (4H, q, Hj+Hk,3J = 8 Hz); 1.81 (2H, p, Hi,3J = 8 Hz); 1.63 (2H, m, Hg); 1.31 (10H, m, Hb-Hf); 1.23 (9H, t, Ho,3J = 8 Hz); 0.88 (3H, t, Ha,3J = 8 Hz); 0.73 (2H, m, Hm).

[0386] 13C NMR (400 MHz, CDCI3): 5 ppm: 171.89 (C9); 64.95 (C8); 58.43 (C15); 41.75 (Cn); 34.28 (C12); 33.27 (C10); 31.78, 29.20, 29.18, 28.59, 25.91 (C2-C6); 18.31 (Cie); 14.09 (Ci); 9.47 (C14).

[0387] ESI-MS: m / z: [M+Na]+= 477.21.

[0388] I R:vmax / cm-1: 2926 (w) and 2857 (w) (C-H stretch); 1736 (s) (C=O stretch).

[0389] EA: Calculated for C19H25NO4S (C, 52.82%; H, 9.31%, N, 0.00%; S, 14.10%), found (C, 54.97%, H, 9.52%; N, 0.00%; S, 14.96%)

[0390] Yielded as a pale yellow oil at a yield of 83%.

[0391] Figure 15 shows a synthetic scheme for making methyl 10-((3-trethoxysilyl)propyl)disulfaneyl)decanoate 18 which is an exemplary SAM precursor in accordance with the invention. It will be appreciated that a corresponding synthesis may be used to make different SAM precursors falling within the same family with standard modifications to the method.

[0392] Figure 16 shows the atom assignments used in the NMR spectroscopy assignments for the products 15, 16, 17 and 18 of the steps V-Z shown in Figure 15 and discussed below.

[0393] Step V: synthesis of 10,10’ -disulfanediyldidecanoic acid (compound 15) 10-bromodecanoic acid 13 (5.0g, 20.00 mmol, 1.0 eq.), thiourea 14 (2.0 g, 26.00 mmol, 1.3 eq) and water (20 mL) are placed in a round bottom flask. The resulting mixture is refluxed at 100°C for 3 hours. Sodium hydroxide (14 mL, 3M) is then added and the mixture is refluxed at 100°C for one additional hour. The reaction mixture is cooled in an ice bath, and dilute sulfuric acid is added dropwise until the solution has a pH of about 2. The cloudy solution is then extracted with diethyl-ether (2 x 25 ml),dried over anhydrous MgSO4, and concentrated under reduced pressure to form a yellow oil with white precipitate suspended in it. Sodium iodide (15 mg) is added to ethyl acetate (20 mL) along with the yellow oil and stirred at 40°C until the contents of the mixture dissolve. To the solution is added aqueous hydrogen peroxide (30% w / w) dropwise until the reaction mixture turns dark red. The resulting mixture is left to stir for 30 minutes. Afterwards, the contents of the reaction are transferred to a separating funnel along with a saturated aqueous solution of sodium thiosulfate and shaken, causing a colour change from red to colourless of the organic phase. The organic phase is washed with brine (3 x 15mL) and the combined aqueous phases are washed with ethyl acetate (3 x 15mL). The combined organic phases are dried over anhydrous magnesium sulfate and the solvent removed in vacuo to yield the crude product as a cream powdered solid. The crude product is purified via recrystallisation using warm ethyl acetate and cold hexane to form a white precipitate which is collected by suction filtration and washed with cold hexane (3 x 20 mL) to form a white powdered solid of 10-mercaptodecanoic acid disulfide 3 (1.08g, 2.66 mmol, 26%).

[0394] 1H NMR (400 MHz, CDCh): 6 ppm: 1.34(20H, m, Hd-Hh); 1.68(8H, sep,3J = 8Hz, Hc+ Hi); 2.38 (4H, t,3J = 8Hz, Hb); 2.70(4H, t,3J = 8Hz, Hj).

[0395] 13C NMR (400 MHz, CDCI3): 5 ppm: 24.62(C3 / C9); 28.39(C4-C8); 28.77(C3 / C9); 28.86(C4-C8); 28.95(C4-C8); 29.05(C4-C8); 29.12(C4-C8); 33.96(C2); 39.32(CIO); 179.60(CI).

[0396] TOF MS ASAP+: m / z: [M + H]+= 407.22

[0397] IR:vmax / cm’1: 1688(vs) (C=O); 2848(s) and 2912(s) (C-H); 3048(b) (O-H).

[0398] Step X: synthesis of dimethyl 10,10’-disulfanediyldidecanoate (compound 16) To a round bottom flask is added 15 (1.00 g, 2.46 mmol, 1.0 eq.), dicyclohexyldicarboiimide (DCC) (1.01 g, 4.92 mmol, 2.0 eq.) and 4-dimethylaminopyridine (DMAP) (61.1 mg, 0.50 mmol, 0.2 eq.). The flask is sealed with a septum and degassed with dry nitrogen gas for 10 minutes at 25°C. To the flask is added anhydrous dichloromethane (20 mL) and the resulting mixture stirred until the solid contents are fully dissolved. To the flask is added, via a syringe, methanol (0.2 mL, 0.16 g, 4.92 mmol, 2.0 eq.). The resulting mixture is stirred at 25°C under dry nitrogen gas for 24 hours. Once the reaction is complete, the white precipitate (DCC-urea byproduct) is removed via filtration, washed withdichloromethane (3 x 20 mL). The filtrates are combined and the solvent removed in vacuo to form the crude product mixture, which is subsequently purified over silica using a dichloromethane eluent via flash column chromatography to yield the product as a pale yellow oil (0.59g, 1.36 mmol, 55%).

[0399] 1H NMR (400 MHz, CDCh): 6 ppm: 1.25(20H, m, Hd-Hh); 1.56(8H, m, Hc-Hj); 2.23(4H, t,3J = 8Hz, Hb); 2.61 (4H, t,3J = 8Hz, Hj); 3.60(6H, s, Ha).

[0400] 13C NMR (400 MHz, CDCh): 6 ppm: 24.93(C4 / CIO); 28.48(C5-C9); 29.1O(C4 / CIO); 29.15(C5-C9); 29.17(C5-C9); 29.19(C5-C9); 34.08(C3); 39.14(CH); 51.44(CI); 174.29(C2).

[0401] MS: m / z: [M]+= 434.25

[0402] IR: Vmax / crn-1: 1737 (vs) (C=O); 2851(s) and 2924(s) (C-H).

[0403] Step Y: synthesis of methyl 10-((1,3-dioxoisoindolin-2-yl)thio)decanoate

[0404] To a stirring mixture of pyridine (1 mL) and acetonitrile (1 mL) at 40°C is added 16 (0.50 g, 1.15 mmol, 1.0 eq.) and phthalimide (0.32 g, 2.18 mmol, 1.9 eq.). The mixture is stirred until the contents are fully dissolved. Once the contents are dissolved, the mixture is cooled to 0°C in an ice bath and stirred, whereby bromine (0.24 g, 1.32 mmol, 1.15 eq.) is added dropwise to the solution. After the bromine is added, the resulting solution is stirred 2.5h at 25°C. Afterwards, the contents of the reaction mixture are transferred to a separating funnel along with a saturated solution of aqueous sodium thiosulfate (15 mL), and then partitioned with dichloromethane (30 mL). The aqueous phase is washed with dichloromethane (3 x 30 mL) and the combined organic phases are dried over anhydrous magnesium sulfate. The dichloromethane is removed in vacuo and to the resulting residue is added toluene (25 mL) which forms a white-cream precipitate, which is unreacted phthalimide. The precipitate is removed via filtration and the resulting filtrate is reduced in volume in vacuo and purified over silica via flash column chromatography (eluent system: ethyl acetate: hexane, 1:1) to yield the final product as a (0.34g, 0.94 mmol, 35%).

[0405] 1H NMR (400 MHz, CDCh): 6 ppm: 1.19(8H, m, Hd-Hg); 1.34(2H, m, Hh); 1.52(4H, m, Hc / Hj); 2.22(2H, t,3J = 8Hz, Hb); 2.80(2H, t,3J = 8Hz, Hj); 3.59(3H, s, Ha); 7.71(2H, m, Hi); 7.85(2H, m, Hk).13C NMR (400 MHz, CDCh): 6 ppm: 24.91 (C4 / C10); 28.12(C5-C9); 28.38(C4 / CIO); 29.02(C5-C9); 29.06(C5-C9); 29.11(C5-C9); 29.20(C5-C9); 34.08(C3); 28.65(Cn); 51.46(Ci); 123.87(CI4); 132.08(CI3); 134.58(CI5); 168.56(CI2); 127.33(C2).

[0406] MS: m / z: [M-H]+= 364.16

[0407] IR: Vmax / crrr1: 1713 (vs) and 1717(vs) (C=O); 2852(s) and 2917(s) (C-H).

[0408]

[0409] To multi-neck round bottom flask is added methyl 17 (0.31 g, 0.852 mmol, 1.00 eq.). The flask is fitted with a reflux-condenser, sealed with an airtight rubber septum and then flushed with nitrogen for 10 minutes. To the flask under a nitrogen atmosphere is added anhydrous toluene (2 mL), the temperature raised to 110°C and the contents stirred. Once there are no signs of undissolved solid / / oil left, mercaptopropyltriethoxysilane (MPTES) (0.11 g, 0.47 mmol, 0.55 eq.), is added via a syringe. The resulting mixture is stirred for 48 h at 110°C under nitrogen. After completion, the mixture is cooled to room temperature whereby a white crystalline solid forms in the mixture. The mixture is filtered and the resulting white crystalline solid washed with anhydrous toluene. The collected filtrates are combined and toluene removed in vacuo to form the crude product mixture which is subsequently purified via flash column chromatography over silica using an ethyl acetate and hexane eluent system (1:1) to yield the final product as a pale yellow oil (0.14g, 0.30 mmol, 64%).

[0410] 1H NMR (400 MHz, CDCh): 6 ppm: 0.67(2H, m, Hm); 1.16(9H, t,3J = 8Hz, Ho); 1.22(10H, m, Hd-Hh); 1.57(4H, m, Hc+Hi); 1.74(2H, m, Hi); 2.23(2H, t,3J=8Hz, Hb); 2.64(4H, m, H Hk); 3.6(3H, s, Ha); 3.75(6H, q,3J=8Hz, Hn).

[0411] 13C NMR (400 MHz, CDCh): 6 ppm: 9.49(CI4); 18.32(Cie); 22.68(CI3); 24.94(C4 / CIO); 28.51(C5-C9); 29.21 (C4 / Cio); 29.17(C5-C9); 29.19(C5-C9); 29.31(C5-C9); 34.10(C3); 39.16(C5-C9); 34.10(C3); 39.16(CH / CI2); 41.96(CH / CI2); 51.46(CI); 58.42(CI5); 174.33(C2).

[0412] MS (DCM+NH3Cl): m / z: [M]+= 454.22

[0413] IR: Vmax / crn-1: 1738 (vs) (C=O); 2854(s) and 2971(s) (C-H).Fabrication of Self-Assembled Monolayers (SAMs)

[0414] Si Wafers (front polished and back etched, n-type, P-doped; >100> surface lattice orientation; resistivity 1-10 Qcnr1; thickness: 525 ± 25 pm; surface roughness: <2 A, purchased from Si-Mat Silicon Materials, Kaufering, Germany) were used as the substrates. The SAM forming solvent, toluene, was purchased as a highly anhydrous solution, stored in an Aero seal bottle over molecular sieves and de-gassed under dry nitrogen gas. Acetone, iso-propyl-alcohol (I PA), methanol, chloroform, hexane, sulfuric acid (aq, cone) and hydrogen peroxide (aq, 30% w / w) were purchase across Sigma-Aldrich, VWR and Thermo- fischer.

[0415] Step 1

[0416] Using a diamond tipped scribe, a 1 x 2 cm section of Si wafer is cut. The wafer is blown under a heavy stream of N2 gas to remove any dust / residue formed during the cutting of the wafer. The wafer is subsequently transferred to a 15 mL glass vial filled with acetone. The vial is transferred to a sonicating water bath and the wafer sonicated for 3 minutes. This is repeated for I PA and methanol, for a total sonication time of 9 minutes.

[0417] Step 2

[0418] The wafer is then rinsed with copious amounts of deionised water. To a separate 15 mL vial is added piranha solution (made by mixing concentrated aqueous sulfuric acid and aqueous hydrogen peroxide (30% w / w) in a 7:3 ratio (by-volume) respectively). The wafer is submerged in the solution for 30 minutes at 25°C.

[0419] Step 3

[0420] The liquid contents of the vial are removed and then rinsed with copious amounts of deionised water (whilst the wafer remains in the vial). Once rinsed, the vial and wafer are blown dry under a stream of dry nitrogen.

[0421] Step 4

[0422] The vial is then sealed airtight, placed under a nitrogen atmosphere by a flow of dry nitrogen via syringe needles and heated to 150°C for 90 minutes.Step 5

[0423] The vial and wafer, whilst still under a nitrogen atmosphere, are cooled to 25°C. To the vial is added 15 mL of dry toluene, followed by the corresponding SAM precursor (15 mg). The vial is gently shaken and then left at 25°C for 24 h.

[0424] Step 6

[0425] The wafer is then removed from the vial, rinsed with dry-toluene, then chloroform and then hexane, blow dried under a stream of dry-nitrogen and then stored under nitrogen for subsequent use.

[0426] Figure 17 shows a schematic methodology for A) obtaining X-ray photoelectron spectroscopy (XPS) data of a self-assembled monolayer following exposure to metastable (e.g. helium) atoms during metastable de-excitation spectroscopy (MDS) ( / .e. MDS-XPS); and B) obtaining control XPS data ( / .e. C-XPS) for a self-assembled monolayer which has not been exposed to metastable (e.g. helium) atoms.

[0427] To obtain the MDS-XPS data, a pristine SAM on a substrate is provided and an XPS spectrum is recorded 170. The pristine SAM is then exposed to metastable atoms (M*, e.g. He*) in an MDS process 172. An XPS is then recorded on the metastable atom exposed SAM. The MDS-XPS spectrum is then calculated by subtracting the initial XPS spectrum from step 170 from the XPS spectrum following exposure to metastable atoms in step 174. To obtain the control C-XPS data, a pristine SAM on a substrate is provided and an initial XPS spectrum is recorded 176. A second XPS spectrum is then recorded 178. The C-XPS spectrum is then calculated by subtracting the initial XPS spectrum provided in step 176 from the second XPS spectrum provided in step 178 to account for the changes in the SAM induced by exposure to X-ray radiation.

[0428] By subtracting the C-XPS spectrum from the MDS-XPS spectrum, changes in the selfassembled monolayer induced by the metastable (e.g. helium) atoms alone ( / .e. absent changes induced by X-ray radiation in the XPS technique) can be determined and differences in the configuration of the SAM molecules with respect to the efficacy of the scission of the cleavage moiety may be interrogated. Data for the XPS study for a number of self-assembled monolayers is shown in Table 4 below.Table 4 shows the XPS data for numerous self-assembled monolayers with the corresponding MDS data shown in Figure 18.

[0429]

[0430] Figure 18 shows the corresponding MDS data to the XPS data shown in Table 4 for the same six self-assembled monolayers. For ease of reference, the structure of the SAM molecule molecule is shown to the right of the metastable de-excitation spectroscopy data. MDS reveals information about the molecular spectroscopy of the self-assembled monolayer, ( / .e. at kinetic energy values above 10 eV) e.g. by probing the molecular orbitals. The MDS further reveals information regarding the number (and energy) of emitted electrons that are detected at the detector ( / .e. at kinetic energy values below 10 eV).

[0431] Figures 18A and 18B show the MDS data for the self-assembled monolayers formed from the SAM molecules octadecyltrichlorosilane (OTS) (Sigma Aldrich) and 3-(dodecyldisulfaneyl)propyl)triethoxy silane respectively. It will be appreciated that neither of these SAM molecules fall within the scope of the present invention. For example, although 3-(dodecyldisulfaneyl)propyl)triethoxy silane does comprise both a triethoxy silane (-Si(OEt)s) surface attachment moiety and a disulfide (S-S) cleavage moiety, it does notinclude an electron directing moiety (EDM) comprising a dipole within the meaning of the present invention. These spectra are therefore shown for comparative purposes with respect to the MDS data (shown in Figures 11C-F) from self-assembled monolayers formed from SAM molecules falling within the scope of the present invention.

[0432] Figures 18C and 18D show MDS data for self-assembled monolayers from SAM molecules 9-((3-(triethoxysilyl)propyl)disulfaneyl)nonyl acetate and methyl 10-((3-(triethoxysilyl)propyl)disulfaneyl)decanoate respectively. As shown, 9-((3-(triethoxysilyl)propyl)disulfaneyl)nonyl acetate and methyl 10-((3-(triethoxysilyl)propyl)disulfaneyl)decanoate differ only in that the dipole provided by the ester functional group ( / .e. electron directing moiety) is reversed. For ease of reference, the direction of the dipole ( / .e. from positive to negative) is depicted adjacent to the ester electron directing group. Thus, as shown, 9-((3-(triethoxysilyl)propyl)disulfaneyl)nonyl acetate has the dipole of the electron directing ester group that points “up” away from the surface attachment moiety and therefore away from the substrate surface on which the selfassembled monolayer is provided. In contrast, methyl 10-((3-(triethoxysilyl)propyl)disulfaneyl)decanoate has the dipole of the electron directing ester group pointing “down” towards the surface attachment moiety / substrate surface.

[0433] Comparison of the data at energies below 10 eV ( / .e. the data indicative of emitted electrons) in Figures 18C and 18D indicates that, when the dipole is pointing “down” towards the substrate surface ( / .e. Figure 18D), more emitted electrons are detected at the detector compared to when the dipole is pointing “away” from the substrate surface. This in turn indicates that the direction of the dipole within the SAM molecule is materially impactful of the direction in which the emitted electrons are being generated, which in turn will impact the efficiency of the lithography process. This is also supported by the corresponding XPS data shown in Figure 4 which shows that there is a slight improvement in the change in carbon content (and thus scission of the cleavage moiety) for methyl 10-((3-(triethoxysilyl)propyl)disulfaneyl)decanoate which indicates that the direction of the dipole may encourage electron ejection towards the cleavage moiety which in turn may increase the likelihood of scission of the cleavage moiety.

[0434] Without wishing to be bound by theory, it is thought that when the dipole points “away” from the substrate surface, the electrons generated by excitation of the electron directing ester moiety are more electrostatically repulsed by the negative side of the dipole, thus resultingin the electron being effectively harpooned towards the cleavage moiety in the direction of the substrate surface, this in turn leads to more efficient and effective scission of the disulfide bond.

[0435] The same behaviour is also observed in Figures 18E and 17F which show MDS data for self-assembled monolayers from SAM molecules 2-((3-(triethoxysilyl)propyl)disulfaneyl)ethyl nonanoate and octyl 3-((3-(triethoxysilyl)propyl)disulfaneyl)propanoate respectively, which again differ from each other only in the direction of the ester dipole. As with 9-((3-(triethoxysilyl)propyl)disulfaneyl)nonyl acetate and methyl 10-((3-(triethoxysilyl)propyl)disulfaneyl)decanoate, when the dipole is pointing towards the substrate surface ( / .e. for octyl 3-((3-(triethoxysilyl)propyl)disulfaneyl)propanoate in Figure 18F), there are more counts at kinetic energy up to 10 eV ( / .e. indicative of emitted electrons) when compared to when the dipole is pointing away from the substrate surface ( / .e. 2-((3-(triethoxysilyl)propyl)disulfaneyl)ethyl nonanoate in Figure 18E). Again, this is supported by the corresponding XPS data shown in Table 4 which clearly shows that there is a negligible change in the self-assembled monolayer comprising octyl 3-((3-(triethoxysilyl) propyl)disulfaneyl) propanoate before and after exposure to metastable ( / .e. helium) atoms. In contrast, there is a much more significant change for 2-((3-(triethoxysilyl)propyl)disulfaneyl)ethyl nonanoate which indicates that the direction of the dipole pointing away from the cleavage moiety may more efficiently direct the emitted electron towards the cleavage group.

[0436] When Figures 18E and 18F are compared to Figures 18C and 18D, it can be seen that the position of the electron directing group (and its dipole) also impacts ( / .e. in addition to the direction of the dipole) the number of emitted electrons detected. For example, methyl 10-((3-(triethoxysilyl)propyl)disulfaneyl)decanoate (MDS data in Figure 18D) and octyl 3-((3-(triethoxysilyl)propyl)disulfaneyl)propanoate (MDS data in Figure 18F) both have dipoles that point towards from the substrate surface, and thus differ only in the fact that the ester electron directing moiety of octyl 3-((3-(triethoxysilyl)propyl)disulfaneyl)propanoate is buried deeper ( / .e. it is further away from the surface formed by the self-assembled monolayer) within the self-assembled monolayer compared to methyl 10-((3-(triethoxysilyl)propyl)disulfaneyl)decanoate which essentially has the ester electron directing moiety at a substantially terminal position.Comparison of the corresponding MDS data for methyl 10-((3-(triethoxysilyl)propyl)disulfaneyl)decanoate and octyl 3-((3- (triethoxysilyl)propyl)disulfaneyl)propanoate ( / .e. Figures 18D and 18E) leads us to the (non-limiting) belief that the “deeper” position of the electron directing moiety in octyl 3-((3-(triethoxysilyl)propyl)disulfaneyl)propanoate results in it being harder for the metastable helium atom to probe the TT molecular orbitals of the electron directing moiety and thus an increase in electrons from o molecular orbitals with lower kinetic energies.

[0437] Furthermore, there is an increase in the number of emitted electrons ( / .e. at kinetic energies below 10 eV) detected for octyl 3-((3-(triethoxysilyl)propyl)disulfaneyl)propanoate with respect to methyl 10-((3-(triethoxysilyl)propyl)disulfaneyl)decanoate which indicates to us that when the electron directing moiety is closer to the surface, there is an increase in the selectivity of the direction in which the emitted electrons are generated. This is also supported by the XPS data shown in Table 4.

[0438] The MDS data shown in Figure 18 and the XPS data shown in Table 4 therefore evidence the improvement in control that is observed in atom lithography using SAM molecules with different electron directing group positions and dipole directions in accordance with the present invention.

[0439] It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention.

[0440] It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and / or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

CLAIMS1. A method of performing atom lithography, the method comprising:forming a self-assembled monolayer comprising a plurality of SAM molecules by exposing a substrate surface to a plurality of SAM precursors, wherein the plurality of SAM precursors comprise a backbone having:iv. a surface attachment moiety (SM) at or proximate to an end of the backbone and configured to attach the SAM precursor to a substrate when forming a selfassembled monolayer;v. a cleavage moiety (CM); andvi. an electron directing moiety (EDM) comprising a dipole; anddirecting a source of metastable atoms at the self-assembled monolayer, transferring energy from the metastable atoms to the self-assembled monolayer to break a bond within the cleavage moiety of at least one of said one or more SAM molecules such that part of the one or more SAM molecules is removed to provide a modified self-assembled monolayer,wherein the modified self-assembled monolayer comprises one or more broken SAM molecules attached to the substrate surface, andwherein preferably one of the following conditions may be satisfied, either wherein the cleavage moiety (CM) comprises the electron directing moiety (EDM) or wherein the electron directing moiety (EDM) and the cleavage moiety (CM) are distinct.

2. The method of Claim 1 , wherein one or more of the plurality of SAM precursors and / or SAM molecules comprise a fluorophore, and the method further comprises:detecting fluorescence, for example detecting a change in fluorescence, emitted from the self-assembled monolayer concurrent with, or following the step of, directing the metastable atoms at the self-assembled monolayer.

3. The method of Claim 2, wherein the part of the one or more SAM molecules that is removed comprises the fluorophore such that the one or more unbroken SAM molecules each comprise the fluorophore but the one or more broken SAM molecules do not comprise the fluorophore.

4. The method of any one of Claim 2 or Claim 3, wherein the fluorophore may be a distinct moiety or wherein the electron directing moiety (EDM) may comprise or provide the fluorophore; and optionally, wherein the fluorophore is or is derived from naphthalene or azulene.

5. The method of any one of Claims 1-4, wherein the method further comprises:exposing at least part of the self-assembled monolayer to a protecting group before the source of metastable atoms is directed at the self-assembled monolayer such that one or more of the SAM molecules comprise the protecting group;wherein the protecting group is configured to modify removal of at least part of the self-assembled monolayer.

5. The method of any one of Claims 1 to 4, further comprising bridging two or more SAM molecules with a bridging moiety by reacting two or more SAM molecules with a bridging molecule comprising multiple functional groups,wherein each of the functional groups is configured to react with a functional group present on each of the two SAM molecules to provide a bridged group,wherein the bridged group comprises two or more cleavage moieties and one or more electron directing moieties,optionally, wherein the bridging molecule provides one or more of said one or more electron directing moieties.

6. The method of any one of Claims 1 to 4, wherein before the substrate surface is exposed to the plurality of SAM precursors, the plurality of SAM precursors are reacted with a bridging molecule comprising multiple functional groups to provide one or more bridged pairs of SAM precursors, wherein the substrate surface are exposed to the one or more bridged pairs of SAM precursors;wherein each of the functional groups is configured to react with a functional group present on each of the two SAM precursors to provide a bridged group,wherein the bridged group comprises two or more cleavage moieties and one or more electron directing moieties,optionally, wherein the bridging molecule provides one or more of said one or more electron directing moieties.

7. The method of Claim 5 or Claim 6, further comprising directing at least two metastable atoms at the bridged group to break the two or more cleavage moieties in the bridge pair and thus remove at least part the bridge pair from the self-assembled monolayer.

8. The method of any one of Claims 1 to 7, wherein the one or more broken SAM molecules each comprise the surface attachment moiety and an exposed moiety resulting from breaking the bond in the cleavage moiety; andthe method further comprises:reacting the one or more exposed moieties of the one or more broken SAM molecules with a reactant to modify the reactivity or functionality of the one or more broken SAM molecules.

8. The method of Claim 8, wherein the reactant is one or more of: a (e.g. metal) nanoparticle such as a gold nanoparticle, alkenes, maleimides, polymer brushes, functionalised silsesquixoanes, thiols, oxides, or inorganic oxides such as silicon oxide, aluminium oxide or titanium oxide.

9. The method of Claim 8 or 9, wherein the reactant modifies the reactivity such that the broken SAM molecules are more resistant to a chemical etch compared to the unbroken SAM molecules.

10. The method of any one of Claims 7 to 9, wherein, following reacting the exposed moieties with the reactant, the method further comprises exposing the self-assembled monolayer to a chemical etchant and selectively removing one or more of the unbroken SAM molecules.

11. A substrate comprising a self-assembled monolayer, wherein the self-assembled monolayer comprises a plurality of one or more distinct SAM molecules, wherein each SAM molecule comprises a backbone having:i. a surface attachment moiety (SM) at or proximate to an end of the backbone wherein the SM is attached to the substrate to form the self-assembled monolayer;ii. a cleavage moiety (CM); andiii. an electron directing moiety (EDM) comprising a dipole;wherein the backbone has one of the following linear arrangements of moieties: SM- R1-CM-R2-EDM-X or SM-R1-EDM-R2-CM-X;wherein R1 comprises an aliphatic and / or aromatic group having between 1 and 20 carbon atoms;wherein R2 comprises an aliphatic and / or aromatic group having between 1 and 20 carbon atoms; andwherein X is optional such that when X is not present the electron directing moiety (EDM) or the cleavage moiety (CM) terminate the backbone, wherein, when X is present, X is selected to be one of the following groups:a group R3 comprising an aliphatic group and / or aromatic group having between 1 and 20 carbon atoms ;a group R3’ comprising an aromatic group; ora hydrogen atom or a deuterium atomwherein each group R3 or R3’ may each optionally comprise a terminal reactive group Y, wherein Y is selected from a carboxylic acid group, amine group, amide group, ester group, alkene group, alkyne group or azide group;optionally, wherein the backbone comprises a fluorophore, more optionally, wherein one of R1, R2, R3, R3’, Y or EDM comprises the fluorophore.

12. The substrate of Claim 11, wherein the cleavage moiety (CM) of each of the one or more SAM molecules comprises at least one bond configured to break when energy is transferred to the SAM molecule from one or more metastable atoms directed at the selfassembled monolayer comprising the SAM molecule.

13. The substrate of Claim 11 or Claim 12, wherein the cleavage moiety (CM) of each of the one or more SAM molecules is or comprises one or more of: a disulfide bond, a sulfonamide moiety (e.g. a N-tosyl carboxamide moiety) or a diazene moiety.

14. The substrate of any one of Claims 7 to 8, wherein the cleavage moiety (CM) of each of the one or more SAM molecules is configured such that, when sufficient energy is transferred to the SAM molecule to break a bond in the cleavage moiety, the portion of the SAM molecule that remains attached to the substrate terminates in a sulfhydryl group.

15. The substrate of any one of Claims 11 to 14, wherein the electron directing moiety (EDM) of each of the one or more SAM molecules comprises a permanent dipole moment.

16. The substrate of Claim 15, wherein the permanent dipole moment is arranged such that the vector ( / .e. defined from positive to negative) of the dipole moment in each of the one or more SAM molecules points substantially towards the cleavage moiety within the same SAM molecule.

17. The substrate of any one of Claims 15 or 16, wherein the permanent dipole moment is arranged such that the vector ( / .e. defined from positive to negative) of the dipole moment in each of the one or more SAM molecules points substantially away from the cleavage moiety within the same SAM molecules.

18. The substrate of any one of Claims 11 to 17, wherein the electron directing moiety (EDM) of each of the one or more SAM molecules is or comprises one or more of the following: an ester moiety, a thioester moiety, an amide moiety, pyramidine-based moiety (e.g. a substituted pyrimidine moiety), a naphthalene moiety or derivatives thereof, an azulene moiety or derivatives thereof or a zwitterionic moiety such as sulfobetaine or carboxybetaine.

19. The substrate of any one of Claims 11 to 18, wherein the self-assembled monolayer further comprises a fluorophore, wherein the fluorophore may be a distinct moiety or wherein the electron directing moiety (EDM) of each of the one or more molecules may comprise or provide the fluorophore and wherein the fluorophore may be or may be derived from naphthalene or azulene.

20. The substrate of any one of Claims 11 to 19, wherein the self-assembled monolayer comprises:one or more broken SAM molecules attached to the substrate surface; and one or more unbroken SAM molecules attached to the substrate surface; wherein the one or more unbroken SAM molecules comprise a fluorophore and the one or more broken SAM molecules does not comprise a fluorophore.

21. The substrate of any one of Claims 11 to 20, wherein each of the broken SAM molecules comprise the surface attachment moiety and an exposed moiety resulting from breaking the bond in the cleavage moiety; andwherein the exposed moiety is attached to a reactant to modify the reactivity or functionality of the one or more broken SAM molecules.

22. The substrate of Claim 21, wherein the reactant is one or more of: a (e.g. metal) nanoparticle such as a gold nanoparticle, alkenes, maleimides, polymer brushes, functionalised silsesquixoanes, thiols, oxides, or inorganic oxides such as silicon oxide, aluminium oxide or titanium oxide; and / orwherein the reactant modifies the reactivity such that the broken SAM molecules are more resistant to a chemical etch compared to the unbroken SAM molecules.

23. The SAM precursor of any one of Claims 11 to 22, wherein the surface attachment moiety comprises sulphur (e.g. a thiol group), silicon (e.g. a trichlorosilane (-SiC ) group, a trimethoxysilane (-Si(OMe)s) group, a triethoxysilane (-Si(OEt)s) group), phosphor (e.g. a phosphonate group) or a carbonyl moiety (e.g. a carboxylic acid moiety).

24. A substrate comprising a self-assembled monolayer, wherein the self-assembled monolayer comprises one or more bridged groups of SAM molecules, wherein each bridged group of SAM molecules comprises two or more SAM precursors and a bridging moiety and wherein the bridged group comprises:i. two or more surface attachment moieties (SM), wherein each of the two or more surface attachment moieties attaches one of the two or more SAM precursors to the substrate;ii. two or more cleavage moieties (CM); andiii. one or more electron directing moieties (EDM) comprising a dipole.

25. The substrate of Claim 24, wherein the bridging moiety comprises an aliphatic or aromatic hydrocarbon chain.

26. The substrate of Claim 24 or Claim 25, wherein the bridging moiety is derived from a bridging molecule comprising two or more functional groups, wherein the two or more (e.g. terminal) functional groups may be the same or different functional groups, and wherein each of the functional groups are configured to react with a functional group present on each of the two SAM precursors to connect the two or more SAM precursors together and form the bridged group, for example, wherein the bridging molecule is a polyfunctional molecule derived from a poly-amide, a poly-carboxylic acid or a poly-ester.

27. A SAM precursor molecule comprising a backbone having the following moieties: i. a surface attachment moiety (SM) at or proximate to a first end of the backbone and configured to attach the SAM precursor to a substrate when forming a selfassembled monolayer;ii. a cleavage moiety (CM); andiii. an electron directing moiety (EDM) comprising a dipole.

28. The SAM precursor of Claim 27, wherein the cleavage moiety (CM) comprises the electron directing moiety (EDM) or wherein the electron directing moiety (EDM) is distinct to the cleavage moiety (CM).

29. The SAM precursor of Claim 28, further comprising a linker group connecting the cleavage moiety (CM) to the surface attachment moiety (SM), wherein the linker group comprises an aliphatic and / or aromatic group.

30. The SAM precursor of any one of Claims 27 to 29, further comprising two or more linker groups, wherein each of the moieties are connected to at least one of the other moieties by at least one of the two or more linker groups, wherein the linker group may be an aliphatic group (R).

31. The SAM precursor of any one of Claims 27 to 30, wherein a second end of the backbone is terminated by terminal moiety, wherein the terminal moiety is an aliphatic group (R) comprising between 1 and 20 carbon atoms.

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