Method for directed assembly of colloidal nanoparticles on the surface of a substrate by convective / capillary deposition

Abstract

The present invention relates to a method for directed assembly of nanoparticles dispersed in a non-polar solvent on the surface of a substrate, in the form of a network of three-dimensional (3D) micrometric patterns, by convective / capillary deposition (CSA), as well as to the substrate obtained by implementing this method.

Description

Directional assembly process of colloidal nanoparticles on the surface of a substrate by convective / capillary deposition

[0001] The present invention relates to the field of assembly methods, in particular to the directed assembly of nanoparticles on a structured substrate.

[0002] The present invention relates in particular to a method of assembling nanoparticles dispersed in a non-polar solvent on the surface of a substrate, in the form of a network of micrometric patterns in 3 dimensions (3D) by convective / capillary deposition, as well as the substrate obtained by implementing this method.

[0003] Directed assembly of colloidal nanoparticles involves transferring nanoparticles from their liquid dispersion medium to predefined areas on a solid surface. This assembly is achieved by applying a force or group of forces to the nanoparticles or by increasing the intensity of pre-existing forces. The combined intensity of these forces must be sufficient to destabilize the colloidal equilibrium and direct the assembly of the nanoparticles to specific areas of the solid surface. These assemblies enable in-depth studies and characterization of the physical properties of the nanoparticles, or leverage these properties for the development of innovative functional devices.

[0004] The assembly of nanoparticles on patterned surfaces is particularly useful for fabricating devices at the nanoscale and microscopic scale, for example electronic and electrochemical systems, sensors, photonic devices, biosensors, information storage media, display devices and optical devices, as well as medical devices (e.g., for drug delivery).

[0005] A first approach to achieving directed assembly of colloidal nanoparticles involves the localized deposition of a small volume (from a few tens of nanoliters to a few microliters) of colloidal dispersion. Following this deposition, evaporation of the solvent allows the nanoparticles to adhere to the surface through capillary forces. This technique enables the assembly of a wide range of colloidal nanoparticle dispersions (metallic, organic, or inorganic) in numerous solvents and on many different substrates. Among the various techniques based on this principle, we can mention electrohydrodynamic inkjet printing and dip-pennanolithography (DPN), for example, using the tip of an atomic force microscope (AFM) like a fountain pen dipped in ink, here replaced by a dispersion of colloidal nanoparticles.The meniscus formed when the AFM tip, impregnated with the colloidal dispersion, contacts the sample surface traps the nanoparticles by capillary action. However, the difficulty in efficiently impregnating the AFM tip with certain colloidal dispersions and the rapid evaporation of some solvents limit the range of colloidal dispersions that can be used with this technique.

[0006] As an alternative to localized deposition of a small volume of dispersion for directed assembly of colloidal nanoparticles, convective self-assembly (CSA) relies on coupling capillary forces with convection currents. These convective currents are generated to compensate for the progressive evaporation of the solvent from the colloidal dispersion deposited on the substrate at the triple line of surface / solvent / air. They lead to an increase in the nanoparticle concentration at this triple line. The assembly of the nanoparticles on the substrate surface then occurs via capillary action within the meniscus of the colloidal dispersion created at the interface between the substrate and the ambient air. Movement of the meniscus allows for 2D and 3D assemblies of colloidal nanoparticles with a compact arrangement and controlled height.The meniscus movement speed can be controlled, for example, by forcibly retracting the contact line. Several techniques are based on horizontal or vertical retraction of the contact line. Varying the meniscus movement speed and the solvent evaporation rate (adjusted by the substrate and / or environmental temperature) allows control over the type of assembly obtained. This technique is particularly well-suited to assembling colloidal dispersions containing nanoparticles, typically ranging from ten nanometers to a few micrometers in diameter, in a polar solvent, such as water. However, a number of nanoparticles are synthesized in nonpolar solvents, and it is difficult to stably transfer them to polar solvents to enable their subsequent assembly by CSA.

[0007] The inventors therefore aimed to provide a process for assembling colloidal nanoparticles by CSA when these particles are suspended in a non-polar solvent, without having to transfer the nanoparticles to a polar solvent. The inventors also aimed for this process to provide one or more pattern matrices consisting of a compact assembly of identical or different nanoparticles, in the form of micrometric patterns with a very high height (approximately 1.5-2 µm) compared to the size of the nanoparticles (approximately 10 nm).

[0008] These goals are achieved by the invention which will be described below. Objects of the invention

[0009] The invention therefore relates primarily to a method for manufacturing a matrix of nanoparticle patterns on the surface of a substrate, in the form of a network of three-dimensional micrometric patterns, said method comprising at least the following steps: a) providing a solid substrate having a surface supporting a resin layer, said layer having a thickness EpR, b) forming cavities in the thickness of said resin layer by lithography to obtain a topographically structured resin layer, c) silanizing the assembly formed by said substrate and said resin layer, d) deposition of said nanoparticles in the cavities formed in said topographically structured resin layer by convective / capillary deposition (CSA) from a colloidal solution comprising said nanoparticles and a non-polar solvent, to obtain said matrix of nanoparticle patterns,said process being further characterized in that: - the thickness EpR of said resin layer is greater than or equal to 1 µm, - said silanization step c) is carried out before or after lithography step b) and before said step d), - the cavities of the topographically structured resin layer have a depth Pc equal to EpR, - said non-polar solvent is chosen from solvents having a contact angle with said resin before silanization (θ, S R ) such that θ S R> 5°- said step d) comprises the following sub-steps:d1) the deposition of a volume Vs of said colloidal solution between the surface of said topographically structured resin and a blade forming an angle of at least 30° approximately with respect to the surface of said topographically structured resin to form a meniscus,d2) the spreading of said colloidal solution by applying a relative translational movement between said meniscus and the assembly formed by the substrate and the topographically structured resin layer, during the evaporation of said solvent so as to fill said cavities with said colloidal solution and deposit a layer of colloidal solution of height Hs on the surface of the resin layer outside of said cavities; and- said patterns have a total height Hm equal to Pc + Hs and greater than 1 µm.

[0010] The invention also relates to the substrate comprising a surface supporting a matrix of nanoparticle patterns directly obtained by implementing the process as defined according to the first object of the invention, said substrate being characterized in that each of the patterns consists of a compact assembly of nanoparticles in the form of three-dimensional patterns, said patterns having a height Hm greater than 1 µm. Definitions

[0011] The contact angle is a measure of a liquid's ability to wet the surface of a solid. The shape a droplet takes on a surface depends on the liquid's surface tension and the nature of the surface. At the boundary between the droplet and the surrounding gas, surface tension can create a curved outline. At the edge of the droplet, where the outline becomes the contact surface, the contact angle is formed between the liquid / solid interface and the tangent to the liquid / gas interface. If the liquid flows uniformly over the solid surface, wetting is complete with a contact angle of 0°. If the angle is between 0° and 90°, the surface is wettable. The surface is said to be hydrophilic in the case of an aqueous solution. An angle between 90° and 150° indicates that the surface is not wettable. It is hydrophobic in the case of an aqueous solution.

[0012] In this application, all contact angle values ​​between a liquid and a surface were determined by depositing a drop of the liquid onto the surface, then taking a photograph of said drop and analyzing its profile. The contact angle values ​​given in this application are given with an uncertainty of ± 5°.

[0013] According to the invention, compact patterns are understood to be patterns not having gaps of sizes greater than or equal to the size of two adjacent nanoparticles, said patterns being composed of an assembly of individual and non-fused nanoparticles.

[0014] Surface roughness is characterized by a complex shape consisting of a continuous series of peaks and valleys of varying heights, depths, and spacing. The surface condition in which irregular features occur continuously or in cycles relatively shorter than the depth is called surface roughness. Roughness can be expressed by "Ra," which is the mean deviation, that is, the arithmetic mean of the absolute values ​​of the deviations, between the peaks and valleys. "Ra" measures the distance between this mean and the center line. It is generally accepted that this concept approximately summarizes the various parameters involved in surface roughness.

[0015] According to the invention, a non-polar solvent is understood to be a solvent whose dipole moment is zero or very low (less than or equal to 0.5 Debye at a temperature of 20 to 25°C). Detailed description

[0016] Thanks to the process according to the present invention, it is now possible to obtain a matrix of nanoparticle patterns by convective / capillary deposition (or CSA) using colloidal solutions of these nanoparticles in a nonpolar solvent, without the need to first transfer these nanoparticles into a polar solvent typically used for CSA deposition. Furthermore, the process according to the invention leads to compact nanoparticle patterns with a significant height (generally greater than 1 µm) despite the very small size of the nanoparticles. Obtaining a significant height is particularly advantageous when the compact patterns are composed of photoluminescent nanoparticles, since in this case, the intensity of the photoluminescence is directly proportional to the height of the patterns. Finally, the patterns formed have regular contours after dissolution of the resin.These results are made possible by the silanization step, which increases the difference in contact angle between the nonpolar solvent of the colloidal solution and the surface of the resin and the surface of the cavities. These results are particularly remarkable when silanization step c) is performed after lithography step b). In this case, the topographically structured surface of the resin, as well as the lateral walls and the bottom of the cavities (which corresponds to the free surface of the substrate), are silanized, further promoting the accumulation of nanoparticles as compact patterns within the cavities formed in the resin layer during CSA deposition step d).

[0017] The substrates usable according to the present invention can be rigid or flexible and are typically chosen from substrates exhibiting low roughness, i.e., having an Ra value less than or equal to 0.5 nm. Examples include glass, silicon, polymers such as polyethylene terephthalate (PET), polyimides, etc.

[0018] According to one embodiment, the substrate supporting the resin layer is preferably chosen from glass and silicon such as silicon wafers (or according to the corresponding English expression "siliconwafer").

[0019] The lithography process used is not critical. Thus, step b) of cavity formation within the thickness of the resin layer can be carried out by photolithography, electron beam lithography or thermal nanoprinting.

[0020] Similarly, the type of resin is not critical. The choice of resin depends on the lithography process used to topographically structure the resin. For example, it could be a photosensitive resin for topographic structuring by photolithography, an electrosensitive resin for topographic structuring by electron beam lithography, or a thermoplastic resin for topographic structuring by thermal nanoprinting.

[0021] The nature of the photosensitive resin is not critical as long as it can be photolithographed in such a way as to be topographically structured (formation of cavities in the thickness of the resin layer) by photolithography.

[0022] The nature of the electrosensitive resin is not critical as long as it can be lithographed in such a way as to be topographically structured (formation of cavities in the thickness of the resin layer) by electron lithography.

[0023] The nature of the thermoplastic resin is not critical as long as it can be lithographed in such a way as to be topographically structured (formation of cavities in the thickness of the resin layer) by thermal nano-imprinting.

[0024] The resin is preferably a photosensitive resin.

[0025] The photosensitive resin is preferably a positive resin, that is to say, one in which the part exposed to UV light becomes soluble in the developer and the unexposed part of the photosensitive resin remains insoluble.

[0026] By way of non-limiting example of positive photosensitive resins usable according to the invention, one may in particular mention resins based on propylene glycol monomethyl ether acetate (PMA) such as those sold in the S1800 series by Microposit, or based on polydimethylglutarimide (PMGI) such as those sold in the LOR series by Kayaku AM.

[0027] The EpR thickness of the resin layer is generally about 1 to 2 µm and preferably about 1.1 to 1.5 µm.

[0028] Step b) of lithography leads to the formation of cavities within the thickness of the resin layer. These cavities can have various shapes, depending on the patterns of the mask used during exposure to UV radiation.

[0029] When the resin is a photosensitive resin, step b) of lithography is a photolithography step which can be carried out according to techniques known to those skilled in the art, in particular by exposing the surface of the photosensitive resin to UV radiation through a mask (physical or digital) having a pattern corresponding to the shape, dimensions and positioning that one wishes to give to the cavities in the resin layer.

[0030] When the resin is an electrosensitive resin, step b) of lithography can in particular be carried out by electron lithography according to techniques known to those skilled in the art, in particular by exposing the resin to an electron beam.

[0031] When the resin is a thermoplastic resin, step b) of lithography can be carried out according to the techniques known to those skilled in the art, in particular by thermal impression of the resin using a mold, having the negative of the pattern of the cavities, then removal of the residual resin in the bottom of the cavities by engraving.

[0032] As previously stated, the cavities in the topographically structured resin layer have a depth Pc equal to the thickness EpR of the resin layer, such that after the lithography step, the bottom of the cavities corresponds to the free surface of the substrate.

[0033] Step c) of silanization can be carried out before or after step b) of lithography.

[0034] According to a first embodiment of the process according to the invention, step c) of silanization is carried out before step b) of lithography. In this case, only the surface of the topographically structured resin layer will be silanized, the lateral walls and the free surface of the substrate present at the bottom of the cavities not being silanized.

[0035] According to a second embodiment of the process according to the invention, step c) of silanization is carried out after step b) of lithography. In this case, the surface of the topographically structured resin layer, the lateral walls, and the free surface of the substrate present at the bottom of the cavities are silanized. This second embodiment is preferred because it allows for a greater difference in contact angles (Δθ) (generally greater than or equal to 6°) between the contact angle of the nonpolar solvent and the surface of the silanized resin (θ S2) and the contact angle of the non-polar solvent with the surface of the silanized substrate at the bottom of the cavities (θ S 1) thus promoting the accumulation of nanoparticles in the cavities of the resin and discouraging the deposition of a layer of nanoparticles on the resin outside the cavities.

[0036] According to a preferred embodiment of the invention, said cavities have a square or rectangular horizontal cross-section. Their lateral dimensions are preferably approximately 2.5x2.5 µm, 5x5 µm or 10x10 µm.

[0037] The spacing between two cavities is preferably about 2 to 50 µm, and even more preferably about 10 to 50 µm.

[0038] The silanization step can be carried out by immersing the substrate and resin layer, topographically structured or not, in a silanization bath containing a silanizing agent in solution in an organic solvent. In this case, the immersion time in the silanization bath can range from approximately 10 to 60 minutes, and preferably from approximately 20 to 40 minutes. The silanization step can also be carried out in the gas phase in a vacuum chamber by evaporating the silanizing agent.

[0039] Examples of silanizing agents include octadecyltrichlorosilane (OTS), hexamethyldisilazane (HMDS), 3-(chloropropyl)-triethoxysilane (CPTES) and 3-aminopropyl-triethoxysilane (APTES).

[0040] When silanization is performed by immersion, the quantity of silanizing agent is preferably approximately 0.1 to 2% (v / v) of the total volume of the silanizing bath. Typically, this quantity might vary, for example, from approximately 0.1 to 0.3% when the silanizing agent is OTS, or from approximately 1 to 2% when the silanizing agent is HMDS.

[0041] The solvent for the silanization bath can, for example, be chosen from heptane, octane, n-hexane and cyclohexane.

[0042] After the silanization stage, the assembly formed by the substrate and the resin is preferably rinsed with water and then dried.

[0043] The nature, shape and size of the colloidal nanoparticles are not critical according to the invention.

[0044] In general, colloidal nanoparticles are compounds stabilized by themselves or by ligands and / or charges, having physical properties included in the set formed by plasmonic, conductive, magnetic, luminescent, catalytic, electrochromic, photochromic properties.

[0045] According to a particular embodiment of the invention, colloidal nanoparticles are luminescent nanoparticles and in particular photoluminescent (fluorescent or phosphorescent) or electroluminescent.

[0046] As examples of luminescent nanoparticles, quantum dots composed of binary semiconductors such as indium phosphide (InP) or cadmium selenide (CdSe) can be particularly mentioned.

[0047] Nanoparticles can have a size ranging from 2 to 100 nm, preferably from 4 to 50 nm.

[0048] The concentration of the colloidal solution of nanoparticles is preferably 0.01 to 0.2% (v / v), and even more preferably 0.05 to 0.1% (v / v) relative to the total volume of the colloidal solution.

[0049] The solvent of the colloidal nanoparticle solution is a nonpolar solvent forming a contact angle with said resin before silanization (θ S R ) such that θ S R > 5 and preferably such that θ SR ≥10. It is preferably chosen from toluene (dipole moment = 0.31 D), cyclohexane (dipole moment = 0 D), and n-hexane (dipole moment = 0.08 D).

[0050] The blade used in step d) can, for example, be a glass blade.

[0051] According to a preferred embodiment of the invention, during substep d1), the blade forms an angle of 30° to 40° ± 5° with respect to the surface of said topographically structured resin.

[0052] During substep d1), the volume Vs of the colloidal solution deposited between the surface of said topographically structured resin and the slide may be 5 to 15 µL, and preferably about 7 to 10 µL.

[0053] During substep d2), the spreading of said colloidal solution is achieved by applying a relative translational movement between said meniscus and the assembly formed by the substrate and the topographically structured resin layer. In a preferred embodiment, the speed of said relative movement is approximately 0.5 to 10 µm / sec, and even more preferably approximately 1 to 4 µm / s.

[0054] The application of such movement can in particular be obtained by using a device equipped with a movable plate on which the assembly formed by the substrate and the topographically structured resin is placed and which allows the said assembly to be moved relative to the meniscus of the colloidal solution, manually or automatically, along a horizontal axis at the determined speed.

[0055] According to a particular and preferred embodiment of the process of the invention, and when the solvent of the colloidal nanoparticle solution is highly volatile, a supplementary solvent injection is performed simultaneously in substep d2). The solvent is injected at the meniscus of the colloidal solution, for example, using a syringe connected to a syringe pump. This supplementary solvent injection compensates for the very rapid evaporation of the nonpolar solvent during the spreading of the colloidal nanoparticle solution onto the resin. According to this embodiment, the injection rate of the supplementary solvent is adjusted according to the evaporation rate of the nonpolar solvent in the colloidal nanoparticle solution. For example, when the solvent used is cyclohexane, the supplementary solvent injection rate is typically 5 to 15 µL / min, and even more preferably 10 to 12 µL / min.

[0056] The additional solvent used during substep d2) is of the same nature as the non-polar solvent used for the colloidal solution.

[0057] According to a particular embodiment, the process further comprises, after step d), at least one repetition of steps b) and c), (either i) by first carrying out a new step b) and then a new step c), or ii) by carrying out a new step c) and then a new step b), to obtain a resin layer having new cavities, in a new topography, i.e., next to the cavities previously formed, and then repeating step d) using a colloidal solution comprising nanoparticles of a different species than those present in the colloidal solution used previously in the first iteration of step d). This results in a substrate having on its surface a matrix of motifs of at least two different species of nanoparticles. According to this embodiment, the new step c) is preferably carried out after the new step b).

[0058] When step (d) is completed, and depending on the intended applications for the pattern matrix, the process may further include a step (e) of removing the topographically structured resin layer. When performed, this resin layer removal step may be carried out using techniques known to those skilled in the art, such as dissolving the resin in a solvent suitable for dissolving the chosen resin, such as acetone for a photosensitive resin.

[0059] According to a particular embodiment of the process of the invention, steps a) to d) can further be repeated at least once on the same substrate before or after the possible performance of step e).

[0060] The second object of the invention is the substrate directly obtained by implementing the process as defined according to the first object of the invention, said substrate comprising a surface supporting a pattern matrix and being characterized in that each of said patterns is made up of an assembly of nanoparticles in the form of a three-dimensional pattern, said patterns having a height Hm greater than 1 µm.

[0061] According to a preferred embodiment, said motifs have a height Hm greater than 1.0 and up to about 2.0 µm, and preferably from about 1.2 to 1.5 µm.

[0062] According to a further preferred embodiment of the invention, the height Hm of said motifs is equal to Pc, the height Hs then being almost zero. The process according to the invention makes it possible to preferentially fill the cavities and minimize the deposition of nanoparticles on the resin.

[0063] According to another embodiment, said pattern matrix comprises at least two different species of nanoparticles.

[0064] The pattern matrices obtained by implementing the process as defined according to the first object of the invention or as defined according to the second object of the invention can have various applications depending on the nature of the nanoparticles used. For example, when the nanoparticles are luminescent, said pattern matrix can be used for display applications, particularly in light-emitting diode (LED) displays.

[0065] The attached drawings illustrate the invention:

[0066] is a schematic cross-sectional representation along a vertical axis of an assembly 1 formed by a substrate 2 and a resin layer 3,3' comprising cavities 4,4' of square horizontal cross-section. The upper surface 5 of the resin 3,3', as well as the lateral walls of the cavities 6,6' and the surface 7,7' of the substrate 2 present at the bottom of the cavities 4,4', have a silanized coating;

[0067] is a schematic representation of a CSA deposition step according to the process of the invention on the surface of a resin layer and on which a droplet 8 of colloidal solution is deposited on the surface of the resin 3,3' between the substrate 2 and a blade 9 inclined so as to form an angle of 30° with respect to the surface of the resin 3,3': the droplet 8 will spread over the width of the blade 9 forming a meniscus 10. The horizontal straight arrow between the meniscus 10 and the substrate 2 represents the application of a relative translational movement between the meniscus 10 and the substrate 2; is a fluorescence optical microscopy photograph of a pattern array (lateral dimensions 10x10 µm) on the surface of a substrate V-RS according to the invention according to Example 1 before (Fig. 4a) and after (Fig.4b) Dissolution of the resin layer; is a fluorescence optical microscopy photograph of a pattern array (lateral dimensions 10x10 µm) on the surface of a VS-RS substrate according to the invention of Example 1 before (Fig. 5a) and after (Fig. 5b) dissolution of the resin layer; is a fluorescence optical microscopy photograph of a pattern array (lateral dimensions 10x10 µm) on the surface of a V-R substrate not according to the invention of Example 1 before (Fig. 6a) and after (Fig. 6b) removal of the resin layer; is a fluorescence optical microscopy photograph of a pattern array (lateral dimensions 10x10 µm) on the surface of a VS-R substrate not according to the invention of Example 1 before (Fig. 7a) and after (Fig. 7b) dissolution of the resin layer ; is a graph representing the intensity of photoluminescence (PL) (a dashed line curve in arbitrary units ua)) under excitation in blue light (wavelength 455 nm) and the height of the nanoparticle patterns (solid line curve, in µm) as a function of the solvent injection rate (in µL / min) of a CdSe / ZnS nanoparticle assembly of Example 2 according to a process according to the invention;

[0068] is a fluorescence optical microscopy photograph of a pattern array (lateral dimensions 10x10 µm) obtained from a colloidal solution of CdSe / ZnS nanoparticles in octane before (Fig. 9a) and after (Fig. 9b) dissolution of the resin layer according to example 3;

[0069] Figure 10a is a fluorescence optical microscopy photograph of a pattern array (lateral dimensions 10 x 10 µm) obtained from a colloidal solution of CdSe / ZnS nanoparticles in heptane before (Fig. 10a) and after (Fig. 9b) dissolution of the resin layer according to Example 3. Figure 9b is a fluorescence optical microscopy photograph of a pattern array (lateral dimensions 10 x 10 µm) obtained with nanoparticles of two different species according to Example 5, namely red-emitting photoluminescent CdSe / ZnS nanoparticles and green-emitting CdSe / ZnS nanoparticles. The lighter squares correspond to the assemblies of green-emitting nanoparticles, while the darker squares correspond to the assemblies of red-emitting nanoparticles.

[0070] is a transmission optical microscopy photograph of a pattern array (lateral dimensions 2.5x2.5 µm) obtained with silver nanoparticles according to example 6, after dissolution of the resin. EXAMPLES

[0071] Example 1: Assembly of nanoparticles on a glass substrate according to the process of the invention and comparison with a process not forming part of the invention

[0072] In this example, 3D arrays of compact nanoparticle assemblies were created on a glass substrate coated with a photosensitive resin layer in which cavities were formed by photolithography according to the process of the invention. A silanization step of the assembly formed by said substrate and resin layer was carried out, either before the photolithography step (EssaiV-RS) or after the photolithography step (EssaiVS-RS).

[0073] The same experiment was performed for comparison by omitting the silanization step (V-R Tests) or by performing the silanization step of the glass substrate before the creation of the resin layer (VS-R). These two tests, VR and VS-R, are not in accordance with the present invention.

[0074] The operating procedures for each of the tests V-RS, VS-RS, V-RetVS-R are given below.

[0075] Before use, the glass substrates (Epredia, ISO 8037 / 1, 1mm thick, dimensions 37.5x25 mm) were previously cleaned with acetone and then with isopropanol, rinsed in deionized water and then dried with nitrogen.

[0076] 1.1 Preparation of the V-RS substrate according to the invention

[0077] 1.1.1 Formation of the photosensitive resin layer

[0078] The glass substrate was heated to 100°C by contact with a hot plate for 1 minute. A layer of positive photosensitive resin, sold under the trade name Microposit® S1813 by DuPont (The Dow Chemical Company), was applied to the surface of the glass substrate by spin coating at a speed of 3000 rpm for 30 seconds. The resin was then cured at 100°C by placement on a hot plate for 1 minute. The resin layer thickness was 1.3 µm. 1.1.2 Silanization of the resin

[0079] The surface of the resin was silanized by soaking the substrate bearing the resin layer in a 0.23% (v / v) octadecyltrichlorosilane (OTS) solution in heptane for 30 minutes, then rinsing in deionized water. 1.1.3 Photolithography

[0080] A matrix of square-section cavities was then fabricated by photolithography. A digital mask containing square patterns (lateral dimensions 10 µm x 10 µm), spaced 50 µm apart, was applied to the resin, which was then exposed to ultraviolet radiation at a wavelength of 385 nm with an intensity of 65 mW / cm² for 2 seconds. The resin was then developed using the development solution sold under the trade name Microposit® MF26 by DuPont (The Dow Chemical Company), diluted with deionized water in a 3:1 ratio (150 mL of Microposit® MF26 to 50 mL of deionized water) for 40 seconds. The assembly formed by the substrate and the resin layer was then rinsed with deionized water and dried with nitrogen, then annealed at 100°C for 1 min on a hot plate.We obtained a matrix of square cavities formed in the thickness of the resin layer, said cavities having the same dimensions as the patterns of the mask (10 µm x 10 µm, spacing of 50 µm between the cavities) and a depth corresponding to the thickness of the resin layer, i.e. 1.3 µm.

[0081] The resulting assembly 1V-RS is schematically represented in cross-section along a vertical axis in the attached figure. In this figure, the glass substrate 2 is covered with a resin layer 3,3' containing cavities 4,4' with a square cross-section. The upper surface of the resin 3,3' is silanized 5,5' by the OTS.

[0082] 1.2 Substrate preparation VS-RS according to the invention

[0083] 1.2.1 Formation of the photosensitive resin layer

[0084] The photosensitive resin layer was produced according to the process described in step 1.1.1 above for the V-RS substrate. 1.2.2 Photolithography

[0085] The photolithography step was carried out before the silanization step, according to the process described in step 1.1.3 above for the V-RS substrate. 1.2.3 Silanization

[0086] The silanization step of the assembly formed by the glass substrate with a photolithographed resin layer was carried out according to the process described above in step 1.1.2.

[0087] The resulting assembly 1VS-RS is schematically represented in cross-section along a vertical axis in the attached figure. In this figure, the glass substrate 2 is covered with a resin layer 3,3' containing square cavities 4,4'. The upper surface 5 of the resin 3,3', as well as the lateral walls of the cavities 6,6' and the surface 7,7' of the glass substrate 2 at the bottom of the cavities 4,4', have a hydrophobic coating based on OTS.

[0088] 1.3 Preparation of the substrate V-R according to the invention

[0089] Only steps 1.1.1 of photosensitive resin layer formation and 1.1.2 of photolithography as described above were carried out.

[0090] We obtained a V-R substrate (not shown) structurally similar to the V-RS and VS-RS substrates except that it did not have any silanized coating (no silanization step).

[0091] 1.4 Substrate preparation VS-Rnon according to the invention

[0092] A VS-Rnon substrate according to the invention was prepared by carrying out in this order: - a silanization step of the glass substrate according to the process described above in step 1.1.2, then - the formation of a photosensitive resin layer according to the process described above in step 1.1.1 above, then - a photolithography step according to the process described above in step 1.1.3.

[0093] We obtained a VS-R substrate (not shown) where the substrate, having become hydrophobic, does not allow optimal deposition of the resin layer and therefore does not allow for uniform thickness and cavities.

[0094] 1.5 Nanoparticle assembly tests by CSA on V-RS, VS-RS, V-Re and V-SR substrates

[0095] A colloidal solution of red photoluminescent CdSe / ZnS nanoparticles (diameter 25 nm) at 0.01% by volume in cyclohexane was prepared.

[0096] The contact angle of cyclohexane with the resin is approximately 10°.

[0097] The deposition of nanoparticles onto the various substrates was performed using a device equipped with a movable platform for positioning the substrate, and a solvent injection system consisting of a 500 µL Hamilton syringe and a PTFE tube with an internal diameter of 1 / 16" or 1 / 32", one end of which is fixed to the slide at the meniscus. The flow rate was controlled by a New Era Pump Systems, Inc. NE-300 syringe pump, according to the following steps in the attached document:

[0098] - Deposition of a droplet of colloidal solution on the surface of the resin between the substrate and a glass slide 1 cm wide inclined at an angle of 30° to the surface of the resin: the droplet will spread across the width of the slide, forming a meniscus; - Application of a relative translational movement represented by the horizontal straight arrow between the meniscus and the substrate; and under the following conditions:

[0099] - Concentration of the colloidal nanoparticle solution (v / v): 0.01%; - Initial volume of the colloidal nanoparticle solution droplet: 8-12 µL; - Substrate translation velocity: 1 µm / s; - Solvent injection: cyclohexane; - Solvent injection rate: 11.7 µL / min; - Relative solvent evaporation rate (relative to butyl acetate): 5.60.

[0100] During the nanoparticle deposition step, the combination of solvent evaporation, convective movements towards the contact line and capillary forces perpendicular to the interface of the colloidal nanoparticle solution allows for a local increase in the concentration of nanoparticles close to the substrate and induces an interaction between the nanoparticles and the substrate, which promotes the filling of cavities by the nanoparticles.

[0101] When the deposition of nanoparticles in the cavities by CSA was completed, the resin layer was dissolved by treatment with acetone for 20 sec.

[0102] The contact angles (θ) of the cyclohexane solvent on the different constituent materials of these substrates were measured by analyzing the profile of a 5 µL drop of cyclohexane on said substrates and are reported in Table 1 below:

[0103] Material Contact angle θ S cyclohexane (°) with the materials Non-silanized After silanization Effect of silanization Glass 11.7 13.7 + 2 Resin 12.2 5.2 - 7

[0104] The respective contact angles of cyclohexane on the prepared V-RS, VS-RS, V-Re and VS-R substrates are given in Table 2 below:

[0105] SubstratesMaterial 1 (M1)Material 2 (M2)θ S / M1 θ S / M2Δ θV-RSNon-silanized glassSilanized resin11.75.2+ 6.5VS-RSSilanized glassSilanized resin13.75.2+ 8.5V-R (*)Non-silanized glassNon-silanized resin11.712.2- 0.5VS-R (*)Silanized glassNon-silanized resin13.712.2+ 1.5

[0106] (*) substrate not conforming to the invention

[0107] The results obtained are shown in Figures 4 to 7, which are fluorescence optical microscopy photographs of the different substrates after the deposition process. Figure 1 corresponds to the deposition on the V-RS substrate according to the invention before dissolution of the resin layer (Fig. 4a) and after dissolution of the resin layer (Fig. 4b); Figure 2 corresponds to the deposition on the VS-RS substrate according to the invention before dissolution of the resin layer (Fig. 5a) and after dissolution of the resin layer (Fig. 5b); Figure 3 corresponds to the deposition on the V-R substrate not part of the invention before dissolution of the resin layer (Fig. 6a) and after dissolution of the resin layer (Fig. 6b); and Figure 4 corresponds to the deposition on the VS-R substrate not part of the invention before dissolution of the resin layer (Fig. 7a) and after dissolution of the resin layer (Fig. 7b).

[0108] The height of the nanoparticle patterns in the cavities of the different substrates was also determined by vertical scanning interferometry (VSI). These heights are given in Table 3 below:

[0109] SubstratesHeight of nanoparticle patternsV-RS1.3-1.5VS-RS1.5-1.8 µmV-R (*)Not measurableVS-R20-50 nm

[0110] All these results show that when the substrate is not silanized (substrateV-Rnon conforming to the invention), CSA deposition leads to the formation of a layer of nanoparticles that is too thick on the surface of the resin, with the formation of irregular structures whose shape does not follow the shape chosen by photolithography, aggregates of nanoparticles form on the surface of the resin, outside the patterns (Fig. 6b).

[0111] In the case of the non-silanized VS-R substrate according to the invention, that is, when the glass substrate undergoes a silanization step prior to the formation of the resin layer, only the bottom of the cavities is silanized. In this configuration, the glass becomes hydrophobic and does not allow good adhesion of the photosensitive resin layer. Furthermore, the small difference in contact angle (Δθ = 1.5°) between the contact angle of the solvent with the surface of the unsilanized resin (θ SR = 12.2°) and the contact angle of the solvent with the silanized glass (θ S VS = 13.7°) does not allow the complete filling of the cavities by the nanoparticles and the thickness of the cluster of nanoparticles remains limited to 20 to 50 nm.

[0112] However, with the V-RS substrate according to the invention, the deposition of nanoparticles in the cavities is favored by the significant difference in contact angle (Δθ = 6.5°) between the contact angle between the solvent and the surface of the silanized resin (θ SRS = 5.2°) and the contact angle between the solvent and the unsilanized glass (θ S V = 11.7°). This difference in contact angle is even more pronounced (Δθ = 8.5°) in the case of the VS-RS substrate also according to the invention, for which the contact angles between the solvent and the silanized glass (θ SVS ) and between the solvent and the silanized resin (θ SRS ) are respectively 13.7° and 5.2°. We can thus see in figures 4 and 5 corresponding respectively to the deposits made on the substrates V-RS and VS-RS, that the deposition of nanoparticles is preferably done in the cavities rather than on the resin, minimizing the thickness Hs and maximizing the height of the motifs.

[0113] Example 2: Assembly of nanoparticles on a glass substrate according to the process of the invention with variation of the solvent injection rate during the CSA step

[0114] In this example, CSA deposition of CdSe / ZnS nanoparticles (diameter 25 nm) dispersed in cyclohexane onto a VS-RStel glass substrate as prepared above in Example 1, under the same conditions as those detailed above in Example 1, step 1.5, but varying the solvent (cyclohexane) injection rate between 5 µL / min and 25 µL / min during the deposition of the nanoparticles.

[0115] The results obtained are given by the attached graph, which represents the intensity of the photoluminescence (in arbitrary units ua) (measured with an Ocean Insight OceanHDX spectrometer from Ocean Optics) and the height of the nanoparticle patterns (in µm) (measured with a Profilm 3D optical profilometer from Filmetrics), as a function of the solvent injection rate (in µL / min).

[0116] Solvent injection during the CSA step is not mandatory. However, as can be seen from the results presented, solvent injection partially compensates for the very rapid evaporation of non-polar solvents. It allows the "effective" evaporation rate of the solvent to be adjusted to the optimal deposition conditions, resulting in the thickest nanoparticle patterns (greater than 1 µm) on larger surfaces. Indeed, optimal nanoparticle deposition conditions are met when the solvent injection rate during the CSA step is between approximately 10 and 15 µL / min.Moreover, when the injection rate is optimal (between 10 and 12 µL / min) the compact patterns of nanoparticles obtained have a significant height (greater than 1 µm and up to 1.5 µm) which is of particular interest in the case of photoluminescent nanoparticles, the intensity of the photoluminescence being higher as the height of the patterns is greater ().

[0117] Example 3: Assembly of nanoparticles on a glass substrate using a nonpolar solvent that is inappropriate and not part of the invention

[0118] In this example, CdSe / ZnS nanoparticles were assembled by CSA on a VS-RS glass substrate as prepared above in Example 1, under the same conditions as those detailed above in Example 1, step 1.5, but using colloidal solutions of CdSe / ZnS nanoparticles (25 nm diameter) at 0.01% (v / v) prepared with unsuitable nonpolar solvents, namely: - octane, whose contact angle with the resin is close to 0°, and

[0119] - heptane whose contact angle with the resin is approximately 4°.

[0120] The results obtained are presented in Figures 9 and 10, which are fluorescence optical microscopy photographs of the different deposits obtained. Figure 1 corresponds to the deposits obtained with the dispersion of nanoparticles in octane before (Fig. 9a) and after (Fig. 9b) dissolution of the resin layer, and Figure 1 corresponds to the deposits obtained with the dispersion of nanoparticles in heptane before (Fig. 10a) and after (Fig. 10b) dissolution of the resin layer. These figures should be interpreted in conjunction with Figures 4a and 4b, which correspond to the deposit carried out in Example 1 on the same substrate but with a colloidal solution of nanoparticles in cyclohexane, in accordance with the process of the invention.

[0121] As can be seen in Figures 9 and 10, the deposits obtained with colloidal solutions prepared using non-polar solvents having a contact angle with the resin of less than 5° lead to patterns with a height of around 10 nm, unlike the patterns obtained in Example 1 with a colloidal solution of nanoparticles prepared in cyclohexane and whose contact angle with the resin is 10°.

[0122] Example 4: Assembly of nanoparticles on a glass substrate using a nonpolar solvent and different types of silanization

[0123] In this example, assemblies of photoluminescent nanoparticles based on indium phosphide (InP) were made from a colloidal solution of InP particles (diameter 5 nm) at 0.10% (v / v) in toluene.

[0124] The CSA deposition was carried out on the following substrates: - substrate V-R not conforming to the invention and as prepared above in example 1.3, - substrate VS-RS conforming to the invention and as prepared above in example 1.2,

[0125] - substrateVS-RS according to the invention, prepared as described above in example 1.2, but by soaking the substrate in a 2% (v / v) hexamethyldisilazane (HDMS) solution in heptane and further containing 1% (v / v) ethanol for 30 minutes, then rinsing in deionized water.

[0126] For each of the substrates tested, CSA deposition was carried out according to the process described above in example 1.5, under the following conditions: - Initial volume of the drop of colloidal nanoparticle solution: 8 µL; - CSA speed: 1 µm / sec; 10 µm / sec or 100 µm / sec.

[0127] After the nanoparticles were deposited onto the different substrates, the thicknesses of the deposits were measured and recorded in Table 4 below:

[0128] CSA velocity (µm / sec) Motif height (in µm) Substrate V-RS Substrate VS-RS (OTS) Substrate VS-RS (HMDS) 10, 20, 90, 9100, 41, 21, 1100(*) 0, 10, 40, 3

[0129] (*) example not in accordance with the invention

[0130] These results confirm the effect of silanization which allows the surface properties of the resin and substrate (glass at the bottom of the cavities to be changed), and therefore the shape of the colloidal solution meniscus (solvent + NPs) to be modified during CSA.

[0131] Following the silanization of the resin, we observe for the VS-RS(OTS) and VS-RS(HMDS) substrates conforming to the invention a better filling of the cavities, leading to a higher height of the patterns, on the order of 3 to 4 times greater than that obtained for the deposition carried out on the non-silanized V-R substrate and not conforming to the invention.

[0132] These results also show that the nature of the silanizing agent does not influence the quality of the deposits, the heights obtained using an OTS solution and an HDMS solution being similar.

[0133] These results also show that the nature of the nanoparticles does not influence the quality of the deposits, the heights obtained using InP nanoparticles also being greater than 1 µm.

[0134] Finally, we can also observe that when the CSA speed is too high (100 µm / sec), the deposit has a lower height (0.3 to 0.4 µm) than that obtained (1.1 to 1.2 µm) with a speed of 10 µm / sec, but still with a higher height on the silanized substrate compared to the non-silanized substrate, showing the general nature of the silanization of the substrate.

[0135] Example 5: Assembly of two different types of nanoparticles on a glass substrate according to the process of the invention

[0136] A VS-RS substrate was prepared as described above in Example 1.2 above, and then a compact array of red-emitting CdSe / ZnS photoluminescent nanoparticles (diameter 25 nm) was created by CSA according to the process described above in Example 1.5.

[0137] The substrate thus obtained then underwent a second photolithography step according to the process described above in example 1.1.3 in order to create a second matrix of square cross-section cavities (lateral dimensions 10 µm x 10 µm), spaced 50 µm apart and offset by 30 µm from the first matrix of cavities formed previously.

[0138] A second network of compact assemblies of photoluminescent nanoparticles was created by CSA according to the process described above in example 1.5 but this time from a colloidal solution of CdSe / ZnS nanoparticles (diameter 20 nm) emitting in the green at 0.02% by volume in cyclohexane.

[0139] Following this second deposit by CSA, the resin layer was dissolved by treatment with acetone for 20 seconds.

[0140] The attached image is a fluorescence optical microscopy photograph of the substrate obtained after the resin was dissolved. In this figure, the lighter squares correspond to assemblies of green-emitting nanoparticles, while the darker squares correspond to assemblies of red-emitting nanoparticles.

[0141] These results show that the first series of structures is robust and undamaged during the second deposition. This makes it possible to create distinct networks of different nanoparticles on the same substrate, which is of interest for display applications.

[0142] Example 6: Assembly of silver nanoparticles on a glass substrate according to the process of the invention

[0143] In this example, the assembly of dodecanethiol functionalized silver nanoparticles (diameter 10 nm) at 0.02% (v / v)) in hexane was carried out by CSA on a VS-RStel glass substrate as prepared above in example 1.2, under the same conditions as those detailed above in example 1.5.

[0144] We obtained a pattern matrix made up of assemblies of silver nanoparticles with a height of 1-1.5 µm.

[0145] The appendix is ​​a transmission optical microscopy photograph of said pattern matrix (dimensions 2.5x2.5 µm) thus obtained after dissolution of the resin.

Claims

A method for manufacturing a nanoparticle pattern matrix on the surface of a substrate (2), in the form of a three-dimensional micrometer-sized pattern array, said method comprising at least the following steps: a) providing a substrate (2) having a surface supporting a resin layer (3,3'), said layer having a thickness EpR, b) forming cavities (4,4') in the thickness of said resin layer (3,3') by lithography to obtain a topographically structured resin layer (3,3'), c) silanizing the assembly formed by said substrate (2) and said resin layer (3,3'), d) deposition of said nanoparticles in the cavities (4,4') formed in said topographically structured resin layer (3,3') by convective capillary deposition (CSA) from a colloidal solution comprising said nanoparticles and a nonpolar solvent, to obtain said pattern matrix of nanoparticles,said process being further characterized in that: - the thickness EpR of said resin layer (3,3') is greater than or equal to 1 µm, - said silanization step c) is carried out before or after lithography step b) and before said step d), - the cavities (4,4') of the topographically structured resin layer (3,3') have a depth Pc substantially equal to EpR, - said non-polar solvent is chosen from solvents having a contact angle with said resin (3,3') before silanization (θ, S R ) such that θ S R> 5°- said step d) comprises the following sub-steps:d1) the deposition of a volume Vs of said colloidal solution between the surface of said topographically structured resin (3,3') and a blade (9) forming an angle of at least 30° with respect to the surface of said topographically structured resin (3,3') to form a meniscus (10),d2) the spreading of said colloidal solution by applying a relative translational movement between said meniscus (10) and the assembly formed by the substrate (2) and the topographically structured resin layer (3,3'), during the evaporation of said solvent so as to fill said cavities (4,4') with said colloidal solution and deposit a layer of colloidal solution of height Hs on the surface of the resin layer (3,3') outside of said cavities (4,4'); and- said motifs have a total height Hm equal to Pc + Hs and greater than 1 µm. A method according to claim 1, characterized in that the substrate supporting the resin layer is chosen from glass and silicon. Method according to claim 1 or 2, characterized in that the EpR thickness of the resin is 1 to 2 µm. A process according to any one of the preceding claims, characterized in that step c) of silanization is carried out after step b) of lithography. A method according to any one of the preceding claims, characterized in that said cavities have lateral dimensions of 2.5x2.5 µm, 5x5 µm or 10x10 µm. A method according to any one of the preceding claims, characterized in that the spacing between two cavities is from 2 to 50 µm. A method according to any one of the preceding claims, characterized in that the nanoparticles are luminescent nanoparticles. A process according to any one of the preceding claims, characterized in that the concentration of the colloidal solution of nanoparticles is 0.01 to 0.2% (v / v) relative to the total volume of the colloidal solution. A process according to any one of the preceding claims, characterized in that the solvent of the colloidal solution of nanoparticles is a nonpolar solvent forming a contact angle with said resin before silanization (θ S R ) such that θ S R ≥10. A process according to any one of the preceding claims, characterized in that the non-polar solvent is selected from toluene, cyclohexane, and hexane. A method according to any one of the preceding claims, characterized in that during substep d1), the blade forms an angle of 30° to 40° ± 5° with respect to the surface of said topographically structured resin. A method according to any one of the preceding claims, characterized in that during substep d1), the volume Vs of the colloidal solution deposited between the surface of said topographically structured resin and the blade is 5 to 15 µL. Method according to any one of the preceding claims, characterized in that during substep d2), the speed of the relative translational movement between said meniscus and the assembly formed by the substrate and the topographically structured resin layer is 0.5 to 10 µm / sec. A method according to any one of the preceding claims, characterized in that an additional solvent injection is carried out simultaneously with substep d2). A process according to claim 14, characterized in that the injection rate of the complementary solvent is 5 to 15 µL / min. A method according to any one of the preceding claims, characterized in that it further comprises after step d) at least one reiteration of steps b) and c) to obtain a resin layer having new cavities, according to a new topography, then the reiteration of step d) using a colloidal solution comprising nanoparticles of a different species from those present in the colloidal solution used previously in the first iteration of step d). A method according to any one of the preceding claims, characterized in that step b) of forming cavities in the thickness of said resin layer is carried out by photolithography, electron lithography or thermal nanoprinting. Substrate (2) directly obtained by implementing the process as defined in any one of the preceding claims, said substrate (2) comprising a surface supporting a pattern matrix and being characterized in that each of said patterns is made up of an assembly of nanoparticles in the form of a three-dimensional pattern, said patterns having a height Hm greater than 1 µm. Substrate according to claim 18, characterized in that said motifs have a height Hm greater than 1.0 and up to 2.0 µm. Substrate according to claim 18 or 19, characterized in that said pattern matrix comprises at least two different species of nanoparticles.

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