Pericle film of multi-layer, several-layer, and single-layer carbon nanotube mixtures

Abstract

Nanofiber membranes are disclosed that include multiple layers of nanofiber structures, each structure being a composite composition of multi-walled carbon nanotubes and one or more single-walled and / or few-walled carbon nanotubes. By selecting the relative proportions of multi-walled carbon nanotubes and one or more single-walled / few-walled carbon nanotubes in the nanofiber film, the membrane can be fabricated to withstand the heating that occurs during operation in an EUV lithography machine, while possessing sufficient mechanical integrity to withstand pressure changes between 1 atmosphere (atm) and 2 atm during the operation cycle of the EUV lithography machine.

Description

Technical Field

[0001] Related Applications This application claims priority to U.S. Provisional Patent Application No. 62 / 855,432, filed May 31, 2019, and entitled "FILMS OF MULTIWALL, FEW WALL, AND SINGLE WALL CARBON NANOTUBE MIXTURES", and U.S. Provisional Patent Application No. 62 / 976,449, filed February 14, 2020, and entitled "FILMS OF MULTIWALL, FEW WALL, AND SINGLE WALL CARBON NANOTUBE MIXTURES", both of which are hereby incorporated by reference in their entirety.

[0002] The present disclosure generally relates to carbon nanofibers. Specifically, the present disclosure relates to films formed from mixtures of multiwalled carbon nanofibers and one or more few-walled and single-walled carbon nanotubes.

Background Art

[0003] Nanofibers are known to have unique mechanical, optical, and electrical properties. However, devising nanofiber configurations that can be incorporated into commercial products has been difficult due to the nanoscale dimensions of nanofibers. PCT Publication No. WO 2007 / 015710 is an example of progress in the development of commercially useful embodiments of nanofibers. This publication describes the conversion of nanofiber "forests" into sheets and / or threads of nanofibers. Nanofiber sheets and threads can then be applied in a variety of situations.

Summary of the Invention

[0004] Example 1 is a nanofiber membrane having a first layer of carbon nanofibers, which contains 50 wt% to 80 wt% of multi-layer carbon nanofibers and 20 wt% to 50 wt% of single-layer or few-layer carbon nanofibers so as to total 100 wt%.

[0005] Example 2 includes the subject matter of Example 1, a second layer of carbon nanofibers which contains 50 wt% to 80 wt% of multi-layer carbon nanofibers and 20 wt% to 50 wt% of single-layer or few-layer carbon nanofibers so as to total 100 wt%, and a third layer of carbon nanofibers which is between the first layer and the second layer, contains 50 wt% or more of single-layer and / or few-layer carbon nanofibers and less than 50 wt% of multi-layer carbon nanofibers so as to total 100 wt%.

[0006] Example 3 includes the subject matter of Example 2, provided that the multi-layer carbon nanofibers have 4 to 20 layers, the few-layer carbon nanofibers have 2 and / or 3 layers, and the single-layer carbon nanofibers have 1 layer.

[0007] Example 4 includes the subject matter of either Example 1 or Example 2, provided that the multi-layer carbon nanofibers have a cross-sectional diameter of 6 nm to 100 nm and a length of 250 μm to 400 μm, the few-layer carbon nanofibers have a cross-sectional diameter of 2 nm to 6 nm and a length of 0.5 μm to 30 μm, and the single-layer carbon nanofibers have a cross-sectional diameter of 0.2 nm to 2 nm and a length of 0.5 μm to 30 μm.

[0008] Example 5 includes the subject matter of any one of the preceding examples, provided that the first layer, the second layer, and the third layer contain multi-layer, few-layer, and single-layer carbon nanofibers that are randomly oriented and randomly distributed.

[0009] Example 6 includes the subject matter of any one of the preceding examples, provided that the exposed surface includes one of the first layer or the second layer in which the multi-layer carbon nanofibers mostly occupy.

[0010] Example 7 includes the subject matter of any one of the prior examples, provided that the first exposed surface includes a nanofiber film mostly occupied by multi-layer carbon nanofibers, and the second exposed surface includes a nanofiber film mostly occupied by several layers and / or single-layer carbon nanofibers.

[0011] Example 8 includes the subject matter of any one of the prior examples, and further has a frame that is in contact with the peripheral edge of the third layer of carbon nanofibers but not in contact with the self-supporting part of the third layer.

[0012] Example 9 includes the subject matter of any one of the prior examples, and further has a fourth layer of carbon nanofibers between the frame and the third layer, and most of the fourth layer is composed of several layers and single-layer carbon nanofibers.

[0013] Example 10 includes the subject matter of any one of the prior examples, provided that one or more of the layers of carbon nanofibers constitute a film.

[0014] Example 11 includes the subject matter of any one of the prior examples, provided that at least one of the layers is uniform, and the variation in thickness across its diameter is less than 50%.

[0015] Example 12 includes the subject matter of any one of the prior examples, provided that at least one of the layers or films is non-uniform and the thickness varies by more than 10%.

[0016] Example 13 includes the subject matter of any one of the prior examples, provided that at least one of the layers has a first region and a second region, and the first areal density of the nanofibers in the first region is at least twice as high as the second areal density of the nanofibers in the second region.

[0017] Example 14 includes the subject matter of Example 13, provided that the first region is at the margin of the film.

[0018] Example 15 is a pellicle film including the subject matter of any one of the prior examples, and is a pellicle film having a transmittance of radiation with a wavelength of 550 nm exceeding 85%.

[0019] Example 16 is a nanofiber membrane comprising a first layer of carbon nanofibers including a sheet in which multi-layer carbon nanofibers are aligned in the plane of the sheet, and a second layer of carbon nanofibers including 50 wt% to 80 wt% multi-layer carbon nanofibers and 20 wt% to 50 wt% single-layer or multi-layer carbon nanofibers such that the total is 100 wt%.

[0020] Example 17 includes the subject matter of Example 10 and further has a third layer of carbon nanofibers on the side of the second layer facing the first layer, and the third layer has one of a layer including more than 50 wt% single-layer or multi-layer carbon nanofibers and a sheet in which multi-layer carbon nanofibers are aligned in the plane of the sheet, which is different from that.

Brief Description of the Drawings

[0021]

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DETAILED DESCRIPTION OF THE INVENTION

[0022] The drawings depict various embodiments of the present disclosure for illustrative purposes only. Numerous variations, arrangements, and other embodiments will become apparent from the following detailed description.

[0023] Overview Carbon nanofiber structures generally consist of one type of multi-walled carbon nanotubes (MWCNT), few-walled carbon nanotubes (FWCNT), or single-walled carbon nanotubes (SWCNT), and generally are not formed by combinations thereof. In some cases, this is because much of the development effort to date has focused on forming pure (e.g., greater than 90%) forms consisting of one type of carbon nanotube. By doing so, the properties of the nanofibers of that type can be elucidated and optimized. Moreover, the processes used to form pure form multi-walled carbon nanotubes (e.g., carbon nanotubes having 4 to 20 concentric layers and a diameter of 4 nm to 100 nm), few-walled carbon nanotubes (e.g., carbon nanotubes having 2 or 3 concentric layers and a diameter of 2 nm to 6 nm), and single-walled carbon nanotubes (e.g., 1 layer and a tube diameter of 0.2 nm to 4 nm) can potentially be different from each other. For example, multi-walled carbon nanotubes can be produced using a chemical vapor deposition process with a relatively thick catalyst layer (e.g., 10 nm to several microns thick) on a substrate, while few-walled and single-walled carbon nanofibers are formed using laser ablation, a carbon arc process, or chemical vapor deposition (e.g., using acetylene or ethane as a precursor) with a thin (e.g., 0.2 nm to 10 nm thick) and potentially discontinuous catalyst layer across the substrate. Laser ablation generally produces shorter carbon nanotubes than those produced by chemical vapor deposition and may produce nanotubes with fewer crystallographic defects. At least for this reason, the processes generally used to produce one type of nanofiber do not produce measurable amounts of other types of nanofibers.

[0024] These three different types of carbon nanotubes each have different properties. In one example, it may be more convenient to disperse multi-walled carbon nanotubes and single-walled carbon nanotubes in a solvent to continue to form a sheet of randomly oriented carbon nanotubes (i.e., most of the nanotubes are individually floating and not adsorbed to other nanotubes). This ability of individual nanotubes to disperse uniformly in the solvent results in dimensional uniformity in the nanotube film formed by removing the solvent from the suspended nanofibers. The nanofiber sheet of this arrangement may be referred to as a "filtration film". This physical uniformity (which is further improved by laminating multiple filtration films on top of each other) can also improve the uniformity of properties (such as transparency to radiation) across the film.

[0025] The strength of the van der Waals forces between the nanofibers also differs between single / multi-layer nanofibers and multi-walled nanofibers. Generally, single / multi-layer nanofibers have stronger van der Waals forces acting on each other than those observed in multi-walled nanofibers. The increasing attractive force between single / multi-layer nanofibers may improve the ability of multi-walled / single-walled carbon nanotubes to adhere to each other and form a coherent nanofiber structure such as a filtration film. Sheets or films formed from single-walled carbon nanotubes and multi-walled carbon nanotubes can follow the topography of the underlying surface with smaller dimensions than sheets or films formed from multi-walled carbon nanotubes. In some examples, sheets or films formed from single-walled carbon nanotubes and / or multi-walled carbon nanotubes can follow the topography of the underlying surface as small as only 10 nm, which is at least 50% smaller than the shape that a multi-walled carbon nanotube film can follow. In some cases, multi-walled carbon nanotubes are more likely to aggregate into a single mass than single / multi-layer nanotubes, thereby producing a structurally non-uniform film, and such a film is less likely to follow and / or adhere to the underlying surface.

[0026] Filtration treatment films, especially those made of single-layer and / or multi-layer carbon nanotubes, are generally also more transparent to some radiation wavelengths. In some examples, the transmittance of the incident radiation can be as high as 90% or 95%. In some cases, this transmittance is significantly higher than that of a stretched sheet of multi-layer carbon nanotubes (e.g., one stretched from a carbon nanotube forest as described below). Without being bound by theory, it is believed that the alignment and orientation of the nanotubes in the stretched sheet increase the scattering of radiation compared to the filtration treatment film. In part, because the filtration treatment film (with randomly oriented nanotubes) is more transparent, interest has been driven in forming transparent filters and membranes from filtration treatment carbon nanotube films for various applications.

[0027] Despite the advantages of the above single-layer and multi-layer carbon nanotubes, multi-layer carbon nanotubes also have advantages, although they are not necessarily observed to the same extent as nanotube structures formed from single-layer or multi-layer nanotubes. For example, structures formed from multi-layer carbon nanotubes are generally observed to have a higher emissivity than those formed from multi-layer / single-layer carbon nanotubes. Without being bound by theory, it is believed that the larger number of layers and larger diameter of multi-layer carbon nanotubes are factors contributing to the increase in emissivity. For example, multi-layer carbon nanotube structures (e.g., nanotube forests, nanotube sheets) have a higher thermal emissivity than nanotube structures formed from multi-layer / single-layer nanotubes. In one comparative example, the emissivity of a nanofiber structure containing multi-layer carbon nanotubes is on the order of 0.275 (+ / - 15%), while on the other hand, a nanofiber structure containing single-layer carbon nanotubes may have a significantly lower emissivity of 0.05 (+ / - 15%). The high emissivity can cause heating within the nanofiber structure, but it may be particularly advantageous in engineering applications that include processes where the conduction or convective cooling mechanisms of the nanofiber structure are limited or not technically feasible.

[0028] For example, a nanofiber structure having transparency to a specific radiation wavelength (e.g., extreme ultraviolet or "EUV" in the range of 10 nm to 124 nm) is expected to be used as a filter (also referred to as a "pellicle film") of an EUV lithography apparatus. The pellicle film can act as a particle filter to prevent foreign particles from landing on the surface of the material to be patterned and / or on the surface of the lithography mask used to pattern the photosensitive surface. Thereby, the defect rate introduced in lithography is reduced, and thus the manufacturing yield of the patterned device is improved.

[0029] Despite the high transparency in the EUV radiation wavelength range, there are still problems in adopting the nanofiber EUV pellicle film. For example, during lithography patterning, cooling of the pellicle film may be important to prevent overheating of the pellicle film due to absorption of EUV energy. The temperature rise of the pellicle film may damage the nanofiber structure integrity. However, considering that EUV lithography is performed in a vacuum and most of the pellicle film is floating (the peripheral edges are fixed to the frame), there are few opportunities for convective and / or conductive cooling of the nanofiber structure in this environment. For this reason, heat radiation becomes the main mechanism for cooling the nanofiber pellicle film used for EUV applications.

[0030] A multi-layer carbon nanotube structure generally has a high emissivity, which may solve the cooling problem in the EUV pellicle film. However, when the multi-layer carbon nanotubes are aligned in a stretched sheet, this results in lower permeability than that of single-layer / multi-layer carbon nanofibers randomly oriented in a filtration film. The higher the transparency (but lower the radioactivity) of the multi-layer / single-layer nanofiber film, the more mechanically delicate it becomes and is often not suitable for use as a pellicle film. In some cases, due to their relatively short length (e.g., less than 100 μm), films and sheets made of multi-layer / single-layer nanofibers are fragile and will collapse when subjected to the pressure cycles commonly used in EUV lithography machines (e.g., a pressure change of + / - 1 atm to 2 atm (from atmospheric pressure to vacuum)).

[0031] Accordingly, in accordance with some examples of the present disclosure, a multi-layer carbon nanofiber structure that is a composite of multi-layer carbon nanotubes and one or more single-layer and / or multi-layer carbon nanotubes (e.g., a multi-layer structure including a plurality of laminated films and / or sheets) is described. By selecting the relative ratio of multi-layer nanotubes to one or more single-layer / multi-layer carbon nanotubes in the nanofiber film, it is possible to manufacture an extreme ultraviolet radiation filter (which may also be referred to as a "pellicle film" in some cases) that can withstand a pressure change between 1 atm and 2 atm during the operating cycle of an EUV lithography machine and has a sufficiently high emissivity to withstand the heating that may occur in an EUV lithography machine during operation. In some cases, the structural durability of the film and membrane can be improved by including 50 wt% to 80 wt% of multi-layer carbon nanotubes in a mixture that also includes single-layer / multi-layer carbon nanotubes.

[0032] Before describing examples of the film, nanofiber forests and nanofiber sheets are described below.

[0033] Nanofiber Forest As used herein, the term "nanofiber" means a fiber having a diameter of less than 1 μm. Although embodiments herein are mainly described as being made from carbon nanotubes, other carbon allotropes, such as graphene, micron or nano-scale graphite fibers and / or plates, and even composites of other nano-scale fibers such as boron nitride, can be densified using the techniques described below, regardless of which one they are. As used herein, the terms "nanofiber" and "nanotube" are used synonymously and both include single-walled carbon nanotubes, multi-walled carbon nanotubes, and / or multi-layer carbon nanotubes in which carbon atoms are connected to each other to form a cylindrical structure. Depending on the embodiment, multi-layer carbon nanotubes have 6 to 20 layers when referred to herein. As used herein, "nanofiber sheet" or simply "sheet" refers to a sheet of nanofibers aligned by a stretching process (as described in PCT Publication No. WO 2007 / 015710, which is hereby incorporated by reference in its entirety) such that the long axis of the nanofibers in the sheet is parallel to, rather than perpendicular to, the major plane of the sheet (i.e., in its as-deposited form on the sheet, often referred to as a "forest"). This is illustrated in FIGS. 3 and 4, respectively.

[0034] The dimensions of carbon nanotubes can vary greatly depending on the manufacturing method used. For example, the diameter of carbon nanotubes can range from 0.4 nm to 100 nm, and their length can range from 10 μm to over 55.5 cm. Carbon nanotubes can also have a very high aspect ratio (length-to-diameter ratio), and in some cases, can be as high as 132,000,000:1 or more. Considering the wide range of possible dimensions, the properties of carbon nanotubes are highly adaptable, i.e., "tunable". Although numerous interesting properties of carbon nanotubes have been identified, in order to utilize the properties of carbon nanotubes in actual applications, an extensible and controllable manufacturing method that enables the maintenance or improvement of the characteristics of carbon nanotubes is required.

[0035] Due to their unique structure, carbon nanotubes have special mechanical, electrical, chemical, thermal, and optical properties, which make them very suitable for certain applications. Specifically, carbon nanotubes exhibit excellent electrical conductivity, high mechanical strength, good thermal stability, and are also hydrophobic. In addition to these properties, carbon nanotubes may also exhibit useful optical properties. For example, carbon nanotubes can be used in light-emitting diodes (LEDs) and photodetectors to emit or detect light at a narrowly selected wavelength. Carbon nanotubes have also been shown to be useful for photon transport and / or phonon transport.

[0036] In accordance with various embodiments of the present disclosure, nanofibers (including, but not limited to, carbon nanotubes) can be arranged in various configurations, including a configuration referred to herein as a "forest". As used herein, a "forest" of nanofibers or carbon nanotubes refers to a configuration in which nanofibers having substantially equal dimensions are arranged substantially parallel to each other on a substrate. FIG. 1 shows an example of a nanofiber forest on a substrate. The substrate can have any shape, but in some embodiments, the substrate has a flat surface on which the forest is assembled. As can be seen in FIG. 1, the nanofibers of the forest may have substantially equal height and / or diameter.

[0037] As disclosed herein, nanofiber forests can be relatively dense. Specifically, the disclosed nanofiber forests can have a density of at least 1 billion nanofibers / cm 2 In some specific embodiments, the nanofiber forests as described herein can have a density of 10 billion nanofibers / cm 2 ~30 billion nanofibers / cm 2 In other examples, the nanofiber forests as described herein can have a density in the range of 90 billion nanofibers / cm 2 The forest can have a high or low density range, and the specific range can be a blank area of nanofibers. The nanofibers in the forest can also exhibit inter-fiber connections. For example, adjacent nanofibers in a nanofiber forest can be attracted to each other by van der Waals forces. In any case, the nanofiber density in the forest can be increased by applying the techniques described herein.

[0038] A method for manufacturing nanofiber forests is described, for example, in PCT No. WO2007 / 015710, which is hereby incorporated by reference in its entirety.

[0039] A nanofiber precursor forest can be generated using various methods. For example, in some embodiments, the nanofibers can be grown in a high-temperature furnace as schematically illustrated in FIG. 2. In some embodiments, a catalyst can be deposited on a substrate, placed in a reactor, and then contacted with a fuel compound supplied to the reactor. The substrate can withstand high temperatures exceeding 800°C, even up to 1000°C, and may be an inert material. The substrate may include stainless steel or aluminum disposed on a silicon (Si) wafer forming a lower layer, although other ceramic substrates may be used in place of the Si wafer (e.g., alumina, zirconia, SiO 2 , glass ceramics). In an example where the nanofibers of the precursor forest are carbon nanotubes, a carbon-based compound, such as acetylene, can be used as the fuel compound. After being introduced into the reactor, the fuel compound(s) can then begin to accumulate on the catalyst and build up by growing upward from the substrate to form a forest of nanofibers. The reactor can also include a gas inlet through which the fuel compound(s) and a carrier gas can be supplied to the reactor, as well as a gas outlet through which the spent fuel compound and carrier gas can be discharged from the reactor. Examples of the carrier gas include hydrogen, argon, and helium. These gases, particularly hydrogen, can also be introduced into the reactor to promote the growth of the nanofiber forest. Also, a dopant to be incorporated into the nanofibers can be added to the gas stream.

[0040] In the process used to manufacture a multi-layer nanofiber forest, when one nanofiber forest is formed on a substrate, subsequently, a second nanofiber forest grows in contact with the first nanofiber forest. The multi-layer nanofiber forest can be formed by a number of suitable methods, such as forming the first nanofiber forest on a substrate, depositing a catalyst on the first nanofiber forest, and then introducing an additional fuel compound into the reactor to grow the second nanofiber forest from the catalyst located on the first nanofiber forest. Depending on the growth method used, the type of catalyst, and the location of the catalyst, the second nanofiber layer can grow from the top of the first nanofiber layer or, after regeneration of the catalyst (e.g., using hydrogen gas), grow directly from the substrate and thus grow under the first nanofiber layer. In any case, the second nanofiber forest can be aligned with the nanofibers of the first nanofiber forest with their ends almost facing each other, but there is an easily detectable interface between the first forest and the second forest. The multi-layer nanofiber forest can contain any number of forests. For example, the multi-layer precursor forest can contain two, three, four, five, or more forests.

[0041] Nanofiber sheet In addition to being arranged in a forest configuration, the nanofibers of the present application can also be arranged in a sheet configuration. As used herein, the terms "nanofiber sheet", "nanotube sheet", or simply "sheet" refer to an arrangement of nanofibers in which the nanofibers are aligned in a plane with their ends facing each other. An illustration of an example of a nanofiber sheet is shown in FIG. 3, together with the markings of each dimension. In some embodiments, the sheet has a length and / or width that exceeds 100 times the thickness of the sheet. In some embodiments, the length, width, or both are 10 3 , 10 6 , or 10 9It is many times larger. The nanofiber sheet can have, for example, a thickness of about 5 nm to 30 μm, as well as any length and width appropriate for the intended use. In some embodiments, the nanofiber sheet may have a length of 1 cm to 10 meters and a width of 1 cm to 1 meter. Such lengths are provided for illustrative purposes only. The length and width of the nanofiber sheet are subject to the constraints of the arrangement of the manufacturing equipment, not due to any physical or chemical properties of the nanotubes, forests, or nanofiber sheets themselves. For example, sheets of any length can be manufactured by a continuous process. Such sheets can be wound onto a roll as they are manufactured.

[0042] As can be seen in FIG. 3, the axis along which the nanofibers are aligned with their ends facing each other is referred to as the nanofiber alignment direction. In some embodiments, the nanofiber alignment direction may be continuous throughout the nanofiber sheet. The nanofibers do not necessarily have to be completely parallel to each other, and naturally, the nanofiber alignment direction is an average or overall measure of the direction of alignment of the nanofibers.

[0043] The nanofiber sheet can be assembled using any suitable process of any kind that can manufacture the sheet. In some exemplary embodiments, the nanofiber sheet can be drawn from a nanofiber forest. An example of a nanofiber sheet drawn from a nanofiber forest is shown in FIG. 4.

[0044] As can be seen in FIG. 4, the nanofibers can be drawn laterally from the forest and then aligned with their ends facing each other to form a nanofiber sheet. In embodiments where the nanofiber sheet is drawn from a nanofiber forest, each dimension of the forest can be controlled to form a nanofiber sheet having specific dimensions. For example, the width of the nanofiber sheet may be approximately equal to the width of the nanofiber forest from which the sheet is drawn. Also, the length of the sheet can be controlled, for example, by terminating the drawing process when the desired sheet length is achieved.

[0045] The nanofiber sheet has many properties that can be utilized for various applications. For example, the nanofiber sheet may have adjustable opacity, high mechanical strength and flexibility, thermal and electrical conductivity, and may also exhibit hydrophobicity. Considering that the nanofibers are highly aligned within the sheet, the nanofiber sheet can be extremely thin. In some examples, the nanofiber sheet is on the order of about 10 nm thick (as measured within normal measurement durability), and thus the sheet is almost two-dimensional. In other examples, the thickness of the nanofiber sheet can also reach 200 nm or 300 nm. Therefore, the thickness added by the nanofiber sheet to the component can be minimized.

[0046] Similar to the nanofiber forest, the nanofibers of the nanofiber sheet can also be functionalized with a treatment agent by adding a chemical group or element to the surface of the nanofibers of the sheet, thereby bringing about a chemical activity different from that of the nanofibers alone. The functionalization of the nanofiber sheet can be carried out with pre-functionalized nanofibers if possible, or with non-pre-functionalized nanofibers. The functionalization can be carried out using any of the techniques described herein, and such techniques include, but are not limited to, CVD and various doping techniques.

[0047] When the nanofiber sheet is extended from the nanofiber forest, it can also have high purity. In some cases, the nanofibers occupy more than 90%, more than 95%, or more than 99% of the weight percentage of the nanofiber sheet. Similarly, the nanofiber sheet may contain more than 90%, more than 95%, more than 99%, or more than 99.9% carbon by weight.

[0048] Nanofiber Membrane Structures and Forming Techniques As described above, the examples described herein include nanofiber films formed from a combination of multi-walled carbon nanotubes and one or both of single-walled and few-walled carbon nanotubes. Since these are combinations or mixtures of different nanofiber species, they can be described as "composite films". In some examples, the relative weight ratio is up to 80 weight (wt.)% multi-walled carbon nanotubes and at least 20 weight % single-walled and / or few-walled nanotubes. The length of the multi-walled carbon nanotubes, as described above, can be controlled by extending or shortening the growth process in a chemical vapor deposition reactor. However, for example, herein, the multi-walled carbon nanotubes can have a median length of about 300 μm (+ / - 10%). As will be understood in light of the following description, multi-walled carbon nanotubes having a length of at least 250 μm or more can generally be included in a filtration treatment film that also includes shorter (e.g., 0.5 μm to 30 μm) single-walled and / or few-walled carbon nanotubes to improve the mechanical stability of the filtration treatment film. Films containing either long multi-walled nanotubes or short few-walled / single-walled carbon nanotubes generally have less durability than those containing a mixture of multi-walled nanotubes and few-walled / single-walled nanotubes.

[0049] FIG. 5 is a schematic diagram of a composite nanotube filtration treatment film 500 in an example of the present disclosure. As shown in the figure, the composite nanotube filtration treatment film 500 includes single-layer / multi-layer nanotubes 504 mutually dispersed with multi-layer carbon nanotubes 508. In this exemplary film 500, the single-layer / multi-layer carbon nanotubes 508 may generally have at least two beneficial effects on the structure of the film 500. For example, the single-layer / multi-layer carbon nanotubes 508 can increase the number of indirect connections between adjacent multi-layer carbon nanotubes 508 by bridging the gaps between them. The interconnection between short nanofibers and long nanofibers may improve the transmission and distribution of the force applied to the film, and thus may improve the durability. Such interconnections also improve the heat conduction between the nanofibers. In another example of beneficial effects, the single-layer / multi-layer carbon nanotubes 504 may reduce the median or average value of the gap dimensions between adjacent and / or overlapping multi-layer carbon nanotubes 508. Moreover, if there are too many long multi-layer carbon nanotubes, they may aggregate when dispersed in a solvent. This may result in a non-uniform film. Short nanotubes are more easily dispersed by a solvent and thus are more likely to form a dimensionally uniform film with a uniform nanotube density per unit deposition.

[0050] FIG. 6 is a cross-sectional view of an example of a composite nanofiber membrane 600 in an example of the present disclosure. As can be seen, the composite nanofiber membrane 600 can be said to be a composite not only in that there are a plurality of different types of nanofibers in each individual layer, but also in that it is a multi-layer composite, with each layer containing different types of nanofibers in different ratios. As will be presented in the following chapter on experimental results, it will be understood that by individually adjusting the composition of each layer in a multi-layer structure, and further adjusting the number and order of the layers, it is possible to affect the emissivity and mechanical durability of the embodiments of the present disclosure.

[0051] The composite nanofiber membrane 600 shown in FIG. 6 has a first layer and a second layer 604A, 604B, which are on opposite sides of a third layer 608. The weight composition of the first layer and the second layer 604A, 604B is such that most (e.g., 50 wt% - 80 wt%) is composed of multi-walled carbon nanotubes (i.e., nanotubes having 4 - 20 layers). The composition of the third layer 608 is such that most (e.g., more than 50 weight percent) is composed of few-layer (e.g., nanotubes having 2 - 3 layers) and / or single-walled carbon nanotubes. The ratio of multi-walled carbon nanotubes to few-layer and single-walled carbon nanotubes is higher in the third layer than in one or both of the layers 604A and 604B.

[0052] The composite nanofiber membrane 600 can be formed in any of a variety of manners. Different layer nanotubes can be blended in the desired ratio, on a dry basis or a wet basis. For example, each layer can be made from a dry mixture of the desired ratio of multi-walled carbon nanotubes and few-layer / single-walled carbon nanotubes, and the desired ratio of multi-walled carbon nanotubes and few-layer / single-walled carbon nanotubes can be mixed and then suspended in a solvent. In another example, separate suspensions of known concentration are prepared with multi-walled carbon nanotubes and one or more few-layer carbon nanotubes and / or single-walled nanotubes. The suspensions can then be mixed in the ratio that reaches the desired relative weight of multi-layer and few-layer / single-layer nanotubes in the final filtration treatment film.

[0053] When preparing one or more suspensions, dry carbon nanotubes can be mixed with a solvent to distribute the nanotubes uniformly in the solvent to form a suspension. Examples of mixing include mechanical mixing (e.g., using a magnetic stir bar and a stirring plate), ultrasonic stirring (e.g., using an immersion ultrasonic probe), or other means. In some examples, the solvent can be a protic or aprotic polar solvent, such as water, isopropyl alcohol (IPA), N-methyl-2-pyrrolidone (NMP), dimethyl sulfide (DMS), and combinations thereof. In some examples, a surfactant can also be included to assist in the uniform dispersion of the carbon nanofibers in the solvent. Examples of surfactants include, but are not limited to, sodium cholate, sodium dodecyl sulfate (SDS), and sodium dodecylbenzene sulfonate (SDBS). The weight percentage of the surfactant in the solvent can be anywhere from 0.1 wt% to 10 wt% of the solvent. In one embodiment, a mixture of 50 wt% multi-walled carbon nanotubes and 50 wt% few-layer / single-layer carbon nanotubes can be prepared and dispersed in water and an SDS surfactant.

[0054] The concentration of nanotubes in the suspension can be varied according to the type of nanotubes and the properties desired for the resulting film. In various embodiments, the nanotube suspension can be prepared at a weight / weight concentration of greater than 1%, greater than 0.1%, greater than 100 ppm, greater than 10 ppm, or greater than 1 ppm. Other concentrations include greater than 1 ppm, greater than 100 ppm, greater than 1000 ppm, greater than 1%, or greater than 5% by weight. Specific ranges include 0.1 - 100 ppm, 1 - 100 ppm, 1 - 1000 ppm, and 10 - 10,000 ppm. The suspension can also be developed from a masterbatch containing a high concentration of carbon nanotubes. For example, the masterbatch can contain 0.1%, 1%, 2%, or 3% by weight / volume or more of nanotubes in a solvent. A more dilute suspension may be more stable, and in some cases, for example, a suspension of 100 ppm or less may be stable for more than 1 minute, more than 1 hour, or more than 5 hours. The dilute suspension can be produced from the masterbatch using the same or a different solvent as that used for the masterbatch.

[0055] Next, the solution can be introduced into a structure that causes the removal of the solvent and the formation of a film of randomly oriented nanofibers on the substrate. Examples of this process include, but are not limited to, vacuum filtration on a porous substrate such as filter paper. Since this composite "filtered film" of nanotubes is hydrophobic, the filtered film can be separated from the filter paper (or other substrate) by immersing the substrate and the film in water, thereby causing the composite film to float on the water surface. In some cases, hydrophilic filter paper may be used to make the film easier to separate. By flowing water between the filter paper filter and the film, the membrane can be separated from the filter paper. Since the film is hydrophobic and the filter paper is hydrophilic, when water flows between the two, the film can be gently lifted from the substrate without tearing or deformation. Next, the film is lifted from the water surface using a frame, thereby placing the filtered film on the frame. If necessary, the surface tension of water (or other solvent) can be modified by adding a surfactant or other solvent. The film can then be dried (e.g., using a low humidity environment, heat, vacuum). This process can be repeated to optionally form different films consisting of mixtures of different configurations of multi-layer, multi-layer, and / or single-layer nanotubes.

[0056] It may be important that the entire area of the substrate be subjected to an equal fluid flow. In some cases, baffles spanning the diameter of the filter can be used to assist in promoting a uniform flow and / or preventing vortices or rotations of the fluid. Although the baffle can be installed above the substrate, the baffle should not contact the substrate so that the baffle does not contact the nanotube film. In some cases, the baffle may be installed more than 1 mm above the surface of the substrate.

[0057] The film and the membrane can be formed such that the film thickness is either uniform or non-uniform. For example, the thickness of a uniform film may vary by less than 50%, less than 20%, or less than 10% across the film. In other cases, a non-uniform film may be desirable to provide different features for each portion of the film. For example, by increasing the concentration of carbon nanotubes along the edge of the film, a strong edge can be provided to the membrane. The region with a high concentration of carbon nanotubes has a higher areal density (weight of nanotubes per area) than the region with a low concentration of carbon nanotubes. Different portions of the film may have a carbon nanotube areal density that differs by more than 10%, more than 20%, or more than 50%. The ratio of the carbon nanotube areal density of these regions may exceed 1.1, 1.2, 1.5, 2.0, or 3.0. The film may have two, three, four, or more different ranges of areal density.

[0058] The areal density of carbon nanotubes at the edge of the membrane can be increased by increasing the flow of suspended nanotubes passing through the edge portion of the membrane. This can be achieved, for example, by passing a greater amount of fluid through the edge of the membrane than through other portions of the membrane, and by increasing the flow rate through the edge of the membrane compared to other areas of the membrane. The increase in concentration along the edge of the membrane can also be achieved by passing the carbon nanotube suspension through the edge portion of the substrate and not through other portions of the substrate. For example, while flowing fluid through the underlying substrate, it can be poured onto the edge of the membrane from four different containers containing different amounts of nanotubes. The increase in flow through different sections of the film, for example at the edge, can be done by varying the resistance to flow at various points on the substrate (e.g., filter paper) on which the film is deposited. For example, the edge portion of the filter paper can be one layer thick, while the portion of the filter other than the edge can be two or three layers thick. This causes more material flow to bypass passing through multiple layers and instead pass through the single layer of filter paper, resulting in a greater amount of nanotubes depositing in the area that has only a single layer of filter paper. Additional filter paper layers can be placed on the top, bottom (e.g., using an adhesive) of the two-layer filter paper extending to the edge, or in between. For example, a 9×9 cm filter paper can be placed on top of or under a 10×10 cm filter paper piece, and using the same pressure gradient, a membrane can be made that is 10×10 cm square with a 5 mm edge boundary that is thicker by passing the liquid portion of the suspension through both filter papers.

[0059] In other cases, the flow passing through different portions of the substrate (filter paper) can be increased or decreased at different times during the film formation process. For example, film formation can start with a consistent flow passing through the entire exposed surface, and once a certain surface density of nanotubes is achieved, a template can be brought into contact with the underside of the filter paper to block the flow through the filter paper in the portion in contact with the template. The flow passing through the area avoiding the template will continue, and nanotube film formation will continue in such regions, resulting in areas where the density and thickness of the nanotubes are increased. The shape of the template can be changed and may match the overall shape of the porous substrate, or it may have a smaller diameter to form a high-density boundary region at the edge.

[0060] This exemplary process can be repeated multiple times to produce a multilayer film of carbon nanotubes. In some examples, individual films (the ratio of multilayer carbon nanotubes to few-layer / single-layer carbon nanotubes in each film may be the same or different) are stacked on top of each other to form a multilayer composite film. Stacking two or more films can produce a more uniform laminate with more uniform properties. For example, if one film of the laminate has a local defect (such as a hole or a tear, like those shown in FIG. 11), without an adjacent film in the laminate, the physical continuity and uniformity of the properties may be lost at the location of the defect, but with an adjacent film, the physical continuity and uniformity of the properties can be provided. A multilayer nanofiber film, like those shown in FIG. 11, provides a solution to defects such as holes that may occur during film formation. Depending on the embodiment, the laminate can include any number of individual films from 2 to 10, and each film can have the same or a different composition (i.e., for example, different relative ratios of multilayer to single-layer / few-layer carbon nanotubes) from the other films of the laminate.

[0061] In some examples, the laminated film can be exposed to a densification solvent, and examples of the densification solvent include water, IPA, NMP, dimethylformamide (DMF), toluene, or a combination thereof. By exposing to the densification solvent, the films of the laminate can be adhered to each other. In some cases, the films of the laminate not only adhere to each other but also fuse such that they are indistinguishable from each other, and become indistinguishable even when microscopic observation techniques are used to inspect the cross-section of the laminate. In other words, the densified laminate has no visually or microscopically detectable interface between the layers and is a single uniform layer.

[0062] As shown in FIG. 6, the first layer and the second layers 604A, 604B are on the exposed surface of the film 600. As described above, the first layer and the second layers 604A, 604B are composed mostly (e.g., 50 wt% to 80 wt%) of multi-walled carbon nanotubes. Also as described above, a film formed from multi-walled carbon nanotubes has a higher thermal emissivity than one formed from few-layer / single-layer nanotubes. By configuring it in this way, the exposed first layer and second layers 604A, 604B can improve the reliability of the film 600 when used in an environment including EUV and / or vacuum. By releasing thermal energy (formed in the film by incident radiation) more efficiently than a film composed mainly of few-layer / single-layer nanotubes, the film 600 can better withstand the operating environment of an EUV lithography apparatus. This arrangement further reduces the reabsorption of thermal radiation emitted by and / or conducted out from the film 600.

[0063] FIG. 7 illustrates an alternative embodiment of a composite nanofiber membrane 700 formed from a laminate of filtration-treated carbon nanotube films. Similar to the film 600, the film 700 has a first layer and a second layer 704A, 704B formed mainly from multi-walled carbon nanotubes. The third layer and the fourth layer 708A, 708B are formed mainly from single-layer / few-layer carbon nanotubes.

[0064] FIG. 8 illustrates an assembly 800 having a membrane frame 804 in which an exemplary carbon nanotube membrane (membrane 700 in the example of the figure) is disposed. It will be understood that any membrane within the scope of the present disclosure can be installed in the frame 804. Membrane 700 is depicted in FIG. 8 as merely an example of an embodiment. In some examples, the frame 804 can be manufactured from polymers such as polyethylene, polycarbonate, composite materials such as carbon fiber epoxy composites, and metals such as aluminum and stainless steel. In some examples, the frame 804 is sized and configured to fit within an EUV lithography machine such that it can expose a light - active surface forming a lower layer in a lithographically - defined shape. In some examples, the frame 804 is sized and configured for convenient transport from a membrane manufacturing site to an EUV lithography site. In this example, the frame 804 is configured, as described herein, to primarily hold free - standing carbon nanotubes and to conveniently release a free - standing membrane for subsequent placement in a different frame that is configured to be inserted into an EUV lithography machine. In some examples, having separate transport and lithography frames allows the transport frame to be manufactured according to design criteria that are more easily met and using materials that are less expensive than those typically used when manufacturing components of an EUV lithography machine. Moreover, a frame configured specifically for an EUV lithography machine tends to be expensive, but since it can be maintained only within a lithography manufacturing location (e.g., a clean room), the rate of wear, breakage, and / or contamination can be reduced.

[0065] FIG. 9 illustrates an alternative embodiment assembly 900 that includes the elements described above and an adhesive layer 904 disposed between the frame 804 and the nanofiber membrane 700. Although the carbon nanotubes of the membrane 700 will adhere to the frame 804 (regardless of whether it is made of polymer, metal, or composite), generally, the adhesion of carbon nanotubes is strongest with other carbon nanotubes. This is particularly likely to be the case when the diameter of the carbon nanotubes is smaller, i.e., in the case of single-layer and / or multi-layer carbon nanotubes. To combine the benefits of the frame 804 and the benefits of strong nanofiber-to-nanofiber adhesion, the adhesive layer 904 of carbon nanotubes can be deposited directly on the frame 804 and then the membrane 700 can be installed on the frame.

[0066] The adhesive layer 904 can be produced by first preparing a suspension of carbon nanotubes and then forming the "filtered film" as described above. The filtered film can be configured to match the exposed area of the frame 804, which will ultimately come into indirect contact and adhere to the membrane 700. The portion of the adhesive layer filtered film that extends to the frame structure can be removed so that there is no film within and / or extending into the opening(s) defined by the frame 804. Techniques for removing excess film from areas that do not directly overlap the frame 804 include the use of lasers, electrical discharge machining (EDM), and mechanical techniques (cutting with a blade such as a surgical scalpel or the fractured surface of a silicon wafer). Depending on the technique, a solvent can be mechanically applied using an applicator such as a thin rod. For example, acetone, IPA, NMP, DMF, toluene, or other solvents (and mixtures thereof) can be applied to the rod and then the rod can be passed through the film to excise the desired location of the filtered film.

[0067] In some examples, to further improve adhesion when in direct contact with the adhesive layer 904, the bottom layer of the membrane can be formulated to include a higher percentage (e.g., greater than 50 wt%, greater than 60 wt%, greater than 70 wt%) of multi-layer and / or single-layer carbon nanotubes.

[0068] In some examples, a coating can be conformally deposited on the exposed surface of the membrane. Examples of coatings include, but are not limited to, one or more layers of metal (e.g., in particular, tungsten, iron, or other carbide-forming metals, gold, silver, boron, ruthenium, silicon nitride). Depending on the embodiment, the coating can be 1 nm to 10 nm thick. Thicker coatings are possible, but there is a possibility of reduced transparency for some radiation wavelengths (depending on the coating properties and radiation wavelength). The coating can make it easier to removably adhere the structures to each other. This is because the coating can reduce the van der Waals forces between the facing layers. Coatings applied after assembling and adhering the various layers generally do not affect the heat transfer from a single-layer / multilayer carbon nanotube filtration film (e.g., between the exposed surfaces of the membrane) to a multi-layer carbon nanotube fiber tube extended sheet with higher heat dissipation forming the exposed surface of the membrane in some examples. In some examples, the conformal layer on the exposed surface of the nanofiber sheet can reduce the decomposition of the membrane caused by hydrogen ions present in the lithography exposure chamber.

[0069] In other examples, one or more major surfaces of the membrane can be formed from a nanofiber sheet of multi-layer carbon nanotubes extended from a nanoforest of aligned nanotubes. Thus, the membrane can be a composite in which a carbon nanotube extended sheet (aligned nanotubes) and a carbon nanotube filtration film (random nanotubes) are laminated together. The experimental results corresponding to some embodiments of this arrangement are shown in Table 1 for sample numbers 5 - 11.

[0070] Experimental Results The following table reproduces the results measured from a plurality of samples prepared according to some embodiments of the present disclosure. The measured samples include a nanofiber sheet stretched from a nanofiber forest or contain one or two layers (as described above in the context of FIGS. 3 and 4), and various laminates of a "filtered film" (for example, a film formed from nanofibers suspended in a solution as described above). The number and type of layers are specified in the second and third columns from the left. The fourth column from the left is labeled "CNT height", which specifies the height of the nanofiber forest used to stretch the nanofiber sheet. That is, this column specifies the length of the multi-layer carbon nanofibers used to form the stretched sheet. The column labeled "transmittance" specifies the percentage of the intensity of light with a wavelength of 550 nm that has passed through the laminate of the filtered film and / or the stretched sheet. "Void size" specifies the average of the void sizes between bundles of nanofibers.

[0071] As can be observed, the filtered film of nanotubes has nanotubes randomly oriented within the film as described above, and as a property of their composites (i.e., a mixture of multi-layer carbon nanotubes and one or more single-layer and multi-layer nanotubes), it has a higher transmittance. In some examples, in the case of a membrane with two layers of the filtered film, this transmittance can be as high as 89% (for 550 nm wavelength radiation). By including one or more stretched sheets in which the multi-layer carbon nanotubes of the sheet are aligned in the stretching direction, the transmittance decreases to between 72% and 79%. In some examples (for example, sample numbers 3-8), the stretched sheet layer is on one or both of the major surfaces of the intervening filtered film.

[0072]

Table 1

[0073] Figures 10A - 10D illustrate, in one embodiment, the results of mechanical property and gas permeability data when the total areal mass is divided among a plurality of nanofiber membrane layers. Figure 10A illustrates the experimental results comparing the transparency of nanofiber membranes with 1, 2, and 4 layers before and after densification with isopropyl alcohol (IPA). Figure 10A shows that the transparency is similar for 1, 2, and 4 layers. The experimental results in Figure 10B illustrate that when the total areal mass of the nanofiber membrane is divided among a plurality of layers, the total areal density and transparency are maintained similarly, but the result is a reduction in film deflection under pressure. The experimental results in Figure 10C illustrate that when the total areal mass of the nanofiber membrane is divided among a plurality of layers, the total areal density and transparency are maintained similarly, but the result is an increase in the burst pressure of the film. The experimental results in Figure 10D illustrate that when the total areal mass of the nanofiber membrane is divided among a plurality of layers, the total areal density and transparency are maintained similarly, but the result is an increase in the permeability of the film. This data supports the improved functionality and desirability of the laminated nanofiber membranes described herein.

[0074] Further Considerations The foregoing description of the embodiments of the present disclosure has been provided for purposes of illustration. It is not intended to be exhaustive or to limit the claims to the precise forms disclosed. Those skilled in the relevant art will appreciate that many modifications and variations are possible in light of the above disclosure.

[0075] The language used herein has been chosen primarily for readability and for the purpose of instruction and not to delineate or circumscribe the scope of the invention. Accordingly, the scope of the present disclosure is not intended to be limited by this detailed description but rather is intended to be defined by any claims arising out of an application based on this specification. Thus, the disclosure of embodiments is intended to be illustrative and not to limit the scope of the invention, which scope is defined in the following claims.

Claims

1. A first layer of carbon nanofibers comprising a mixture randomly oriented and randomly distributed such that the total is 100% by weight of 50% to 80% by weight of multi-layer carbon nanofibers and 20% to 50% by weight of single-layer and / or few-layer carbon nanofibers A pellicle film comprising a nanofiber film comprising, wherein the multi-layer carbon nanofibers comprise 4 to 20 layers, wherein the few-layer carbon nanofibers comprise 2 and / or 3 layers, wherein the single-layer carbon nanofibers comprise 1 layer, wherein the multi-layer carbon nanofibers have a first emissivity higher than a second emissivity of the single-layer carbon nanofibers or a third emissivity of the few-layer carbon nanofibers, a pellicle film.

2. Further comprising at least one second layer of carbon nanofibers, comprising 50% by weight or more of single-layer and / or few-layer carbon nanofibers and less than 50% by weight of multi-layer carbon nanofibers so that the total is 100% by weight, wherein the nanofiber film comprises at least one of the first layers of carbon nanofibers, and one of the at least one first layers forms a first exposed surface of the nanofiber film, one of the at least one second layer of carbon nanofibers is disposed directly on the surface of the at least one first layer, one of the at least one second layer of carbon nanofibers forms a second exposed surface of the nanofiber film, and the second exposed surface of the nanofiber film faces the side opposite to the first exposed surface of the nanofiber film The pellicle film according to claim 1.

3. Further comprising a second layer of carbon nanofibers, wherein the second layer of carbon nanofibers comprises 50% by weight or more of single-layer and / or few-layer carbon nanofibers and less than 50% by weight of multi-layer carbon nanofibers so that the total is 100% by weight, wherein the nanofiber film comprises a plurality of the first layers, the second layer is disposed between a first layer and a second layer among the plurality of the first layers, the first layer and the second layer among the plurality of the first layers respectively form exposed surfaces of the nanofiber film The pellicle film according to claim 1.

4. The pellicle film according to claim 1, further comprising a frame in contact with a peripheral edge of the nanofiber film.

5. The variation in the thickness of the nanofiber film is less than 50 percent of the maximum thickness of the nanofiber film, the pellicle film according to claim 1.

6. The nanofiber film has a thickness variation greater than 10 percent of the maximum thickness of the nanofiber film, the pellicle film according to claim 1.

7. The nanofiber film has a first region and a second region, and the first areal density of the nanofibers in the first region is at least twice as high as the second areal density of the nanofibers in the second region, the pellicle film according to claim 1.

8. The first region is at the edge of the nanofiber film, the pellicle film according to claim 7.

9. The transmittance of radiation having a wavelength of 550 nm is more than 85 percent, the pellicle film according to claim 1.

10. A first layer of carbon nanofibers including the sheet composed of multilayer carbon nanofibers aligned in the plane of the sheet, and A second layer of carbon nanofibers including 50 wt% to 80 wt% of multilayer carbon nanofibers and 20 wt% to 50 wt% of single-layer or multi-layer carbon nanofibers so that the total is 100 wt%, A pellicle film including a nanofiber film, comprising: The multilayer carbon nanofibers include 4 to 20 layers, The multi-layer carbon nanofibers include 2 and / or 3 layers, The single-layer carbon nanofibers include 1 layer, The multilayer carbon nanofibers have a first emissivity that is higher than the second emissivity of the single-layer carbon nanofibers or the third emissivity of the multi-layer carbon nanofibers, the pellicle film.

11. The second layer opposite to the first layer further has a third layer of carbon nanofibers, and the third layer is A layer including more than 50 wt% of single-layer or multi-layer carbon nanofibers, and One of a second sheet of multilayer carbon nanofibers aligned in the plane of the sheet, the pellicle film according to claim 10.

12. The multilayer carbon nanofibers have a cross-sectional diameter of 6 nm to 100 nm and a length of 250 μm to 400 μm, The multi-layer carbon nanofibers have a cross-sectional diameter of 2 nm to 6 nm and a length of 0.5 μm to 30 μm, and The single-layer carbon nanofibers have a cross-sectional diameter of 0.2 nm to 2 nm and a length of 0.5 μm to 30 μm, the pellicle film according to claim 1, claim 2 or claim 3.

13. The second layer is the pellicle film according to claim 2 or claim 3, comprising randomly oriented and randomly distributed multi-layer carbon nanofibers, few-layer carbon nanofibers, and single-layer carbon nanofibers.

14. The first layer of the carbon nanofibers has a first emissivity that is higher than the second emissivity of the second layer of the carbon nanofibers, the pellicle film according to claim 2.

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