METHOD FOR PREPARING A CONDUCTIVE, TRANSPARENT AND FLEXIBLE MEMBRANE

Abstract

The technique relates to a method for preparing a nanomesh metal membrane 5 transferable on a very wide variety of supports of different types and shapes comprising at least one step of de-alloying 1 a thin layer 6 of a metal alloy deposited on a substrate 7, said method being characterized in that said thin layer 6 has a thickness less than 100 nm, and in that said de-alloying step 1 is carried out by exposing said thin layer 6 to an acid vapor in the gas phase 8, in order to form said nanomesh metal membrane 5.

Claims

1. Nanomesh metal membrane obtainable by a method comprising a step of de-alloying a thin layer of a metal alloy deposited on a substrate, said thin layer having a thickness between 1 and 100 nm, and said de-alloying step being carried out by exposing said thin layer to an acid vapor in order to form said nanomesh metal membrane, wherein the nanomesh metal membrane has a thickness between 1 and 100 nm.

2. Nanomesh metal membrane according to claim 1, wherein said metal alloy comprises at least a first metal element intended to enter the composition of said nanomesh metal membrane, and at least one second metal element to be etched chemically on said substrate.

3. Nanomesh metal membrane according to claim 2, wherein the standard redox potential of said first element with an acid is greater than the standard redox potential of the second metal element with an acid, and wherein the atomic concentration of said second metal element in said thin metal layer is greater than a predetermined threshold below which the chemical etching of said second metal element on said substrate is reduced.

4. Nanomesh metal membrane according to claim 1, wherein said metal alloy comprises a plurality of first metal elements intended to penetrate the composition of said nanomesh metal membrane.

5. Nanomesh metal membrane according to claim 1, wherein said thin layer has a thickness less than 100 nm.

6. Nanomesh metal membrane according to claim 1, wherein the method comprises a detaching step of said nanomesh metal membrane from said substrate by immersion in a detaching solution.

7. Nanomesh metal membrane according to claim 6, wherein the method comprises a subsequent step of transferring said nanomesh metal membrane on an object by immersion of a surface portion of said object in said detaching solution causing the percolation of nanomesh domains.

8. Nanomesh metal membrane according to claim 1, wherein the method comprises a step of depositing said thin metal layer on said substrate implemented by cathodic magnetron sputtering, cathodic sputtering of an alloy, evaporation, co-evaporation, chemical vapor deposition or laser ablation.

9. Nanomesh metal membrane according to claim 7, wherein the surface of the object is flat, developable or non-developable; or the surface of the object has planar, non-planar, adapted and/or left as is portions.

10. A nanomesh metal membrane, having a thickness between 1 and 100 nm.

11. Nanomesh metal membrane according to claim 10, wherein it is continuous.

12. Nanomesh metal membrane according to claim 10, comprising a percolated network of nanomesh metal domains.

13. Nanomesh metal membrane according to claim 12, wherein the network of nanomesh metal domains comprises pores, and wherein said pores have sizes varying between 10 and 100 nm.

14. Nanomesh metal membrane according to claim 12, wherein the network of nanomesh metal domains is in the form of interconnected metallic nanoligaments, these nanomesh metal domains each having a size less than 10,000 square micrometers.

15. Nanomesh metal membrane according to claim 10, wherein its transparency in the visible spectrum varies between 78% and 85%.

16. Nanomesh metal membrane according to claim 10, wherein its sheet resistance varies between 44 and 1700 Ohm/square.

17. Nanomesh metal membrane according to claim 10, comprising a first metal element chosen from the group consisting of gold, platinum, silver, zinc, nickel and copper or at least two elements chosen from the group consisting of gold, platinum, silver, zinc, nickel and copper.

18. Nanomesh metal membrane according to claim 10, having a Haacke merit factor of 2.13×10.sup.−3Ω.sup.−1.

19. A method of conducting electricity comprising coating an object with a nanomesh metal membrane of claim 10, wherein the nanomesh metal membrane is a transparent coating.

20. A method of detecting cracks or tears on a surface comprising coating the surface with a nanomesh metal membrane of claim 10.

Description

4. FIGURES

[0060] The features and advantages of the invention will become apparent upon reading the following description of a particular embodiment, given by way of illustrative and nonlimiting example, and through the appended figures, wherein:

[0061] FIG. 1A shows a scanning electron microscopy (SEM) field image at a scale of 1 μm, of a nanomesh gold membrane obtained by de-alloying a layer of gold-copper alloy in nitric acid in the liquid phase, according to a method known from the prior art,

[0062] FIG. 1B shows an SEM field image, at a scale of 100 nm, of a nanomesh gold membrane obtained by de-alloying a layer of gold-copper alloy in liquid phase nitric acid according to a method known from the prior art,

[0063] FIG. 2 shows schematically the successive steps of a method for preparing a nanomesh metal membrane according to one particular embodiment of the invention,

[0064] FIG. 3A shows an SEM image in the field, at a scale of 1 μm, of a nanomesh gold membrane according to one embodiment of the invention, after transfer onto a transparent and flexible support made of PET,

[0065] FIG. 3B shows an SEM field image, at a scale of 100 nm, of a nanomesh gold membrane according to one embodiment of the invention, after transfer onto a transparent and flexible support made of PET,

[0066] FIG. 4 shows a graph illustrating the variations in optical transmittance at a wavelength of 550 nm for different types of membranes or thin layers, as a function of their electrical resistance Ohms/square,

[0067] FIG. 5A shows a photograph showing the experimental device used for a fatigue resistance test of a nanomesh gold membrane according to one embodiment of the invention which undergoes curvature cycles,

[0068] FIG. 5B shows a graph illustrating the respective electrical resistance variations of a nanomesh gold membrane according to one embodiment of the invention, and of a thin layer, as a function of the number of iterations of 1% of their deformation.

[0069] The various elements illustrated in the figures are not necessarily represented on a real scale, the emphasis being more on the representation of the general operation of the invention.

5. DETAILED DESCRIPTION OF A PARTICULAR EMBODIMENT OF THE INVENTION

[0070] The general concept of a method for preparing a nanomesh metal membrane according to one embodiment of the invention is to implement a step of de-alloying an initial thin layer of a metal alloy in which the latter is exposed to an acid vapor, and not to a liquid consisting of an acid solution. A particular embodiment of the invention is presented in the following description. It is to be understood that the present invention is not limited by this particular embodiment and that other embodiments may be implemented without problem.

5.1 Method for Preparing a Nanomesh Metal Membrane

[0071] As shown in FIG. 2, a method for manufacturing a nanomesh metal membrane (5) comprises, according to a particular embodiment of the invention, a first step 1 of depositing a thin layer (6) on a substrate (7), followed by a second de-alloying step 2 of this thin layer (6) by exposure to an acid vapor (8), which makes it possible to obtain the membrane (5), followed by a third detaching step 3 of this membrane (5) of the substrate (7) by immersion in a dedicated solution (9), and a final transfer step of this membrane (5) on the surface of an object to be coated (10).

[0072] During the deposition step 1, a thin layer (6) made of a gold-copper (Au—Cu) binary alloy is deposited on a glass substrate (7). Within this metal alloy, and as detailed in the following description, the gold is intended to enter the composition of the future membrane (5) while the copper is to be etched chemically on the substrate (7) during a subsequent de-alloying step 2 of the thin layer (6).

[0073] According to alternative embodiments, any combination of metal elements can be used to form the thin layer (6), provided that the difference between the standard redox potentials of the latter is sufficiently high to allow their de-alloying. Thus, in a known manner, in the case of a metal alloy comprising at least a first metal element intended to enter the composition of said membrane (5), and at least a second metal element to be etched on the substrate (7) after exposure to an acid vapor (8), it is desirable for the first metal element to have an electrochemical oxidation potential E°1 with the acid (8) greater than the electrochemical oxidation potential E°2 of the second metal element with this same acid (8).

[0074] However, the de-alloying method is not limited only to the differences existing between the respective redox potentials of the different elements constituting the alloy.

[0075] Of course, these differences in redox potentials are a point to consider when working with noble metals such as gold and platinum (Pt). For example, to make nanoporous gold or a nanomesh gold membrane, the most commonly used binary alloys are gold-copper and gold-silver alloys. The standard redox potential of solid silver in Ag.sup.+ ion is +0.8 V, whereas that of solid copper in Cu.sup.2+ ions is +0.34 V. The standard redox potential of gold is +1.83 V. The difference between the potentials allows the selective dissolution of copper or silver.

[0076] On the other hand, in order to achieve de-alloying based on metals other than gold or platinum, such as copper or silver for example, other parameters having an influence on the chemical de-alloying reaction must also be taken into account. For example, in the case of a silver-aluminum alloy, it is possible to etch aluminum in a solution of hydrochloric acid in order to obtain nanoporous silver or a nanomesh silver membrane (5). However, It is not only the difference of potentials which allows this selective dissolution but also the taking into account of the formation of a layer of silver chloride on the surface of the metal silver, this same layer protecting the silver from dissolution during the de-alloying.

[0077] Non-limiting examples of binary metal alloys that may be used include gold-silver, gold-copper, zinc-copper, platinum-copper, nickel-aluminum and copper-aluminum alloys.

[0078] According to an alternative embodiment, the metal alloy constituting the initial thin layer (6) can also be composed of three metal elements (then called ternary alloy) or more. In this case, a single element of the ternary alloy may be removed in order to obtain a binary alloy membrane.

[0079] The additional metal element, intended to penetrate with the first metal element in the composition of said membrane, may advantageously have the function of improving one or more physico-chemical characteristics of the metal membrane.

[0080] Thus, by way of nonlimiting example, the thin layer (6) may consist of a nickel-copper-magnesium ternary alloy, in which the magnesium is intended to be etched on the substrate while the copper and nickel are intended to enter the final composition of the metal membrane (5). The function of the nickel is to increase the resistance of the copper to oxidation.

[0081] Alternatively, several ternary alloys may be considered, such as nickel-silver-magnesium, nickel-copper-aluminum, or nickel-silver-aluminum alloys.

[0082] With respect to the thin layer made of a gold-copper binary alloy, the atomic concentration of copper is set at 40 at. %. This threshold of concentration of the least noble element of the alloy, called “parting limit”, corresponds to the concentration value below which the dissolution of this less noble element is reduced. This is related to the formation of a passivation layer of the most noble element at the very beginning of the de-alloying method, because of its high concentration in the alloy. This passivation layer acts as a protective layer which prevents the penetration of the acid solution into the alloy and thus prevents the dissolution of the least noble element of volume of the alloy. In the context of the de-alloying method, it is preferable that the concentration of the least noble element should be greater than this “parting limit” threshold concentration. In the case of gold-copper, the threshold concentration of dissolution is 40% copper while in the case of Au—Ag this threshold is 60% silver, as discussed in the publication “Unusual Dealloying Effect in Gold/Copper Alloy Thin Films: The Role of Defects and Column Boundaries in the Formation of Nanoporous Gold, by El Mel, A.-A.; Boukli-Hacene, F.; Molina-Luna, L.; Bouts, N.; Chauvin, A.; Thiry, D.; Gautron, E.; Gautier, N.; Tessier, P. Y., ACS Appl. Mater. Interfaces 2015, 7, 2310-2321.

[0083] According to alternative embodiments, the thickness of the thin layer (6) can vary between 1 and 100 nm, wherein this leads to the production of metal membranes (5) having conductivity and transparency variations. In this context and as discussed in the following description, it has been observed that as the thickness of the membrane (5) increases, the electrical conductivity also increases while its transparency decreases, and vice versa.

[0084] The composition of the substrate (7) chosen to serve as a support for the thin layer of metal alloy (6) at the base of the embodiment of the membrane (5) may vary from one embodiment to another. This composition is chosen so that the metal elements intended to form the membrane (5) have the least possible chemical affinity with the chosen substrate (7). This reduces the adhesion of the alloy to the substrate and consequently facilitates the subsequent detaching step of this membrane (5). In addition, the substrate must not disintegrate or react with the acid vapors or the solution used for the separation (5). As a nonlimiting example, and as illustrated in FIG. 2, the use of a glass substrate makes it possible to fulfill these requirements in the case of nanomesh membranes prepared by vapor phase etching of a layer of gold-copper. In fact, the metal element(s) remaining after the de-alloying interact(s) very weakly with the substrate (7) and the membrane (5) detaches very easily. In addition, the glass does not react with the acid used in the method.

[0085] Conversely, in the context of the formation of a silver membrane by de-alloying a silver-aluminum layer in hydrochloric acid, the use of a glass substrate is inappropriate, given its strong reaction potential with this acid.

[0086] According to alternative embodiments, any type of substrate having a known low affinity with the thin layer in question can be used.

[0087] As shown in FIG. 2, the deposition of the thin layer (6) is implemented by magnetron co-sputtering. Such a technique has the advantage of allowing the formation of a thin layer whose concentration is precisely controlled. Its implementation is therefore particularly advantageous for the preparation of a thin layer 6 before de-alloying.

[0088] According to alternative embodiments, this deposition step (1) is carried out by cathodic sputtering of an alloy, evaporation or co-evaporation (thermal or by electron gun), by chemical vapor deposition, by laser ablation or via any known method for synthesizing an alloy in the form of a thin layer.

[0089] During the de-alloying step (2), the gold-copper thin film (6) is de-alloyed by exposure to a nitric acid vapor (8). For this purpose, the nitric acid (8) selectively oxidizes and etches the metal element having the lowest oxidation potential with the nitric acid, in this case: copper. The elimination by etching of the less noble metal and the reorganization of the noblest metal lead to the formation of nanomesh metal domains (5b) consisting of interconnected metal nanoligaments (5c), wherein these domains (5b) cover the surface of the substrate (7) and each has a size smaller than 10,000 square micrometers. All these domains (5b) constitute the nanomesh membrane (5). By choosing the precursor alloy, one can define the metal forming the membrane (5), in this case: gold.

[0090] An essential point of the manufacturing method according to the invention lies in the fact that the nitric acid used for the de-alloying is in the form of vapor and not liquid. In fact, and as described in the description of the prior art, a direct immersion of the thin layer (6) in a nitric acid solution would cause its complete disintegration given the capillary forces generated at the interface between the thin layer and the acid solution. On the other hand, the exposure of the thin layer (6) to an acid vapor (8) makes it possible to significantly limit the phenomenon of disintegration of the latter. In fact, the inventors have observed that surprisingly, under these conditions, the de-alloying takes place in a very low volume liquid phase. This is due to the condensation of the acid vapor which forms an ultrathin layer of concentrated acid on the surface of the thin metal layer. The de-alloying takes place in this layer of ultrathin acid allowing the alloy to be de-alloyed while maintaining a very low surface tension. Consequently, the capillary adhesion of the dealloyed thin layer (6), i.e. the membrane (5), to the acid (8) is also reduced, which limits the stresses generated within the membrane (5), the appearance and/or the development of cracks, and the risk of detaching.

[0091] The de-alloying step (2) thus makes it possible, after de-alloying (2) of a thin gold-copper layer (6), to obtain a nanomesh gold metal membrane (5) having a thickness of less than 100 nm, for a macroscopic size surface.

[0092] Once the gold membrane (5) is formed on the surface of the glass substrate (7), the latter is immersed (3) in a deionized water solution (9) in order to detach the membrane (5) from the substrate (7). The deionized water (9) has the advantage of having a very low chemical affinity with gold. Such a choice thus makes it possible to limit the risks of solubilization of the membrane (5). Following the immersion of the substrate (7), the membrane (5), which is hydrophobic, is detached from the glass slide, which is hydrophilic. Following the immersion step (3), the nanomesh gold metal membrane (5) floats on the surface of the deionized water solution (9) without it disintegrating. For a layer of the prior art that would have been de-alloyed in the liquid phase without undergoing disintegration in the acid, it would disintegrate during immersion in water. The disintegration is thus not limited only to the de-alloying step (2), but it can also occur during the immersion step (3) in the detaching solution (9). The de-alloying step (2) via an acid vapor (8) makes it possible to avoid this disaggregation.

[0093] The composition of the detaching solution (9) can obviously vary from one embodiment to another, the latter being chosen so that the metal elements forming the membrane (5) have the least possible chemical affinity with the chosen solution (9).

[0094] In order to carry out the transfer (4) of the membrane (5) onto an object to be coated (10), a surface portion of this object (10) is immersed in the deionized water solution (9) on the surface of which the membrane (5) floats. During this transfer step (4), there is percolation of the nanomesh metal domains, which thus form a continuous nanomesh membrane (5) over the entire submerged surface portion of the object (10).

[0095] According to particular embodiments of the invention, this object to be coated may take the form of a solar cell, a flexible and extensible surface, a proton exchange membrane (PEM), a PET, polydimethylsiloxane (PDMS), silicon and/or glass, or any other support that can benefit from the advantageous properties of the membrane (5) in the context of a particular industrial application. Moreover, the surface of the object to be coated can be flat, adapted or left as is without the conductive and transparent properties being altered. For example, this surface (10) may be that of a cylinder, a cone, a sphere or an ellipsoid. The surface of the object to be coated may also have a more complex shape with a surface that may comprise both flat, non-planar, adapted and/or left as is portions. For example, it can be a bottle, a tube or a bottle, especially glass or polymer or any other type of material. For example, the membrane (5) can be transferred to the surface of a glass tube (i.e., non-planar surface): this surface remains transparent, and the conductivity of the object thus coated makes it possible to light an LED (photographs not shown).

[0096] According to one embodiment of the invention, the membrane (5) thus obtained is used as a coating for electrical conduction, for example on the surface of a touch screen, this screen being flexible.

[0097] According to an alternative embodiment, the membrane (5) may be used as a coating for detecting breaks in the surface of an object (10), the electrical resistance of the membrane varying as a function thereof. By way of example, the use of such a membrane for coating a laboratory glove made of nitrile or latex may make it possible to detect the occurrence of a tear.

5.2 Characterization of a Nanomesh Metal Membrane

[0098] In the remainder of the description, a nanomesh gold membrane (5) produced according to one embodiment of the invention has been subjected to SEM observations, optical transmittance tests and electrical resistance tests, and curvature tests.

[0099] 5.2.1 Observations with a Scanning Electron Microscope

[0100] FIGS. 3A and 3B show images obtained by SEM field observation, at a scale of 1 μm and 100 nm respectively, of a nanomesh gold membrane obtained via a method according to an embodiment of the invention. More specifically, this membrane (5) was obtained from a thin layer (6) with a thickness of 10 nm, consisting of a gold-copper alloy composed of 24 at. % of gold. The thin film (6) was first deposited on a glass substrate by magnetron sputtering of a gold target and a copper target in the cofocal position. The thin layer was subsequently de-alloyed by exposure for 2 hours to nitric acid vapor (8), before being immersed in deionized water (9). Finally, the membrane obtained was transferred to a transparent and flexible PET support (10), for observation.

[0101] As a comparative example, a gold membrane obtained according to a known method from a thin layer having the same atomic composition and the same thickness as that described above was also observed through SEM. The major difference between these two methods lies in the fact that according to the invention, the de-alloying step is conducted in gaseous phase, and not liquid.

[0102] Thus, FIG. 1A shows an image obtained by scanning electron microscope (SEM) field image, at a scale of 1 μm, which illustrates the surface appearance of a gold membrane obtained by a known method. The PET substrate used in this experiment allows good adhesion of the membrane (5). The observation of this membrane (5) reveals the presence of microcracks (5a) between the nanomesh gold domains (5b). The cracks (5a) result from the stresses generated during the de-alloying method. The formation of these cracks (5a) and nanomesh domains (5b) is described in particular in the publications “In Situ Observation of Strain Development and Porosity Evolution in Nanoporous Gold Foils”, by Dotzler, C. J. et al, Adv. Funct. Mater. 21, 3938-3946 (2011), and “Microstructure, stability and thermomechanical behavior of crack-free thin films of nanoporous gold”, by Sun, Y., Kucera, K. P., Burger, S. A. & John Balk, Scr. Mater. 58, 1018-1021 (2008). By examining the domains (5b), it has been found that the latter are formed of nanoligaments (5c) physically disconnected from each other. This is the reason why the membranes are electrically insulating in this case. A problem of nanoligament stability relating to a transformation of nanoligaments into nanobeads has also been revealed during the aging of the membranes. The transformation of ligaments into beads is linked to the use of PET as a support to which the gold ligaments of strongly adhere, which is a factor limiting the relaxation of the mechanical stresses of the ligaments, generated during the de-alloying method.

[0103] Another reaction has been observed using glass substrates instead of PET or PDMS as the support (7). Depending on the gold content in the alloy and their thicknesses, the layers can detach and degrade during their immersion in the acid or survive the acid attack without detaching or agglomeration of the film in the acid solution. Although in the latter case, nanomesh domains are formed of nanoligaments, the membrane obtained is electrically insulating due to the presence of microcracks separating the nanomesh domains from each other. Finally, the membrane disintegrates during its immersion in the detaching solution and/or when it is transferred to a flexible substrate (e.g., PET).

[0104] In comparison with FIG. 1A, FIG. 3A shows the reduction of the cracks (5a) separating the nanomesh domains (5b) from each other and the percolation thereof. FIG. 5B makes it possible to highlight the bonds existing between the nanoligaments (5c) forming each of these nanomesh domains (5b). This interconnectivity of the metal nanoligaments (5c) gives the membrane (5) its ability to conduct electricity satisfactorily, as described below.

5.2.2 Optical Transmittance and Electrical Resistance Test Per Square

[0105] For this test, a nanomesh gold membrane was obtained from a thin layer (6) made of a gold-copper alloy having 17 at. % gold and 5 nm thickness in the initial state. Layer (6) was created by magnetron co-sputtering. The sample was then exposed to nitric acid vapor 8 for 30 minutes. The created membrane (5) was subsequently transferred to a PET carrier using deionized water (9).

[0106] For a comparison of the characteristics of the membrane studied with the known membranes, the transmittance at 550 nm as well as the resistance per square of the sample were measured.

[0107] The electrical resistance of the thin film is expressed as a resistance per square, which is dimensionally equivalent to Ohm, but whose symbol is Ω/□.

[0108] FIG. 4 shows a graph expressing transmittance values at 550 nm as a function of the resistance per square, in particular for membranes known from the prior art consisting of:

[0109] a mixture of poly (3,4-ethylenedioxythiophene) and sodium polystyrene sulphonate, also known under the name PEDOT:PSS,

[0110] carbon nanotubes,

[0111] graphene,

[0112] silver nanowires,

[0113] nanomesh.

[0114] By way of comparison, the performance of 3 nanomesh gold membranes (denoted “Our membranes” made according to one embodiment of the invention are also shown in FIG. 4.

[0115] The properties of PEDOT:PSS are described in the publication “Highly Conductive PEDOT:PSS Electrode with Optimized Solvent and Thermal Post-Treatment for ITO-Free Organic Solar Cells”, by Kim, Y. H. et al., Adv. Funct. Mater. 21, 1076-1081 (2011).

[0116] The respective properties of carbon nanotubes, graphene, silver nanowires, and nanomesh are described in the following publications:

[0117] “Past achievements and future challenges in the development of optically transparent electrodes”, by Ellmer, K, Nat. Photonics 6, 809-817 (2012).

[0118] “A transparent electrode based on a nanotrough network metal”, by Wu, H. et al., Nat. Nanotechnol. 8, 421-425 (2013).

[0119] “Silver Nanowire Networks as Flexible, Transparent, Conducting Films: Extremely High DC to Optical Conductivity Ratios”, by De, S. et al, ACS Nano 3, 1767-1774 (2009).

[0120] As shown in FIG. 4, the membrane studied has a resistance of 44Ω/□ and an optical transmittance of 79%. The maximum optical transmittance values are 86% and the minimum square resistance values are 33Ω/□. These performances confer a factor of merit for this membrane (in English Haacke's factor of merit) of 2.13×10.sup.−3Ω.sup.−1.

[0121] By way of comparison, the membrane studied possesses resistance and transmittance values comparable to those of carbon nanotubes deposited on PET. The resistance and transmittance values are also comparable to the performances obtained with silver nanowires or with PEDOT:PSS layers.

[0122] A nanomesh membrane (5) obtained according to the method described above thus has the advantage of having both transparency and a satisfactory electrical conductivity.

5.2.3 Curvature Resistance Tests—Deformation Resistance

[0123] In the context of a first test, the experimental device that is represented in FIG. 5A, is a nanomesh gold membrane (5) deposited on a PET substrate, which has the same technical characteristics as the membrane tested with optical transmittance and electrical resistance as described above, was subjected to a bending force between two clamps (11). An LED (12) positioned in the background of FIG. 5A shows the passage or not of the electric current through the membrane (5).

[0124] During the test, it was observed that the membrane (5) undergoes a deformation of 2.5% and remains conductive (the LED (12) remains on, and confirms the passage of electric current in the membrane).

[0125] In the context of a second test, a gold membrane such as that described above and a thin layer having the same characteristics as the initial gold-copper alloy described above, have respectively undergone a deformation of 1% repeated 10,000 times.

[0126] FIG. 5B shows a graph illustrating the respective electrical resistance variations of the thin layer (6) before de-alloying and the resistance of the nanomesh membrane (5) after de-alloying of the thin layer (6), as a function of the number of iterations of their deformation.

[0127] Following the 10,000 deformation cycles, an increase in electrical resistance of less than 10% was observed in the case of the membrane (5) while the increase in electrical resistance of the thin layer (6) is more than 50%. In comparison, a thin layer of indium tin oxide (ITO) known from the prior art sees its electrical resistance increase by 2000% after less than 100 deformation cycles, as described in the article “A nanotrough network”, by Wu, H. et al., Nature nanotechnology 8, 421-425 (2013).

[0128] The curvature of a membrane (5) according to the invention is therefore significantly improved in comparison with known membranes of the prior art.