Method for producing conductive structures or surfaces

Abstract

The present invention relates to a method for producing an electrically conductive structure, in which a composition comprising at least one reducing agent and at least one metal complex is applied to a substrate, either in the form of nanofibers, in particular by electrospinning, or in the form of a layer, after which the metal complex is reduced to metal by the action of a reducing agent, heat and / or electromagnetic radiation.

Description

[Technical Field]

[0001] The present invention relates to a method for producing metallic, in particular electrically conductive, structures or surfaces, as well as compositions for their production, such electrically conductive structures or surfaces, and their uses. [Background technology]

[0002] Electrospinning produces fibers with very high aspect ratios, making them advantageous for applications requiring large surface areas in small volumes. For example, TiO nanofibers coated with silver nanoparticles have been used in surface-enhanced Raman spectroscopy, antibacterial coatings, photocatalysis, and energy conversion. Conductive nanofibers have also been proposed as electrodes or for touchscreens.

[0003] Known fibers made of conductive materials include fibers made of conductive polymers or other conductive materials such as metals or graphene.

[0004] Another possibility is an ink containing, in addition to the polymer, a metal compound and possibly a reducing agent. Such inks are described, for example, in US Pat. No. 5,629,499. Some of the inks described in US Pat. No. 5,629,499 are reduced by heat, but contrary to the information provided, high temperatures are always used. For example, an ink containing PEO and PVP is described. Silver acetate is used as the silver source and formic acid is used as the reducing agent. The composition is spun onto glass and heat-treated for a short time at temperatures above 300°C.

[0005] These processes are not suitable for production on film substrates such as polycarbonate or PET, particularly since they involve high temperatures. They also often involve multiple steps. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0077403 Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide a method that allows the production of metallic structures, in particular transparent conductive structures, based on nanofibers or conductive surfaces. [Means for solving the problem]

[0008] This problem is solved by the invention with the features of the independent claims. Advantageous further embodiments of the invention are characterized in the dependent claims. All claim language is to be read in accordance with the content of this specification. The invention also includes all useful, in particular all mentioned, combinations of the independent and / or dependent claims.

[0009] This problem is solved by a method for producing metallic structures and / or surfaces.

[0010] The individual process steps are described in more detail below. These steps do not necessarily have to be performed in the order shown, and the described method may also include additional steps not mentioned. The method comprises the following steps: a) providing a composition comprising at least one metal complex or a precursor thereof, at least one reducing agent, and at least one matrix material or at least one precursor thereof; b) applying the composition to a substrate, the application being by surface contact or application as spun nanofibers; c) reducing at least one metal complex to a metallic structure or surface by exposure to electromagnetic radiation and / or heating; Includes.

[0011] In step c), a metal layer or a layer of metallic fibers is usually formed, depending on the application method. In this context, a metallic layer in the sense of the present invention is understood to mean a layer of metal. Such a layer can also be conductive if it is thick enough. Such a conductive layer is particularly preferred. Conductivity does not necessarily mean the production of a structure that itself is a conductor path. The production of dots from a conductive material also generally represents a conductive structure. In the case of fibers, multiple fiber layers can also be applied.

[0012] The composition includes at least one metal complex. The metal complex includes at least one metal ion and at least one ligand. The metal ion is, for example, an ion of copper, silver, gold, nickel, zinc, aluminum, titanium, chromium, manganese, tungsten, platinum, or palladium. In a preferred embodiment, the metal complex is a silver, gold, or copper complex, and a silver complex is particularly preferred. The composition may include multiple types of metal complexes or a mixture of metal complexes.

[0013] As the ligand, a chelating ligand is generally used. A chelating ligand can form a particularly stable complex. A chelating ligand is a compound having multiple hydroxyl and / or amino groups. Compounds with a molecular weight of less than 200 g / mol are preferred, and compounds having at least one hydroxyl and at least one amino group are particularly preferred. Examples of possible compounds are 3-amino-1,2-propanediol, 2-amino-1-ethan-1-ol (ethanolamine), 2-amino-1-propan-1-ol, 3-amino-1-propan-1-ol, 2-amino-1-butanol, tris(hydroxymethyl)aminomethane (TRIS), NH3, nicotinamide, or 6-aminohexanoic acid. Mixtures of these ligands can also be used.

[0014] For the preferred silver complexes, ethanolamine or NH3 are the preferred ligands.

[0015] Particularly when NH3 is used, it may be necessary to add alkaline compounds such as hydroxides like NaOH, KOH, and / or tetramethylammonium hydroxide, which is particularly preferred when silver salts are used.

[0016] A ligand having an amino group or an amino group and a hydroxyl group is preferred, which can act as a reducing agent for the metal complex under the conditions of step c). In this preferred case, the metal complex of the composition is formed from a reducing agent and a metal salt. Therefore, when an excess amount of the reducing agent is used, the metal complex and free reducing agent are present in the composition. In this case, it is preferred that the composition does not contain any more reducing agent.

[0017] In a preferred embodiment, the molar ratio of amino or NH3-based ligand to metal salt is at least 1.2:1, preferably at least 1.5:1, particularly 1.2:1 to 10:1, and particularly preferably 1.5:1 to 10:1. Excess ligand forms a complex with the metal salt, dissolving it and subsequently reducing it. The ligand also supports the reduction reaction when a photocatalytic substrate is used.

[0018] The metal complex is preferably formed in the composition from at least one metal salt and at least one ligand, preferably from at least one metal salt and a reducing agent as a ligand. The complex is preferably formed in situ in the composition.

[0019] The metal salt is preferably selected from copper, silver, gold, nickel, zinc, aluminum, titanium, chromium, manganese, tungsten, platinum or palladium salts, preferably from silver, gold or copper salts, particularly preferably silver salts.

[0020] The salts are preferably selected from fluorides, chlorides, bromides, iodides, nitrates, nitrites, sulfates, or acetates. Salts that are soluble in the composition are preferred. Nitrates and acetates are preferred. Silver nitrate and silver acetate are particularly preferred.

[0021] Preferably, the at least one metal complex is soluble in the composition.

[0022] The composition further comprises at least one matrix material or at least one precursor thereof. This may be an organic matrix-forming material, an inorganic matrix-forming material, or an organically modified inorganic matrix-forming material. In particular, these may be inorganic binders or organically modified inorganic hybrid materials. Examples of this include organically modified oxides, hydrolysates, and (poly)condensates of at least one glass- or ceramic-forming element M, in particular an element M from groups 3 to 5 and / or 12 to 15 of the periodic table of the elements, preferably Si, Al, B, Ge, Pb, Sn, Ti, Zr, V, and Zn, or mixtures thereof. Elements from groups 1 and 2 of the periodic table (e.g., Na, K, Ca, and Mg) and groups 5 to 10 of the periodic table (e.g., Mn, Cr, Fe, and Ni), or lanthanides, may also be present in the oxide, hydrolysate, or (poly)condensate. For example, it may be a sol containing Ti, which may be a precursor of a photocatalytically active component.

[0023] For organic matrix materials, organic polymers and / or oligomers, preferably those having polar groups such as hydroxyl groups, primary, secondary, or tertiary amino groups, carboxyl groups, or carboxylate groups, can be used. Typical examples include polyvinyl alcohol, polyethylene oxide (PEO), polyvinylpyrrolidone, polyacrylamide, polyvinylpyridine, polyallylamine, polyacrylic acid, polyvinyl acetate such as polyvinyl butyral, polymethyl methacrylic acid, starch, gum arabic, polyethylene-polyvinyl alcohol copolymer, polyethylene glycol, polypropylene glycol, and other polymer alcohols such as poly(4-vinylphenol), or monomers or oligomers derived therefrom. Preferred are polyethylene oxide or polyvinylpyrrolidone (PVP).

[0024] Preferably, the weight average Mw ) to 6,000,000 g / mol, preferably to 4,500,000 g / mol.

[0025] The composition may also contain at least one solvent. All components must be soluble or dispersible in the solvent. These may be, for example, alcohols such as methanol, ethanol, n-propanol, i-propanol, or water. Preference is given to one or more solvents having a boiling point below 150°C, in particular below 101°C. Particularly preferred is a solvent that contains at least water. Mixtures of solvents can also be used, preferably a mixture of water and ethanol. Suitable mixing ratios are 50:50% by weight to 20:80% by weight of H2O:alcohol, preferably ethanol. Water is particularly preferred as the sole solvent.

[0026] Other additives such as surfactants, antioxidants, or plasticizers may be present, although preferably no additives are present.

[0027] The viscosity of the composition can be adjusted depending on the application method.

[0028] Depending on the type of composition, the content of the matrix component in the case of an organic matrix component is preferably 0.1% to 10% by weight, particularly 0.1% to 5% by weight of the composition.

[0029] The content of the metal complex and the ligand may vary depending on the application.

[0030] The composition may need to be mixed for 1 hour to 72 hours before electrospinning, especially if the composition contains a hydrolyzable compound.

[0031] The preferred conditions for electrospinning are a spinning material flow rate of 0.3 mL / h to 1.5 mL / h and a voltage of 8 kV to 20 kV. The distance to the surface where the fibers are collected is preferably 10 cm to 30 cm. A needle with an inner diameter of 0.1 mm to 2 mm is preferably used.

[0032] Alternatively, the composition can be applied to the surface of the substrate by conventional methods such as, for example, dipping, rolling, squeegeeing, flow coating, drawing, spraying, spin coating, or brush coating.

[0033] The composition can also be applied in multiple successive applications.

[0034] In a next step, the at least one metal complex is reduced to a metallic structure or surface by exposure to electromagnetic radiation and / or heating.

[0035] Due to the presence of a reducing agent, the reduction can be carried out under mild conditions, which can be adapted to the substrate.

[0036] The reduction can also be carried out in multiple steps with repeated irradiation and / or heating.

[0037] In the case of heating, it is preferable to heat to a temperature below 200°C, preferably 50°C to 150°C.

[0038] Heating is preferably carried out for at least 6 hours, preferably 6 to 36 hours.

[0039] Heating is preferably carried out under ambient atmosphere.

[0040] In one embodiment of the present invention, the composition is applied to a photocatalytically active coated substrate. Preferably, the substrate is coated with at least one layer of photocatalytically active titanium dioxide. The titanium dioxide can be amorphous titanium dioxide (anatase or rutile), and mixtures thereof. Titanium dioxide can also be doped, for example with indium. It is only important that the substrate be photocatalytically active under the conditions required to reduce the metal complex.

[0041] The electromagnetic radiation is radiation of a wavelength required to excite the photocatalytic component. Irradiation can be carried out using a surface radiation source such as a lamp, or a laser. Preferably, wavelengths in the visible or ultraviolet (UV) region of the electromagnetic spectrum are used, preferably radiation having a wavelength of less than 500 nm, for example, 200 nm to 450 nm, or 250 nm to 410 nm. Preference is given to radiation having a wavelength of less than 400 nm.

[0042] Any suitable light source can be used as the light source, examples of which include a mercury lamp or a xenon lamp.

[0043] The light source is positioned at an appropriate distance from the substrate to be exposed, which can be, for example, 2.5 cm to 50 cm. The intensity of the radiation is 30 mW / cm in the spectral range of 250 nm to 410 nm. 2 ~70mW / cm 2 It can be said that:

[0044] It is desirable to irradiate as perpendicularly as possible to the surface to be exposed.

[0045] The irradiation is carried out for the duration necessary to form a metallic layer or structure. This duration will vary depending on the substrate, the composition, the type of lamp, the wavelength range used, and the intensity of the irradiation. Longer irradiation may be necessary if a conductive structure is to be produced. The preferred duration of irradiation is between 5 seconds and 30 minutes, preferably between 20 seconds and 15 minutes.

[0046] When a laser is used for irradiation, for example, an argon ion laser (351 nm) with 10 mW can be used, and the laser beam is focused and collimated and directed onto the substrate to be irradiated at a speed of 2 mm / s.

[0047] The substrate to which the composition is applied can be any material suitable for this purpose. Examples of suitable materials include metals or metal alloys, glass, ceramics (including oxide ceramics, glass ceramics, or plastics), as well as paper and other cellulose-containing materials. Of course, substrates having a surface layer of the aforementioned materials can also be used. The surface layer can be, for example, a metallization, an enamel coating, a glass or ceramic layer, or a paint system.

[0048] Examples of metals or metal alloys are steel, including stainless steel, chromium, copper, titanium, tin, zinc, brass, and aluminum. Examples of glass are soda-lime glass, borosilicate glass, lead crystal, and silica glass. The glass can be, for example, hollow glass, such as plate glass, container glass, or laboratory glass. The ceramic can be, for example, a ceramic based on the oxides SiO2, Al2O3, ZrO2, or MgO, or the corresponding mixed oxides. Examples of plastics that can exist as films, similar to metals, include polyethylene (e.g., HDPE or LDPE), polypropylene, polyisobutylene, polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene chloride, polyvinyl butyral, polytetrafluoroethylene, polychlorotrifluoroethylene, polyacrylate, polymethacrylate (e.g., polymethyl methacrylate (PMMA)), polyamide, polyethylene terephthalate (PET), polycarbonate, regenerated cellulose, cellulose nitrate, cellulose acetate, cellulose triacetate (TAC), cellulose acetate butyrate, or rubber hydrochloride. Lacquered surfaces can be formed from conventional base coats or lacquers. In a preferred embodiment, the substrate is a film, particularly a polyethylene terephthalate film or a polyimide film. If a structure has already been fabricated on the surface, the surface must be able to withstand the fabrication conditions, such as temperature.

[0049] The reduction of nanofibers allows the formation of metallic structures depending on the fiber, allowing for thinner conductive structures. The reducing agent in the composition ensures that the reduction is selective. The composition itself is not photosensitive or only slightly photosensitive, making it much easier to handle. The metallic, preferably conductive, structures are also transparent due to the thinness of the nanofibers.

[0050] The composition itself does not contain any photocatalytically active components such as titanium dioxide or ZnO.

[0051] Preferably, the nanofibers have an average length of more than 10 μm, in particular more than 20 μm, especially preferably more than 50 μm.

[0052] In a preferred embodiment of the present invention, the nanofibers are obtained by electrospinning.

[0053] For this purpose, a composition is prepared which comprises at least one metal complex, at least one reducing agent and at least one matrix material or precursor.

[0054] The composition is spun into nanofibers using an electrospinning process.

[0055] Multiple layers of nanofibers can be applied to the substrate until the desired amount and density of nanofibers is applied to the substrate.

[0056] It may also be necessary to treat the fibers, for example, dry them, at temperatures below 200° C., especially below 150° C. These low temperatures allow the use of delicate substrates such as films, especially plastic films.

[0057] Immediately after electrospinning, the fibers may need to rest for at least 12 hours before further processing.

[0058] It may be necessary to apply the nanofibers to the final substrate.

[0059] Preferably, the nanofibers after electrospinning have an average diameter of less than 1 μm, particularly less than 500 nm (determined by ESEM), especially less than 400 nm. Preferably, the fibers have a circular cross section. The diameter is preferably between 30 nm and 500 nm, especially between 50 nm and 350 nm.

[0060] The composition may need to be mixed for 1 hour to 72 hours before electrospinning.

[0061] The preferred conditions for electrospinning are a flow rate of the spinning material of 0.3 mL / h to 1.5 mL / h and a voltage of 8 kV to 20 kV. The distance to the surface where the fibers are collected is preferably 5 cm to 30 cm. A needle with an inner diameter of 0.2 mm to 2 mm is preferably used.

[0062] In a further embodiment of the present invention, the substrate is further treated after reduction of the composition. For example, the surface can be cleaned, for example, by rinsing the surface with deionized water or another suitable substance. The coated substrate can then be dried, for example, by heating in an oven, with compressed air, and / or by drying at room temperature.

[0063] The substrate can also be irradiated multiple times, for example, two, three, or four times.

[0064] In a preferred embodiment, the coated substrate is treated with plasma, preferably Ar plasma, after reduction. The treatment can last from 30 seconds to 30 minutes. Ar plasma is preferred.

[0065] Additional layers may be applied, for example, to protect the coated surface from oxidation and moisture or from UV radiation.

[0066] In one embodiment of the present invention, structuring is carried out during application and / or reduction of the composition. In the context of the present invention, structuring is understood to mean preparation for the creation of spatially limited metallic structures. Structuring is possible in various ways. On the one hand, it is possible to coat the substrate with a composition, for example nanofibers, only in specific areas. It is also possible to apply the composition only in specific areas. Furthermore, it is of course possible to limit the action of electromagnetic radiation to specific areas. These methods can also be used in combination. For example, it is possible to apply the composition over a wide area and then expose it through a mask. It is of course also possible to apply the composition selectively and then expose it over a wide area.

[0067] When using electrospinning, it is also possible to apply the spun fibers to a structured substrate, in particular a substrate having elongated depressions, the length of which causes the fibers to align themselves along the depressions.

[0068] Additional layers may be applied after processing, for example to protect the coated surface of the substrate from UV radiation.

[0069] The structures that can be applied by structuring are practically unlimited. For example, connected structures such as conductive circuits can be applied. It is also possible to apply dot-like structures. Due to the high resolution, it is possible to apply invisible conductive dots to the film. This plays an important role in the production of surfaces for touchscreens.

[0070] The present invention also relates to a coated substrate obtainable by the method according to the invention. Such a substrate is preferably characterized by a layer containing metallic nanofibers. This layer has a thickness of 50 nm to 200 μm. Preferred layer thicknesses are 100 nm to 1 μm, preferably 50 nm to 700 nm.

[0071] The coating on the substrate is particularly preferably conductive. This is understood to mean a structure in which the resistance in at least one direction is less than 3 MΩ, preferably less than 2 MΩ, and most preferably less than 1 MΩ at a distance of 5 mm. The fibrous structure allows the produced structure to have anisotropic resistance. This means that the resistance increases at least 2 times, at least 10 times, and particularly 100 times depending on the direction of measurement.

[0072] In a particularly advantageous embodiment of the present invention, the coating on the substrate is at least partially transparent, in particular completely transparent. This can be achieved by having the degree of fiber coverage in the coated area of ​​the surface of the substrate after electrospinning be less than 20%, in particular 10% to 20%, preferably 10% to 15% of the coated surface of the substrate. This can be influenced, for example, by the duration of electrospinning. The coverage can be determined by measuring the average transmittance and haze as a function of the duration of electrospinning.

[0073] Preferably, the coating with fibers reduces the average transmittance by no more than 5%.

[0074] In a further development of the invention, the metallic structure has a structured portion with structural elements having an extent of less than 50 μm, preferably less than 10 μm. The structural elements may be metallic and / or non-metallic regions. The metallic structure is particularly preferably made of metallic nanofibers.

[0075] In a particularly advantageous further development of the invention, the coated substrate has at least partially transparent metallic structures, which can be achieved, for example, by applying structures with a resolution of less than 20 μm, preferably less than 10 μm, to a transparent substrate.

[0076] The composition or fiber according to the invention can itself become a conductive coating without the need for applying an additional composition, making it easy to obtain a conductive, especially a transparent, coating.

[0077] The coated substrates obtained by the method according to the invention can be used in many applications.

[0078] On the one hand, this method is suitable for applying reflective metal layers to surfaces, which can be used, for example, as reflective layers in holographic applications.

[0079] A particular advantage of the present invention is the production of conductive structures, which are suitable as conductive circuits in electronic devices, particularly in touchscreen displays, solar collectors, displays, RFID antennas, or transistors. In particular, transparent structures and structures with anisotropic resistance can be obtained.

[0080] However, these structures can also be used in the field of transistors.

[0081] Further details and features can be found in the following description of preferred embodiments together with the dependent claims, where each feature can be realized individually or in combination with one another. The solution possibilities are not limited to the example embodiments. For example, the specification of ranges always includes all unmentioned intermediate values ​​and all possible subranges.

[0082] The embodiments are illustrated diagrammatically in the figures, in which the same reference numbers in the different figures indicate identical or functionally identical elements or elements that correspond to each other in terms of their functionality. [Brief explanation of the drawings]

[0083] [Figure 1] FIG. 1 shows optical microscope images of spun fibers with Ink 1 on a) glass or b) PC film. [Figure 2] 1A and 1B show optical microscope images (a) and (b) of spun fibers with ink 2 on TiO2-coated PET film. [Figure 3]a) and b): Optical microscope images of spun fibers with ink 5. [Figure 4] FIG. 1 shows an optical microscope image of spun fibers with ink 5. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0084] Ink Composition Ink 1: A composition of 0.8 g of silver acetate, 0.627 g of ethanolamine, and 1.404 g of polyethylene oxide solution (PEO, 1 wt % in H2O, approximately 4,000,000 g / mol) was prepared.

[0085] This composition was electrospun (temperature 23.7°C; relative humidity 40%, Y-axis speed: 150 mm / s, X-axis pitch: 10 mm, pump speed 0.3 mL / h; needle / collector distance: 5 cm; voltage 10 kV, cannula (needle) diameter 0.3 mm). Display glass (rubbed with ethanol) or polycarbonate film (PC, Makrofol DE 1-1CG) was used as the substrate. After spinning, the film was dried overnight (18 hours) at 130°C in a convection oven. The coated PC film was then treated with MHz-Ar plasma for 10 minutes after the oven. The results are shown in Table 1 and Figure 1a and b.

[0086] Ink 2: A composition of 0.8 g of silver acetate, 0.734 g of ethanolamine, and 1.689 g of polyethylene oxide solution (PEO, 1 wt % in H2O, approximately 4,000,000 g / mol) was prepared.

[0087] This composition was electrospun (temperature 23.0°C; relative humidity 40%, Y-axis speed: 150 mm / s, X-axis pitch: 10 mm, pump speed 0.3 mL / h; needle / collector distance: 5 cm; voltage 10 kV, cannula diameter 0.3 mm). Cosmoshine PET film (11 × 11 cm) with a TiO coating (3%, 0.5 m / min, 120°C) was used as the substrate. The coated substrate was then exposed to UV light in a Beltron UV dryer and then dried overnight at 130°C in a convection oven. The results are shown in Table 2 and Figure 2.

[0088] Ink 3: A composition was prepared from 0.798 g of silver acetate, 0.605 g of polyethylene oxide solution (PEO, 2% by weight in H2O, approximately 4,000,000 g / mol), 1.216 g of 30% ammonia in water, and 30 mg of tetramethylammonium hydroxide or potassium hydroxide.

[0089] This composition was spun onto a PC film at 5 mm intervals. After heating at 130°C overnight, individual conductive fibers were present. After coating on PC or glass and heating at 125°C, a surface resistance in the mΩ range (measured non-contact using an eddy current method) was achieved.

[0090] Ink 4: A composition was prepared from 1 g of a solution (1.28 g of tris(hydroxymethyl)aminomethane and 0.86 g of silver nitrate in 20 g of water) and 0.253 g of polyethylene oxide solution (PEO, 1 wt % in H2O, approximately 4,000,000 g / mol).

[0091] This composition was coated onto a TiO2-coated PET film and irradiated with 77.25 mW / cm 2 The ink was exposed to UV light for 10 minutes. After rinsing with water, a layer with a sheet resistance of 410 mΩ was obtained (measured contactlessly using the eddy current method). Ink 4 is in principle spinnable, and the areas are conductive after exposure.

[0092] Ink 5: A composition was prepared containing 0.3 g of silver acetate, 0.297 g of ethanolamine, and 1.010 g of a 1:1 mixture of polyvinylpyrrolidone and polyethylene oxide solutions (PVP 4 wt %, 1,300,000 g / mol in ethanol; PEO 2 wt % in H2O, approximately 4,000,000 g / mol).

[0093] This composition was electrospun (temperature 20.8°C; relative humidity 20%, Y-axis speed: 500 mm / s, X-axis pitch: 10 mm, pump speed 0.5 mL / h; needle / collector distance: 7 cm; voltage 10 kV, cannula diameter 0.3 mm). PC film (Makrofol DE 1-1CG) was used as the substrate. The coated substrate was then exposed twice to UV light in a Beltron UV dryer and then dried in a convection oven at 140°C for 26 hours. The results are shown in Table 3, Figure 3a and b, and Figure 4.

[0094] The ink was used to obtain conductive samples on glass.

[0095] [Table 1]

[0096] [Table 2]

[0097] [Table 3]

Claims

1. 1. A method for producing a metallic structure or surface, comprising the steps of: a) providing a composition comprising at least one metal complex or a precursor thereof, at least one reducing agent, and at least one matrix material or at least one precursor thereof; b) applying the composition to a substrate, said application being by surface contact or application as spun nanofibers; c) reducing said at least one metal complex to a metallic structure or surface by exposure to electromagnetic radiation and / or heating; A method comprising:

2. 2. The method of claim 1, wherein the nanofibers are obtained by electrospinning.

3. 3. The method of claim 1, wherein the metal complex in the composition is formed from at least one metal salt and at least one ligand.

4. 4. The method according to claim 3, wherein the at least one ligand is a ligand having an amino group or an amino group and a hydroxyl group, and the ligand is capable of acting as a reducing agent under the conditions of step c).

5. The method according to any one of claims 1 to 4, characterized in that the substrate is a photocatalytically active substrate.

6. 6. The method according to claim 1, wherein the metal complex is a silver, gold, or copper complex.

7. The method according to any one of claims 1 to 6, characterized in that the nanofibers have an average length of more than 10 μm.

8. A coated substrate obtainable by the method according to any one of claims 1 to 7.

9. The coated substrate of claim 8, characterized in that the coated substrate has at least a portion of its appearance that is transparent.

10. 10. The coated substrate of claim 8 or 9, characterized in that the coating is electrically conductive.

11. The coated substrate of claim 10, wherein the coating has anisotropic resistance.

12. 10. Use of a substrate according to claim 8 or 9 as a conductive circuit in an electronic device, a touch screen display, a solar collector or a display, as an RFID antenna or in a transistor.

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