Method for the production of conductive structures or layers

Abstract

The invention relates to a method for the production of conductive structures, a composition comprising at least one reducing agent and at least one metal complex being applied to a substrate either in the form of nanofibers, particularly by electrospinning, or in the form of a layer. After this step, the metal complex is reduced to metal by the reducing agent, heating and / or the effect of electromagnetic radiation.

Description

[0001] Process for producing conductive structures or surfaces

[0002] Description

[0003] Field of the invention

[0004] The invention relates to a method for producing metallic, in particular conductive structures or surfaces, as well as compositions for their production, such conductive structures or surfaces and their use.

[0005] State-of-the-art Fibers obtained by electrospinning exhibit a very high aspect ratio. This is advantageous for applications that require a large surface area in a small volume. For example, TiO2 nanofibers coated with silver nanoparticles have been used for surface-enhanced Raman spectroscopy, antibacterial coatings, photocatalysis, and energy conversion. Conductive nanofibers have also been proposed as electrodes or for touchscreens. Fibers made of conductive materials include fibers made of conductive polymers or other conductive materials such as metals or graphene.

[0006] Another possibility is inks that contain a polymer, a metal compound, and sometimes also a reducing agent. This is described, for example, in US 2017 / 0077403 A1. Some of the inks described there are thermally reduced, although, contrary to the specifications, high temperatures are always used. For example, an ink is described that contains PEO and PVP. Silver acetate is used as the silver source, and formic acid as the reducing agent. The composition is spun onto glass and briefly thermally treated at 300°C or more.

[0007] These processes are not suitable for production on film substrates such as polycarbonate or PET, particularly due to the high temperatures involved. They also often involve multiple steps.

[0008] Task

[0009] The object of the invention is to provide a method which allows the production of metallic structures based on nanofibers or conductive surfaces, in particular transparent conductive structures.

[0010] Solution

[0011] This object is achieved by the inventions having the features of the independent claims. Advantageous developments of the inventions are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into the content of this description. The inventions also encompass all reasonable and, in particular, all mentioned combinations of independent and / or dependent claims.

[0012] The problem is solved by a process for producing metallic structures and / or surfaces.

[0013] Individual method steps are described in more detail below. The steps do not necessarily have to be carried out in the order given, and the method to be described can also have further, unmentioned steps. 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, at least one matrix material or at least one precursor thereof; b) applying the composition to a substrate, wherein the application takes place by surface contacting or application as a spun nanofiber; c) reducing the at least one metal complex to the metallic structure or surface by the action of electromagnetic radiation and / or heating.

[0014] In step c), a metal layer or layer of metallic fibers is usually formed, depending on the type of application. In this case, a metallic layer in the sense of the invention is understood to be a layer of a metal. Such layers can also be conductive if they are sufficiently thick. Such conductive layers are particularly preferred. In this case, conductive does not necessarily mean the production of structures which in themselves represent a conductor track. The production of dots from conductive material also represents a conductive structure in principle. In the case of fibers, several layers of fibers can also be applied.

[0015] The composition comprises at least one metal complex. This comprises at least one metal ion and at least one type of 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, particularly preferably a silver complex. The composition can also comprise several types of metal complexes or mixtures of metal complexes.

[0016] Chelate ligands are generally used as ligands. These are able to form particularly stable complexes. These are compounds which have a plurality of hydroxyl groups and / or amino groups. Preference is given to compounds having a molecular weight of less than 200 g / mol, particular preference being given to compounds having at least one hydroxyl group and at least one amino group. Examples of possible compounds are 3-amino-l, 2-propanediol, 2-amino-l-ethanol-l-ol (ethanolamine), 2-amino-l-propan-l-ol, 3-amino-l-propan-l-ol, 2-amino-l-butanol, tris(hydroxymethyl)aminomethane (TRIS), NH3, nicotinamide or 6-aminohexanoic acid. Mixtures of these ligands can also be used.

[0017] In the case of the preferred silver complex, ethanolamine or NH3 is preferred as the ligand. It may be necessary, especially when using NH3, to add an alkaline compound, such as a hydroxide such as NaOH, KOH, and / or tetramethylammonium hydroxide. This is particularly preferred when using silver salts.

[0018] Preferred ligands are those containing amino groups or amino and hydroxyl groups, which can serve as reducing agents for the metal complex under the conditions of step c). In this preferred case, the metal complex is formed from the composition of the reducing agent and a metal salt.

[0019] If the reducing agent is used in excess, the composition therefore contains both the metal complex and free reducing agent. The composition then preferably contains no additional reducing agent.

[0020] In a preferred embodiment, the molar ratio of ligand, based on the amino groups or NH3, to metal salt is at least 1.2:1, preferably at least 1.5:1, in particular 1.2:1 to 10:1, particularly preferably 1.5:1 to 10:1. The excess of ligand complexes and dissolves the metal salt, and subsequently reduces it. The ligand also supports the reduction reaction when a photocatalytic substrate is used.

[0021] The metal complex is preferably formed in the composition of at least one metal salt and at least one ligand, preferably at least one metal salt and the reducing agent as ligand. The complex is preferably formed in situ in the composition.

[0022] Preferably, the metal salt is selected from salts of copper,

[0023] Silver, gold, nickel, zinc, aluminum, titanium, chromium, manganese, tungsten, platinum or palladium, preferably silver, gold or copper, particularly preferably a silver salt.

[0024] The salt is 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 most preferred.

[0025] Preferably, the at least one metal complex is present in dissolved form in the composition.

[0026] The composition further comprises at least one matrix material or at least one precursor thereof. It can be an organic, an inorganic or organically modified inorganic matrix-forming material. These can be inorganic sols or organically modified inorganic hybrid materials. Examples of these are optionally 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 from groups 5 to 10 of the Periodic Table (e.g. Mn, Gr, Fe and Ni) or lanthanides can also be present in the oxide, hydrolysate or (poly)condensate.For example, it may be a sol comprising Ti, which may also be the precursor of the photocatalytically active component.

[0027] In the case of an organic matrix material, organic polymers and / or oligomers, preferably organic polymers and / or oligomers which have polar groups such as hydroxyl, primary, secondary or tertiary amino, carboxyl or carboxylate groups, can be used. Typical examples are polyvinyl alcohol, polyethylene oxide (PEO), polyvinylpyrrolidone, polyacrylamide, polyvinylpyridine, polyallylamine, polyacrylic acid, polyvinyl acetate such as polyvinyl butyral, polymethyl methacrylic acid, starch, gum arabic, other polymeric alcohols such as polyethylene-polyvinyl alcohol copolymers, polyethylene glycol, polypropylene glycol and poly(4-vinylphenol) or monomers or oligomers derived therefrom. Polyethylene oxide or polyvinylpyrrollidone (PVP) are preferred.

[0028] Organic polymers with a molecular mass of more than 200,000 g / mol (weight average M w ) to 6000000 g / mol, preferably from over 1000000 g / mol to 4500000 g / mol.

[0029] 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 with a boiling point below 150°C, in particular below 101°C. The solvent particularly preferably comprises at least water. Mixtures of the solvents can also be used, preferably mixtures of water and ethanol. A suitable mixing ratio is 50:50 wt.% up to 20:80 wt.% of H2O:alcohol, preferably ethanol. Water is particularly preferably the sole solvent.

[0030] Other additives, such as surfactants, antioxidants, or plasticizers, may also be included. Preferably, no additives are present. The viscosity of the composition can be adjusted depending on the application method.

[0031] Depending on the composition, the content of matrix component in the case of an organic matrix component is preferably between 0.1 and 10 wt.% of the composition, in particular between 0.1 and 5 wt.%.

[0032] The content of metal complex and ligand may vary depending on the application.

[0033] It may be necessary to mix the composition for 1 hour to 72 hours prior to electrospinning, particularly if the composition comprises hydrolyzable compounds.

[0034] The preferred conditions for electrospinning are a voltage of 8 to 20 kV and a dope flow rate of 0.3 to 1.5 mL / h. The distance to the surface on which the fibers are collected is preferably 10 to 30 cm. A needle with an inner diameter of 0.1 mm to 2 mm is preferably used.

[0035] Alternatively, the composition can be applied flatly to a substrate. Conventional methods can be used to apply the composition, for example, dipping, rolling, doctoring, flow coating, drawing, spraying, spinning, or brushing.

[0036] The order can also be placed several times in succession.

[0037] In the next step, the reduction of at least one metal complex to the metallic structure or surface takes place by exposure to electromagnetic radiation and / or heating. The reducing agent present allows this to occur under mild conditions. The conditions can be adapted to the substrate.

[0038] The reduction can also be carried out in several steps in which the irradiation and / or heating is repeated.

[0039] In case of heating, heating to below 200 ° C, preferably 50 ° C to 150 ° C is preferred.

[0040] Heating is preferably carried out for at least 6 hours, preferably 6 to 36 hours.

[0041] Heating is preferably carried out under ambient atmosphere.

[0042] In one embodiment of the invention, the composition is applied to a photocatalytically active coated substrate. The substrate is preferably coated with at least one layer of photocatalytically active titanium dioxide. This can be amorphous titanium dioxide, anatase or rutile, or mixtures thereof. The titanium dioxide can also be doped, for example with indium. It is only important that it is photocatalytically active under the conditions necessary to reduce the metal complex.

[0043] The electromagnetic radiation is radiation of the wavelength required to excite the photocatalytic component. The irradiation can be carried out using a planar radiation source, such as a lamp, or by laser. A wavelength in the visible or ultraviolet (UV) range of the electromagnetic spectrum is preferably used, preferably radiation with a wavelength of < 500 nm, for example between 200 and 450 nm or between 250 nm and 410 nm. Radiation with a wavelength of < 400 nm is preferred.

[0044] Any suitable light source can be used. Examples include mercury vapor lamps or xenon lamps.

[0045] The light source is arranged at a suitable distance from the substrate to be exposed. The distance can be, for example, between 2.5 cm and 50 cm. The intensity of the radiation can be in a spectral range from 250 nm to 410 nm between 30 mW / cm 2 and 70 mW / cm 2 lay .

[0046] The irradiation should be carried out as perpendicular as possible to the surface to be exposed.

[0047] Irradiation is carried out for a time sufficient to form the metallic layer or structure. The duration depends on the substrate, as well as on the composition, the type of lamp, the wavelength range used, and the intensity of the irradiation. If conductive structures are to be created, longer irradiation may be necessary. An irradiation duration of between 5 seconds and 30 minutes is preferred, more preferably between 20 seconds and 15 minutes.

[0048] If a laser is used for irradiation, an argon ion laser (351 nm) with 10 mW, for example, can be used. The laser beam is focused and collimated and moved over the substrate to be irradiated at a speed of 2 mm / s. The substrate to which the composition is applied can be any material suitable for this purpose. Examples of suitable materials are metals or metal alloys, glass, ceramics, including oxide ceramics, glass ceramics or plastics, as well as paper and other cellulosic materials. Substrates which have a surface layer made of the materials mentioned above can of course also be used. The surface layer can be, for example, metallization, enamel, a glass or ceramic layer or a paint coating.

[0049] Examples of metals or metal alloys include steel, including stainless steel, chromium, copper, titanium, tin, zinc, brass, and aluminum. Examples of glass include soda-lime glass, borosilicate glass, lead crystal, and fused silica. These can include flat glass, hollow glass such as container glass, or glass used for laboratory equipment. Ceramics include ceramics based on the oxides SiO2, Al2O3, ZrO2, or MgO, or the corresponding mixed oxides. Examples of the plastic, which, like the metal, can be in the form of a film, are polyethylene, e.g. HDPE or LDPE, polypropylene, polyisobutylene, polystyrene (PS), polyvinyl chloride (PVC), polyvinylidene chloride, polyvinyl butyral, polytetrafluoroethylene, polychlorotrifluoroethylene, polyacrylates, polymethacrylates such as polymethyl methacrylate (PMMA), polyamide, polyethylene terephthalate (PET), polycarbonate, regenerated cellulose, cellulose nitrate, cellulose acetate, cellulose triacetate (TAG), cellulose acetate butyrate or rubber hydrochloride.A painted surface can be formed from conventional primers or varnishes. In a preferred embodiment, the substrates are films, particularly polyethylene terephthalate films or polyimide films. If the structures are already fabricated on the surface, the surface must be able to withstand the manufacturing conditions, such as the temperatures.

[0050] By reducing the nanofibers, the metallic structures can be formed in a manner that matches the fibers, thus enabling thinner conductive structures. The reducing agent present in the composition ensures that the reduction is selective. Since the composition itself is not, or only slightly, light-sensitive, it can be handled much more easily. Furthermore, the metallic, preferably conductive, structure is transparent simply due to the thinness of the nanofibers.

[0051] The composition itself does not contain any photocatalytically active component such as titanium dioxide or ZnO.

[0052] The nanofibers preferably have an average length of more than 10 pm, in particular more than 20 pm, particularly preferably more than 50 pm.

[0053] In a preferred embodiment of the invention, the nanofibers are obtained by electrospinning.

[0054] For this purpose, a composition comprising at least one metal complex, at least one reducing agent, at least one matrix material or a precursor is prepared.

[0055] This is spun into a nanofiber using electrospinning.

[0056] Multiple layers of nanofibers can also be applied to the substrate. The application is continued until the desired quantity and density of nanofibers has been deposited on the substrate. It may be necessary to treat the fibers, for example, by drying them at temperatures below 200°C, especially below 150°C. These low temperatures allow the use of sensitive substrates, such as films, especially plastic films.

[0057] It may be necessary to allow the fibers to rest for at least 12 hours immediately after electrospinning before further processing.

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

[0059] After electrospinning, the nanofibers preferably have an average diameter of less than 1 pm, in particular less than 500 nm (determined by ESEM), in particular less than 400 nm. The fibers preferably have a round cross-section. The diameter is preferably between 30 nm and 500 nm, in particular between 50 and 350 nm.

[0060] It may be necessary to mix the composition for 1 hour to 72 hours prior to electrospinning.

[0061] The preferred conditions for electrospinning are a voltage of 8 to 20 kV and a dope flow rate of 0.3 to 1.5 mL / h. The distance to the surface on which the fibers are collected is preferably 5 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 invention, the substrate is further treated after the reduction of the composition. For example, the surface can be cleaned by rinsing the surface, for example with deionized water or another suitable substance. The coated substrate can then be dried, for example by heating in an oven, compressed air, and / or by drying at room temperature.

[0063] It can also be irradiated multiple times, for example 2, 3 or 4 times.

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

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

[0066] In one embodiment of the invention, structuring occurs during application of the composition and / or during reduction. In the context of the invention, this means preparation for the spatially limited production of the metallic structure. This can be done in different ways. Firstly, the substrate can be coated with the composition, for example with the nanofibers, only in certain areas. It is also possible to apply the composition only to certain areas. Furthermore, the effect of the electromagnetic radiation can of course also be limited to certain areas. These methods can of course also be used in combination. For example, it is possible to apply the composition over a large area and then expose it through a mask. It is of course also possible to apply the composition in a targeted manner and then expose it over a large area.

[0067] Especially when using electrospinning, it is also possible to apply the spun fibers to a structured substrate, especially one with elongated recesses. Due to their length, the fibers arrange themselves along the recesses.

[0068] After the process, additional layers can be applied, for example to protect the coated surface of the substrate against UV radiation.

[0069] There are essentially no limitations on the structures that can be applied by structuring. For example, connected structures such as conductor tracks can be applied. Furthermore, it is also possible to apply dot-like structures. Due to the high resolution, the process makes it possible to apply conductive dots to a film that are invisible to the naked eye. This plays a major role in the production of touchscreen surfaces.

[0070] The invention also relates to a coated substrate obtained by a process according to the invention. Such a substrate is preferably characterized by a layer comprising metallic nanofibers. This layer has a thickness between 50 nm and 200 pm. Preferred layer thicknesses are between 100 nm and 1 pm, preferably 50 nm to 700 nm.

[0071] The coating on the substrate is particularly preferably conductive. This is understood to mean a structure which, at a distance of 5 mm, has a resistance in at least one direction of less than 3 M, preferably less than 2 M, very particularly preferably less than 1 M. Due to the fibrous structure, the structures produced can have an anisotropic resistance. This means that the resistance increases by at least a factor of 2, at least a factor of 10, in particular a factor of 100, depending on the direction of the measurement.

[0072] In a particularly advantageous embodiment of the invention, the coating on the substrate is at least partially transparent, in particular completely transparent. This can be achieved by ensuring that the degree of coverage of the fibers after electrospinning in the coated regions on the surface of the substrate is less than 20% of the coated surface of the substrate, in particular between 10-20%, preferably between 10 and 15%. This can be influenced, for example, by the duration of the electrospinning. The coverage can be determined by measuring the average transmission and haze as a function of the duration of the electrospinning.

[0073] Preferably, the coating with fibers reduces the average transmission by only up to 5%.

[0074] In a further development of the invention, the metallic structure has a structuring with structural elements with an extension of less than 50 pm, preferably less than 10 pm. The structural elements can be metallic and / or non-metallic regions. The metallic structure is particularly preferably made of metallic nanofibers.

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

[0076] The compositions or fibers according to the invention reduce themselves to form conductive coatings without the need for additional compositions. This allows conductive and, in particular, transparent coatings to be obtained in a simple manner.

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

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

[0079] A particular advantage of the invention lies in the production of conductive structures. These are suitable as conductor tracks in electronic applications, particularly in touchscreen displays, solar collectors, displays, as RFID antennas, or in transistors. Transparent structures, as well as structures with anisotropic resistance, can be obtained.

[0080] The structures can also be used in the field of transistors.

[0081] Further details and features will become apparent from the following description of preferred embodiments in conjunction with the subclaims. The respective features can be implemented individually or in combination with one another. The possibilities for solving the problem are not limited to the embodiments. For example, range specifications always include all intermediate values ​​(not mentioned) and all conceivable subintervals.

[0082] The exemplary embodiments are illustrated schematically in the figures. Identical reference numerals in the individual figures denote identical or functionally equivalent elements, or elements that correspond to one another in terms of their functions. In detail:

[0083] Fig. 1 Light micrographs of the spun fibers with ink 1 on a) glass or b) PC film;

[0084] Fig. 2 Light micrographs (a) and b) of the spun fibers with ink 2 on TiC^-coated PET film;

[0085] Fig. 3 a) and b): Light micrographs of the spun fibers with ink 5;

[0086] Fig. 4 Light micrograph of the spun fibers with ink 5.

[0087] Examples

[0088] Composition of the inks

[0089] Ink 1:

[0090] A composition of 0.8 g silver acetate, 0.627 g ethanolamine and 1.404 g polyethylene oxide solution (PEO, 1 wt% in H2O, ca. 4,000,000 g / mol) was prepared.

[0091] The composition was spun by electrospinning (temperature 23.7 °C; relative humidity 40%, Y-axis speed: 150 mm / s, X-axis pitch: 10 mm, pumping rate 0.3 mL / h; needle / collector distance: 5 cm; voltage 10 kV, cannula 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 at 130 °C overnight (18 h) in a circulating air drying oven. The coated PC film was treated in a MHz Ar plasma for 10 minutes after the oven. The results are shown in Table 1 and Figure 1 a) and b).

[0092] Ink 2:

[0093] A composition of 0.8 g silver acetate, 0.734 g ethanolamine and 1.689 g polyethylene oxide solution (PEO, 1 wt% in H2O, ca. 4,000,000 g / mol) was prepared.

[0094] The composition was spun by electrospinning (temperature 23.0 °C; relative humidity 40%, Y-axis speed: 150 mm / s, X-axis pitch: 10 mm, pumping rate 0.3 mL / h; needle / collector distance: 5 cm; voltage 10 kV, cannula diameter 0.3 mm). Cosmoshine PET film (11 x 11 cm) with a TiO2 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 subsequently dried overnight at 130 °C in a circulating air drying cabinet. The results are shown in Table 2 and Figure 2.

[0095] Ink 3:

[0096] A composition was prepared from 0.798 g of silver acetate, 0.605 g of polyethylene oxide solution (PEO, 2 wt.% in H2O, approx. 4,000,000 g / mol), 1.216 g of 30% ammonia in water, and 30 mg of tetramethylammonium hydroxide or potassium hydroxide. The composition was spun onto PC foil at 5 mm spacing. After heating overnight at 130 °C, individual conductive fibers were present. When coated onto PC or glass, after heating to 125 °C, sheet resistances (measured contactlessly using eddy current measurement) in the mOhm range were achieved.

[0097] Ink 4:

[0098] A composition of 1 g of a solution (1.28 g tris(hydroxymethyl)aminomethane and 0.86 g silver nitrate in 20 g water) and 0.253 g polyethylene oxide solution (PEO, 1 wt% in H2O, ca. 4,000,000 g / mol) was prepared.

[0099] The composition was spread on a TiO2 coated PET film and irradiated for 10 minutes with 77.25 mW / cm 2exposed to UV light. After rinsing with water, a layer with a sheet resistance of 410 mOhm was obtained (measured contactlessly using the eddy current method). Ink 4 is spinnable in principle, and areas are conductive after exposure.

[0100] Ink 5:

[0101] A composition of 0.3 g silver acetate, 0.297 g ethanolamine and 1.010 g 1:1 mixture of polyvinylpyrrolidone solution and polyethylene oxide solution (PVP, 4 wt%, 1,300,000 g / mol in ethanol; PEO, 2 wt% in H2O, approx. 4,000,000 g / mol) was prepared.

[0102] The composition was spun by electrospinning (temperature 20.8 °C; relative humidity 20%, Y-axis speed: 500 mm / s, X-axis pitch: 10 mm, pumping rate 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 to UV twice in a Beltron UV dryer and then dried for 26 hours at 140 °C in a circulating air drying cabinet. The results are shown in Table 3 and Figures 3 a) and b) as well as Figure 4. Conductive samples were also obtained on glass using the ink.

[0103] Table 1

[0104] Table 2

[0105] Table 3

Claims

Patent claims 1. A method for producing metallic structures or surfaces, comprising the following steps: a) providing a composition comprising at least one metal complex or a precursor thereof, at least one reducing agent, at least one matrix material or at least one precursor thereof; b) applying the composition to a substrate, the application being carried out by surface contact or application as a spun nanofiber; c) reducing the at least one metal complex to the metallic structure or surface by the action of electromagnetic radiation and / or heating. 2 . Method according to one of the preceding claims, characterized in that the nanofibers are obtained by electrospinning. 3 . Process according to one of the preceding claims, characterized in that the metal complex is formed in the composition from at least one metal salt and at least one ligand.

4. Process according to claim 3, characterized in that the at least one ligand is a ligand with amino groups or amino and hydroxyl groups, which can serve as a reducing agent under the conditions of step c). 5 . Method according to one of claims 1 to 4, characterized in that the substrate is a photocatalytically active substrate.

6. Process according to one of the preceding claims, characterized in that the metal complex is a silver, gold or copper complex.

7. Method according to one of the preceding claims, characterized in that the nanofibers have an average length of more than 10 pm.

8. Coated substrate obtained by the process according to any one of claims 1 to 7.

9. Coated substrate according to claim 8, characterized in that the coated substrate appears at least partially transparent.

10. Coated substrate according to one of claims 8 or 9, characterized in that the coating is conductive.

11. Coated substrate according to claim 10, characterized in that the coating has an anisotropic resistance.

12. Use of a substrate according to one of claims 8 to 9 as a conductor track in electronic applications, in touch screen displays, in solar collectors, in displays, as an RFID antenna or in transistors.

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