Plasma-induced crystallization and densification of amorphous coatings

Abstract

The present invention relates to a method for coating a substrate and the respective coated substrate. The resulting coating is characterized by a crystalline and dense structure, which is particularly suitable for applying further coating layers thereon. The method uses plasma instead of thermal curing to cure the applied solution, which is therefore faster, less energy-consuming, and applicable to more temperature-sensitive substrates.

Description

[Technical Field]

[0001] The present invention relates to a method for coating a substrate and the respective coated substrate. The coating produced is characterized by a crystalline and dense structure, which is particularly suitable for applying further layers of coating thereon. [Background technology]

[0002] Many substrates are provided with coatings to achieve specific desired effects or property enhancements. Depending on the application, the coatings have thicknesses ranging from a few nanometers to several millimeters. For example, for optical and ophthalmic lenses, glass or polymers are typically coated with several layers in the nanometer to micrometer range to provide UV filtering, anti-reflective and anti-scratch properties, and chemical resistance.

[0003] To apply such thick coatings, the sol-gel process is generally used. A solution of the coating medium or its precursor is prepared in a first step, which is then applied to the substrate by various techniques to produce a thin liquid film. Finally, the solvent is evaporated from the film to obtain the coating.

[0004] Since these coatings on substrates are often amorphous after this initial coating step, a further curing step in the form of a thermal annealing step is usually applied to crystallize, densify, and / or modify the coating. Thermal annealing leads to various film modifications depending on the temperature program applied. While solvent evaporation in the initial coating step is achieved by heating the substrate (if heated) only to moderate temperatures, the curing step requires much higher temperatures. Coatings are always applied to substrates with specific limitations regarding the maximum temperature that can be applied in the thermal annealing step. The temperatures required for common coating materials are often too high for temperature-sensitive substrates, such as polymers. Furthermore, the curing step is often very time- and energy-consuming. Conventional annealing of sol-gel coatings is usually performed at high temperatures of several hundred degrees Celsius for durations of up to several hours.

[0005] A typical example of a coating on a glass lens made of soda-lime glass is a UV protection layer made of ZnO. In a standard sol-gel coating process on soda-lime glass, the ZnO coating is applied via dip coating (v = 30 cm / min), dried at 145 °C for 6 minutes in the first step, and annealed at 500 °C for 60 minutes in the second step. The second heating step is intended to convert the coating from an amorphous state to a crystalline state and burn off the organic binders in the system. The goal is to achieve a dense, crystalline ZnO film on the soda-lime glass. However, in the case of ZnO coatings on glass, the second heating step only leads to the burn-off of the binder and the crystallization of the ZnO, resulting in a highly porous film. Such highly porous films are unsuitable for applying additional coating layers, or at best, are very limited. Furthermore, the high temperature places a significant thermal load on the substrate. Crystallization of ZnO coating systems on polymer substrates is not feasible using thermal annealing due to the temperature limitations of the substrate.

[0006] This example of a ZnO coating is illustrative of the problems faced by sol-gel coatings of various types of coating materials on various substrates. While cure times and temperatures can be varied, the fundamental problems of high temperatures, long annealing times, high energy consumption, poor crystallinity, and poor density remain.

[0007] Furthermore, the problems illustrated using the example of sol-gel processes and especially ZnO coatings also affect other coating processes that use liquid solutions and require a thermal annealing step to harden the initially produced amorphous layer. Summary of the Invention [Problem to be solved by the invention]

[0008] The problem underlying the present invention is therefore to provide an improved coating process that does not have the problems of the prior art, or at least has them to a lesser extent, and in particular a coating process that results in a coating that is suitable for applying further layers thereon should be provided. [Means for solving the problem]

[0009] This problem is solved by the present invention.

[0010] The present invention may be used in the field of coatings, especially sol-gel coatings, on substrates (e.g., glass, polymers, metals or other materials), including annealing steps aimed at densifying, crystallizing or otherwise morphologically changing the coating, in particular to make the coating suitable as a base layer for further layers.

[0011] Because the method uses plasma instead of thermal curing to cure the applied solution, it is faster, less energy consuming, and applicable to more temperature-sensitive substrates.

[0012] The inventors have discovered that a thermal annealing step for modifying the morphology (crystallization / modification and / or density and surface roughness state) and the resulting film properties (e.g., UV absorbance, hardness, chemical durability) can be advantageously replaced by a plasma treatment step. Surprisingly, not only can the treatment temperature and time be reduced, but the resulting coating and achievable properties are simultaneously improved. This is highly unexpected, since crystallization of an amorphous coating would be expected to require a sufficiently high temperature and sufficient time to form a dense microcrystalline morphology. Therefore, there was concern that applying plasma instead of thermal treatment would worsen surface roughness, porosity, and crystallite size.

[0013] However, in contrast to these expectations, the advantage achieved is the ability to bring high energies to the film system, leading to desired film properties that would not be possible with thermal annealing at the same time and / or at low substrate temperatures as in plasma processes, which allows for new combinations of film and substrate variations (especially for thermally sensitive substrates).

[0014] In a first aspect, the present invention provides a method of coating a substrate, comprising the steps of: a) providing a substrate; b) applying a coating solution onto the surface of the substrate; c) drying the coating solution by heat to form an amorphous coating; d) treating said amorphous coating with a plasma treatment to form an at least partially crystallized coating. The present invention relates to the method comprising the steps of:

[0015] This method solves the problem of providing a coating suitable as a base layer for further coating layers in an excellent manner. The resulting coating can have much fewer pores, a higher average crystallinity, a higher density, and / or a lower surface roughness. The crystallites are small enough to achieve low porosity and have only a small area of ​​less than 100% crystallinity. Even when a binder is used in the coating solution, the coating can still have very low porosity and an improved microstructure compared to prior art coating processes, particularly sol-gel processes, that use thermal annealing. Furthermore, the process can be easily adjusted by varying the plasma treatment time and energy to produce a specific desired microstructure of the coating.

[0016] In a particularly preferred embodiment, the coating solution is a sol-gel based coating solution and is applied in a sol-gel process, where the term "sol-gel based coating solution" relates to a coating solution that is a colloidal solution that can act as a precursor for an integrated network or gel and is thus suitable for use in a sol-gel coating process.

[0017] In an embodiment, the plasma treatment involves generating a radio frequency plasma or microwave plasma, particularly at frequencies between 10 MHz and 300 MHz or between 300 MHz and 300 GHz. Preferably, the plasma is generated at frequencies between 10 MHz and 100 MHz or between 1 GHz and 100 GHz. While plasma generators using one of the standard frequencies are suitable for use in the present invention, specific fine-tuning of the coating properties can be achieved by applying non-standard frequencies within the claimed range. This allows for flexible adaptation of the method to the desired combination of substrate and coating medium, as well as the properties required for the final coating for its intended function and suitability as a base layer for further layers.

[0018] Preferably, the plasma is generated by a radio frequency plasma generator with a capacitive electrode arrangement or a pulsed magnetron microwave generator.

[0019] In an embodiment, the generator for generating the plasma is operated with a power output of 0.2 kW to 10 kW, preferably 0.3 kW to 7 kW.

[0020] In a preferred embodiment, the plasma is generated in an oxygen, argon, nitrogen, air, or hydrogen atmosphere at atmospheric pressure or reduced pressure, particularly in vacuum. Preferably, the plasma is generated in an oxygen, air, argon, or nitrogen atmosphere, more preferably in an oxygen or air atmosphere. A hydrogen atmosphere, or a certain percentage of hydrogen in an argon or nitrogen atmosphere, can be used for doping. When a binder is used in the coating solution, oxygen plasma is often particularly advantageous because it can help burn off the binder. When a specific precursor of the coating medium is used in the coating solution, oxygen plasma can also be the preferred atmosphere.

[0021] In a preferred embodiment, the plasma treatment time is 0.1 seconds to 120 minutes, preferably 1 second to 60 minutes, or 30 seconds to 30 minutes, or 1 minute to 10 minutes. The plasma treatment time may be at least 0.1 seconds, at least 1 second, at least 30 seconds, or at least 1 minute. The plasma treatment time may be up to 120 minutes, up to 60 minutes, up to 30 minutes, or up to 10 minutes. The plasma treatment time can be selected depending on the type of plasma used and its output. For example, a treatment time of 30 minutes to 120 minutes can be selected for high-frequency plasma, while a treatment time of 1 second to 10 minutes can be selected for microwave plasma.

[0022] In embodiments, the maximum processing temperature does not exceed 400°C, preferably does not exceed 300°C, or does not exceed 150°C. The maximum processing temperature may be at least 25°C, at least 30°C, at least 35°C, at least 40°C, or at least 50°C. In this regard, the maximum processing temperature is the maximum temperature to which the substrate bearing the coating is exposed during processing, i.e., all stages. This corresponds to the furnace temperatures in the thermal annealing stages of the prior art. These temperatures are significantly lower than those of the prior art and allow for the use of more temperature-sensitive substrates.

[0023] In particularly preferred embodiments, the substrate temperature during the plasma treatment does not exceed 400° C., preferably does not exceed 300° C. or does not exceed 150° C. The substrate temperature may be at least 25° C., at least 30° C., at least 35° C., at least 40° C., or at least 50° C. This allows all kinds of new substrates, especially polymers, to be used for the coating process, which previously could not be used due to their temperature sensitivity.

[0024] In a particularly preferred embodiment, the coating is exposed to a maximum temperature of preferably up to 150°C to 400°C during the entire process for a duration of up to 0.1 minutes to 90 minutes, preferably up to 0.5 minutes to 60 minutes, or up to 1 minute to 30 minutes. Here, this maximum temperature refers to the actual temperature reached by the substrate and its coating when exposed to the treatment, and the time range over which they remain at this temperature. These preferred conditions result in lower temperatures for shorter times than prior art thermal annealing steps, while still producing excellent crystallization, low porosity, and dense coatings suitable for multilayer structures.

[0025] In an embodiment, treating the amorphous coating with plasma treatment according to step d) results in the formation of a crystallized coating having a reflectivity of 0.05 to 0.3 when specified in the range from 250 nm to 850 nm, in particular a reflectivity of 0.05 to 0.15 when specified in the range from 250 nm to 380 nm, on a coating having a thickness of 100 nm to 120 nm at an angle of 6° according to ISO 15368:2001. The reflectivity is not only an indicator of the crystallinity of the coating, but also an important property of the coating.

[0026] In a highly preferred embodiment, the amorphous coating is treated with plasma according to step d) to form a crystallized coating having a porosity of less than 20%, preferably less than 15%, as determined by the ratio of the area between crystallites in a scanning electron microscope (SEM) image to the total area examined. To determine this ratio, an SEM image of the coating is prepared and evaluated by image processing. 1.51 x 1.04 μm 2 In a predetermined inspection area having a size of , the area of ​​the pores between the crystallites is detected based on the difference in contrast and brightness, respectively. The porosity is then calculated by dividing the area of ​​the pores by the area of ​​the inspection area. Crystallized coatings having a porosity in this range are particularly suitable as base layers for further layers.

[0027] In an embodiment, the method can include repeating steps b) through d) one or more times to form one or more additional layers of a crystallized coating on the crystallized coating formed in the previous repetition, preferably with a coating solution in step b) that is different from the one in the previous repetition of step b). The application of additional, different coating layers can be used to provide the substrate with additional functionality, as described above. For example, a lens can be provided with UV protection, anti-reflective, and anti-scratch properties.

[0028] Of course, if a specific coating of a thicker layer is desired, the same coating solution can be used more than once in succession.This can be advantageous because thinner layers tend to be of higher quality and more likely to crystallize, and are less prone to forming high porosity than thicker layers.The coating layer produced by the method of the present invention is an excellent base layer for further layers, so that the overall quality of two layers with half the thickness, for example, will be higher than that of a single layer.

[0029] Preferably, the substrate comprises or consists of glass, a polymer, a metal or alloy, or a combination thereof.

[0030] In a preferred embodiment, the coating solution contains a metal or metal oxide, particularly a transition metal or transition metal oxide, or a combination thereof, preferably ZnO, ZrO2, TiO2, VO2, WO3, SnO, indium tin oxide, antimony tin oxide, or precursors of these components, particularly their acetates and carbonates, and optionally a binder, particularly SiO2 or TiO2. These components can be used to provide a wide range of functionality to the substrate. The precursors react to form the metal or metal oxide during the coating process. They are primarily used for their better solubility rather than for facilitating the preparation of the coating solution. For this reason, acetates and carbonates are particularly preferred as precursors. They generally have good solubility and can easily transfer to the metal or metal oxide they form. The binder can provide structure to the crystallized coating.

[0031] Preferably, the precursor is decomposed by the action of plasma into a metal or metal oxide and its organic components, which are then transferred to the gas phase, and the precursor preferably reacts with the plasma gas. These precursors are typically organic compounds of metals or metal oxides. Therefore, the plasma preferably serves to decompose the precursor and transfer the organic components, such as CO2, to the gas phase. This is particularly effective with a plasma gas capable of reacting with the precursor. In many cases, oxygen is suitable for this purpose. It not only drives off the organic components by oxidation, but also further oxidizes the metal to its oxide, which is why this gas is particularly preferred for coating solutions for metal oxide coatings.

[0032] In an embodiment, the coating comprises or consists of a metal or metal oxide, particularly a transition metal or transition metal oxide, or a combination thereof, preferably ZnO, ZrO2, TiO2, VO2, WO3, SnO, indium tin oxide, or antimony tin oxide. As described above, these components can provide the substrate with a wide range of functions. In some cases, one or more additional components, such as additives or activators, may be required for the intended function or structure of the coating. However, typically, the coating consists of a single metal or metal oxide.

[0033] In a particularly preferred embodiment, step d) forms a crystallized coating on a coating having a thickness of 80 nm to 120 nm, with an average crystallite size of less than 40 nm, preferably less than 20 nm, and greater than 5 nm, preferably greater than 10 nm, as determined by image processing of SEM images. Average crystallite sizes within this range have been proven to be optimal for producing highly dense coatings with low porosity. The inventors have found that the larger the crystallite size, the larger the pores (and thus the porosity). Furthermore, the processing time can be advantageously very short, which reduces process time, saves energy, and results in a highly uniform particle size distribution.

[0034] In a preferred embodiment, the morphology of the amorphous coating is modified with respect to state of crystallization and / or state of modification and / or density and / or surface roughness.

[0035] In a particularly preferred embodiment, the resulting crystalline coating has a UV absorption of 15% to 90%. The method according to the invention is particularly suitable for producing high-quality UV-protective coatings. Of course, other types of functional coatings can be produced in this manner as well.

[0036] In an embodiment, applying the coating solution in step b) includes spin-coating, printing, spray-coating, roll-coating, air-knife-coating, or dip-coating the coating solution onto the surface of the substrate. Depending on the substrate, the type of coating solution and its viscosity, and the required thickness, these methods are particularly suitable for applying the coating solution.

[0037] In a second aspect, the present invention relates to a substrate comprising an at least partially crystalline coating, preferably obtainable by the method of the present invention, said coating having a porosity of less than 20%, preferably less than 15%, as determined as the ratio of the area between crystallites in a scanning electron microscope image to the total area examined.

[0038] In an embodiment, the coating on the substrate has an average crystallite size of less than 40 nm, preferably less than 20 nm, and greater than 5 nm, preferably greater than 10 nm, as determined on a coating having a thickness of 80 nm to 120 nm. This range has been proven to be optimal for the density and porosity of the coating. Furthermore, if the crystallite size becomes too small, the proportion of amorphous structure increases due to the dominance of amorphous grain boundaries. The crystallite size can be adjusted by combining the plasma treatment time and energy. Furthermore, the choice of plasma treatment type (microwave or radio frequency) affects the overall crystallite size. Increasing the treatment time increases the degree of crystallinity and / or crystallite size.

[0039] In a third aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: the substrate comprises glass and / or polymer; the coating comprises ZnO, and The coating has an average crystallite size of less than 30 nm; Regarding the substrate.

[0040] In a fourth aspect, the present invention provides a method for producing a composition comprising: the substrate comprises glass and / or polymer; the coating comprises ZnO, and The refractive index of the coating is 1.55 to 2.10 when specified at a wavelength of 590 nm and a coating thickness of 100 nm to 120 nm. Regarding the substrate.

[0041] In an embodiment, the coating of the substrate comprises two or more layers, preferably layers that are different from their adjacent layers. [Brief explanation of the drawings]

[0042] [Figure 1] FIG. 1 is a scanning electron micrograph of a ZnO coating produced in a prior art sol-gel process with a thermal annealing step (top: after drying, bottom: after annealing). [Figure 2] FIG. 2 is a scanning electron micrograph of a ZnO coating produced in a sol-gel process according to the present invention using 90 minutes of O 2 radio frequency plasma (top: dried sample from FIG. 1, bottom: after annealing). [Figure 3] FIG. 3 is a scanning electron micrograph of a ZnO coating produced in a sol-gel process according to the present invention using a 300-second O 2 microwave plasma (top: dried sample from FIG. 1, bottom: after annealing). [Figure 4] For comparison, Figure 4 shows scanning electron micrographs of the annealed ZnO coatings of Figures 1-3 (top: thermally annealed sample of Figure 1, center: radio frequency plasma annealed sample of Figure 2, bottom: microwave plasma annealed sample of Figure 3). [Example]

[0043] A ZnO coating on a soda-lime glass substrate was selected as a model coating to demonstrate the effectiveness of the present invention. Such ZnO coatings are typically provided as UV protection layers.

[0044] Comparative Example For comparison, a corresponding ZnO coating was produced using a conventional sol-gel process with a thermal annealing step. The ZnO coating was applied via dip coating in an ethanol solution (v = 30 cm / min) and dried at 145°C for 6 minutes in the first step. The dried coating is shown in the top of Figure 1. It has a thickness of 200-220 nm. The coating was then annealed by heating it at 500°C for 60 minutes. The annealed coating is shown in the bottom of Figure 1. It has a thickness of 110-120 nm. It is clear from the photograph that the thermal annealing process results in high open porosity and low density. After the annealing step, the coating is suitable for its intended use of UV protection, but it is not possible to apply additional coatings on top of this highly porous layer to provide, for example, anti-reflective or scratch protection.

[0045] To further quantify the effect, the 2D porosity of the coating was measured using scanning electron microscopy and image processing as described above. The standard sol-gel processed sample with thermal annealing showed a porosity of 26.7%, which is too high to adequately bond further coating layers.

[0046] First example For the inventive example, the sol-gel process of the comparative example described above was repeated for the first stage. The resulting dried coating was then subjected to radio-frequency plasma in an oxygen atmosphere for 90 minutes. The plasma was generated using a standard frequency of 13.56 MHz at 540 W using a capacitive electrode configuration. During plasma treatment, the substrate temperature did not exceed 250°C. The annealed coating is shown in the bottom of Figure 2 and has a thickness of 100-120 nm. Compared to the annealed coating of the reference material, the radio-frequency plasma-treated example has a much smaller grain size, a denser structure (as confirmed by reflectance measurements), and higher crystallinity. Furnace experiments confirmed that these effects are clearly caused by the action of the plasma, not simply the effect of the reduced substrate temperature.

[0047] The 2D porosity of the coating was measured to be 7.4%. This dramatic improvement in porosity makes the coating suitable for coating with additional layers. In this example, the treatment time was longer than the thermal treatment time, while the substrate temperature was reduced by half (from 500°C to 250°C). The porosity, density, and crystallite size are much smaller than in the reference case. This makes radio-frequency plasma the perfect choice for coating solutions that can be degraded by high-energy treatments. Furthermore, treatment times in the 60-minute range are also possible, since the porosity of the coating is then already in a range suitable for coating with additional layers.

[0048] Second Example For the second example, the plasma treatment step was performed in an oxygen atmosphere for 300 seconds using a magnetron-generated microwave plasma. The magnetron was operated at a standard frequency of 2.45 GHz with an average power of 2.2 kW. Again, the substrate temperature did not exceed 250°C during the plasma treatment. The annealed coating is shown in the bottom of Figure 3. Again, it has a thickness of 100-120 nm. The 2D porosity of the coating was measured to be 7.1%. Compared to the annealed coating of the first example, the microwave plasma-treated example has a smaller grain size, a denser structure, and higher crystallinity. The porosity is only slightly lower than in the first example, where excellent values ​​were already achieved. A 12-fold reduction in treatment time was achieved compared to prior art thermal annealing (300 seconds vs. 60 minutes). The higher energy input of microwave plasma further enables the use of precursors that are less easily decomposed and therefore require higher temperatures in the thermal treatment step.

[0049] These examples show that the method according to the invention has many parameters related to the plasma treatment that allow the adjustment of the properties of the resulting coating, and that plasma treatment in general procedure leads to much better quality than prior art thermal treatments. In addition, the method is more versatile because a wider choice of coating solutions and substrates is available.

[0050] A summary of the improved porosity is shown in Figure 4, in direct comparison with the annealed coating. The table below summarizes the respective 2D porosity.

[0051] [Table 1]

Claims

1. 1. A method of coating a substrate, comprising: a) providing a substrate; b) applying a coating solution onto the surface of the substrate; c) drying the coating solution with heat to form an amorphous coating; d) treating said amorphous coating with a plasma treatment to form an at least partially crystallized coating. The method comprising:

2. The method of claim 1 , wherein the coating solution is a sol-gel based coating solution and is applied in a sol-gel process.

3. 3. The method according to claim 1 or 2, wherein the maximum processing temperature does not exceed 400°C, preferably does not exceed 300°C, or does not exceed 150°C.

4. 4. The method according to any one of claims 1 to 3, wherein during the entire method the coating is exposed to a maximum temperature of up to 150°C to 400°C for a duration of up to 0.1 minutes to 90 minutes, preferably up to 0.5 minutes to 60 minutes, or up to 1 minute to 30 minutes.

5. 5. The method according to claim 1, wherein the amorphous coating is treated with a plasma treatment according to step d) to form a crystallized coating having a reflectivity of 0.05 to 0.3 when specified in the range from 250 nm to 850 nm, in particular a reflectivity of 0.05 to 0.15 when specified in the range from 250 nm to 380 nm, at an angle of 6° according to ISO 15368:2001 on a coating having a thickness of 100 nm to 120 nm.

6. 6. The method according to any one of claims 1 to 5, wherein treating the amorphous coating with plasma treatment according to step d) results in a crystallized coating having a porosity of less than 20%, preferably less than 15%, as determined as the ratio of the area between crystallites in a scanning electron microscope image to the total area examined.

7. 7. The method of any one of claims 1 to 6, comprising repeating steps b) to d) one or more times to form one or more further layers of a crystallized coating on the crystallized coating formed in the previous repetition, preferably wherein the coating solution in step b) is different from the one in the previous repetition of step b).

8. 8. The method of any one of claims 1 to 7, wherein the substrate comprises or consists of glass, a polymer, a metal or alloy, or a combination thereof.

9. The coating solution contains a metal or metal oxide, in particular a transition metal or transition metal oxide, or a combination thereof, preferably ZnO, ZrO 2 , TiO 2 , V.O. 2 , W.O. 3 , SnO, indium tin oxide, antimony tin oxide, or precursors of these components, in particular their acetates and carbonates, and optionally a binder, in particular SiO 2 or TiO 2 9. The method of any one of claims 1 to 8, comprising:

10. 10. The method according to claim 9, wherein the precursor is decomposed by the action of the plasma into metal or metal oxide and its organic components, which pass into the gas phase, preferably the precursor reacts with the plasma gas.

11. The coating is preferably a metal or metal oxide, in particular a transition metal or transition metal oxide, or a combination thereof, preferably ZnO, ZrO 2 , TiO 2 , V.O. 2 , W.O. 3 11. The method of claim 1, wherein the oxide comprises or consists of SnO, indium tin oxide, or antimony tin oxide.

12. 12. The method according to any one of claims 1 to 11, wherein step d) results in the formation of a crystallized coating on a coating having a thickness of 80 nm to 120 nm, with an average crystallite size of less than 40 nm, preferably less than 20 nm, and more than 5 nm, preferably more than 10 nm, as determined by image processing of SEM images.

13. 13. The method according to any one of claims 1 to 12, wherein the plasma treatment comprises generating a radio frequency or microwave plasma, in particular at a frequency of 10 MHz to 300 MHz or 300 MHz to 300 GHz, preferably at a frequency of 10 MHz to 100 MHz or 1 GHz to 100 GHz.

14. 14. The method according to any one of claims 1 to 13, wherein the plasma is generated in an atmosphere of oxygen, argon, nitrogen, air or hydrogen at atmospheric or reduced pressure, in particular in vacuum.

15. The method according to any one of claims 1 to 14, wherein the plasma treatment time is between 0.1 seconds and 120 minutes, preferably between 1 second and 60 minutes, or between 30 seconds and 30 minutes, or between 1 minute and 10 minutes.

16. 16. The method according to any one of claims 1 to 15, wherein the substrate temperature during the plasma treatment does not exceed 400°C, preferably does not exceed 300°C or does not exceed 150°C.

17. 17. The method according to any one of claims 1 to 16, wherein the plasma is generated by a radio frequency plasma generator with a capacitive electrode arrangement or a pulsed magnetron microwave generator.

18. The method according to any one of the preceding claims, wherein the generator for generating the plasma is operated with a power of 0.2 kW to 10 kW, preferably 0.3 kW to 7 kW.

19. 19. The method according to any one of claims 1 to 18, wherein the morphology of the amorphous coating is modified with respect to state of crystallization and / or state of modification and / or density and / or surface roughness.

20. 20. The method of any one of claims 1 to 19, wherein the resulting crystalline coating has a UV absorption of 15 to 90%.

21. 21. The method of any one of claims 1 to 20, wherein applying the coating solution in step b) comprises spin-coating, printing, spray-coating, roll-coating, air-knife-coating, or dip-coating the coating solution onto the surface of the substrate.

22. 22. A substrate comprising an at least partially crystalline coating, preferably obtainable by the method according to any one of claims 1 to 21, said coating having a porosity of less than 20%, preferably less than 15%, determined as the ratio of the area between crystallites in a scanning electron microscope image to the total area examined.

23. 23. The substrate of claim 22, wherein the coating has an average crystallite size of less than 40 nm, preferably less than 20 nm, and more than 5 nm, preferably more than 10 nm, as determined on a coating having a thickness of 80 nm to 120 nm.

24. the substrate comprises glass and / or a polymer; the coating comprises ZnO, and the coating has an average crystallite size of less than 30 nm; 24. The substrate according to claim 22 or 23.

25. the substrate comprises glass and / or a polymer; the coating comprises ZnO, and the refractive index of the coating is between 1.55 and 2.10 when specified at a wavelength of 590 nm and a coating thickness of 100 nm to 120 nm; 25. The substrate of any one of claims 22 to 24.

26. 26. A substrate according to any one of claims 22 to 25, wherein the coating comprises two or more layers, preferably layers which are different from their adjacent layers.

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