RU2574249C2 - Network micro- and nanostructure, in particular for optically transparent conductive coatings, and method for obtaining thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical industry, microelectronics and nanotechnology and can be applied in production of transparent conductive coatings, light-absorbing and light-transforming layers for optical and photovoltaic devices, self-cleaning surfaces, biometric materials, membranes, catalysts. Network micro- and nanostructure is obtained by formation on the substrate of substance layer, which forms cracks in the process of chemical and/or physical reaction, and application of obtained layer as template for setting geometry of micro- and nano-structure. Obtained network micro- and nanostructure contains conductive or dielectric layer, made in form of single open-work structure, corresponding to geometry of cracks.

EFFECT: invention makes it possible not to apply complicated methods of lithography, increase mechanical reliability of structure and its electric conductivity.

16 cl, 2 dwg

Description

The group of inventions relates to micro- and nanostructured coatings used in such fields as transparent conductive coatings, in particular optically transparent conductive coatings, light-absorbing and light-converting layers for optical and photovoltaic devices, self-cleaning surfaces, biomimetic materials, selective and supporting membrane layers, catalysts and others, and to a method for their preparation.

There is an increasing need for micro- and nanostructured coatings that would form over large areas and have a low unit cost. These coatings are used in fields such as transparent conductive coatings, in particular optically transparent conductive coatings (Hu, L. B., Wu, H. & Cui, Y. Mater. Res. Soc. Bull. 36, 760-765 (2011 )), light-absorbing and light-converting layers for optical and photovoltaic devices (Garnett Е and Yang Р 2010 Nano Lett. 10 1082; Kang MG, Xu T, Park HJ, Luo X and Guo L J. 2010. Adv. Mater. 22 4378; Ahn SW, Lee KD, Kim JS, Kim SH, Park JD, Lee SH and Yoon PW 2005 Nanotechnology 16 1874; Kwak MK, Kim T, Kim P, Lee HH and Suh K Y. 2009. Small 5 928; Chanda D, Shigeta K, Gupta S, Cain T, Carlson A, Mihi A, Baca AJ, Bogart GR, Braun P and Rogers J A. 2011. Nature Nanotechnol. 6 402; Shalaev V M. 2007. Nature Photon. 1 41), self-cleaning on top aws (Jeong HE, Kwak MK, Park C I and Suh K Y. 2009. J. Colloid Interface Sci. 339 202; Lau KKS, Bico J, Theo K B K, Chhowalla M, Amaratunga GAJ, Milne WI, McKinley GH and Gleason K K. 2003. Nano Lett. 3 1701), biomimetic materials (Kwak MK, Pang C, Jeong H E, Kim H N, Yoon H, Jung H S and Suh K Y. 2011. Adv. Funct. Mater. 21 3606), selective and supporting layers of membranes (patent RU 2389536, IPC B01D 71/00, published 05/20/2010), etc.

Existing methods for specifying micro- and nanostructured coatings based on optical or imprint lithography (Moon Kyu Kwak, Jong G Ok, Jae Yong Lee et al. Nanotechnology 23 (2012) 344008 (6pp); Ahn SH and Guo L J. 2008 Adv. Mater. 20 2044; Ahn SH, Kim JS and Guo L. 2007. J. Vac. Sci. Technol. 25,2388; Henzie J, Barton JE, Stender C L and Odom T W. 2006. Acc. Chem Res. 39,249; Lee TW, Jeon S, Maria J, Zaumseil J, Hsu JWP and Rogers J A. 2005. Adv. Funct. Mater. 15 1435; Rogers JA, Paul KE, Jackman RJ and Whitesides G M. 1997 . Appl. Phys. Lett. 70 2658), do not provide the performance and cost parameters required for applications associated with large areas of coverage.

Therefore, in particular, objects such as optically transparent conductive coatings are currently manufactured by other methods. Conductive coatings with optical transparency, as well as transparency in other spectral ranges, are of practical importance. They find their application in the manufacture of such technical objects as electric heated and electrochromic glasses, display panels, including touchscreens (touchscreens), electrodes for organic LEDs, electronic paper, solar panels, various optoelectronic devices, substrates for the electrostimulated growth of living cells, protection against electrostatics and shielding systems of electromagnetic fields, etc.

For transparent conductive coatings, the determining technical parameters are specific surface resistance and transparency coefficient. For a number of applications, the transparency spectrum (the dependence of transparency on wavelength), the chemical resistance of the coating, its mechanical flexibility and resistance to cyclic mechanical deformations, the spectrum of substrate materials that are acceptable from the point of view of the technological process of coating formation, acceptable geometry and dimensions are also significant. substrates, etc. The main economic parameter is the cost of forming a unit area of a transparent coating.

The current level of technology includes a whole range of solutions, to one degree or another, providing requirements for the specified parameters of transparent conductive coatings. However, each of the available solutions has significant drawbacks.

Currently, the most common technical solution is the use of coatings based on conductive metal oxides. In particular, a coating based on indium tin oxide (ITO) was widely used (patent GB 2361245, IPC class C03C 17/245, published October 10, 2001, application for the grant of patent KR 20130027991, class IPC H01L 33/36, published March 18. 2013, etc.). The main disadvantages of coatings of this type include the relatively high cost and the forecast for its increase (depletion of indium reserves), significant limitations on acceptable substrates (due to the formation method), a significant loss of transparency in the infrared region of the spectrum, and low mechanical flexibility and elasticity. Advantages include a high ratio of optical transparency to surface resistance: about 10 ohms / square at 90% transparency.

Recently, alternative methods of forming transparent conductive coatings have been increasingly developed, in particular, using a system of nanowires as a coating (nanowires with a high aspect ratio; a special case of nanorods, which are also nanoparticles with a high aspect ratio, but may not be conductors) . One of the main branches of this direction is the use of single-walled carbon nanotubes as nanowires (Zhang, M. et al. Science 309, 1215-1219 (2005); Hecht, DS, Hu, LB & Irvin, G. Adv. Mater. 23, 1482-1513 (2011)). In the framework of this approach, carbon nanotubes are deposited in various ways on a substrate (one or another variant of deposition from a colloid, dry deposition, etc.) or grown on a substrate by the method of deposition from the gas phase. The advantages of coatings based on carbon nanotubes include the mechanical flexibility of the coatings obtained, preservation of transparency in the infrared region of the spectrum, increased chemical resistance, and the possibility of using a wider range of substrates (in the general case). However, there are significant disadvantages. High optical transparency can be provided only by coatings based on single-walled carbon nanotubes and their bundles, which, taking into account the current market value of the material of single-walled nanotubes, leads to a relatively high cost of coatings of this type. In addition, carbon nanotube-based coatings of the state of the art have a relatively high surface resistance of 100 Ohm / square and higher (A. Kaskela, AG Nasibulin, MY Timmermans et al. Nano Lett. 2010, 10, 4349-4355) with a transparency of 90%, while the resistance of ITO-based coatings with a similar transparency can be less than 10 ohms / square.

To reduce surface resistance, approaches are used to combine carbon nanotubes with a conductive polymer, conductive nanoparticles, graphene islands, etc., however, in general, the resistance of such coatings still does not significantly reach the ITO level. Recently, another branch of the technology of transparent conductive coatings based on nanowires, namely coatings based on a system of metal nanowires of a certain geometry (N. Wu, D. Kong, Z. Ruan. Nature nanotechnology. 10.1038 / NNANO.2013.84; De, S. et al. ACS Nano 3, 1767-1774 (2009); Garnett, EC et al. Nature Mater. 11, 241-249 (2012); patent application US 2009129004, IPC class B05D 5/12, published 21.05 .2009). Metal micro and nanoconductors have a band structure similar to multi-walled CNTs, and the transparency mechanism of the final coating is based on the presence of extended free windows between the conductors (while a layer of single-walled CNTs, as a rule, almost completely fills the surface and has transparency only due to the unique electronic single-walled CNT structures). Unlike single-walled CNTs, light is absorbed on metal conductors, however, the averaged transparency parameters can be quite large (especially taking into account the effect of light diffraction on conductors, the contribution of which increases as the width of the conductor approaches 1.0-0.3 μm). Currently, this class of coatings shows its high potential and ability to provide significant advantages relative to other types of coatings. So, in the work (N. Wu, D. Kong, Z. Ruan. Nature nanotechnology. 10.1038 / NNANO.2013.84) it was shown that coatings based on a system of metal nanowires can provide a surface resistance of up to 2 Ohm / square with a transparency of 90%, at the same time, unlike ITO, the coating is characterized by high mechanical flexibility, record-breaking spectral characteristics, and also allows the use of a wide range of substrates. The main current drawback of the proposed coatings based on metal nanowires is their relatively high cost. Thus, the coating proposed in this work (N. Wu, D. Kong, Z. Ruan. Nature nanotechnology. 10.1038 / NNANO.2013.84), involves the formation of a suspended template from polymer nanofibre by electrospinning, followed by vacuum deposition on a suspended system of metallic nanofibers layer, transferring the suspended system to the target substrate, etching the polymer fiber, while maintaining the metal shell. At the same time, a system of extended metal "nanogutches" with a width of about 400 nm and a thickness of about 80 nm is formed on the substrate. The relatively high cost of this method is determined by the use of vacuum deposition of metal and electrospinning processes (sequential deposition of suspended polymer nanofibers on a conducting frame). In addition, the allowable size of the frame on which the suspended layer of nanofibers is formed is currently limited to 6 inches.

As analogues of the present invention, it is also worth highlighting a number of technical solutions based on obtaining a network of conductors as a result of the self-organization process that occurs when emulsions containing nanoparticles are dried on a substrate. So, in the patent application US 2011003141, IPC class B32B 5/16, published on January 6, 2011, a method for producing a microstructured product is disclosed, which includes forming a network of paths connected to each other, consisting of nanoparticles surrounding arbitrary-shaped cells (clusters) on the surface substrate, by aggregation (assembly) of these nanoparticles from the emulsion. Also, said patent discloses a structure consisting of a network of connected paths surrounding cells of arbitrary shape, where said connected paths consist of at least partially connected nanoparticles.

International application WO 2012170684, IPC class B05D 5/12, published December 13, 2012, discloses a method for producing an article comprising a) providing a mixture containing a non-volatile component in a volatile liquid carrier, wherein the liquid carrier is an emulsion comprising a continuous phase and a second phase where the second phase is in the form of domains dispersed in a continuous phase; b) coating the surface of the initial substrate with said mixture and drying said mixture to remove the liquid carrier, with the application of external force during application and / or drying to ensure selective growth of these dispersed domains, relatively continuous phase, in selected areas of the substrate, after which the non-volatile component self-organizes and forms a coating in the form of a structure that includes paths surrounding cells having a regular arrangement, determined by the configuration of external force along erhnosti substrate.

In the patent US 2011273085, IPC class B05D 5/12, published 10.11.2011, discloses a method of obtaining products, including: a) applying a liquid emulsion consisting of a continuous phase comprising conductive nanoparticles to the surface of the substrate; b) drying the emulsion and then forming a transparent conductive coating, including the mesh structure of paths formed from at least partially connected nanoparticles surrounding randomly shaped cells, mostly transparent to light, and where at least some of these cells are filled with filler.

The basis of these technical solutions is the general process of self-organization, the mechanism of which differs from that proposed in the present invention and is as follows. An emulsion is used, which is two immiscible liquids (for example, oil and water). One of the fluids is present in the first fluid in the form of domains (droplets). When planted on a substrate, these drops form a system of cells (clusters) surrounded by a first liquid. The first liquid also contains solid nanoparticles that cannot penetrate the second liquid (i.e., the cells remain free of nanoparticles). When the first liquid dries, the nanoparticles are pulled together into paths bordering the drops of the second liquid. After removal of the indicated droplets, a network of tracks formed from adhered nanoparticles remains.

As in the case of the present invention, the considered technical solutions have the advantage that they use the self-organization process and allow a simple way to obtain a micro- and nanostructured surface in the form of a grid of conductive tracks. However, a number of disadvantages are associated with the considered technical solutions.

- The conductive paths are formed from nanoparticles that are at least partially in contact with each other. This leads to the inclusion of contact resistances between individual nanoparticles in the overall resistance of the resulting structure, which reduces the achievable conductivity of the resulting network. The same reason leads to a decrease in the mechanical strength of the resulting mesh relative to the case of a mesh made in the form of a single structure.

- The method causes the imposition of significant restrictions on the range of acceptable materials used nanoparticles, since it is expected dispersion of these nanoparticles in a liquid carrier. So, most metals undergo oxidation upon contact with liquids, which is especially important for nanoparticles, with their increased reactivity. Therefore, only nanoparticles of noble metals or metals having conductive oxides can retain conductive properties. In addition, the permissible materials of the nanoparticles are subject to restrictions related to their ability to form a stable colloid in the first liquid. The solution to this problem is usually associated with the use of surface-active substances (surfactants), which further complicates the technology and raises the problem of removing surfactant residues from nanoparticles in the final structure, in order to improve the electrical contact of the nanoparticles with each other. It should be noted that in any case, the first liquid containing nanoparticles, upon evaporation, will leave an impurity layer on the surface of the nanoparticles, which affects the contact of the nanoparticles. This is an integral property of methods based on the deposition of objects from the liquid phase.

- The method causes the imposition of significant restrictions on the ratio of the width and thickness of the tracks obtained during the agglomeration of nanoparticles, since these tracks are formed by capillary forces. When the first liquid dries, its capillary surface contracts and compacts the particles in the form of tracks. However, capillary forces tend to minimize the difference in the width and thickness of the yeast (the law of minimizing the surface area leads to a rounding effect), therefore, the degree of freedom in arbitrary variation of this ratio is lost, which in turn can be important for a number of end applications (for example, for optically transparent coatings) . In addition, the indicated effect of minimizing the surface area with the liquid phase leads to a rounding of the corners of the resulting cells, which, in particular, leads to a thickening of the tracks at their intersections, which may be important for a number of end applications, since the heterogeneity of the tracks in width increases. In particular, this can lead to a decrease in the overall transparency coefficient of the structure (the places where the tracks expand take up additional area).

- The capillary nature of the mechanism of formation of the structures under consideration also imposes restrictions on the allowable ratio of the cell size and the width of the tracks between them, since with increasing cell size (i.e., with increasing diameter of the initial drop of the second liquid) and decreasing track width (i.e. with decreasing the width of the initial layer of the first liquid), the likelihood that two adjacent drops of the second liquid will overcome the layer of the first liquid and merge, thereby minimizing their free energy. Therefore, if there is a requirement for cell size growth, the effect of increasing the width of the tracks separating the cells occurs. This limitation is an integral consequence of the capillary forces underlying the formation of the structure through the interaction of two liquid phases.

A technical solution is also known (see application US 2009129004), which is selected as the closest analogue of the proposed structure, which describes a transparent conductor, including: a substrate, a conductive layer on the specified substrate, the conductive layer includes many metal nanoconductors. It is indicated that this solution provides a combination of high electrical conductivity and optical transparency with high mechanical flexibility. It also indicates the achievement of high fault tolerance, which is due to the fact that if some separate conductive path is damaged, the presence of a large number of conductive paths (in this case, nanoconductors and their chains) allows you to provide paths for current flow.

The disadvantages of this structure include:

- in the General case, the structure includes contact resistances, which always occur between individual nanoconductors that make up many nanoconductors;

- exclusively nanowires are used. That is, objects whose one size is less than 100 nm. For a number of applications, it may be more appropriate, from a technical and technological point of view, to use micro-range objects;

- only conductors are used. For a number of applications, it may be more appropriate, from a technical and technological point of view, to use a grid of non-conductive tracks. For example, mesh tracks made of polymeric material. In particular, a material having a certain biocompatibility (for example, for application in the field of biomimetic coatings);

- in the general case, the arrangement of nanoconductors on a substrate is random, while for a number of applications it is necessary to provide a certain size and spread of gaps between nanoconductors (that is, the size and spread of window sizes in the grid). This may be relevant, for example, for optically transparent coatings, membranes, superhydrophobic (self-cleaning) materials, biomimetic coatings, etc.

Also, from the indicated technical solution, there is known a method for forming a transparent conductor, comprising: depositing a plurality of metal nanoconductors dispersed in a liquid onto a surface of a substrate and forming a network of metal nanoconductors on a substrate when said liquid is dried. The disadvantages of the method include:

- the need for the operation of preliminary synthesis of metal nanoconductors, which are then dispersed in the specified liquid. The operation of synthesizing metal nanoconductors per se is not trivial from a technological point of view and is generally associated with certain restrictions (technological complexity, limitations on specific conductivity, the presence of defects and impurities in the nanoconductors obtained, restrictions on the aspect ratio of the nanoconductors obtained, and their confusion and etc.);

- the need for the operation of deposition of nanoconductors on a substrate from a liquid. This operation is inextricably linked with the effects of coagulation (entanglement) of nanowires, with a corresponding violation of the uniformity of the formed mesh. Related to this circumstance is the difficulty of regulating the average size of gaps (windows) in the grid;

- the network is formed from individual nanoconductors, due to which its overall electrical conductivity is reduced, since the contact resistances formed at the points of contact of the individual nanoconductors with each other are additionally included in the circuit. For a similar reason, the mechanical strength of the mesh is reduced, which may be important for some applications (for example, in the case of using the mesh as a carrier or selective membrane layer);

- deposition from the liquid phase, as a rule, requires the use of additional components in a colloidal solution (in order to increase its stability), which, after deposition on the substrate, act as foreign substances that reduce the conductivity of the formed network (by the growth mechanism of the contact resistance value), and others its operational parameters.

The problem solved by the proposed group of inventions is to eliminate the above-mentioned disadvantages of the known technical solutions.

The technical result achieved by the claimed group of inventions is to create a new method for the formation of micro- and nanostructured coatings, as well as to create a new micro- and nanostructure, which increase the mechanical reliability of the structure, increase the electrical conductivity (in the particular case of the invention), increase the controllability of geometric structure parameters, increasing the manufacturability of its production while expanding the scope of both the new structure and the method ba receiving it.

The indicated technical result is achieved in a method for producing a cross-linked micro- and nanostructure, during the implementation of which a layer of a substance is formed on the substrate, which is capable of forming cracks during the chemical and / or physical reaction; carry out the operation of cracking in the specified layer using a chemical and / or physical reaction; carry out operations on the use of the obtained layer containing cracks as a template for specifying the geometry of the micro- and nanostructures.

Through operations to use the obtained crack-containing layer, the geometry of the micro- and nanostructures on the specified substrate or on the second substrate can be specified as a template, or so that the specified micro- and nanostructure is partially or completely mechanically free from any substrate.

The operation of using the obtained layer containing cracks as a template for specifying the geometry of the micro- and nanostructures may include the operation of forming a conductive or dielectric layer on top of the layer containing cracks, and the subsequent operation of the complete or partial removal of the layer containing cracks.

The operation of applying a conductive or dielectric layer can be carried out by vacuum deposition or deposition from the melt or from the liquid or gas phase, and the operation of the complete or partial removal of the layer containing cracks can be carried out by etching or by thermal or mechanical action.

The operation of using the obtained layer containing cracks as a template for specifying the geometry of the micro- and nanostructures may include the operation of forming a layer of liquid precursor or melt over the layer containing cracks, the operation of introducing a layer containing cracks into contact with the second substrate, with the surplus liquid precursor or melt, the operation of converting a liquid precursor into the target material or the operation of solidification of the melt.

As a substrate on which a layer of a substance containing cracks is formed, a porous substrate capable of accommodating a portion of said precursor or melt can be used.

As the specified liquid precursor, a solution of silver salts or a colloid of silver nanoparticles can be used.

A layer of a substance that is capable of cracking during a chemical and / or physical reaction may contain additional layers or components that affect the deposition of a conductive or dielectric layer by vacuum deposition or the deposition process from a melt or from a liquid or gas phase by blocking or slowing down the deposition process relative to deposition on the substrate material on which a layer containing cracks is formed.

The operation of using the obtained layer containing cracks as a template for specifying the geometry of the network micro- and nanostructures of the structure may include the operation of galvanic deposition of a conductive substance in the gaps formed by cracks.

The operation of using the obtained layer containing cracks as a template for specifying the geometry of the network micro- and nanostructures of the structure may include the operation of mechanical contact of the specified substrate with the second substrate, in order to transfer the template and / or micro- and nanostructures to the specified second substrate.

The operations of using the obtained layer containing cracks as a template for specifying the geometry of the mesh micro- and nanostructures of the structure may include the operations of applying additional layers, followed by the formation of a layer of material of the mesh micro- and nanostructures of the structure on top or between these additional layers.

The specified technical result, in addition, is achieved by creating a mesh micro- and nanostructures obtained by the above method and containing a conductive or dielectric layer made in the form of a single openwork structure, and the specified openwork structure corresponds to the geometry of cracks formed in the layer of the substance used as a template in the formation of the specified mesh micro- and nanostructures.

As the material of said openwork structure, a metal or a conductive metal oxide deposited from a melt, a liquid or gas phase, or deposited by a vacuum method can be used.

As the material of this openwork structure, a composite material may be used, including conductive nanoparticles, or carbon nanotubes, or conductive nanorods distributed in a matrix, in particular in a matrix made of a conductive polymer.

The specified openwork structure can be fixed on a substrate, including a porous or optically transparent substrate.

The specified openwork structure may be partially or completely mechanically free from any substrate.

The essence of the proposed group of inventions is illustrated by drawings, where in FIG. 1 shows a schematic representation of a structure (side view and top view) at various stages of its formation according to one embodiment of the invention. In FIG. 2 is a schematic illustration of a structure (side view) at various stages of its formation according to a second embodiment of the invention.

The problem is solved, and the technical result is achieved through the use of the following features in technical solutions.

- The sign "the specified openwork structure corresponds to the geometry of cracks formed in the layer of the substance used as a template" ensures that the layer is penetrated by through windows, and the size of these windows is gravitating to a certain average size, since the way to obtain a template through the described self-organization mechanism for a uniform layer in thickness means approximately the same size of the windows, and, importantly, the windows have a certain spread in shape and size. It should be noted that, for example, for such an application as an optical coating (in particular, an optically transparent coating), the presence of a certain spread in the shape and size of the coating elements may be a desirable result, since it eliminates the effect of interference at certain wavelengths. The indicated nature of the geometry of the openwork structure provided by the indicated feature is also relevant for the case of the openwork layer of a dielectric material, for example, for applying this layer as a carrier or selective membrane layer or as a biomimetic layer (a layer imitating biological tissue). In the latter case, this feature is especially relevant, since it is as a result of the self-organization process underlying the invention that leads to the breaking of a single layer into clusters by means of cracks, the geometry of many clusters repeats to some extent the geometry of many living cells (T.A. Yakhno, V.G. Yakhno. Journal of Technical Physics, 2009, Volume 79, Issue 8. P. 133-141). Also, this feature means that the size of the elements of the openwork structure can lie in the range from less than 100 nm to more than 100 μm, because, as shown by the applicant, this method of self-organization provides such wide ranges of structuring. The prototype indicates that the structure consists of nanoconductors (objects, one of whose dimensions is less than 100 nm), while expanding the range of allowable geometric sizes of structural elements may be important for individual practical applications of the structure (for example, for the case of a carrier or selective layer membranes, biomimetic and superhydrophobic coatings, etc.).

- The sign "containing a conductive or dielectric layer" provides the ability to perform the structure from a wider than in the case of the prototype spectrum of materials, in particular from dielectric materials such as polymers, which expands the range of practical applications of the structure.

- The sign “made in the form of a single openwork structure” provides the circumstance that, in particular, the problem of contact electrical resistances, which always exists for the option of organizing a structure from “many conductors,” is excluded. This allows to increase the achieved conductivity of the structure. In addition, for many conductors (or dielectric objects), the problem of the strength of their mechanical contact with each other is relevant, which may be important for a number of applications, for example, for the case when the specified layer functions as a carrier or selective membrane layer. The indicated feature provides an increase in the mechanical strength of the structure (the contact patch of two objects made of the same type of material is mechanically less durable than a continuous transition of the same geometry between these objects).

- The proposed method in the General case allows you to form a single openwork structure, which eliminates the problem of contact electrical resistances, which always exists for the option of organizing the structure of "nanoparticles" or "many nanoconductors." This improves the achievable conductivity of the structure. In addition, for many conductors or nanoparticles, the problem of the strength of their mechanical contact with each other is relevant, which may be important for a number of applications.

- The method dramatically expands the range of acceptable materials from which the resulting openwork structure is formed. Using the template formed within the method (a layer containing cracks), it is possible to form the final openwork structure from almost any material using any of the existing deposition methods: vacuum deposition, deposition from a liquid or gas phase, deposition from a melt, etc.

- The method dramatically expands the allowable ratio of the width and thickness of the tracks of a single openwork structure. There is an additional degree of freedom in the independent variation of the magnitude of the indicated parameters, since the stage of forming the template at which the width of the cracks is set (determines the width of the tracks of the openwork structure) is not associated with the stage of forming the tracks by one of the deposition methods, within which it is possible to independently set the track thickness from units nanometers to a value not exceeding the thickness of the layer containing cracks (can reach tens and hundreds of micrometers).

- The method dramatically expands the allowable ratio of the size of cells (clusters) and the width of the tracks between them. In the formation of cracks in a layer subjected to a drying operation or a chemical or physical reaction, the competition between the adhesion forces of the layer to the substrate and the forces of mechanical contraction of the layer acts as a self-organization mechanism. Due to this competition, at a certain moment, it becomes energetically favorable to divide the layer into a system of individual clusters separated by cracks. The specified process of self-organization allows you to widely control the relationship between the width of the cracks and the cluster size by controlling the concentration of the vaporized or chemical agent in the layer, the thickness of the layer, humidity or composition of the medium in which the cracking occurs, and other parameters. It should be separately noted that after initial cracking, due to specially specified humidity or chemical composition of the medium, the clusters can begin to increase again (in particular, swell) and the formed cracks can narrow in a controlled way to a few nanometers and even until the clusters completely close. Therefore, cluster sizes and crack widths can generally vary widely independently independently of each other, which is not achieved in these analogues using a capillary self-organization mechanism and in a prototype using the deposition of finished nanowires (for example, cracks less than 100 nm wide with a length of reach clusters over 100 microns).

Detailed description

This group of inventions proposes a structure of mesh geometry and a method for its preparation, which provide a further expansion of the scope of application of self-organized structures. The method of obtaining the structure is based on the process of self-organization, in which, with the growth of mechanical stresses in the layer of matter, this initially continuous layer breaks up at a certain stage into separate clusters separated from each other by gaps (cracks). The growth of stresses in the specified layer of the substance may have as the cause a physical or chemical reaction or a combination thereof. As an example of a physical reaction, you can specify the drying process, that is, the removal of the liquid phase from the system (in the particular case, the removal of water or another liquid solvent), or the process of swelling of one of the components of the specified layer of the substance by absorbing another liquid component, or the process reduction or expansion of the specified layer, where the specified reduction or expansion does not coincide in size with the reduction or expansion of the substrate (for example, due to mismatch of TCR, elasticity, modulus of elasticity or other physical layer and substrate parameters). As an example of a chemical reaction, polymerization, decomposition, etc. reactions can be cited. In a combined embodiment, both chemical and physical reactions take place (for example, a polymerization reaction with the evaporation of one of the components of the reaction products). Within the framework of the existing level of science and technology, this process of cracking in a layer of a substance has received a certain study and use, however, it was considered mainly from the standpoint of a parasitic effect, or from the standpoint of a means of indicating quality parameters of physiological or industrial fluids (T.A. Yakhno, V. . G. Yakhno. Journal of Technical Physics, 2009, Volume 79, Issue 8. P. 133-141).

In this group of inventions, this self-organization process is the basis of the low-cost method of forming a template used to obtain the final mesh micro- and nanostructures, which in a particular case have electrically conductive functions. The inventors have found that, by adjusting parameters such as the chemical and physical composition of the layer, its thickness, viscosity and adhesion to the substrate, the concentration of the components entering into the physical or chemical reaction, the rate of the indicated physical or chemical reaction, temperature and pressure in the system, and By adjusting the conditions for the subsequent processing of the cracked layer, it is possible to adjust, over a wide range, such parameters as the average size and shape of the resulting clusters, the width and shape of the cracks separating the clusters. Moreover, the width of the cracks can vary from values less than 100 nm to values more than 100 microns. The width of the tracks of the resulting net structure may vary even wider than the width of the primary cracks. For this, the operations of further processing the cracked layer can be applied. Such, for example, as exposure of the cracked layer with the corresponding liquid or gas phase, with the resulting swelling (due to physical or chemical mechanisms) of the substance of the cracked layer and further narrowing of the cracks, up to their complete disappearance. Or, for example, by applying additional layers, which, after applying the target layer forming the final paths, are removed by one or another etching method (the so-called sacrificial layers) or enter into a chemical or physical reaction with the applied target layer.

In general, the number of methods for using the template formed by the indicated method to form the final mesh structure can be practically unlimited. They are widely developed in microelectronics technology and related fields. A particular case is the application by one method or another of the target layer on a substrate containing the described template, followed by removal of the cluster of the template, so that the target layer is saved only in the crack region, repeating their geometry. A variant of the deposition of the substance selectively in the region of cracks. For this purpose, for example, the method of galvanic deposition or deposition by electrophoresis on a conductive substrate covered by dielectric clusters separated by cracks can be used. Or, for example, the preliminary functionalization of the surface of a layer capable of cracking, which would, after cracking, be different for the surface of cracks and the surface of clusters, followed by the deposition reaction sensitive to functionalization (for example, a surface sensitive to the pH factor or the presence of certain molecules on the surface) . Or, for example, the deposition and modification of additional (in particular, sacrificial) layers, to change the width and geometry of cracks or create suspended layers in the final structure (suspended layers can be formed by removing the sacrificial layer). Or, for example, the formation of a layer of a liquid precursor or melt on top of a template formed by the indicated method (i.e., on top of a layer containing cracks), followed by the introduction of the substrate with the template into mechanical contact with the second substrate so that excess liquid precursor or melt is displaced and the precursor or melt remained mainly in the region of cracks. Next, the implementation of the operation of converting the specified liquid precursor into the target material (for example, the deposition of the target substance from the specified liquid precursor by heating the latter) or the operation of obtaining the target material by solidification of the specified melt. In this case, the target material forms tracks on both the first and second substrates. Depending on the ratio of the adhesion forces of the target material to the substrates, when the second substrate is removed from mechanical contact with the first substrate, tracks from the target material can remain on both the first and second substrates or on both substrates. The second substrate in this case can also be used as a finished product, with the advantage that for it in the particular case there is no need for the template removal operation, since when the second substrate is removed from mechanical contact with the first substrate, the template in the specified particular case remains on the first substrate . In the general case, depending on the ratio of the adhesion forces of the template to the indicated substrates, when the second substrate is removed from mechanical contact with the first substrate, the template can also remain on both the first and second substrates or on both substrates. It should be noted that one of the methods for mechanical removal of the template is based on this principle, in which the cluster of the template is captured by one of the substrates in the mechanical contact, while the other substrate stores / receives only the tracks of the final openwork structure. The mechanical method for removing the template can also include any method that provides the occurrence of mechanical stresses aimed at disconnecting the cluster of the template from the substrate. One example is the heating of a system in which the template clusters will tend to disconnect from the substrate due to the difference in the TCR of the substrate material and the template substance. An alternative to mechanical removal of the template is its etching in one way or another, as well as dissolution, washing or other operations. In general, the template may not be removed and used as part of the final product, along with the tracks of the openwork structure. For example, if the template is made of a transparent substance, then removal of the template may not be required to obtain a transparent conductive structure. With the caveat that in this case, it may be necessary to introduce an additional layer into the system having a refractive index corresponding to the refractive index of the template substance (the so-called immersion layer) in order to eliminate interference effects on the template clusters. Said first substrate may be made of a porous material capable of containing part of a precursor or melt. A porous substrate saturated with a precursor or a melt, with a template of the type under consideration applied to it, can act as an analog of the distributed head of an inkjet printer, the nozzles of which are formed by cracks between the clusters of the template covering the porous surface. The process of forming a micro- and nanostructured coating in this case can be reduced to applying the specified porous structure with a template to the surface to be treated, followed by extruding part of the precursor or melt through the template. In this embodiment, there is an analogy with the imprint lithography method, with the peculiarity that a self-organized template is used. By precursor is meant a substance involved in the reaction leading to the formation of the target material. An example of a precursor may be a solution of silver salts or a colloid of silver nanoparticles. Under the melt is understood the liquid-phase state of the target material associated with its heating above the melting temperature. With sufficient mechanical strength of the resulting openwork structure, it can be completely or partially mechanically disconnected from the first or second substrates. The applicant has shown the possibility of such detachment by, for example, mechanical locking of one edge of the openwork structure, followed by mechanical separation of the rest of the structure from the substrate. Thus obtained free mesh structure can be used as a membrane, mesh electrode, catalytic structure, etc.

Common to all methods of forming the final openwork structure based on the described template is the correspondence of the shape of the resulting tracks and the space between them to the original shape of cracks and clusters of the template. The geometric dimensions of the elements of the final structure and the original template may not coincide (however, the period of arrangement of the elements of the structure and the template always coincides).

In the general case, no restrictions are imposed on the target material, from which the resulting openwork structure is formed using the described template. It can be a single or multicomponent (in particular, composite) conductive or non-conductive substance. In the particular case, a composite material may be used, including conductive nanoparticles, or carbon nanotubes, or conductive nanorods (nanowires) distributed in a matrix, in particular in a matrix made of a conductive polymer.

The feasibility of the proposed group of inventions is demonstrated by the following examples.

On the glass substrate 1 (Fig. 1), a layer 2 of the substance is applied in the form of an aqueous suspension of latex. When dried, this layer forms a percolated system of cracks 3. Next, a metal layer 4 (for example, copper) is deposited by vacuum deposition on a substrate prepared in this way, or a layer of silver or copper is deposited by the reaction of a silver or copper mirror or by deposition of silver or copper nanoparticles from a solution. The application of these layers 4 of copper or silver is carried out so that their thickness is, for example, 90 nm. Next, an operation is performed to remove the latex layer 2, for example, by treating the substrate with acetone. In this case, only that part of the metal coating that was located in the cracks 3 remains on the glass substrate. As a result, the glass substrate becomes coated with a single grid of metal tracks separated by windows. There is no contact resistance between the tracks (the tracks are part of an openwork structure obtained from a single metal layer). The specific surface resistance of such a coating, depending on the parameters of the initial template (primarily, depending on the size of the clusters and the width of the cracks), can range from units to tens of Ohms / square, with transparency from 80% to 95% or more. The resulting structure has the functionality of an optically transparent conductive coating.

In the framework of the second embodiment of the invention, a layer 2 of the substance is applied to the porous substrate 1 (Fig. 2) in the form of an aqueous suspension of latex. When dried, this layer forms a percolated system of cracks 3. Then, layer 5 of a liquid precursor in the form of a solution of silver salts is applied over layer 2. A second substrate 6 is pressed against the layer 2 so that the excess liquid precursor is displaced and the precursor mainly remains in the region of cracks 3. Next, a silver layer is deposited from the precursor on the second substrate 6 by heating the second substrate 6. The second substrate 6 with deposited on it silver tracks 7 can be considered as the final product. The porosity of the first substrate 1 allows absorption of a part of the precursor, whereby the first substrate 1 acts as an additional capacity for the precursor. This ensures the exchange of the precursor located in the region of cracks 3 with the precursor absorbed into the substrate. This makes it possible to compensate for the depletion of the precursor that occurs when the target material (in this case, silver) is deposited from it, which in turn allows one to deposit a thicker layer of the target material (in this case, the silver layer).

In the framework of the third example embodiment of the invention, on the substrate 1 (Fig. 2) is applied a layer 2 of the substance in the form of an aqueous suspension of latex. When dried, this layer forms a percolated system of cracks 3. Then, layer 5 is applied over layer 2 in the form of a liquid polymer melt. A second substrate 6 is pressed against the layer 2 so that the excess liquid melt is displaced and the melt mainly remains in the region of cracks 3. Then, the liquid melt solidifies, resulting in the formation of a polymer network, the geometry of the tracks 7 of which correspond to the geometry of the cracks of the initial template. Depending on the ratio between the adhesion forces of the polymer to the first 1 and second 6 substrate, when these substrates are removed from mechanical contact with each other, the polymer network remains on either the first or second substrate. The specified polymer micro- or nanostructure can be used as a layer for super-hydrophobic coatings (application of self-cleaning coatings), either being freed from substrates or transferred to a porous substrate, as a selective or supporting layer for the membrane thus obtained, or made of a biocompatible polymer, having a certain affinity for living cells, as a biomimetic coating, or in other tasks.

The above examples of the implementation of the invention ensure the achievement of the claimed technical result.

Claims (16)

1. A method for producing a cross-linked micro- and nanostructure, during the implementation of which a layer of a substance is formed on the substrate, which is capable of cracking during the chemical and / or physical reaction; carry out the operation of cracking in the specified layer using a chemical and / or physical reaction; carry out operations on the use of the obtained layer containing cracks as a template for specifying the geometry of the micro- and nanostructures. 2. The method according to p. 1, characterized in that through the operations of using the obtained layer containing cracks, the geometry of the micro- and nanostructures on the specified substrate or on the second substrate is set as a template, or so that the specified micro- and nanostructure is partially or completely mechanically free from any substrate. 3. The method according to p. 1, characterized in that the operation of using the obtained layer containing cracks as a template for specifying the geometry of the micro- and nanostructures includes the operation of forming a conductive or dielectric layer on top of the layer containing cracks, and the subsequent operation of complete or partial removal layer containing cracks. 4. The method according to p. 3, characterized in that the operation of applying a conductive or dielectric layer is carried out by vacuum deposition or deposition from the melt or from the liquid or gas phase, and the operation of the complete or partial removal of the layer containing cracks is carried out by etching or by thermal or mechanical stress. 5. The method according to p. 1, characterized in that the operation of using the obtained layer containing cracks as a template for specifying the geometry of the micro- and nanostructures includes the operation of forming a layer of liquid precursor or melt over the layer containing cracks, the operation of introducing a layer containing cracks in contact with the second substrate with the displacement of excess liquid precursor or melt, the operation of converting the liquid precursor into the target material or the operation of solidification of the melt. 6. The method according to p. 5, characterized in that as a substrate on which to form a layer of a substance containing cracks, use a porous substrate that can accommodate part of the specified precursor or melt. 7. The method according to p. 5, characterized in that as the specified liquid precursor using a solution of silver salts or a colloid of silver nanoparticles. 8. The method according to p. 3, characterized in that said layer of a substance that is capable of forming cracks during a chemical and / or physical reaction contains additional layers or components that affect the deposition of a conductive or dielectric layer by vacuum deposition or on a process of deposition from a melt or from a liquid or gas phase, blocking or slowing down said deposition process relative to deposition on a substrate material on which a layer containing cracks is formed. 9. The method according to p. 1, characterized in that the operation of using the obtained layer containing cracks as a template for specifying the geometry of the mesh micro- and nanostructures of the structure includes the operation of galvanic deposition of a conductive substance in the gaps formed by cracks. 10. The method according to p. 1, characterized in that the operation of using the obtained layer containing cracks as a template for specifying the geometry of the mesh micro- and nanostructures of the structure includes the operation of mechanical contact of the specified substrate with the second substrate in order to transfer the template and / or micro- and nanostructures onto said second substrate. 11. The method according to p. 1, characterized in that the operation of using the obtained layer containing cracks as a template for specifying the geometry of the mesh micro- and nanostructures of the structure include the operation of applying additional layers with subsequent formation of a layer of material of the mesh micro- and nanostructures of the structure on top of or between the specified additional layers. 12. Mesh micro- and nanostructure obtained by the method according to claim 1, containing a conductive or dielectric layer made in the form of a single openwork structure, said openwork structure corresponding to the geometry of cracks formed in the layer of the substance used as a template during the formation of the specified mesh micro - and nanostructures. 13. The mesh micro- and nanostructure according to claim 12, characterized in that a metal or a conductive metal oxide deposited from a melt, liquid or gas phase, or vacuum-deposited is used as the material of said openwork structure. 14. The mesh micro- and nanostructure according to claim 12, characterized in that a composite material including conductive nanoparticles or carbon nanotubes or conductive nanorods distributed in a matrix, in particular in a matrix made of conductive, is used as the material of the specified openwork structure polymer. 15. The mesh micro- and nanostructure according to claim 12, characterized in that said openwork structure is fixed on a substrate, including a porous or optically transparent substrate. 16. The mesh micro- and nanostructure according to claim 12, characterized in that said openwork structure is partially or completely mechanically free from any substrate.

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