WO2018019820A1 - Transparent electroconductive layer having a protective coating - Google Patents

Transparent electroconductive layer having a protective coating Download PDF

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Publication number
WO2018019820A1
WO2018019820A1 PCT/EP2017/068744 EP2017068744W WO2018019820A1 WO 2018019820 A1 WO2018019820 A1 WO 2018019820A1 EP 2017068744 W EP2017068744 W EP 2017068744W WO 2018019820 A1 WO2018019820 A1 WO 2018019820A1
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substrate
group consisting
coating
surface
plurality
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PCT/EP2017/068744
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French (fr)
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Byungil HWANG
Stefan Becker
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Basf Se
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    • CCHEMISTRY; METALLURGY
    • C23COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23CCOATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
    • C23C16/40Oxides
    • C23C16/403Oxides of aluminium, magnesium or beryllium
    • CCHEMISTRY; METALLURGY
    • C23COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23CCOATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
    • C23C16/40Oxides
    • C23C16/405Oxides of refractory metals or yttrium
    • CCHEMISTRY; METALLURGY
    • C23COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23CCOATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
    • C23C16/455Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
    • C23C16/45523Pulsed gas flow or change of composition over time
    • C23C16/45525Atomic layer deposition [ALD]
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00Nanotechnology for materials or surface science, e.g. nanocomposites
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00Manufacture or treatment of nanostructures
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L2251/00Indexing scheme relating to organic semiconductor devices covered by group H01L51/00
    • H01L2251/50Organic light emitting devices
    • H01L2251/53Structure
    • H01L2251/5369Nanoparticles used in whatever layer except emissive layer, e.g. in packaging
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L51/00Solid state devices using organic materials as the active part, or using a combination of organic materials with other materials as the active part; Processes or apparatus specially adapted for the manufacture or treatment of such devices, or of parts thereof
    • H01L51/50Solid state devices using organic materials as the active part, or using a combination of organic materials with other materials as the active part; Processes or apparatus specially adapted for the manufacture or treatment of such devices, or of parts thereof specially adapted for light emission, e.g. organic light emitting diodes [OLED] or polymer light emitting devices [PLED];
    • H01L51/52Details of devices
    • H01L51/5203Electrodes
    • H01L51/5206Anodes, i.e. with high work-function material
    • H01L51/5215Anodes, i.e. with high work-function material composed of transparent multilayers

Abstract

Disclosed is an article comprising a substrate and disposed on a surface of said substrate a plurality of metal nanoobjects and a coating comprising one or more oxides selected from the group consisting of TiO2, ln203, ZnO, Ga203 and SnO2 and one or more oxides selected from the group consisting of Al2O3, ZrO2 and HfO2 deposited on said plurality of metal nanoobjects.

Description

Transparent electroconductive layer having a protective coating

The present invention relates to an article comprising a substrate and a plurality of metal nanoobjects disposed on a surface of said substrate and a coating deposited on said plurality of metal nanoobjects.

Metal nanoobjects, especially metal nanowires like silver nanowires are commonly used for preparing transparent electroconductive layers. The term "transparent electroconductive layer" as used herein refers to a layer which (i) is capable of allowing the flow of an electric current when an appropriate voltage is applied and (ii) has a light transmission of 80 % or more in the visible region (400-700 nm) measured according to ASTM D1003, see e.g. US 8,049,333. Usually, said layer is arranged on the surface of a substrate, wherein said substrate is typically an electrical insulator. Such electroconductive transparent layers are widely used in flat liquid crystal displays, touch panels, electroluminescent devices, organic light emitting diodes, thin film photovoltaic cells, as anti-static layers and as electromagnetic wave shielding layers.

Unfortunately, metal nanoobjects like silver nanowires are sensitive to chemical and thermal deterioration, due to their substantially increased specific surface area compared to the corresponding bulk metals. Oxidation, thermal break-up and aggregation of the metal nanoobjects usually results in a remarkable degradation of the electroconductivity as well as of the optical properties of electroconductive transparent layers comprising such metal nanoobjects. In processes for manufacturing devices, e.g. displays, comprising transparent electroconductive layers, metal nanoobjects may be exposed to temperatures of 350 °C or more.

Furthermore, during use transparent electroconductive layers may be exposed to thermal and oxidative stress from the environment, and high current densities as well as electrostatic discharges, which may occur during use of transparent electroconductive layers, may lead to thermal break-up and aggregation and/or oxidation of the metal nanoobjects, due to the released heat.

Accordingly, there is a need to increase the stability of metal nanoobjects in transparent electroconductive layers against thermal and oxidative stress.

In order to solve these problems, US 2014/0020737 A1 proposes a device comprising a substrate, silver nanowires disposed on the substrate, and an oxidation protection layer coated on the silver nanowires, wherein the oxidation protection layer comprises an oxide. US 2014/0020737 A1 also discloses a method, wherein an oxidation protection layer is applied on a surface of the silver nanowires, preferably by an atomic layer deposition (ALD) process. Preferably, the oxide is a metal oxide or a metalloid oxide comprising at least one selected from the group consisting of Ti, V, Ni, Cu, Zn, Zr, Nb, Y, Al, Si, Sn, and In. Protection layers consisting of titanium dioxide Ti02 are preferred.

Related art is also US 2014/0179040 A1 , US 2016/0096770 A1 and US 2016/0060758 A1.

Unfortunately, it has been found that silver nanowires coated with titanium dioxide can resist only temperatures up to 300 °C. In order to overcome the drawbacks of the prior art, there is provided an article comprising

a substrate

and disposed on a surface of said substrate, a plurality of metal nanoobjects and a coating comprising

one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02

and one or more oxides selected from the group consisting of Al203, Zr02 and Hf02 deposited on said plurality of metal nanoobjects.

In certain preferred cases, an article according to the invention consists of

a substrate

and disposed on a surface of said substrate, a plurality of metal nanoobjects and a coating comprising

one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02

and one or more oxides selected from the group consisting of Al203, Zr02 and Hf02

deposited on said plurality of metal nanoobjects.

Surprisingly it has been found that in an article according to the invention the electrical and optical properties of the transparent electroconductive layer do not degrade when the transparent electroconductive layer is exposed to temperatures up to 380 °C for at least 100 minutes. Moreover, the electrical and optical properties of the transparent electroconductive layer remain unaltered during at least 1000 hours of exposure to a temperature of 85 °C under a relative humidity of 85 %.

In an article according to the invention, a plurality of metal nanoobjects is disposed on a surface of a substrate.

Preferably in said plurality of metal nanoobjects direct contacts exist between individual metal nanoobjects, e.g. junctions or interconnections between adjacent or overlapping metal nanoobjects, and most preferably said plurality of metal nanoobjects is in the form of a continuous network exhibiting junctions or interconnections between adjacent and overlapping nanoobjects, thereby enabling the flow of electrons.

Preferably, said metal nanoobjects are selected from the group consisting of nanowires, nanorods, nanoflakes, nanoplates, nanoribbons and nanospheres.

According to ISO/TS 27687:2008 (as published in 2008), the term "nanoobject" refers to an object having one, two or three external dimensions in the nanoscale, i.e. in the size range from approximately 1 nm to 100 nm. According to ISO/TS 27687:2008, nanoobjects having one external dimension in the nanoscale, while the other two external dimensions are significantly larger, are generally referred to as nanoplates. Said one external dimension in the nanoscale corresponds to the thickness of the nanoplate. The two significantly larger dimensions differ from the nanoscale dimension by more than three times. The two larger external dimensions are not necessarily in the nanoscale.

Another common term for denoting a nanoobject having one external dimension in the nanoscale, while the other two external dimensions are significantly larger, is "nanoflake".

According to ISO/TS 27687:2008, nanoobjects having two similar external dimensions in the nanoscale, while the third external dimension is significantly larger, are generally referred to as nanofibers. The third significantly larger dimension differs from the nanoscale dimension by more than three times. The largest external dimension is not necessarily in the nanoscale. Said largest external dimension corresponds to the length of the nanofibers. Nanofibers typically have a cross section close to circular shape. Said cross section extends perpendicularly the length. Said two external dimensions which are in the nanoscale are defined by the diameter of said circular cross section.

Electrically conductive nanofibers are also referred to as nanowires. Hollow nanofibers (irrespective of their electrical conductivity) are also referred to as nanotubes. Nanoobjects having two similar external dimensions in the nanoscale, while the third external dimension (length) is significantly larger, which are rigid (i.e. not flexible) are commonly referred to as nanorods. Nanoobjects having two similar external dimensions in the nanoscale, while the third external dimension (length) is significantly larger, and have a cross section close to rectangular shape extending perpendicularly the length, are commonly referred to as nanoribbons. According to ISO/TS 27687:2008, nanoobjects having all three external dimensions in the nanoscale, wherein the length of the longest axis and the length of the shortest axis of the nanoobject differ not significantly, are generally referred to as nanoparticles. The length of the longest axis and the length of the shortest axis differ by not more than three times. Approximately isometric nanoparticles, i.e. the aspect ratio (longest : shortest direction) of all three orthogonal external dimensions is close to 1 , are commonly referred to as nanospheres. The term "metal nanoobject" means that the nanoobject comprises or consists of one or more materials selected from the group consisting of metals and alloys of metals. As metals are capable of allowing the flow of electrons, a plurality of such metal nanoobjects disposed on a surface of a substrate may form a conductive network of adjacent and overlapping nanoobjects capable of carrying an electric current, provided that there is sufficient interconnection (mutual contact) between individual metal nanoobjects so as to enable the transport of electrons along the interconnected metal nanoobjects within the network.

Preferably, said metal nanoobjects comprise or consist of one or more metals selected from the group consisting of silver, copper, nickel, gold, palladium, tungsten, iron, cobalt and tin and alloys of two or more of said metals.

Preferably, said metal nanoobjects are metal nanowires, preferably metal nanowires having a length of from 10 μιη to 50 μιη and a diameter in the range of from 10 to 100 nm. Length and diameter of metal nanowires are determined by means of transmission electron microscopy. Preferably said nanowires comprise or consist of one or more metals selected from the group consisting of silver, copper, nickel, gold, palladium, tungsten, iron, cobalt and tin and alloys of two or more of said metals.

Most preferred metal nanoobjects are silver nanowires having the above-mentioned dimensions.

Suitable metal nanoobjects as defined above are known in the art (see e.g. US 7,922,787) and are commercially available.

Silver nanowires (as well as nanowires of other metals) are typically commercially available in the form of an aqueous dispersion wherein polyvinylpyrrolidone is adsorbed onto the surface of the silver nanowires in order to render the dispersion stable. Any matter adsorbed on the surface of the nanowires is not included in the above-defined dimensions and composition of the metal nanoobjects.

In an article according to the present invention, a coating is deposited on said plurality of metal nanoobjects. Said coating comprises

one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02

and one or more oxides selected from the group consisting of Al203, Zr02 and Hf02.

In specific cases the coating deposited on said plurality of metal nanoobjects consists of one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02

and one or more oxides selected from the group consisting of Al203, Zr02 and Hf02.

Without wishing to be bound by theory, it is presently assumed that the oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02, which are semiconducting, enable electron transfer between the coated metal nanoobjects, while the oxides selected from the group consisting of Al203, Zr02 and Hf02, which are resistant against high temperatures, protect the coated metal nanoobjects against thermal stress.

Said coating deposited on said plurality of metal nanoobjects has a thickness in a range of from of 5 nm to 20 nm, preferably 5 nm to 10 nm. The thickness of the coating is determined from transmission electron microscopy (TEM) images of the cross section of a sample from an article according to the invention. Samples for studying the cross- section can be fabricated by means of focused ion beam (FIB).

Preferably in said coating deposited on said plurality of metal nanoobjects the molar ratio between

the total amount of oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02

- and the total amount of oxides selected from the group consisting of Al203, Zr02 and Hf02

is in the range of from 2 : 8 to 8 : 2, preferably from 4 : 6 to 6 : 4, further preferably from 4.5 : 5.5 to 5.5 : 4.5

Particularly preferable, said coating deposited on said plurality of metal nanoobjects consists of Ti02 and Al203, wherein the molar ratio between Ti02 and Al203 is in the range of from 2 : 8 to 8 : 2, preferably from 4 : 6 to 6 : 4, further preferably from 4.5 : 5.5 to 5.5 : 4.5. Quantitative analysis of the composition of the coating is done by means of electron microscopy combined with energy dispersive X-ray analysis (EDAX).

Surprisingly it has been found that the presence of a coating as defined above does not compromise the optical and electrical properties of a transparent electroconductive layer.

An article according to the invention preferably has a sheet resistance in the range of from 10 to 150 ohm/sq, preferably of from 10 to 60 ohm/sq, as measured by the four point probe on said surface of said substrate on which said plurality of metal nanoobjects is disposed and said coating is deposited on said plurality of metal nanoobjects.

The sheet resistance (sometimes also referred to as "square resistance") is a measure of the resistance of a thin body (sheet) namely uniform in thickness. The term "sheet resistance" implies that the current flow is along the plane of the sheet, not perpendicular to it. For a sheet having a thickness t, a length L and a width W, the resistance R is

R = P *— = ^ *— = Rsh *—

Wt t W W

wherein Rsh is the sheet resistance. Accordingly the sheet resistance Rsh is

W

Rsh = R *—

L

In the formula given above the bulk resistance R is multiplied with a dimensionless quantity (W/L) to obtain the sheet resistance Rsh, thus the unit of sheet resistance is Ohms. For the sake of avoiding confusion with the bulk resistance R, the value of the sheet resistance is commonly indicated as "Ohms per Square" (ohm/sq.) because in the specific case of a square sheet W = L and R = Rsh. The sheet resistance is measured by means of a four point-probe.

An article according to the invention preferably has

a light transmittance of from 80 % or more, preferably 90 % or more as measured according to ASTM D1003 (procedure A) and

a haze of 3 % or less, preferably 2 % or less, further preferably of 1.5 % or less as measured according to ASTM D1003 (procedure A). The measurement of haze and light transmission (in ASTM D1003 as published in November 2013 the latter is referred to as "luminous transmittance" which is the ratio of the luminous flux transmitted by a body to the flux incident upon it) by means of a hazemeter is defined in ASTM-D1003 as published in November 2013 as "Procedure A-Hazemeter". The values of haze and light transmission (corresponding to the luminous transmittance as defined in ASTM D1003 as published in November 2013) given in the context of the present invention refer to this procedure.

The parameter "light transmission" refers to the percentage of an incident light which is transmitted through a medium. Preferably the light transmission of an article according to the invention is 85 % or more, more preferably 90 % or more, further preferably 95 % or more, as measured according to ASTM D1003 (Procedure A) as published in November 2013.

Generally, the parameter haze is an index of the light diffusion. It refers to the percentage of the quantity of light which is separated from the incident light and scattered during transmission. Unlike light transmission, which is largely a property of the medium, haze is often a production concern and is typically caused by surface roughness, and by embedded particles or compositional heterogeneities in the medium.

According to ASTM D1003 as published in November 2013, in transmission, haze is the scattering of light by a specimen responsible for the reduction in contrast of objects viewed through said specimen, i.e. the percent of transmitted light that is scattered so that its direction deviates more than a specified angle (2.5 °) from the direction of the incident beam.

Preferably the haze of an article according to the invention is 2 % or less, more 1.8 % or less, most preferably 1.5 % or less, as measured according to ASTM D1003 (Procedure A) as published in November 2013.

Preferably, an article according to the present invention has

a sheet resistance in the range of from 10 ohm/sq. to 150 ohm/sq. as measured by the four point probe on said surface of said substrate on which said plurality of metal nanoobjects is disposed, and a light transmittance of from 80 % or more, preferably 90 % or more as measured according to ASTM D1003 (procedure A), and

a haze of 3 % or less, preferably 2 % or less, further preferably of 1.5 % or less as measured according to ASTM D1003 (procedure A).

Further preferably, said transparent electroconductive layer (as defined above) exhibits one or more of the following features:

a sheet resistance in the range of from 10 ohm/sq. to 60 ohm/sq. as measured by the four point probe on said surface of said substrate on which said plurality of metal nanoobjects is disposed,

a haze of 1 .5 % or less as measured according to ASTM D1003 (procedure A) as published in November 2013,

a light transmission of 90 % or more as measured according to ASTM D1003 (procedure A) as published in November 2013.

Particularly preferably, said transparent electroconductive layer (as defined above) exhibits the following features:

a sheet resistance in the range of from 10 ohm/sq. to 60 ohm/sq. as measured by the four point probe on said surface of said substrate on which said plurality of metal nanoobjects is disposed, and

a haze of 1.5 % or less as measured according to ASTM D1003 (Procedure A) as published in November 2013, and

a light transmission of 90 % or more as measured according to ASTM D1003 (Procedure A) as published in November 2013.

Said substrate preferably comprises a material selected from the group consisting of plastics, glass, metals, silicon, and sapphire.

Said substrate is preferably in a form selected from the group consisting of foils, films, webs, panes and plates. Preferably, said substrate has a thickness in the range of from 10 μιη to 200 μιη, preferably from 50 μιη to 100 μιη.

In specific cases, said substrate comprises an optically transparent material selected from the group of glasses and organic polymers, which is electronically insulating. Preferred types of glass are e.g. float glass, low iron float glass, heat strengthened glass and chemically strengthened glass. Optionally, the glass has a low-emissivity (low-e) coating, sun-protection coating or any other coating on the surface facing away from the above-described transparent electroconductive layer. Preferred organic polymers are selected from the group consisting of polymethylmethacrylate (PMMA, commercially available e.g. as Plexiglas™), polycarbonate (PC), polyethylene (PE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), polypropylene (PP), low density polypropylene (LDPP), polyethylene therephthalate (PET), glycol modified polyethylene therephthalate, polyethylene naphthalate (PEN), cellulose acetate butyrate, polylactide (PL), polystyrene (PS), polyvinyl chloride (PVC), polyimides (PI), polypropyleneoxide (PPO) and mixtures thereof. PET and PEN are particularly preferred.

Preferably, said substrate has a light transmission of 80 % or more measured according to ASTM D1003 (Procedure A) as published in November 2013. The above-defined plurality of metal nanoobjects is arranged on a surface of said substrate in such manner that it extends over the complete surface of said substrate, or only within limited regions of said surface. In specific cases the plurality of nanoobjects forms a pattern on said surface of said substrate. The pattern may be selected from any random and non-random structures, like grids, stripes, waves, dots and circles. Preferred are those articles according to the present invention which exhibit two or more of the above-defined preferred features in combination.

A particularly preferred article according to the invention comprises or consists of

a substrate

and disposed on a surface of said substrate a plurality of silver nanowires having a length of from 10 μιη to 50 μιη and a diameter in the range of from 10 to 100 nm and a coating consisting of Ti02 and Al203 deposited on said plurality of metal nanoobjects, wherein in said coating the molar ratio between Ti02 and Al203 is in the range of from 2 : 8 to 8 : 2, preferably from 4 : 6 to 6 : 4, further preferably from 4.5 : 5.5 to 5.5 : 4.5, wherein said coating arranged on said metal nanoobjects has a thickness in a range of from of 5 nm to 20 nm, preferably 5 nm to 10 nm. According to a further aspect, the present invention relates to a process for preparing an article according to the present invention as defined above. Said process comprises the step of depositing on a plurality of metal nanoobjects a coating comprising

one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02

and one or more oxides selected from the group consisting of Al203, Zr02 and Hf02.

Regarding specific and preferred features of the metal nanoobjects and the coating, reference is made to the disclosure provided above. In a process for preparing an article according to the present invention, either the above- defined coating is first deposited on metal nanoobjects, and then the coated metal nanoobjects are disposed on a surface of a substrate, or metal nanoobjects are first disposed on a surface of a substrate, and then the above-defined coating is deposited on said metal nanoobjects. Depositing the above-defined coating on metal nanoobjects prior to disposing the metal nanoobjects on a surface of a substrate is usually carried out while the metal nanoobjects are dispersed in a carrier liquid. A coating is formed on the surfaces of the metal nanoobjects by precipitation from suitable reagents added to the carried liquid. However, doing so may result in complete encapsulation of individual metal nanoobjects (i.e. coat- ing the entire surface of a metal nanoobject). Thus, when a plurality of such coated metal nanoobjects is disposed on a surface of a substrate, metal-metal junctions between adjacent and overlapping metal nanoobjects can hardly be formed, because due to virtually complete encapsulation of the individual metal nanoobjects, there is virtually no metal exposed on the surfaces of the metal nanoobjects. Therefore, according to the present invention this approach is not preferred.

A preferred process according to the present invention comprises the steps of

disposing a plurality of metal nanoobjects on a surface of a substrate,

and then depositing said coating on said plurality of metal nanoobjects disposed on said surface of said substrate. In this preferred process according to the present invention, a plurality of uncoated metal nanoobjects is first disposed on a surface of a substrate, so that formation of metal-metal junctions between adjacent and overlapping metal nanoobjects is possible. After disposing said plurality of metal nanoobjects on said surface of said substrate, said coating is deposited on the plurality of metal nanoobjects, in order to protect the plurality of metal nanoobjects against thermal and oxidative stress. It is assumed that deposition of the coating on the plurality of metal nanoobjects does not significantly alter the junctions between adjacent and overlapping metal nanoobjects said plurality of metal nanoobjects disposed on said surface of said substrate.

Typically, said plurality of metal nanoobjects is applied to said surface of said substrate in the form of a suspension (commonly referred to as an ink) comprising metal nanoobjects dispersed in a carrier liquid. The carrier liquid usually has a boiling point below 120 °C. Typically, said carrier liquid comprises water. Thus, disposing a plurality of metal nanoobjects on a surface of a substrate is usually carried out by

forming on a surface of said substrate a wet film by applying a suspension of metal nanoobjects dispersed in a carrier liquid to said surface of said substrate and - removing said carrier liquid from the wet film formed on said surface of said substrate.

Preferably said ink is applied to said surface of said substrate by a technique selected from the group consisting of coating and printing techniques. Preferred techniques are selected from the group consisting of doctor blade coating, air spraying, electrostatic spraying, slot-die coating, bar coating and ink-jet printing.

Said carrier liquid having a boiling point of less than 120 °C is removed from the wet film by evaporation. Preferably, said carrier liquid having a boiling point of less than 120 °C is removed by exposing the wet film formed on said surface of said substrate to air having a temperature in the range of from 20 °C to 120 °C. Preferably, the coverage of the surface of said substrate by said plurality of metal nanoobjects is in the range of from 10 % to 65 %, preferably in the range of from 15 % to 35 %. For calculating the coverage, images of the surface having said plurality of metal nanoobjects disposed thereon are taken by optical microscopy or scanning electron microscopy, and the images are analyzed by means of an image analyzing software capable of differentiating within said images said nanoobjects from the bare surface of the substrate and calculating the fraction of the surface covered by the nanoobjects. Depositing the above-defined coating on said plurality of metal nanoobjects is preferably carried out by means of atomic layer deposition (ALD).

Atomic Layer Deposition (ALD) is known in the art. It is a thin-film deposition technique by means of which a film is grown on a surface of an object by exposing said surface to a gas flow comprising a gaseous precursor of an atom species to be deposited on said surface. In order to form a metal oxide layer on a surface, a cycle (a so-called ALD cycle) is carried out comprising the steps of exposing the surface to an oxygen-carrying precursor (e.g. water) which is chemisorbed at the surface, removing excess molecules of the oxygen-carrying precursor by flushing with an inert gas, exposing the surface to a metal- carrying precursor (e.g. an organometallic compound) which reacts with the chemisorbed oxygen-carrying precursor to form the metal oxide, and removing excess molecules of the metal-carrying precursor and gaseous by-products by flushing with an inert gas. Further ALD cycles with the same or other precursors may follow, depending on the desired thickness and composition of the film to be formed. In order to deposit on the plurality of metal nanoobjects (which is disposed on a surface of a substrate) a coating comprising

one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02

and one or more oxides selected from the group consisting of Al203, Zr02 and Hf02 said substrate having said plurality of metal nanoobjects disposed on said surface is exposed to different ALD cycles with different precursors, namely at least one ALD cycle with precursors of an oxide selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02 and at least one ALD cycle with precursors of an oxide selected from the group consisting ofAI203, Zr02 and Hf02. Preferably, ALD cycles with precursors of an oxide selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02, and ALD cycles with precursors of an oxide selected from the group consisting of Al203, Zr02 and Hf02 are carried out alternately, or a sequence consisting of two or more ALD cycles with precursors of an oxide selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02 and two or more ALD cycles with precursors of an oxide selected from the group consisting of Al203, Zr02 and Hf02 are carried out several times. Preferred precursors for producing a coating as defined above are e.g.

for Ti02: tetrakis(dimethylamino)titanium, titanium tetrachloride TiCI4, tetraethyl orthotitanate [Ti(OEt)4] and tetraisopropyl orthotitanate [Ti(OPr/)4]

for ln203: diethyl[bis(trimethylsilyl)amido]indium Et2lnN(TMS)2, lnCI3, indium acetylacetonate [ln(acac)3]15 and trimethylindium

for Sn02: dimethylamino-2-methyl-2-propoxy-tin(ll)

for Al203: trimethylaluminum

for Zr02: tetrakis(dimethylamido)zirconium Zr(NMe2)4, tetrakis(ethylmethylamido) zirconium Zr(NMeEt)4, tetrakis(diethylamido)zirconium Zr(NEt2)4

for Hf02: tetrakis(dimethylamido)hafnium Hf(NMe2)4, tetrakis(ethylmethylamido)hafnium Hf(NMeEt)4, tetrakis(diethylamido)hafnium Hf(NEt2)4.

In the process of atomic layer deposition, the precursor molecules of different atoms are never present simultaneously in the reactor, but they are inserted into the reactor chamber as a series of sequential, non-overlapping pulses, and between the pulses the reactor chamber is flushed with inert gas. In each of these pulses the precursor molecules react with the surface in a self-limiting way, so that the reaction terminates once all the reactive sites on the surface are consumed. Consequently, the maximum amount of material deposited on the surface after a single exposure to all of the precursors of one oxide (a so-called ALD cycle) is determined by the nature of the precursor-surface interaction. By varying the number of cycles it is possible to grow materials uniformly and with high precision on arbitrarily complex and large objects.

Atomic layer deposition allows precise control of the thickness and the chemical composition of the coating. Since by atomic layer deposition technique one mono-layer is deposited per each cycle of gas flow, the composition of the deposited coating can be precisely controlled by the number of cycles for each gas flow.

Coatings deposited by the atomic layer deposition technique exhibit uniform morphology and thickness, are conformal with regard to the surface of the object which has been coated, and are substantially free of pinholes and other defects.

Other possible techniques for depositing said coating on said plurality of metal nanoobjects disposed on the surface of a substrate are chemical vapor deposition (CVD) and sputtering. However, these techniques are less preferred because they do not allow such precise control of the thickness and morphology as it is possible with atomic layer deposition.

According to a further aspect, the present invention relates to the use of an article according to the present invention in a device selected from the group consisting of solar cells, touch screens, wearable electronics, heaters, displays, piezo-electric generators and electrochromic windows.

Examples

The invention is now further described by means of examples which are not limiting. The figures show:

Figure 1 a SEM image of a comparison article of type 1

Figure 2 a SEM image of an article according to the invention

Figure 3 light transmittance and haze as function of the temperature (comparison article of type 1 , labeled "AgNW", and article according to the invention, labeled "AgNW/ATO")

Figure 4 sheet resistance as function of the temperature (comparison article of type 1 , labeled "AgNW", comparison article of type 2, labeled "Ti02@AgNW" and article according to the invention, labeled "AI203:Ti02@AgNW")

Figure 5 light transmittance and haze of the article according to the invention as a function of time of exposure to 380 °C

Figure 6 sheet resistance of the article according to the invention (labeled

"AgNW/ATO") as a function of time of exposure to 380 °C

Figures 7A-C SEM images of the article according to the invention before annealing

(A), after annealing at 200 °C for 20 minutes (B) and after annealing at 380 °C for 20 minutes (C) Figures 8A-C SEM images of the comparison article of type 1 before annealing (A), after annealing at 200 °C for 20 minutes (B) and after annealing at 380 °C for 20 minutes (C) sheet resistance before and after 1080 hours in air having 85 % relative humidity at 85 °C (comparison article of type 1 and article according to the invention)

A plurality of silver nanowires (length about 20 μιη, diameter about 40 nm) was disposed on a surface of a substrate made of glass (for measurement of sheet resistance, light transmittance and haze) resp. silicon (for SEM studies) by

- forming on said surface of said substrate a wet film by applying by means of doctor-blade-coating a suspension of silver nanowires dispersed in a carrier liquid to said surface of said substrate and

removing said carrier liquid from the wet film formed on said surface of said substrate by evaporation. In this way, comparison articles (not according to the invention) consisting of a substrate and disposed on a surface of said substrate a plurality of silver nanowires (comparison articles of type 1 ) were obtained. An exemplary as-obtained comparison article of type 1 exhibited

a sheet resistance of 51.4 ohm/sq measured by the four point probe on said sur- face of said substrate on which said plurality of metal nanoobjects is disposed a light transmittance of 91.1 % measured according to ASTM D1003 (procedure A) and

a haze of 1.10 % measured according to ASTM D1003 (procedure A).

In order to obtain articles according to the present invention, articles obtained in the same way like above-described comparison articles of type 1 were transferred into the reactor chamber of an ALD apparatus and a 5 nm thick coating consisting of Ti02 and Al203 in a molar ratio of 5 : 5 was deposited on the plurality of silver nanowires disposed on the surface of said substrate by carrying out 15 times a sequence consisting of two ALD cycles with precursors of Al203 and two ALD cycles with precursors of Ti02 (total number of 60 ALD cycles). An exemplary as-obtained article according to the invention exhibited a sheet resistance of 51.08 ohm/sq measured by the four point probe on said surface of said substrate on which said plurality of metal nanoobjects is disposed a light transmittance of 91.1 % measured according to ASTM D1003 (procedure A) and

a haze of 1.1 1 % measured according to ASTM D1003 (procedure A).

Comparison articles of type 2 were obtained in the same way like the above-described comparison articles of type 1 , and were transferred into the reactor chamber of an ALD apparatus and a 5 nm thick coating consisting of Ti02 was deposited on the plurality of silver nanowires disposed on the surface of said substrate by carrying out 60 ALD cycles for deposition of Ti02.

An exemplary as-obtained comparison article of type 2 exhibited

a sheet resistance of 51.0 ohm/sq measured by the four point probe on said surface of said substrate on which said plurality of metal nanoobjects is disposed - a light transmittance of 90.7 % measured according to ASTM D1003 (procedure A) and

a haze of 1.16 % measured according to ASTM D1003 (procedure A).

The values of sheet resistance, light transmittance and haze of the as-obtained exemplary articles show that the coating deposited on the plurality of the silver nanowires has no detrimental influence of the electrical and optical properties of the article. Furthermore, comparison of the sheet resistance of the comparison article of type 2 and the article according to the invention shows that incorporation of an oxide selected from the group consisting of Al203, Zr02 and Hf02 into the coating comprising one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02 does not have a significant effect on the sheet resistance of the as-obtained article, although the oxides selected from the group consisting of Al203, Zr02 and Hf02 have a lower electronic conductivity than the oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02.

A comparison article of type 1 and an article according to the invention were examined by means of scanning electron microscopy, see figures 1 and 2. In both articles, the plurality of silver nanowires disposed on the surface of the substrate formed a continuous network of crossing and overlapping nanowires. In the article according to the invention, a coating could be detected on surfaces of the silver nanowires. The presence of Ti02 and Al203 in the article according to the invention was confirmed by means of EDAX.

An article according to the invention and a comparison article of type 1 were examined as to how the light transmittance and the haze change upon exposure to temperatures in the range of from 200 °C to 380 °C. An article according to the invention, a comparison article of type 1 and a comparison article of type 2 were examined as to how the sheet resistance changes upon exposure to temperatures in the range of from 200 to 380 °C. Sheet resistance, light transmittance and haze were measured after annealing the articles at 200 °C, 250 °C, 300 °C, 350 °C and 380 °C. At each temperature the articles were annealed for 20 minutes. The results are shown in figures 3 and 4. The comparison article of type 1 exhibits a significant increase of haze and a remarkable decrease of light transmittance when annealed at temperatures above 200 °C. Electronic conductivity of the comparison article of type 1 was virtually lost at temperatures above 200 °C. Electron- ic conductivity of the comparison article of type 2 was virtually lost at temperatures above 300 °C. In contrast, sheet resistance, light transmittance and haze of the article according to the invention did not degrade remarkably even after annealing at a temperature of 380 °C for 100 minutes, see figures 5 and 6. Comparison of the influence of the annealing temperature on the sheet resistance of the comparison article of type 2 and the article according to the invention shows that incorporation of an oxide selected from the group consisting of Al203, Zr02 and Hf02 into the coating comprising one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02 increases the thermal resistance of the coated plurality of silver nanowires.

SEM images revealed that in an article according to the invention the silver nanowires substantially sustained their original shape even after annealing at 380 °C for 20 minutes (see figures 7A-C), while in a comparison article of type 1 breaking down of the silver nanowires started at 200 °C, and after annealing at 380 °C, insular drop-like aggregates having a larger diameter than the original silver nanowires were formed while the original silver nanowires were almost undetectable (see figures 8A-C). Thus, the degradation of the electrical and optical properties after annealing at temperatures above 200 °C is obviously caused by the break-up of the silver nanowires.

An article according to the invention and a comparison article of type 1 were examined as to how the sheet resistance changes upon long term (1080 hours) exposure to air having 85 % relative humidity at 85 °C. The results are shown in figure 9. The sheet resistance of the comparison article increased by a factor of about 3.5, while the sheet resistance of the article according to the invention remained virtually unchanged.

Claims

Claims
1. An article comprising
a substrate
and disposed on a surface of said substrate a plurality of metal nanoobjects and a coating comprising
one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02
and one or more oxides selected from the group consisting of Al203, Zr02 and Hf02
deposited on said plurality of metal nanoobjects wherein said coating has a thickness in a range of from of 5 nm to 20 nm.
2. An article according to claim 1 , wherein
said metal nanoobjects are selected from the group consisting of nanowires, nanorods, nanoflakes, nanoplates, nanoribbons and nanospheres.
3. An article according to any preceding claim, wherein
said metal nanoobjects comprise one or more metals selected from the group consisting of silver, copper, nickel, gold, palladium, tungsten, iron, cobalt and tin and alloys of two or more of said metals.
4. An article according to any preceding claim, wherein
said metal nanoobjects are nanowires having a length of from 10 μιη to 50 μιη and a diameter in the range of from 10 to 100 nm.
5. An article according to any preceding claim, wherein
said coating consists of
one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02
and one or more oxides selected from the group consisting of Al203, Zr02 and Hf02. BASF SE I 160426 | 160426WO01
6. An article according to any preceding claim, wherein
in said coating the molar ratio between
the total amount of oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02
and the total amount of oxides selected from the group consisting of Al203, Zr02 and Hf02
is in the range of from 2 : 8 to 8 : 2.
7. An article according to any preceding claim, wherein said article has
a sheet resistance in the range of from 10 ohm/sq. to 150 ohm/sq. as measured at a temperature of 25 °C and a pressure of 101.3 kPa by the four point probe on said surface of said substrate on which said plurality of metal nanoobjects is disposed and said coating is deposited on said plurality of metal nanoobjects.
8. An article according to any preceding claim, wherein said article has
a light transmittance of from 80 % or more as measured according to ASTM D1003 (procedure A) and
a haze of 3 % or less as measured according to ASTM D1003 (procedure A).
9. An article according to any preceding claim, wherein
said substrate comprises a material selected from the group consisting of plastics, glass, metals, silicon, and sapphire.
10. An article according to any preceding claim, said article comprising
a substrate
and disposed on a surface of said substrate a plurality of silver nanowires having a length of from 10 μιη to 50 μιη and a diameter in the range of from 10 to 100 nm
and a coating consisting of Ti02 and Al203 deposited on said plurality of metal nanoobjects, wherein in said coating the molar ratio between Ti02 and Al203 is in the range of from 2 : 8 to 8 : 2, preferably from 4 : 6 to 6 : 4, further preferably from 4.5 : 5.5 to 5.5 : 4.5, wherein said coating arranged on said metal nanoobjects has a thickness in a range of from of 5 nm to 20 nm, preferably 5 nm to 10 nm.
1 1. Process for preparing an article according to any of claims 1 to 10, comprising the step of
depositing on metal nanoobjects a coating comprising
one or more oxides selected from the group consisting of Ti02, ln203, ZnO, Ga203 and Sn02
and one or more oxides selected from the group consisting of Al203, Zr02 and Hf02.
12. Process according to claim 1 1 , comprising the steps of
disposing a plurality of metal nanoobjects on a surface of a substrate, and then depositing said coating on said plurality of metal nanoobjects disposed on said surface of said substrate.
13. Process according to claim 12, wherein disposing said plurality of metal nanoobjects on said surface of said substrate is carried out by
forming on a surface of said substrate a wet film by applying a suspension of metal nanoobjects dispersed in a carrier liquid to said surface of said substrate and
removing said carrier liquid from the wet film formed on said surface of said substrate.
14. Process according to claim 12 or 13, wherein said coating is deposited by means of atomic layer deposition.
15. Use of an article according to any of claims 1 to 10
in a device selected from the group consisting of solar cells, touch screens, wearable electronics, heaters, displays, piezo-electric generators and electrochromic windows.
PCT/EP2017/068744 2016-07-29 2017-07-25 Transparent electroconductive layer having a protective coating WO2018019820A1 (en)

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Citations (6)

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Publication number Priority date Publication date Assignee Title
US7922787B2 (en) 2008-02-02 2011-04-12 Seashell Technology, Llc Methods for the production of silver nanowires
US8049333B2 (en) 2005-08-12 2011-11-01 Cambrios Technologies Corporation Transparent conductors comprising metal nanowires
US20140020737A1 (en) 2012-07-18 2014-01-23 Research & Business Foundation Sungkyunkwan University Silver nanowire conductive film and method of fabricating the same
US20140179040A1 (en) 2008-04-09 2014-06-26 Agency For Science, Technology And Research Multilayer film for encapsulating oxygen and/or moisture sensitive electronic devices
US20160060758A1 (en) 2014-08-29 2016-03-03 University Of Maryland, College Park Protective coated object and method of coating an object
US20160096770A1 (en) 2012-10-12 2016-04-07 Vitro Vidrio Y Cristal, S.A. De C.V. Coating having solar control properties for a substrate, and method and system for depositing said coating on the substrate

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8049333B2 (en) 2005-08-12 2011-11-01 Cambrios Technologies Corporation Transparent conductors comprising metal nanowires
US7922787B2 (en) 2008-02-02 2011-04-12 Seashell Technology, Llc Methods for the production of silver nanowires
US20140179040A1 (en) 2008-04-09 2014-06-26 Agency For Science, Technology And Research Multilayer film for encapsulating oxygen and/or moisture sensitive electronic devices
US20140020737A1 (en) 2012-07-18 2014-01-23 Research & Business Foundation Sungkyunkwan University Silver nanowire conductive film and method of fabricating the same
US20160096770A1 (en) 2012-10-12 2016-04-07 Vitro Vidrio Y Cristal, S.A. De C.V. Coating having solar control properties for a substrate, and method and system for depositing said coating on the substrate
US20160060758A1 (en) 2014-08-29 2016-03-03 University Of Maryland, College Park Protective coated object and method of coating an object

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