JPH0892766A - Production of nickel oxide film by plasma oxidation - Google Patents

Abstract

PURPOSE: To prepare a nickel oxide film high in speed of response and less deteriorated when used as an oxidation color developing material of an electrochromic element by plasma-oxidizing a composite film consisting of metallic nickel and carbon. CONSTITUTION: A composite film consisting of metallic nickel and carbon is formed on a substrate consisting of a conductive or nonconductive material by vacuum deposition, sputtering, etc. The nickel-carbon composite film is preferably treated with the low-temp. plasma using a cylindrical plasma etching device and oxidized. By this method, a transparent nickel oxide film is obtained at 0.05-2Torr vacuum without heating the substrate. This nickel oxide film exhibits a remarkable electrolytic-oxidation color developability and a stable electrochemical characteristic, and hence the film is useful as an electrochromic element, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a nickel oxide film having "electrolytic oxidative coloring" which develops a color in an oxidized state.

[0002]

2. Description of the Related Art The phenomenon in which a thin film-like object undergoes discoloration or color development-bleaching due to the implantation of ions having a positive or negative charge is called electrochromism. This phenomenon is utilized in, for example, electrochromic devices. Has been done.

A typical electrochromic device is a reductive color forming electrochromic material such as tungsten oxide, an electrolyte and iridium oxide,
It is composed mainly of an oxidative coloring electrochromic material such as nickel oxide.

The most widely studied of all solid-state electrochromic devices is a tungsten oxide / iridium oxide based device. However, since iridium oxide is expensive and has poor coloring efficiency, nickel oxide has been actively studied in recent years as an alternative material. From the viewpoint of practical use, it is preferable that the oxidative coloring material for the electrochromic device has a fast response speed and little deterioration. Further, when a device is combined with a tungsten oxide film as a reduction coloring material, a vacuum deposition method, a tungsten oxide film manufactured by a method such as a coating method, ions are not implanted in the manufacturing state, Since it is transparent, the oxidative coloring electrochromic material also needs to be in a transparent state.

Nickel oxide films exhibiting electrochromism were first described in 1986 by Svensson and Granqvist in "Applied Physics Letters".
It has been known that various methods can be used since the electrochromism of nickel oxide prepared by sputtering method was reported in Vol.64. That is, as a method for obtaining a nickel oxide film, a sputtering method, a vacuum deposition method, an electrodeposition method, a sol-gel method and the like have been known so far, but each has a problem to be solved.

The electrodeposition method is, for example, to form a nickel oxide film on the cathode in an aqueous solution of nickel nitrate, which is published in "Solar Energy Materials" Vol.
According to a paper by Carpenter et al., Published in 16, a nickel oxide film obtained by this method is 5
It has been confirmed that, by repeating the coloring and erasing operation about 100 times, the transmittance at the time of erasing exceeds 50% after the initial state of 50% or less, but 50% or less after 500 cycles. In addition, the response speed requires 7 seconds for coloring and 5 seconds for erasing.

Proceedings of "The 8th Technical Meeting on Optical Materials for Energy Efficiency and Solar Energy Conversion" held in 1989 (SPIE Vol.1149 Optical Materials Tech
nology for Energy Efficiency and Solar Energy Conv
ersion VIII) Lampert
According to a paper by Caron-Popowich, the nickel oxide film obtained by the sol-gel method has a transmittance of more than 80% at the time of bleaching due to repeated erasing / decoloring about 200 times. After 200 cycles from the state, a remarkable deterioration of the characteristics of 50% or less is recognized. In addition, they report that the response speed is several to 10 seconds regarding the characteristics of the nickel oxide film obtained by the sputtering method or the vacuum deposition method.

According to the above-mentioned article by Svenson and Grankvist, the nickel oxide film obtained by the sputtering method has a life of about 10,000 times, but its electrochemical characteristics have not been clarified. "Solar, published in 1992.
According to a paper by Conell et al. Published in Energy Materials and Solar Cells ”Vol.25, a nickel oxide film obtained by the sputtering method has been reported to have a coloration / erasing life of more than 2500 times. According to the report, after 2500 cycles, the transmittance at the time of bleaching is reduced to about several percent in the visible light region as compared with the initial period.

As described above, it is known that the nickel oxide film obtained by the sputtering method has the least deterioration. However, in the sputtering under the normal oxygen atmosphere, the oxidation with the high transmittance in the state of fabrication is performed. No nickel film was obtained.
Further, there is no known method for obtaining a nickel oxide film having two excellent characteristics of fast response speed and little deterioration.

[0010]

The main object of the present invention is to:
It is an object of the present invention to provide a method for producing a nickel oxide film which has a fast response speed and little deterioration when used as an oxidative coloring material for an electrochromic device.

[0011]

The present inventor has conducted various studies in view of the current state of the art as described above, and as a result, as described in Japanese Patent Application No. 6-155137 filed earlier. When a composite film made of nickel and carbon formed in advance on the substrate was heated and oxidized in the atmosphere, the heating and oxidation temperature was 40
We have found a new fact that a transparent nickel oxide film can be obtained by a simple heat treatment of 0 ° C. and a heat oxidation time of 10 to 30 minutes.

In the known methods for producing a nickel oxide film, the electrochromic properties of the nickel oxide film are deteriorated by heat treatment at a high temperature during or after film formation on a substrate kept at a high temperature. Is recognized. For example, the proceedings of the "9th Optical Material Technology Conference for Energy Efficiency and Solar Energy Conversion" held in 1990 (SPIE Vol.1272 Optical Material
s Technology for Energy Efficiency and Solar Energ
And Conversion (Ande)
In the paper by rsson) et al., deterioration was observed in the sputtering method at a substrate temperature of 120 ° C. or higher during fabrication.
It is stated that electrochromic properties are lost by annealing at 40 ° C. for 40 hours. Also, 1992
The paper by Miki et al., Published in the proceedings of the joint research presentation of the Japan Solar Energy Society and the Japan Wind Energy Association, states that degradation of characteristics is observed by the electrolysis method by firing at 300 ° C or higher. Therefore, it was unpredictable from the prior art that a nickel oxide film exhibiting good electrochromism can be obtained by heating and oxidizing a composite film made of nickel and carbon in the atmosphere at a temperature of about 400 ° C. .

As described above, Japanese Patent Application No.
Although the content of No. 155137 is based on a new discovery, it is known that a transparent conductive film formed in advance on a substrate, which is used to enhance responsiveness as an electrochromic element, deteriorates at high temperature. Therefore, it is desired to complete a method for forming a nickel oxide film at a lower temperature. For example, the conductive characteristics of the indium oxide transparent conductive film are reversible in the temperature range from room temperature to about 300 ° C., but the change at 400 ° C. or higher is large, and for example, when held in the air at 450 ° C. for 1 hour. Is known to change irreversibly. Therefore, in order to form a nickel oxide film on an indium oxide transparent conductive film having the highest transparency without deteriorating its characteristics, 300
It is necessary to perform the forming operation at a temperature of ℃ or below.

The present inventor has found the following matters as a result of various studies in view of the current state of the art as described above. That is, in order to form the nickel oxide film by the heat treatment in the atmosphere according to the method described in Japanese Patent Application No. 6-155137, it was necessary to heat at least 300 ° C. or higher, whereas it was previously formed on the substrate. When a composite film made of nickel and carbon was plasma-oxidized using a plasma etching apparatus, the substrate was not heated in an oxygen atmosphere under vacuum conditions of about 0.9 to 1.1 Torr and about 400 to 500 W. , A novel fact that a transparent nickel oxide film is obtained by the treatment for 10 to 30 minutes has been found.

The present invention has been completed on the basis of such novel findings, and provides the following method for producing nickel oxide; A method for producing a nickel oxide film, which comprises subjecting a composite film of metallic nickel and carbon to plasma oxidation.

In the present invention, first, a nickel-carbon composite film is formed on a substrate. As the substrate, not only a conductive material such as metal but also non-conductive material such as glass and porcelain can be used.

The nickel-carbon composite film can be formed by a vacuum evaporation method which is generally adopted in the known thin film production, for example, a vacuum evaporation method or a sputtering method. More specifically, (i) a co-evaporation method of evaporating nickel and carbon from different evaporation sources to form a composite film on the same substrate, (ii) targeting nickel on carbon, Examples include a method of forming a composite film by performing sputtering in argon gas.

By controlling the evaporation source, a nickel-carbon composite film having an arbitrary composition ratio can be obtained. When plasma oxidation is performed, the composition ratio of nickel to carbon in the composite film (Ni / C; atomic ratio) is obtained. In the range of 0.2 to 1.1, the nickel oxide film was well formed.

When a non-conductive glass, porcelain or the like is used as the substrate, a transparent conductive film or a conductive metal film is previously provided on the substrate in order to enhance the response as an electrochromic device. It is preferable to form a nickel-carbon composite film.

In the present invention, the nickel-carbon composite film formed on the substrate as described above is then plasma-oxidized in an oxygen atmosphere to obtain a desired nickel oxide film. The method and apparatus for plasma oxidation include
There is no particular limitation, but in order to prevent nickel from being sputtered by physical etching, it is preferable to use low-temperature plasma treatment using a cylindrical plasma etching apparatus. The pressure is preferably in the range of a vacuum degree of 0.05 to 2 Torr at which plasma is stably generated.

The nickel oxide film obtained by the method of the present invention exhibits remarkable electrolytic oxidative coloring and stable electrochemical characteristics.
It is extremely useful as an H sensor and a positive electrode material for batteries.

A known indium oxide film, tin oxide film or the like can be used as the transparent conductive film in the electrochromic device.

[0023]

According to the present invention, the following effects can be obtained.

(1) A transparent nickel oxide film can be formed by an oxidative plasma treatment in a low temperature range in which a transparent conductive film such as indium oxide does not deteriorate.

(2) It is also possible to form a nickel oxide film on the insulating substrate.

(3) Since it is transparent, it is not necessary to electrochemically decolorize it when it is formed into a device.

[0027]

EXAMPLES Examples and comparative examples will be shown below to further clarify the features of the present invention.

Example 1 and Comparative Example 1 Production of Nickel Oxide Film A nickel-carbon composite film was formed by a vacuum vapor deposition method in which carbon was evaporated using an electron gun as a heating source, and nickel was evaporated by resistance heating using a W-boat. Obtained. The time required for film formation was several minutes to 15 minutes. As the substrate, a glass plate on which a tin oxide transparent conductive film was previously formed was used.

Then, the nickel-carbon composite film is heated in a cylindrical plasma etching apparatus under an oxygen atmosphere at a vacuum degree of 0.9 to 1.1 Torr and a temperature of 400 to 500 W without heating the substrate. A nickel oxide film was obtained by processing for 10 minutes.

For comparison, when a nickel-carbon composite film prepared in the same manner was heated and oxidized in the air at a temperature of 300 to 500 ° C. for 10 minutes or 20 minutes, a heat treatment at 300 ° C. × 20 minutes was performed. Showed insufficient desorption of carbon and showed low transmittance. As is clear from FIG. 1 showing the relationship between the heat treatment temperature and the transmittance, it is understood that the heat treatment at 350 ° C. is necessary for the oxidation treatment in the atmosphere. On the other hand, the transmittance of the nickel oxide film obtained by plasma oxidation is 400
The transmittance was similar to or higher than that of the film obtained by the heat treatment at ℃.

The thickness of the nickel-carbon composite film used to obtain the nickel oxide film is about 100 nm,
The ratio of nickel to carbon in the film (Ni / C; atomic ratio) was in the range of 0.8 to 1.1 as a result of photoelectron spectroscopy. Further, as a result of investigating the structure of the film after the thermal oxidation by the X-ray diffraction method, only the diffraction pattern corresponding to the cubic structure of NiO was shown, and the diffraction pattern corresponding to metallic nickel disappeared. In the present invention, since nickel and carbon are evaporated from different evaporation sources, a nickel-carbon composite film having an arbitrary composition ratio can be obtained, but the ratio of nickel to carbon in the film is about 3 or more. In this case, a film having a high transmittance could not be obtained due to insufficient desorption of carbon. Coloring and decoloring test The nickel oxide film prepared on the tin oxide transparent electrode obtained in the present invention was dipped in a 1 molar aqueous solution of potassium hydroxide, and a saturated sweet-kou electrode was used as a reference electrode at 0.6 to -0.5 V. When the potential was scanned in the range, color development and decoloration of the thin film was recognized.

FIGS. 2 and 3 show changes in current density and changes in transmittance at a wavelength of 633 nm when a potential scan is performed. The potential scanning speed was 100 mV / sec. Note that curves d, e, and f in FIG. 3 represent changes in transmittance corresponding to the curves a, b, and c in FIG. 2, respectively. Curves a and d show changes in current density and changes in transmittance immediately after potential scanning, curves b and e at 100th cycle after starting potential scanning, and curves c and f at 500th cycle after starting potential scanning, respectively. As is clear from FIG. 2, at a relatively high potential scanning speed of 100 mV / sec, clear oxidation-reduction peak currents were observed near 0.4 to 0.5 V and 0.2 to 0.3 V, respectively. Therefore, it can be seen that diffusion of ions in the nickel oxide film occurs quickly. Further, as shown in FIG. 3, the nickel oxide film according to the present invention can be already in a decoloring state of more than 80% immediately after the start of potential scanning. Further, as is clear from FIGS. 2 and 3, the change in current density and the change in transmittance increase as the potential scanning is repeated, and neither characteristic is deteriorated.

Subsequently, the potential scanning was repeated continuously up to 1000 cycles, and the "disappearance" in the decolored state reported in the nickel oxide film produced by the electrodeposition method, the sol-gel method or the like was reported. The rest ', no significant changes in the cyclic voltammogram were observed.

[0034] To investigate the response characteristics of the obtained nickel oxide film in response this embodiment, as a reference electrode saturated calomel electrode, the step voltage cycle 4 seconds within a range of ± 0.5V to nickel oxide film Was applied. FIG. 4 shows the change in transmittance at a wavelength of 633 nm. The response speed at the time of erasing is about 0.4 seconds, and it is clear that the response speed is high.

Comparative Example 1 The nickel-carbon composite film produced in the same manner as in Example 1 was heated in the atmosphere at a temperature of 400 ° C. for 10 minutes to form a nickel oxide film on the tin oxide transparent electrode.
When the film was immersed in an aqueous solution of 1 mol of potassium hydroxide and the potential was scanned in the range of 0.6 to -0.5 V with the saturated sweet koh electrode as a reference electrode, color development and decoloration of the thin film was recognized.

FIG. 5 and FIG. 6 show changes in current density and changes in transmittance at a wavelength of 633 nm, respectively, when potential scanning is performed. The potential scanning speed was 100 mV / sec. Curves j, k, and l in FIG. 6 represent changes in transmittance corresponding to curves g, h, and i in FIG. 5, respectively. Curves g and j show the change in current density and change in transmittance immediately after the potential scan, curves h and k at the 100th cycle after the start of the potential scan, and curves i and l at the 500th cycle after the start of the potential scan.

Comparing FIGS. 2 and 3 with FIGS. 5 and 6, it is clear that the nickel oxide film formed by plasma oxidation exhibits the same characteristics as the nickel oxide film oxidized in the atmosphere.

Example 2 A nickel-carbon composite film was obtained in the same manner as in Example 1.
As the substrate, a glass plate on which a tin oxide transparent conductive film was previously formed was used. The film thickness of the nickel-carbon composite film was about 100 nm, and the ratio of carbon to nickel in the film was in the range of 0.2 to 0.4 as a result of the photoelectron spectroscopy analysis.

Then, the obtained nickel-carbon composite film is heated in a cylindrical plasma etching apparatus in an oxygen atmosphere under the conditions of a vacuum of 0.9 to 1.1 Torr and a vacuum of 400 to 500 W. Without treatment, a nickel oxide film was obtained.

Then, the nickel oxide film formed on the tin oxide transparent electrode was immersed in a 1 molar aqueous solution of potassium hydroxide,
When the potential was scanned in the range of 0.7 to -0.3 V with the saturated sweet koh electrode as a reference electrode, color development and decoloration of the thin film was recognized.

The transmittance of the nickel oxide film obtained by plasma oxidation at a wavelength of 633 nm was 81% in the initial state. 2 at potential scanning speed of 100 mV / sec
When 00 scans were performed, a change in transmittance of 87% to 47% was obtained. As the potential scanning was repeated, the change in current density and the change in transmittance increased, and no deterioration in both characteristics was observed.

[Brief description of drawings]

FIG. 1 shows a carbon-nickel composite film prepared at the same time as an example of the present invention in air for comparison with the present invention.
It is a graph which shows the result of having measured the transmittance | permeability in wavelength 550nm of the nickel oxide film obtained by heat-oxidizing for 10 or 20 minutes in the temperature range of 0-500 degreeC.

FIG. 2 shows a nickel oxide film according to an embodiment of the present invention,
It is a graph which shows the electric current density change in a potential scanning speed of 100 mV / sec measured at the initial stage, after 100 cycles, and after 500 cycles.

FIG. 3 shows a nickel oxide film according to an embodiment of the present invention,
A wavelength of 63 at a potential scanning rate of 100 mV / sec, which was measured initially, after 100 cycles, and after 500 cycles.
It is a graph which shows the transmittance | permeability change in 3 nm.

FIG. 4 shows a nickel oxide film according to an embodiment of the present invention,
It is a graph which shows the transmittance | permeability change in wavelength 638nm at the time of applying a step voltage.

FIG. 5 shows a nickel oxide film according to a comparative example of the present invention.
A wavelength of 63 at a potential scanning rate of 100 mV / sec, which was measured initially, after 100 cycles, and after 500 cycles.
It is a graph which shows the transmittance | permeability change in 3 nm.

FIG. 6 shows a nickel oxide film according to a comparative example of the present invention,
A wavelength of 63 at a potential scanning rate of 100 mV / sec, which was measured initially, after 100 cycles, and after 500 cycles.
It is a graph which shows the transmittance | permeability change in 3 nm.

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[Procedure amendment]

[Submission date] November 11, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

FIG. 4 shows a nickel oxide film according to an embodiment of the present invention,
7 is a graph showing a change in transmittance at a wavelength of 633 nm when a step voltage is applied.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 5

[Correction method] Change

[Correction content]

FIG. 5 shows a nickel oxide film according to a comparative example of the present invention.
It is a graph which shows the electric current density change in a potential scanning speed of 100 mV / sec measured at the initial stage, after 100 cycles, and after 500 cycles.

Continued Front Page (72) Inventor Toshiyuki Mihara 1-831 Midorigaoka, Ikeda City, Osaka Prefecture Industrial Technology Institute Osaka Institute of Industrial Technology

Claims (1)

[Claims] 1. A method for producing a nickel oxide film, which comprises subjecting a composite film of metallic nickel and carbon to plasma oxidation.