JP5194427B2 - Photocatalytic tungsten oxide thin film - Google Patents

Description

The present invention relates to a tungsten oxide (WO ₃ ) thin film, and particularly to a tungsten oxide thin film having a visible light responsive photocatalytic function formed by high-speed film formation by gas flow sputtering.

  Tungsten oxide is an excellent photocatalytic material, and it has various functions such as deodorization, water purification, antifouling, self-cleaning (self-cleaning), antibacterial, antiviral, antifungal, sterilization, etc. Application to the field is being attempted. In particular, crystalline tungsten oxide is expected to be used not only outdoors but also indoors because it has visible light responsiveness showing catalytic activity in visible light.

  When tungsten oxide is applied to the photocatalytic material, it is rarely used alone, and it is usually used by being fixed in a thin film on the surface of some substrate. At this time, sputtering has a feature that a tungsten oxide thin film can be formed on any substrate surface with good adhesion, and is excellent as a method for forming a tungsten oxide thin film.

  However, in order to form a transparent tungsten oxide thin film in a reactive sputtering performed using normal sputtering (DC magnetron sputtering) using a W target and introducing oxygen, the film is formed in a so-called oxide mode. The film formation is extremely slow at a speed of about 10 nm / min. Such a low film formation rate does not endure industrial use.

  In addition to the slow deposition rate in conventional sputtering, visible light responsiveness was exhibited only when the substrate was deposited while being heated to about 600 ° C. or higher, and post-baking was performed after deposition at a low temperature. In some cases, the lack of visible light response is also a problem in that the manufacturing method is limited.

  As described above, in the formation of a tungsten oxide thin film by normal sputtering, the film formation rate is low; only when the film is formed while heating the substrate to about 600 ° C. or higher, visible light responsiveness is exhibited, and film formation is performed at a low temperature. However, when post-firing is not performed, visible light responsiveness is not exhibited; however, in general sputtering, in order to exhaust the inside of the vacuum chamber to a high vacuum state, a large exhaust device or a high function is required. Since a control device is required, there is a disadvantage that expensive equipment is required.

  Gas flow sputtering is known for such normal sputtering, and the applicant of the present application previously performed gas flow sputtering on a catalyst layer of a polymer electrolyte fuel cell electrode or a dye-sensitized solar cell. Have proposed a technology applied to the formation of a semiconductor electrode layer for use (Patent Documents 1 to 3).

Gas flow sputtering is a method in which sputtering is performed under a relatively high pressure, and sputtered particles are transported and deposited to a film formation target substrate by a forced flow of a gas such as Ar. Since this gas flow sputtering does not require high vacuum evacuation, it is possible to form a film by mechanical pump evacuation without using a large evacuation device such as conventional ordinary sputtering, and therefore inexpensive equipment. Can be implemented. Moreover, gas flow sputtering can form a film at a high speed 10 to 1000 times that of normal sputtering. Furthermore, since a magnet is not required on the back side of the target, the efficiency of using the target is about 20 to 30% in normal sputtering that requires a magnet on the back side of the target. Is as high as 90% or more. Therefore, according to the gas flow sputtering, it is possible to greatly reduce the film formation cost by reducing the equipment cost, shortening the film formation time, and improving the target utilization efficiency.
Japanese Patent Application No. 2004-319592 Japanese Patent Application No. 2004-319548 Japanese Patent Application No. 2004-319598

  As described above, when forming a tungsten oxide thin film as a photocatalyst material, the conventionally used sputtering has a slow film formation speed; visible light only when the film is formed while heating the substrate to about 600 ° C. or higher. Shows responsiveness and does not show visible light responsiveness when post-baking after film formation at low temperature; it requires expensive equipment, poor target utilization efficiency and high film formation cost; In the past, there has not been provided a method for producing a tungsten oxide thin film having photocatalytic activity at high cost at low cost.

  Accordingly, an object of the present invention is to provide a photocatalytic tungsten oxide thin film formed at low cost by high-speed film formation.

  As a result of intensive studies to solve the above problems, the present inventors have been able to form a tungsten oxide thin film at a low cost by high-speed film formation by employing gas flow sputtering, and further, by heating the substrate. The present invention was completed by finding that a tungsten oxide thin film having excellent visible light responsive photocatalytic activity can be obtained both in the case of forming a film and in the case of post-baking the formed tungsten oxide thin film.

  That is, the gist of the present invention is as follows.

The tungsten oxide thin film according to claim 1 is a tungsten oxide thin film formed by gas flow sputtering, and is formed on a heating base material and exhibits photocatalytic activity by as-deposition. .

  A tungsten oxide thin film according to a second aspect is characterized in that the tungsten oxide thin film according to the first aspect is formed by reactive sputtering using metallic tungsten as a target and introducing oxygen gas.

Tungsten oxide thin film according to claim 3, in claim 1 or 2, as a substrate, a glass plate, metal plate, is characterized in that a metal foil or a ceramic plate.

A tungsten oxide thin film according to claim 4 is characterized in that, in any one of claims 1 to 3 , the film forming pressure in gas flow sputtering is 5 to 200 Pa.

A tungsten oxide thin film according to a fifth aspect is characterized in that, in any one of the first to fourth aspects, the tungsten oxide thin film is formed by gas flow sputtering in which argon gas and oxygen gas are separately introduced.

A tungsten oxide thin film according to claim 6 is formed by a gas flow sputtering apparatus having a cathode structure in which a rectangular target is arranged to face each other according to any one of claims 1 to 5. It is.

A tungsten oxide thin film according to a seventh aspect is characterized in that, in any one of the first to sixth aspects, the tungsten oxide thin film is formed at a film formation rate of 100 nm / min or more by gas flow sputtering.

A tungsten oxide thin film according to an eighth aspect is characterized in that, in any one of the first to seventh aspects, the film is fired after film formation by gas flow sputtering.

The tungsten oxide thin film according to claim 9 is characterized in that, in claim 8 , the firing condition is 400 to 900 ° C.

Gas flow sputtering is a method in which sputtering is performed under a relatively high pressure, and sputtered particles are transported to a deposition target substrate by a forced flow of gas and deposited. Since this gas flow sputtering does not require high vacuum evacuation, it is possible to form a film by mechanical pump evacuation without using a large evacuation device such as conventional ordinary sputtering, and therefore inexpensive. It can be implemented with simple equipment. In addition, gas flow sputtering can form a film at a high speed 10 to 1000 times that of normal sputtering and also has high target utilization efficiency. Therefore, according to the present invention, the tungsten oxide thin film can be formed at low cost by reducing the equipment cost, shortening the film forming time, and improving the film forming efficiency by adopting the gas flow sputtering. Moreover, unlike DC magnetron sputtering, gas flow sputtering does not require a magnet on the back of the target. Accordingly, the utilization efficiency of the target is very high at 90% or more, which is advantageous for cost reduction. (DC magnetron sputtering: 20-30%)
Moreover, in the case of gas flow sputtering, a tungsten oxide thin film having a high photocatalytic activity can be formed even in the case of performing baking after forming a film without heating the substrate in addition to heating the substrate. Can do. Further, since the adhesion of the formed tungsten oxide thin film to the base material is good, a high quality tungsten oxide thin film can be manufactured.

  In addition, the detail of the action mechanism in which the effect by this invention is acquired is as follows.

In a normal sputtering method, when a tungsten oxide film is formed using a W target, the target surface is oxidized when oxygen is introduced to some extent, and the formed thin film becomes a transparent tungsten oxide thin film. The film speed is also very slow. On the other hand, in gas flow sputtering, the pressure is about two orders of magnitude higher, a forced flow of argon gas flows through the target surface, preventing oxygen gas from diffusing to the target surface, and always fresh metal without oxidizing the target surface. Sputtering while maintaining the state, the sputtered particles can be transported onto the substrate with a forced flow of argon, and oxidized on the substrate with oxygen gas. As a result, even when sufficient oxygen is introduced, the film formation speed does not decrease due to the oxide mode unlike normal sputtering, and the tungsten oxide thin film can be formed at high speed. As the level of high-speed film formation, compared with the case of using the normal DC magnetron sputtering method, the density of the tungsten oxide thin film is not the same and the film formation speed changes depending on conditions such as film formation pressure. Although it cannot be compared, when the same power density is applied, a film formation rate of 20 times or more can be obtained. For example, when a power of 4 W / cm ² is applied, a film formation rate of about 9 nm / min in the DC magnetron sputtering method and about 200 nm / min in the gas flow sputtering can be achieved.

  Also, although the catalytic activity height varies depending on the amount of oxygen introduced and other conditions, gas flow sputtering has good photocatalytic activity without any mode change such as a rapid decrease in film formation rate due to the amount of oxygen introduced. You can easily find the conditions. Although the photocatalytic activity tends to be higher as the amount of introduced oxygen increases, an extreme increase in the amount of introduced oxygen induces arcing on the target surface. Therefore, the oxygen flow rate can be appropriately changed within a range where these problems do not occur.

  As described above, the gas flow sputtering method is characterized by high-speed film formation of tungsten oxide having visible light responsive photocatalytic activity. Furthermore, the tungsten oxide thin film prepared by the gas flow sputtering method is crystallized by aztepo crystallization by heating the substrate. In addition, an invention was obtained in which good visible light responsive photocatalytic activity was exhibited even in a crystallization process by post-calcination. Although the reason for this has not been clarified at present, it is possible that the tungsten oxide thin film formed by gas flow sputtering has the possibility of forming nanocrystals to serve as crystal nuclei in the subsequent firing process.

  Hereinafter, embodiments of the tungsten oxide thin film of the present invention will be described in detail.

  First, with reference to FIG. 1, the film-forming method by gas flow sputtering employ | adopted by this invention is demonstrated.

  FIG. 1A is a schematic diagram showing a schematic configuration of a gas flow sputtering apparatus suitable for the implementation of the present invention, and FIG. 1B shows a target and back plate configuration of FIG. It is a perspective view.

  In the gas flow sputtering apparatus, a rare gas such as argon is introduced into the chamber 20 from the sputtering gas inlet 11 and is generated by discharge between the anode 13 connected to the power source 12 such as a DC power source and the target 15 serving as the cathode. The target 15 is sputtered by the plasma, and the sputtered particles that have been blown off are transported to the substrate 16 and deposited by a forced flow of a rare gas such as argon. In the illustrated example, the substrate 16 is supported by a holder 17 and a reactive gas inlet 18 is disposed in the vicinity of the substrate 16 so that a reactive sputtering ring can be performed. Reference numeral 14 denotes a water-cooled backing plate.

  In the present invention, a tungsten oxide thin film is formed using such a gas flow sputtering apparatus.

  Formation of the tungsten oxide thin film by gas flow sputtering is performed by reactive sputtering with metal W as a target and oxygen gas being introduced.

  The shape of the target to be used is not particularly limited, and a target having an arbitrary shape such as a cylindrical target or a rectangular plate target can be used. However, since the processing cost is low, a rectangular plate target is used. Is preferably a face-to-face system as shown in FIG. In addition, as shown in FIG. 1, gas flow sputtering is preferably performed by separately introducing oxygen gas and argon gas in terms of high-speed film formation and stable discharge. In this method, the substrate is transported. While forming a film continuously, it is possible to form a film by feeding a sheet-shaped substrate from one roll and winding it on the other roll, and easily increase the film formation efficiency by increasing the target length. Can do.

  As the substrate, a heat resistant substrate is used, and for example, a glass plate, a metal plate, a metal foil, a ceramic plate, or the like can be used. Here, as a metal of a metal plate and a metal foil, Al, Cu, Au, Fe, Ni, etc., or an alloy (for example, SUS) containing these, etc. are mentioned. Examples of ceramics include zirconia, alumina, yttria, silicon carbide, silicon nitride, and the like.

  By performing substrate heating during film formation, the thin film to be formed becomes a crystalline thin film. Here, the heating temperature is preferably 400 to 900 ° C, particularly preferably 500 to 800 ° C. If it is less than 400 ° C., it will not be sufficiently crystallized. When the temperature is higher than 900 ° C., there is a problem that usable substrates are limited and that a heating mechanism with a high cost is required.

  The thin film formed with the non-heated base material is not heated at the time of film formation and is amorphous in the as-deposited state (the state immediately after film formation without post-baking or other post-treatment on the thin film). It is a thin film. By baking the thin film formed with this non-heated substrate, a crystalline thin film is obtained. As the firing conditions, the firing temperature is preferably 400 to 900 ° C, particularly 500 to 800 ° C. If it is less than 400 ° C., it will not be sufficiently crystallized. When the temperature is higher than 900 ° C., there is a problem that usable substrates are limited and that a heating mechanism with a high cost is required.

  Note that an underlayer such as an oxide, nitride, or oxynitride of silicon (Si) may be formed on the base material used for film formation, if necessary.

  If the film formation pressure during gas flow sputtering is too high, the film formation rate decreases, and arcing easily occurs and becomes unstable. If it is too low, the discharge voltage increases and it is difficult to maintain the discharge. It is preferably 200 Pa, particularly 10 to 120 Pa.

Other gas flow sputtering conditions, such as oxygen gas flow rate and argon gas flow rate, input power, target base material distance, etc., vary depending on the device type, so it is not possible to enumerate numerical values. If so, normal power density: 1 to 25 W / cm ²
Argon gas flow rate: 0.5-30 SLM
Oxygen gas flow rate: 5 to 120 sccm
Target substrate distance: 5-15cm
These conditions can be adopted.

  Here, these conditions are set according to the high film formation rate and discharge stability, and the photocatalytic activity of the formed tungsten oxide thin film.

  According to the present invention, high-speed film formation at a film formation speed of 100 nm / min or more is possible. Here, the film formation rate is the value of the thickness of the film grown in one minute.

  The tungsten oxide thin film thus obtained is preferably 10 ppm or more by visible light irradiation for 120 minutes in the acetaldehyde decomposition activity evaluation test listed in the Examples section below, in a state where it is baked after non-heated film formation on the substrate. Indicates a catalytic activity that results in a concentration drop of 15 ppm or more.

  In the state after the substrate heating film formation, in the acetaldehyde decomposition activity evaluation test listed in the example section, the catalytic activity is such that the concentration is reduced by 15 ppm or more, preferably 20 ppm or more by visible light irradiation for 120 minutes. .

Further, as described above, according to the gas flow sputtering film formation, tungsten oxide having very few oxygen defects and close to the stoichiometric ratio can be formed. Therefore, according to the present invention, x is 3 or WO _x A tungsten oxide thin film close to 3 can be formed.

  Such a photocatalytic tungsten oxide thin film of the present invention has a function of deodorizing, water purification, antifouling, self-cleaning (self-cleaning), antibacterial, antiviral, It can be applied to various fields such as antifungal and sterilization.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

  In the following Examples and Comparative Examples, the photocatalytic activity of the formed tungsten oxide thin film was evaluated by examining the decomposition activity of acetaldehyde, for the following reason. That is, hydrophilicity is widely evaluated as a function of the photocatalyst, but even a sample with low photocatalytic activity that cannot decompose acetaldehyde may exhibit superhydrophilicity with a contact angle of 5 degrees or less by irradiation with visible light. Therefore, the photocatalytic activity was evaluated by examining the decomposition activity of acetaldehyde which requires higher photocatalytic activity by the following method.

[Acetaldehyde Degradation Activity Evaluation Method]
A tungsten oxide thin film formed in an area of 25 cm ² in vertical projection area on a 5 cm square alkali-free glass substrate is placed in a sealed quartz glass container with a capacity of 400 cc so that the concentration becomes about 60 ppm in the quartz glass container. Acetaldehyde is filled in and placed in a dark place for about 1 hour before irradiation with visible light, and changes in the acetaldehyde concentration are measured to confirm that there is no leakage of contents. Then, visible light was irradiated and the change of the acetaldehyde concentration with respect to irradiation time was measured. The sample was irradiated with a light intensity of 1.0 mW / cm ² using a xenon lamp having a central wavelength of 450 nm (“LA-250Xe xenon lamp” manufactured by HAYASHI) for visible light irradiation. 1 ml of the gas phase was extracted with a microsyringe and measured using gas chromatography (“GC-14B” manufactured by Shimadzu Corporation).

  For convenience of explanation, a comparative example is given first.

Comparative Example 1
Using an ordinary DC magnetron pulse sputtering system, alkali-free glass is set as a substrate in a vacuum chamber, exhausted to 1 × 10 ⁻¹ Pa with a roughing pump (rotary pump + mechanical booster pump), and then with a turbo molecular pump. After evacuating to 5 × 10 ⁻⁴ Pa, a tungsten oxide thin film was formed in an oxide mode under the following conditions.

・ Target: Metal tungsten of φ75 mm ・ Cathode shape: Circular magnetron, installed facing the substrate in parallel ・ Substrate position: Distance between target and substrate 100 mm
Deposition pressure: 5Pa
Substrate heating temperature: 600 ° C
Oxygen gas flow rate: 100 sccm
Ar gas flow rate: 0sccm
Input power: 180W
Input power density: 4 W / cm ²
Deposition rate: 9 nm / min
Film thickness: 500nm

  The evaluation results of the acetaldehyde decomposition activity of the formed tungsten oxide thin film are shown in FIG.

  As shown in FIG. 2, the formed tungsten oxide thin film showed acetaldehyde decomposition activity, but the film formation rate was 9 nm / min, which was extremely low.

Comparative Example 2
A tungsten oxide thin film was formed in the same manner as in Comparative Example 1 except that the substrate was not heated, and then post-baked at 600 ° C. for 1 hour.

  The evaluation results of the acetaldehyde decomposition activity of the formed tungsten oxide thin film are shown in FIG. From FIG. 3, it was confirmed that the formed tungsten oxide thin film does not show the decomposition activity of acetaldehyde.

Example 1
Using the gas flow sputtering apparatus shown in FIG. 1, after setting alkali-free glass as a substrate in the chamber and exhausting to 1 × 10 ⁻¹ Pa with a roughing pump (rotary pump + mechanical booster pump), the following conditions Then, a tungsten oxide thin film was formed.

-Target: 80 mm x 160 mm x 6 mm W target-Cathode shape: Parallel plate facing type (using two of the above targets, distance 30 mm)
-Substrate position: 105mm distance between cathode end and substrate
Substrate heating temperature: 600 ° C
Deposition pressure: 70 Pa
Oxygen gas (reactive gas) flow rate: 50 sccm
Ar gas (forced flow) flow rate: 5 SLM
Input power: 1.0kW
Input power density: 3.9 W / cm ²
Deposition rate: 220 nm / min
Film thickness: 500nm

  The evaluation results of the acetaldehyde decomposition activity of the formed tungsten oxide thin film are shown in FIG. From FIG. 4, it was confirmed that the formed tungsten oxide thin film showed an acetaldehyde decomposition activity while being deposited at an ultra-high speed of 220 nm / min.

Example 2
A tungsten oxide thin film was formed in the same manner as in Example 1 except that the substrate was not heated. Thereafter, this tungsten oxide thin film was baked in the atmosphere at 600 ° C. for 1 hour.

  The evaluation results of the acetaldehyde decomposition activity of the formed tungsten oxide thin film are shown in FIG. From FIG. 5, it was confirmed that the formed tungsten oxide thin film showed acetaldehyde decomposition activity.

A summary of the results of Comparative Examples 1 and 2 and Examples 1 and 2 (FIGS. 2 to 4) is shown in FIG. From these results, it is possible to form a tungsten oxide thin film at a high speed for the formation of a photocatalytic tungsten oxide thin film by the gas flow sputtering method. It became clear that it has the visible light responsive photocatalytic activity (decomposition activity of acetaldehyde) also by the method. Since the gas flow sputtering method can be configured with inexpensive equipment, the film forming speed is high, and the target utilization efficiency is high, it is possible to produce a photocatalytic thin film at low cost, and WO ₃ is not in TiO ₂ Since it has visible light responsiveness, it is also promising for indoor use.

FIG. 1A is a schematic diagram showing a schematic configuration of a gas flow sputtering apparatus suitable for the implementation of the present invention, and FIG. 1B shows a target and back plate configuration of FIG. It is a perspective view. It is a figure which shows the measurement result of the acetaldehyde decomposition activity of the tungsten oxide thin film formed into a film in the comparative example 1. FIG. It is a figure which shows the measurement result of the acetaldehyde decomposition | disassembly activity of the tungsten oxide thin film formed into a film in the comparative example 2. It is a figure which shows the measurement result of the acetaldehyde decomposition activity of the tungsten oxide thin film formed into a film in Example 1. FIG. It is a figure which shows the measurement result of the acetaldehyde decomposition | disassembly activity of the tungsten oxide thin film formed into a film in Example 2. FIG. It is the figure which put all the measurement results of the acetaldehyde decomposition activity of the tungsten oxide thin film formed into a film in Comparative Examples 1 and 2 and Examples 1 and 2.

Claims (9)

A tungsten oxide thin film formed by gas flow sputtering , which is formed on a heating base material and exhibits photocatalytic activity by as-deposition .   2. The tungsten oxide thin film according to claim 1, wherein the tungsten oxide thin film is formed by reactive sputtering using metal tungsten as a target and introducing oxygen gas. 3. The tungsten oxide thin film according to claim 1 , wherein a glass plate, a metal plate, a metal foil, or a ceramic plate is used as the base material. In any one of claims 1 to 3, the tungsten oxide thin film characterized by deposition pressure in the gas flow sputtering is 5～200Pa. The tungsten oxide thin film according to any one of claims 1 to 4 , wherein the tungsten oxide thin film is formed by gas flow sputtering in which argon gas and oxygen gas are separately introduced. In any one of claims 1 to 5, tungsten oxide thin film characterized by comprising a film-forming gas flow sputtering apparatus having a cathode structure in which the shape that opposed rectangular target. In any one of claims 1 to 6, the tungsten oxide thin film characterized by comprising been deposited with 100 nm / min or more film forming rate by the gas flow sputtering. In any one of claims 1 to 7, the tungsten oxide thin film characterized after film formation due to gas flow sputtering, that formed by firing. The tungsten oxide thin film according to claim 8, wherein the baking condition is 400 to 900 ° C.

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