Material manufacturing method and photocatalyst

Abstract

To manufacture a new material.SOLUTION: In a plasma CVD apparatus having a chamber, a sputtering target that is arranged in the chamber and is composed of a predetermined element, and a plasma discharge part that discharges a plasma flow into the chamber, a manufacturing method of a material includes: a formation step S110 in which a reactive gas containing at least a carbon compound gas is supplied to the chamber, the plasma flow is discharged to the chamber, a carbon nano wall is formed on a substrate arranged in the chamber, and a predetermined element is doped in the carbon nano wall; and a sputtering step S120 in which after the doping step is implemented, a supply of the reactive gas to the chamber is stopped while the discharge of the plasma flow is maintained.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a material manufacturing method and a photocatalyst. [Background technology]

[0002] In recent years, nanostructures such as metal nanorods and metal oxide nanorods have been shown to possess properties that are dramatically improved over conventional materials or that are not available in conventional materials. For this reason, nanostructures are expected to be used as next-generation functional materials, such as electromagnetic wave absorbing materials, battery electrode materials, catalyst materials, semiconductor materials, electron emitter materials, optical materials, and strength reinforcement materials.

[0003] As a method for producing such nanostructures, for example, Patent Document 1 describes a method for producing a catalyst in which a support and an organometallic complex are dispersed in a liquid, and then the organometallic complex is thermally decomposed to precipitate metal particles on the surface of the support, thereby supporting metal particles with a particle size of 1 nm or less on the surface of the support. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-149280 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, nanostructures are expected to be the next generation of functional materials, and therefore there is a demand for the development of new materials including nanostructures.

[0006] The present disclosure aims to provide a material production method capable of producing a novel material, and a photocatalyst. [Means for solving the problem]

[0007] In order to solve the above problems, a material manufacturing method according to one aspect of the present disclosure includes a chamber, a sputtering target provided in the chamber and composed of predetermined elements, and a plasma emission part that emits a plasma flow into the chamber. The plasma that constitutes the plasma flow emitted by the plasma emission part collides with the sputtering target. The plasma CVD apparatus includes a step of supplying a reactive gas containing at least a carbon compound gas into a chamber, discharging a plasma flow into the chamber, and doping the carbon nanowalls with a predetermined element while forming the carbon nanowalls on a substrate disposed in the chamber, and a step of stopping the supply of the reactive gas into the chamber while maintaining the discharge of the plasma flow after the doping step. The specified element has a lower sputtering rate than iron. .

[0008] Furthermore, after the stopping step, the method may further include a step of reducing carbon from the carbon nanowalls doped with the predetermined element. [Effects of the Invention]

[0011] It becomes possible to produce new materials. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flowchart illustrating the process flow of a material manufacturing method according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating a specific configuration of the plasma CVD apparatus. [Figure 3] FIG. 3 is a diagram illustrating a carbon nanowall. [Figure 4] FIG. 4 is a diagram illustrating the material produced in the forming process. [Figure 5] FIG. 5 is a diagram illustrating the material produced by the carbon reduction process. [Figure 6] FIG. 6 is a diagram illustrating the material produced in the second modified example. [Figure 7] FIG. 7 is a diagram showing an SEM image of the first example. [Figure 8] FIG. 8 shows the results of the XPS analysis. [Figure 9] FIG. 9 shows the results of photoelectrochemical measurement using Example A. [Figure 10] FIG. 10 is a diagram showing an SEM image of the second example. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific values ​​shown in the embodiment are merely examples for ease of understanding and do not limit the present disclosure unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant description, and elements not directly related to the present disclosure are not shown.

[0014] [Material manufacturing method] Fig. 1 is a flowchart illustrating the process flow of a material production method according to this embodiment. As shown in Fig. 1, the material production method according to this embodiment includes a formation step S110, a sputtering step S120, and a carbon reduction step S130. The formation step S110, the sputtering step S120, and the carbon reduction step S130 will be described in detail below.

[0015] [Forming process S110] The forming step S110 is a step of forming carbon nanowalls on a substrate using a plasma CVD (Chemical Vapor Deposition) apparatus 100 and doping the carbon nanowalls with a predetermined element (hereinafter referred to as a "dope element").

[0016] 2 is a diagram illustrating a specific configuration of the plasma CVD apparatus 100. As shown in FIG. 2, the plasma CVD apparatus 100 includes a chamber 110, a substrate holder 120, a target holding unit 130, and a plasma gun 140.

[0017] The chamber 110 is formed with a gas supply port 112. A reactive gas and an inert gas are supplied into the chamber 110 through the gas supply port 112. The reactive gas contains at least a carbon compound gas (e.g., methane (CH4)). The reactive gas may contain hydrogen (H2) in addition to the carbon compound gas. The inert gas is, for example, argon (Ar).

[0018] The flow rate of the carbon compound gas supplied into the chamber 110 is, for example, 5 sccm (standard cc / min) or more and 20 sccm or less (e.g., 10 sccm). The flow rate of the hydrogen supplied into the chamber 110 is, for example, 0 sccm or more and 40 sccm or less (e.g., 10 sccm). The flow rate of the inert gas supplied into the chamber 110 is, for example, 60 sccm or more and 90 sccm or less (e.g., 80 sccm).

[0019] A vacuum pump (not shown) is connected to the chamber 110. The vacuum pump maintains the pressure inside the chamber 110 at a predetermined pressure (for example, not less than 3.0E-3 Torr and not more than 8.0E-3 Torr).

[0020] The chamber 110 is also provided with a heater (not shown). The heater maintains the temperature inside the chamber 110 at 450°C or higher and 750°C or lower, preferably 500°C or higher and 650°C or lower. This allows the plasma CVD apparatus 100 to efficiently form carbon nanowalls.

[0021] The substrate holder 120 is provided in the chamber 110. The substrate holder 120 holds a substrate S. The substrate S contains an element that easily forms a carbide, such as silicon (Si), titanium (Ti), tantalum (Ta), zirconium (Zr), or niobium (Nb).

[0022] The target holder 130 is provided in the chamber 110. The target holder 130 holds a sputtering target T. Furthermore, the target holder 130 continuously (always) applies a voltage (DC) to the sputtering target T at a predetermined frequency.

[0023] In this embodiment, the sputtering target T is composed of a metal element having a sputtering rate lower than that of iron. Under argon plasma and an irradiation energy of 600 eV (hereinafter referred to as "sputtering conditions"), the sputtering rate of iron is 1.26. The sputtering target T may be composed of, for example, aluminum (Al, sputtering rate 1.24 under the above sputtering conditions), iridium (Ir, sputtering rate 1.17 under the above sputtering conditions), osmium (Os, sputtering rate 0.95 under the above sputtering conditions), molybdenum (Mo, sputtering rate 0.93 under the above sputtering conditions), rhenium (Re, sputtering rate 0.91 under the above sputtering conditions), hafnium (Hf, sputtering rate 0.83 under the above sputtering conditions), beryllium (Be, sputtering rate 0.94 under the above sputtering conditions), or the like. 0.80), zirconium (Zr, sputtering rate 0.75 under the above sputtering conditions), vanadium (V, sputtering rate 0.70 under the above sputtering conditions), niobium (Nb, sputtering rate 0.65 under the above sputtering conditions), tungsten (W, sputtering rate 0.62 under the above sputtering conditions), tantalum (Ta, sputtering rate 0.62 under the above sputtering conditions), and titanium (Ti, sputtering rate 0.58 under the above sputtering conditions), or an alloy of multiple metal elements.

[0024] The plasma gun 140 (plasma emission unit) emits a plasma flow PF into the chamber 110. The plasma gun 140 can utilize various existing technologies (for example, Japanese Patent Application Laid-Open No. 2008-056546), and therefore detailed description thereof will be omitted here. When the plasma gun 140 emits the plasma flow PF, the plasma constituting the plasma flow PF decomposes the reactive gas and collides with the sputtering target T. As a result, carbon nanowalls are formed on the substrate S, and the atoms constituting the sputtering target T are emitted (sputtered) from the sputtering target T and doped into the carbon nanowalls.

[0025] Three processing patterns that can be performed in the forming step S110 will be described below.

[0026] [First processing pattern of forming step S110] In the first processing pattern, first, the substrate S is held by the substrate holder 120, and a reactive gas is supplied into the chamber 110 through the gas supply port 112. Then, the plasma gun 140 is driven simultaneously with the application of a voltage to the sputtering target T by the target holder 130. In other words, the doping of the doping element into the carbon nanowalls is carried out simultaneously with the start of the formation of the carbon nanowalls on the substrate S. As a result, the carbon nanowalls doped with the doping element are formed on the substrate S.

[0027] Fig. 3 is a diagram illustrating a carbon nanowall. Fig. 3A is a first diagram illustrating a carbon nanowall. Fig. 3B is a second diagram illustrating a carbon nanowall. Fig. 3C is a third diagram illustrating a carbon nanowall. Fig. 3D is a fourth diagram illustrating a carbon nanowall. In Fig. 3B and Fig. 3D of this embodiment, the X-axis, Y-axis, and Z-axis, which intersect perpendicularly, are defined as shown in the figures.

[0028] Carbon nanowalls are graphene sheets (carbon atoms (C) are indicated by white circles in FIG. 3A) as shown in FIG. 3A, which are erected (grown vertically) on the surface of a substrate S as shown in FIG. 3B. When carbon nanowalls are formed on a substrate S, a graphite layer or an amorphous carbon layer is first formed on the surface of the substrate S as shown in FIGS. 3C and 3D. The graphite layer or amorphous carbon layer is formed on the surface of the substrate S along the in-plane direction of the surface of the substrate S. For example, the graphite layer or amorphous carbon layer is formed on the surface of the substrate S parallel to the in-plane direction of the surface of the substrate S.

[0029] A plurality of carbon nanowalls are formed so as to extend (stretch) in a direction perpendicular to the surface of the substrate S (Y-axis direction in Figures 3B and 3D) via a graphite layer or amorphous carbon layer. Here, the thickness of the carbon nanowalls in a direction parallel to the substrate S (X-axis direction in Figure 3B) is 1 nm or more and 100 nm or less. The distance between the carbon nanowalls in the X-axis direction in Figure 3B is 1 nm or more and 10 μm or less.

[0030] Carbon nanowalls have a self-organizing function. Therefore, simply by generating plasma in a reactive gas atmosphere in the plasma CVD apparatus 100, the carbon nanowalls grow so as to extend in a direction perpendicular to the surface of the substrate S (the Y-axis direction in Figures 3B and 3D), while forming nanometer-sized voids (gaps) between them. Here, nanometer size refers to 1 nm or more and 10 μm or less.

[0031] In the first processing pattern, the carbon nanowalls are doped with a doping element simultaneously with the start of the formation of the carbon nanowalls on the substrate S.

[0032] 4A and 4B are diagrams illustrating the material 200 produced in the forming step S110 of a first processing pattern. FIG. 4B is a diagram illustrating the material 200 produced in the forming step S110 of a second processing pattern. FIG. 4C is a diagram illustrating the material 200 produced in the forming step S110 of a third processing pattern. In addition, in FIGS. 4A, 4B, and 4C of this embodiment, the X-axis, Y-axis, and Z-axis, which intersect perpendicularly, are defined as shown.

[0033] As shown in FIG. 4A, the material 200 (hereinafter referred to as material 200A) produced by the first processing pattern includes a substrate S, an underlayer 210, and a CNW layer 220. The underlayer 210 is a layer formed along the in-plane direction of the surface of the substrate S. The underlayer 210 is made of graphite doped with a doping element (or amorphous carbon doped with a doping element). The CNW layer 220 is made of a plurality of doped-element-containing carbon nanowalls 222. The doped-element-containing carbon nanowalls 222 are carbon nanowalls doped with a doping element. The doped-element-containing carbon nanowalls 222 extend from the underlayer 210 in a direction perpendicular to the surface (in-plane direction) of the substrate S (the Y-axis direction in FIG. 4A). In the CNW layer 220, the doped carbon nanowalls 222 extend from the underlayer 210, with nanometer-sized gaps 222a maintained between adjacent doped carbon nanowalls 222.

[0034] By performing the forming step S110 with the first processing pattern, it is possible to dope the doping element not only into the CNW layer 220 but also into the underlayer 210. This causes the elements constituting the substrate S to bond with the doping element, making it possible to strengthen the bond between the underlayer 210 (CNW layer 220) and the substrate S. For example, if a silicon substrate is used as the substrate S and titanium is used as the doping element, the result is Ti-Si, which can strengthen the bond between the CNW layer 220 (underlayer 210) and the substrate S.

[0035] In this way, a material 200A is produced, which comprises an underlayer 210 (thin film) and a plurality of doping element-containing carbon nanowalls 222 standing upright from the underlayer 210, each having a thickness of 1 nm or more and 10 nm or less and spaced apart from each other by a distance of 50 nm or more and 1 μm or less.

[0036] The execution time of the formation process S110, i.e., the supply time of the reactive gas, the driving time of the plasma gun 140, and the application time of the voltage to the sputtering target T, is from 3 minutes to 24 hours, preferably from 10 minutes to 360 minutes.

[0037] If the execution time of the forming step S110 is less than 3 minutes, the doping element-containing carbon nanowalls 222 are not formed. If the execution time of the forming step S110 is more than 24 hours, it takes an unnecessary amount of time.

[0038] Therefore, the plasma CVD apparatus 100 can efficiently form the doping element-containing carbon nanowalls 222 by setting the execution time of the forming step S110 to 3 minutes or more and 24 hours or less.

[0039] [Second processing pattern of forming step S110] First, the substrate S is held by the substrate holder 120. Then, in the second processing pattern, a reactive gas is supplied into the chamber 110 through the gas supply port 112, and the plasma gun 140 is driven without applying a voltage to the sputtering target T. After a first predetermined time has elapsed since the start of driving the plasma gun 140, the application of a voltage to the sputtering target T is started to perform sputtering. That is, after the start of formation of carbon nanowalls on the substrate S, the carbon nanowalls are doped with a doping element after the first predetermined time has elapsed. Here, the first predetermined time is the time it takes for a graphite layer or an amorphous carbon layer to be formed on the substrate S, and is the time until the carbon nanowalls are formed. Then, carbon nanowalls doped with the doping element are formed on the substrate S, specifically, on the graphite layer (or amorphous carbon layer).

[0040] 4B, the material 200 (hereinafter referred to as material 200B) manufactured by the second processing pattern includes a substrate S, an underlayer 230, and a CNW layer 220. The underlayer 230 is a layer formed along the in-plane direction of the surface of the substrate S. Unlike the material 200A, the underlayer 230 is made of graphite (or amorphous carbon) that does not contain any doping elements.

[0041] By performing the forming step S110 with the second processing pattern, it is possible to manufacture a material 200B in which only the carbon nanowalls are doped with the doping element.

[0042] [Third Processing Pattern of Forming Step S110] First, the substrate S is held by the substrate holder 120. Then, a reactive gas is supplied into the chamber 110 through the gas supply port 112, and the plasma gun 140 is driven without applying a voltage to the sputtering target T. In the third processing pattern, after a second predetermined time has elapsed since the plasma gun 140 started to be driven, the application of a voltage to the sputtering target T is started to perform sputtering. That is, after the formation of carbon nanowalls on the substrate S has started, the doping of the doping element into the carbon nanowalls is performed after a second predetermined time has elapsed. Here, the second predetermined time is a predetermined time after the formation of carbon nanowalls on the substrate S has started. Then, carbon nanowalls doped with the doping element are formed on the carbon nanowalls.

[0043] Specifically, as shown in FIG. 4C, material 200 (hereinafter referred to as material 200C) manufactured by the third processing pattern includes substrate S, underlayer 230, and CNW layer 240. Unlike CNW layer 220 of materials 200A and 200B, CNW layer 240 is partially (i.e., tip portion) composed of carbon nanowalls 242 doped with a doping element. Specifically, as shown in FIG. 4C, carbon nanowalls 242 are not doped with a doping element from their base end (the end on the underlayer 230 side) to a predetermined position, but are doped with a doping element from the predetermined position to their tip. CNW layer 240 includes first layer 244 and second layer 246. First layer 244 is formed on underlayer 230. First layer 244 is composed of carbon nanowalls 244a that do not contain a doping element. Second layer 246 is formed on first layer 244. The second layer 246 is continuous with the first layer 244. The second layer 246 is made up of doping element-containing carbon nanowalls 246a. The doping element-containing carbon nanowalls 246a are carbon nanowalls doped with a doping element.

[0044] Similar to the material 200B, the carbon nanowalls 242 extend from the base layer 230 in a direction (Y-axis direction in FIG. 4C) perpendicular to the surface (in-plane direction) of the substrate S. In the CNW layer 240, the carbon nanowalls 242 extend from the base layer 230 while maintaining nanometer-sized gaps 242a.

[0045] By performing the forming step S110 with the third processing pattern, it is possible to manufacture a material 200C in which only a portion of the carbon nanowalls is doped with the doping element.

[0046] [Sputtering process S120] The sputtering step S120 is a step of stopping the supply of the reactive gas into the chamber 110 after the formation step S110 is performed, while maintaining the emission of the plasma flow (driving the plasma gun 140) and the application of a voltage to the sputtering target T. Note that in the sputtering step S120, a pulse voltage is applied to the sputtering target T.

[0047] By performing the sputtering step S120, the portion of the material 200 containing the doping element can be further doped with the doping element. For example, in the material 200A produced by the first processing pattern, the underlayer 210 and the doping-element-containing carbon nanowalls 222 are further doped with the doping element. In the material 200B produced by the second processing pattern, the doping-element-containing carbon nanowalls 222 are further doped with the doping element, while the underlayer 230 is hardly doped with the doping element. In the material 200C produced by the third processing pattern, the second layer 246 (the doping-element-containing carbon nanowalls 246a) is further doped with the doping element, while the underlayer 230 and the first layer 244 (the carbon nanowalls 244a) are hardly doped with the doping element.

[0048] That is, the carbon nanowalls, graphite, or amorphous carbon doped with the doping element in the formation step S110 are further doped with the doping element by performing the sputtering step S120. On the other hand, the carbon nanowalls, graphite, or amorphous carbon not doped with the doping element in the formation step S110 are not doped with the doping element even when the sputtering step S120 is performed.

[0049] The execution time of the sputtering process S120, i.e., the driving time of the plasma gun 140 and the application time of voltage to the sputtering target T, is 4 minutes or more and 200 minutes or less when the doping element is titanium, and preferably 5 minutes or more and 60 minutes or less.

[0050] If the sputtering step S120 is performed for less than 4 minutes, further doping of the carbon nanowalls, graphite, or amorphous carbon doped with the doping element will be insufficient, and in this case, when the carbon reduction step S130 described below is performed, metal oxide nanowalls will not be formed.

[0051] On the other hand, when the sputtering step S120 is performed for more than 200 minutes, the gaps 222a between the doping-element-containing carbon nanowalls 222 or the gaps 242a between the doping-element-containing carbon nanowalls 246a are filled with the doping element, and in this case, when the carbon reduction step S130 is performed, the metal oxide nanowalls separated from each other are not formed.

[0052] Therefore, by setting the execution time of the sputtering process S120 to be between 4 minutes and 200 minutes, the plasma CVD apparatus 100 is able to produce metal oxide nanowalls that are spaced apart from each other when the carbon reduction process S130 is carried out.

[0053] When the doping element is an element other than titanium, the execution time of the sputtering step S120 is equal to or longer than the time Tmin (minutes) calculated from the following formula (1) and equal to or shorter than the time Tmax (minutes) calculated from the following formula (2). Tmin={4×(SRFe-SRX)} / (SRFe-SRTi) …Equation (1) Tmax={200×(SRFe-SRX)} / (SRFe-SRTi) …Equation (2) In the above formulas (1) and (2), SRFe is the sputtering rate of iron (i.e., the sputtering rate of 1.26 under the above sputtering conditions). SRTi is the sputtering rate of titanium (i.e., the sputtering rate of 0.58 under the above sputtering conditions). SRX is the sputtering rate of a doping element other than titanium (the sputtering rate under the above sputtering conditions). For example, if the doping element is aluminum, SRX is 1.24.

[0054] Furthermore, the temperature inside the chamber 110 in the sputtering step S120 is maintained at 25° C. or higher and 750° C. or lower, preferably 500° C. or higher and 650° C. or lower. This allows the plasma CVD apparatus 100 to efficiently further dope the carbon nanowalls, graphite, or amorphous carbon that has already been doped with the doping element.

[0055] The pressure inside the chamber 110 in the sputtering step S120 is substantially the same as that in the forming step S110. In addition, in the sputtering step S120, no reactive gas is supplied to the inside of the chamber 110, but an inert gas is supplied. The flow rate of argon supplied into the chamber 110 is substantially the same as that in the forming step S110.

[0056] [Carbon reduction process S130] The carbon reduction step S130 is a step of reducing carbon from carbon nanowalls, graphite, or amorphous carbon doped with a doping element. In this embodiment, the carbon reduction step S130 is a step of heating the material 200 in a predetermined atmosphere. Here, the predetermined atmosphere is an atmosphere containing at least oxygen (oxidizing atmosphere), such as air.

[0057] Furthermore, the pressure of the atmosphere in the carbon reduction step S130 is equal to or higher than atmospheric pressure, which can improve the efficiency of desorption (reduction efficiency) of carbon from the material 200.

[0058] Furthermore, the temperature of the atmosphere in the carbon reduction step S130 (hereinafter referred to as "atmospheric temperature") is 400°C or higher and 1400°C or lower, and preferably 400°C or higher and 750°C or lower. If the atmospheric temperature is lower than 400°C, carbon cannot be removed from the material 200. On the other hand, if the atmospheric temperature is higher than 1400°C, the structures (CNW layer 220, CNW layer 240) cannot maintain their nanostructure.

[0059] The carbon reduction step S130 is performed for a period of 10 minutes to 24 hours, preferably 6 minutes to 1200°C. When the carbon reduction step S130 is performed for less than 10 minutes, carbon cannot be sufficiently removed, and the doping element cannot be sufficiently oxidized. On the other hand, when the carbon reduction step S130 is performed for more than 24 hours, the carbon removal rate and the doping element oxidation rate hardly increase compared to when the carbon reduction step S130 is performed for 24 hours. For example, when the doping element is titanium, there is almost no difference in IPCE (photoelectric conversion efficiency) between when the carbon reduction step S130 is performed for a period of 10 minutes to 24 hours and when the carbon reduction step S130 is performed for more than 24 hours.

[0060] By performing the carbon reduction step S130, carbon can be removed from the material 200 (carbon in the material 200 can be reduced).

[0061] 5 is a diagram illustrating the material 300 produced in the carbon reduction step S130. In FIG. 5 of this embodiment, the X-axis, Y-axis, and Z-axis, which intersect perpendicularly, are defined as shown in the figure.

[0062] When the carbon reduction process S130 is performed on the material 200A produced in the first processing pattern formation process S110, a material 300 (hereinafter referred to as material 300A) including a substrate S, an underlayer 310, and a nanostructure layer 320 is produced, as shown in Figure 5.

[0063] The underlayer 310 is a layer (thin film) obtained by removing carbon from the underlayer 210. Therefore, the underlayer 310 is made of an oxide of a doping element (metal oxide), and is a layer formed along the in-plane direction of the surface of the substrate S.

[0064] The nanostructure layer 320 is a layer in which carbon has been removed from the CNW layer 220. Therefore, the nanostructure layer 320 is a layer composed of structures 322, in which an oxide (metal oxide) of a doping element is configured in the shape of a nanowall. That is, the structures 322 are made of metal oxide in the shape of a carbon nanowall. Specifically, the nanostructure layer 320 includes a plurality of structures 322 extending (standing) in a direction perpendicular to the surface of the substrate S (the Y-axis direction in FIG. 5). The thickness of the structures 322 in a direction parallel to the substrate S (the X-axis direction in FIG. 5) is 1 nm to 1 μm (e.g., 1 nm to 10 nm), and the distance between the structures 322 (gaps 322a) in the X-axis direction in FIG. 5 is 50 nm to 1 μm.

[0065] Furthermore, as described above, in the material 200A, the elements constituting the substrate S are bonded to the doped elements of the underlayer 210. Therefore, even when the carbon reduction step S130 is performed, the bond between the underlayer 310 and the substrate S is maintained. In other words, the material 300A is a bond between the underlayer 310 (nanostructure layer 320) and the substrate S.

[0066] In this way, a material 300A is produced that includes an underlayer 310 (thin film) and a plurality of structures 322 standing upright on the underlayer 310, each having a thickness of 1 nm or more and 10 nm or less and spaced apart from each other by a distance of 50 nm or more and 1 μm or less.

[0067] Furthermore, in the carbon reduction step S130, the carbon reduction rate can be adjusted by controlling the atmospheric temperature, atmospheric pressure, and heating time. That is, in the carbon reduction step S130, by controlling the atmospheric temperature, atmospheric pressure, and heating time, it is possible to remove all of the carbon from the material 200, or to remove a portion (a predetermined amount) of the carbon from the material 200.

[0068] The material 300A thus produced can be used as a photocatalyst. That is, by performing the formation step S110, the sputtering step S120, and the carbon reduction step S130, a photocatalyst (material 300A) having nanowall-shaped structures 322 containing at least a metal oxide is produced.

[0069] As described above, the material production method according to this embodiment can produce a novel material, for example, a metal oxide in a nanowall shape (metal oxide nanowall).

[0070] Furthermore, the material production method according to this embodiment includes a sputtering step S120 in addition to the formation step S110. Metal elements have catalytic properties. Therefore, when doping with a metal element having a sputtering rate lower than that of iron, performing the formation step S110 and the carbon reduction step S130 without performing the sputtering step S120 does not allow nanowall-shaped metal oxide to be produced. Therefore, when doping with a metal element having a sputtering rate lower than that of iron, the sputtering step S120 is performed in addition to the formation step S110. This makes it possible to produce nanowall-shaped metal oxide even when using a metal element having a sputtering rate lower than that of iron.

[0071] [First Modification] In the above embodiment, the carbon reduction step S130 is described as heating the material 200 in an oxidizing atmosphere. However, the carbon reduction step S130 may be any step as long as it can reduce carbon from carbon nanowalls, graphite, or amorphous carbon doped with a doping element.

[0072] For example, the carbon reduction step S130 may be a step of heating the material 200 in a reducing atmosphere. In this case, a material can be produced that includes a base layer made of a doping element (metal) and formed along the in-plane direction of the surface of the substrate S, and a nanostructure layer made of a structure in which the doping element (metal) is configured in a nanowall shape. Also, a structure in which the doping element (metal) is configured in a nanowall shape (nanowall-shaped metal) can be produced.

[0073] The nanowall-shaped metal structures thus produced can be used in sensors, imaging devices, optical devices, etc. that utilize the surface plasmon effect.

[0074] [Second Modification] In the above embodiment and the first modified example, the carbon reduction step S130 is described as heating the material 200 in a predetermined atmosphere. However, the carbon reduction step S130 may be any step as long as it can reduce carbon from carbon nanowalls, graphite, or amorphous carbon doped with a doping element.

[0075] For example, the carbon reduction step S130 may be a step of exposing the material 200 to a predetermined plasma atmosphere. Here, the predetermined plasma atmosphere is, for example, hydrogen (H2) plasma, nitrogen (N2) plasma, or oxygen plasma.

[0076] The pressure of the plasma atmosphere is 10 Pa or more and 100 Pa or less (similar to the degree of vacuum in ECR plasma processing or RF plasma processing).

[0077] Furthermore, the temperature of the plasma atmosphere (hereinafter referred to as "plasma atmosphere temperature") is from room temperature (e.g., 25°C) to 800°C, preferably from 500°C to 700°C, and more preferably 600°C. If the plasma atmosphere temperature is below room temperature, carbon cannot be removed from the material 200. If the plasma atmosphere temperature exceeds 800°C, the structures (CNW layer 220, CNW layer 240) cannot maintain their nanostructures.

[0078] By exposing the material 200 to the plasma atmosphere, carbon can be removed from the material 200. When exposing the material 200 to the plasma atmosphere, it is advisable to perform oxygen plasma treatment from the opposite side of the substrate S, i.e., from the tip end side of the CNW layer 220 and the tip end side of the second layer 246. This allows the carbon to be oxidized from the tip end side of the CNW layer 220 and the tip end side of the second layer 246.

[0079] Figure 6 is a diagram illustrating a material 300 produced according to a second modified example. Figure 6A is a first diagram illustrating the material 300 produced according to the second modified example. Figure 6B is a second diagram illustrating the material 300 produced according to the second modified example. In Figures 6A and 6B of this embodiment, the X-axis, Y-axis, and Z-axis, which intersect perpendicularly, are defined as shown in the figures.

[0080] When the material 200B produced in the second processing pattern formation process S110 is exposed to a plasma atmosphere, a material 300 (hereinafter referred to as material 300B) including a substrate S, an underlayer 230, and a nanostructure layer 320 is produced, as shown in FIG. 6A.

[0081] Furthermore, when the material 200C produced in the third processing pattern formation process S110 is exposed to a plasma atmosphere, a material 300 (hereinafter referred to as material 300C) including a substrate S, an underlayer 230, and a nanostructure layer 340 is produced, as shown in Figure 6B.

[0082] The nanostructure layer 340 is a layer in which carbon has been removed from the CNW layer 240. The nanostructure layer 340 includes a plurality of structures 342 extending (standing) in a direction perpendicular to the surface of the substrate S (the Y-axis direction in FIG. 6B). The thickness of the structures 342 in a direction parallel to the substrate S (the X-axis direction in FIG. 6B) is 1 nm or more and 10 nm or less, and the distance between the structures 342 (gaps 342a) in the X-axis direction in FIG. 6B is 50 nm or more and 1 μm or less.

[0083] Specifically, the nanostructure layer 340 is a layer made up of nanowall-shaped structures 342, part of which (tip end) is made of a doped element (metal) and the other part (base end) is made of carbon nanowalls 244a. In other words, the nanostructure layer 340 is made up of a first layer 244 and a second layer 346. The second layer 346 includes nanowall-shaped structures 346a made of the doped element.

[0084] The material 300C manufactured in this manner can be used as a device. Specifically, when the second layer 346 is irradiated with light, the structures 346a are excited and emit electrons. The emitted electrons then flow to the base layer 230 via the first layer 244 (carbon nanowalls 244a). Therefore, the material 300C can be used as a device that detects light.

[0085] Material 300C can also be used as a photoanode in devices that generate hydrogen by water splitting (e.g., Ji-Wook Jang et al., Enabling unassisted solar water splitting by iron oxide and silicon, Nature Communications 6 (2015)).

[0086] Furthermore, the carbon reduction rate can be adjusted by controlling the plasma ambient temperature, plasma ambient pressure, and plasma treatment time. That is, by controlling the plasma ambient temperature, plasma ambient pressure, and plasma treatment time, it is possible to remove all carbon from the material 200, or to remove a portion (a predetermined amount) of carbon from the material 200.

[0087] [First Example] A silicon substrate was used as the substrate S, and titanium was used as the doping element, and the material was produced using a plasma CVD apparatus 100.

[0088] In Example A, the formation process S110 was performed for 360 minutes, the sputtering process S120 for 30 minutes, and the carbon reduction process S130 (in the air atmosphere) for 1 hour. In Example A, the temperature inside the chamber 110 in the formation process S110 and the sputtering process S120 was 600°C, and the ambient temperature in the carbon reduction process S130 (in the air atmosphere) was 500°C.

[0089] In the comparative example, the formation step S110 was performed for 360 minutes, the sputtering step S120 was not performed, and the carbon reduction step S130 (in the air atmosphere) was performed for 1 hour. In addition, in the comparative example, the temperature inside the chamber 110 in the formation step S110 was set to 600°C, and the ambient temperature in the carbon reduction step S130 (in the air atmosphere) was set to 500°C.

[0090] The material was then observed with a scanning electron microscope (SEM) after the sputtering step S120 in Example A but before the carbon reduction step S130, after the carbon reduction step S130 in Example A, after the formation step S110 in the comparative example but before the carbon reduction step S130, and after the carbon reduction step S130 in the comparative example.

[0091] Fig. 7 shows SEM images of Example 1. Fig. 7A shows an SEM image after the sputtering step S120 and before the carbon reduction step S130 in Example A. Fig. 7B shows an SEM image after the carbon reduction step S130 in Example A. Fig. 7C shows an SEM image after the formation step S110 and before the carbon reduction step S130 in the comparative example. Fig. 7D shows an SEM image after the carbon reduction step S130 in the comparative example.

[0092] As shown in Figure 7A, titanium-doped carbon nanowalls were observed after the sputtering step S120 and before the carbon reduction step S130 in Example A. Furthermore, as shown in Figure 7B, nanowall-shaped titanium oxide (TiO2) was observed after the carbon reduction step S130 in Example A.

[0093] On the other hand, as shown in Figure 7C, in the comparative example, titanium-doped carbon nanowalls were confirmed after the formation step S110 and before the carbon reduction step S130. However, as shown in Figure 7D, in the comparative example, no nanowall-shaped titanium oxide was confirmed after the carbon reduction step S130.

[0094] Therefore, it was confirmed that by performing the sputtering step S120 in addition to the formation step S110, the titanium is reinforced and nanowall-shaped titanium oxide can be produced after the carbon reduction step S130. In other words, it was confirmed that by performing only the formation step S110 without performing the sputtering step S120, nanowall-shaped titanium oxide cannot be produced after the carbon reduction step S130.

[0095] Furthermore, the material after the carbon reduction step S130 in Example A was analyzed by XPS (X-ray photoelectron spectroscopy) and Raman spectroscopy.

[0096] FIG. 8 shows the results of analysis by XPS. In FIG. 8, the horizontal axis represents the sputtering depth [nm] in the XPS analysis. In FIG. 8, the vertical axis represents the atomic content [AT% (atomic %)]. In FIG. 8, squares represent oxygen (O). In FIG. 8, triangles represent titanium (Ti). In FIG. 8, circles represent carbon (C).

[0097] As shown in FIG. 8, it was confirmed that the material produced in Example A contained titanium and oxygen throughout the entire depth of the structure, and contained almost no carbon.

[0098] Furthermore, as a result of evaluation of the crystal structure by Raman spectroscopy, it was confirmed that titanium oxide having an anatase structure was produced in Example A.

[0099] Photoelectrochemical measurements were also performed using Example A. Specifically, experiments were performed using a three-electrode electrochemical measurement cell that utilized an FTO (fluorine-doped tin) film with Example A attached as the counter electrode. A platinum wire was used as the working electrode of the three-electrode electrochemical measurement cell. A 0.1 M aqueous sodium sulfate solution (pH 6.4) was used as the electrolyte. The potential was scanned at 20 mV / s.

[0100] Then, ultraviolet (UV) light with a wavelength of 254 nm and a light intensity of 0.83 mW / cm 2 was turned on and off to measure the current flowing between the working electrode and the counter electrode.

[0101] Fig. 9 shows the results of photoelectrochemical measurement using Example A. In Fig. 9, the horizontal axis represents the voltage value [V] relative to the reference electrode, and the vertical axis represents the current density [µA / cm2].

[0102] As shown in Figure 9, when UV light was not irradiated, the current density was 0 [μA / cm2], meaning that no current flowed. On the other hand, when UV light was irradiated, the current density exceeded 0 [μA / cm2], meaning that current flowed.

[0103] From the above results, it was confirmed that the nanowall-shaped titanium oxide produced in Example A functions as a photocatalyst.

[0104] [Second Example] A silicon substrate was used as the substrate S, and titanium was used as the doping element, and the material was produced using a plasma CVD apparatus 100.

[0105] In Example B, the formation step S110 was performed for 10 minutes, the sputtering step S120 for 5 minutes, and the carbon reduction step S130 (in the air atmosphere) for 60 minutes. In Example B, the temperature inside the chamber 110 in the formation step S110 and the sputtering step S120 was 650°C, and the ambient temperature in the carbon reduction step S130 (in the air atmosphere) was 500°C.

[0106] In Example C, the formation step S110 was performed for 60 minutes, the sputtering step S120 was performed for 60 minutes, and the carbon reduction step S130 (in the air atmosphere) was performed for 60 minutes. In Example C, the temperature inside the chamber 110 in the formation step S110 and the sputtering step S120 was set to 500°C, and the ambient temperature in the carbon reduction step S130 (in the air atmosphere) was set to 500°C.

[0107] In Example D, the formation step S110 was performed for 360 minutes, the sputtering step S120 for 30 minutes, and the carbon reduction step S130 (in the air atmosphere) for 60 minutes. In Example D, the temperature inside the chamber 110 in the formation step S110 and the sputtering step S120 was set to 600°C, and the ambient temperature in the carbon reduction step S130 (in the air atmosphere) was set to 600°C.

[0108] In the forming step S110 of Examples B to D, the flow rates of methane, hydrogen, and argon supplied into the chamber 110 were set to 10 sccm, 10 sccm, and 80 sccm, respectively.

[0109] The materials produced in Examples B to D were then observed with a scanning electron microscope (SEM).

[0110] Fig. 10 shows SEM images of Example 2. Fig. 10A shows SEM images of Example B. Fig. 10B shows SEM images of Example C. Fig. 10C shows SEM images of Example D.

[0111] As shown in FIGS. 10A to 10C, it was confirmed that in all of Examples B to D, nanowall-shaped titanium oxide (TiO2) could be produced.

[0112] [Third Example] A silicon substrate was used as the substrate S, titanium was used as the doping element, and the material was manufactured using a plasma CVD apparatus 100. In the third example, the execution time of the formation step S110 was set to 30 minutes, the execution time of the sputtering step S120 was set to 360 minutes, and the execution time of the carbon reduction step S130 (in the air atmosphere) was set to 1 hour or 10 hours.

[0113] In the third example, the crystal structure of titanium oxide depending on the ambient temperature in the carbon reduction step S130 (in the air atmosphere) was analyzed using Raman spectroscopy.

[0114] It was confirmed that when the atmospheric temperature of the carbon reduction step S130 was 400°C or higher and 450°C or lower and the execution time was 1 hour, the structure contained titanium oxide and graphite with an anatase structure. In other words, it was confirmed that carbon nanowalls containing titanium oxide could be produced by performing the carbon reduction step S130 (in air) at an atmospheric temperature of 400°C or higher and 450°C or lower.

[0115] Furthermore, it was confirmed that when the atmospheric temperature in the carbon reduction step S130 was between 600°C and 750°C and the execution time was 10 hours, the structure contained titanium oxide with both anatase and rutile structures. In other words, it was confirmed that by performing the carbon reduction step S130 (in air) at an atmospheric temperature between 600°C and 750°C, it was possible to produce carbon-free nanowall-shaped titanium oxide. It was also confirmed that the higher the atmospheric temperature, the less titanium oxide with anatase structure there was and the more titanium oxide with rutile structure there was.

[0116] Although the embodiments have been described above with reference to the accompanying drawings, it goes without saying that the present disclosure is not limited to such embodiments. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that such modifications also fall within the technical scope.

[0117] For example, in the above-described embodiment, the doping element is a metal element having a sputtering rate lower than that of iron. However, the doping element may be a nonmetallic element (including a semimetallic element) having a sputtering rate lower than that of iron. For example, the doping element may be either or both of silicon (Si) and germanium (Ge). In this case, a nanowall-shaped structure composed of a nonmetallic element is manufactured.

[0118] The doping element may also be an element (metal element or nonmetal element) having a sputtering rate equal to or higher than that of iron.

[0119] The doping element may be two or more metal elements. In this case, a nanowall-shaped structure composed of an alloy containing two or more metal elements is produced. The doping element may be a metal element and a nonmetal element. In this case, a nanowall-shaped structure containing a metal element and a nonmetal element is produced.

[0120] In the above embodiment, the structure 322 is vertically erected from the surface of the substrate S. However, the structure 322 may be erected from the substrate S, and there is no limitation on the angle.

[0121] In the above embodiment, a configuration in which carbon is completely removed in the carbon reduction step S130 has been described as an example. However, a desired amount of carbon may be left behind in the carbon reduction step S130. Note that if the carbon reduction step S130 is performed to completely remove carbon from materials 200B and 200C, only nanowall-shaped structures 322 are produced. Furthermore, if the carbon reduction step S130 is performed to leave some carbon remaining in materials 200B and 200C, materials with less carbon than materials 200B and 200C are produced.

[0122] In the above embodiment, the carbon reduction step S130 is performed as an example. However, the carbon reduction step S130 is not an essential step. By performing the formation step S110 and the sputtering step S120, novel materials 200A, 200B, and 200C can be manufactured.

[0123] In the above embodiment, an example was given of manufacturing a structure 322 composed of a nanowall-shaped metal oxide. However, the nanowall-shaped structure may contain an additive in addition to the metal oxide. The additive is any one or more of all elements except hydrogen (H), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). When the nanowall-shaped structure contains an additive in addition to the metal oxide, the photocatalytic function can be improved.

[0124] Furthermore, in the above embodiment, the target holding unit 130 constantly applies a voltage in the forming step S110 and applies a pulse voltage in the sputtering step S120. However, the target holding unit 130 may constantly apply a voltage in the forming step S110 and the sputtering step S120, may apply a pulse voltage in the forming step S110 and the sputtering step S120, or may apply a pulse voltage in the forming step S110 and the sputtering step S120, or may constantly apply a voltage in the forming step S110 and the sputtering step S120.

[0125] This disclosure can contribute, for example, to Sustainable Development Goal (SDG) 6, "Ensure access to water and sanitation for all," and SDG 7, "Ensure access to affordable, reliable, sustainable and modern energy." [Explanation of symbols]

[0126] T Sputtering Target S110 Forming process S120 sputtering process S130 Carbon Reduction Process 100 Plasma CVD equipment 110 Chamber 140 Plasma gun (plasma emission part) 300A Material (Photocatalyst) 322 Structure

Claims

1. In a plasma CVD apparatus having a chamber, a sputtering target provided in the chamber and composed of a predetermined element, and a plasma discharger for discharging a plasma flow into the chamber, wherein the plasma constituting the plasma flow discharged by the plasma discharger collides with the sputtering target, the apparatus comprises: supplying a reactive gas containing at least a carbon compound gas into the chamber; discharging the plasma flow into the chamber; and doping the carbon nanowalls with the predetermined element while forming carbon nanowalls on a substrate provided in the chamber; After performing the doping step, stopping the supply of the reaction gas into the chamber while maintaining the emission of the plasma flow; Including, A material manufacturing method, wherein the predetermined element is an element having a lower sputtering rate than iron.

2. The method for producing a material according to claim 1 , further comprising the step of reducing carbon from the carbon nanowalls doped with the predetermined element after the step of stopping.

Images