Diamond formation device and diamond-coated substrate

Abstract

One embodiment of the present invention provides a diamond formation device that comprises a reaction vessel and an electrode unit. The reaction vessel holds: a starting material liquid that includes a carbon source; and a substrate that is provided in the starting material liquid. The electrode unit can generate plasma in the starting material liquid, and the substrate has at least one recess in a principal surface that is opposite the electrode unit. Another embodiment of the present invention provides a diamond-coated substrate that comprises: a substrate that has at least one recess in a principal surface; and diamond that is directly formed on the principal surface of the substrate.

Description

Diamond-forming device and diamond-coated substrate

[0001] The present invention relates to a diamond-forming device and a diamond-coated substrate.

[0002] Gas phase synthesis has long been known as a method for forming diamond. Among the gas phase synthesis methods, there is a plasma method using plasma, and one of these methods has been proposed, which is a "submerged plasma chemical vapor deposition method" in which plasma is generated in a liquid using high frequency waves, microwaves, etc. Attempts have already been made to use the submerged plasma chemical vapor deposition method to generate plasma in a raw material liquid containing a carbon source and thereby form diamond on a substrate (see Patent Document 1).

[0003] JP 2008-150246 A: Interlayers Applied to CVD Diamond Deposition on Steel Substrate, Djoille Denner Damm, Andre Contin, et al., Coatings 2017, 7, 141

[0004] Here, in the embodiment using the submerged plasma chemical vapor deposition method, it has been considered that the conventional method is to separately provide an intermediate layer on a substrate, specifically a substrate containing iron as a main component, or to form diamond after seeding with minute diamonds (see Non-Patent Document 2). Among these, in particular, in order to provide an intermediate layer on a substrate, various formation conditions need to be adjusted, and it is difficult to stably and repeatedly form an intermediate layer with a predetermined quality. Therefore, from the viewpoint of production efficiency, it is desirable to form diamond without separately providing inclusions such as an intermediate layer.

[0005] Therefore, an object of the present invention is to provide a diamond-forming device capable of directly forming diamond on a substrate, and a diamond-coated substrate obtained from the device.

[0006] In order to achieve the above object, one embodiment of the present invention provides a diamond formation device comprising: a reaction vessel in which a raw material liquid containing a carbon source is held and in which a substrate is placed in the raw material liquid; and an electrode unit capable of generating plasma in the raw material liquid, wherein the substrate has at least one recess on a main surface facing the electrode unit.

[0007] In order to achieve the above object, one embodiment of the present invention provides a diamond-coated substrate comprising a substrate having at least one recess on a main surface thereof, and a diamond formed directly on the main surface of the substrate.

[0008] According to one embodiment of the present invention, it is possible to obtain a diamond-coated substrate in which diamonds are formed directly on the substrate.

[0009] FIG. 1 is a cross-sectional view schematically showing a diamond-forming device according to one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a diamond-forming device according to one embodiment of the present invention in a plasma generating state. FIG. 3 is a plan view schematically showing a diamond formed directly on a substrate. FIG. 4 is a cross-sectional view schematically showing a diamond formed directly on a substrate. FIG. 5A is a cross-sectional view schematically showing an embodiment of cutting a substrate. FIG. 5B is a plan view schematically showing a substrate after cutting. FIG. 5C is a cross-sectional view schematically showing a diamond-forming device according to one embodiment of the present invention in which a substrate with a recess is placed. FIG. 6 is a cross-sectional view schematically showing a state in which a sintered body composed of the subcomponents of the substrate is provided on the main surface of the substrate. FIG. 7 is a cross-sectional view schematically showing a state in which carbon is attached to the surface of the subcomponents (chromium and / or nickel, etc.) located on the main surface of the substrate. FIG. 8 is a cross-sectional view schematically showing a state in which plasma is provided on the main surface side of a substrate with a recess. FIG. 9 is a cross-sectional view schematically showing a state in which the diamond is not easily peeled off from the substrate. FIG. 10 is a plan view schematically showing a diamond-forming device according to another embodiment of the present invention. Fig. 11 is a schematic cross-sectional view taken along line II' in Fig. 10. Fig. 12A is a side view schematically showing a drill used to form a recess in a substrate, which is a component of a diamond-forming device according to one embodiment of the present invention. Fig. 12B is a photograph of a drill used to form a recess in a substrate, which is a component of a diamond-forming device according to one embodiment of the present invention. Fig. 13 shows (a) to (c) SEM images ((b) and (c) correspond to the enlarged SEM image of the circled region in (a)) and (d) Raman spectrum of the substrate surface in Comparative Example 1 (a case in which a substrate whose main surface facing the electrode was polished with sandpaper was used). Fig. 14 shows (a) to (c) SEM images ((b) and (c) correspond to the enlarged SEM image of the circled region in (a)) and (d) Raman spectrum of the substrate surface in Comparative Example 2 (a case in which a substrate whose main surface facing the electrode was polished with a metal file was used).15 shows (a) to (c) SEM images ((b) and (c) correspond to the enlarged SEM image of the circled region in (a)) and (d) Raman spectrum of the substrate surface in Comparative Example 3 (when a substrate whose main surface facing the electrode was polished with a flat drill was used). FIG. 16 shows (a) to (c) SEM images ((b) and (c) correspond to the enlarged SEM image of the circled region in (a)) and (d) Raman spectrum of the substrate surface in Example 1 (when a substrate whose main surface facing the electrode was cut with a drill with a tip angle of 118 degrees was used) (diamond formed on the edge region forming the opening of the recess in the substrate). FIG. 17 shows an SEM image of the substrate surface in Example 1 (when a substrate whose main surface facing the electrode was cut with a drill with a tip angle of 118 degrees was used) (diamond formed on the edge region forming the opening of the recess in the substrate). 18 shows (a) to (c) SEM images ((b) and (c) correspond to the enlarged SEM image of the circled area in (a)) and (d) Raman spectrum of the substrate surface in Example 2 (when a substrate was used in which the main surface facing the electrode was cut with a drill with a tip angle of 118 degrees) (a version in which diamond was also formed on the main surface of the substrate extending from the edge area forming the opening of the recess in the substrate). FIG. 19 shows (a) to (c) SEM images ((a) 30x, (b) 500x, (c) 2000x; (b) and (c) correspond to the enlarged SEM image of the circled area in (a)) and (d) Raman spectrum of the substrate surface in Example 3 (when a substrate was used in which the main surface facing the electrode was cut with a drill with a tip angle of 118 degrees). 20 shows (a) to (c) SEM images ((a) 30x, (b) 500x, (c) 2000x; (b) and (c) correspond to the enlarged SEM image in the circled area in (a)) of the substrate surface in Example 4 (a substrate was used in which the main surface facing the electrode was plastically deformed by pressing a cemented carbide alloy with a tip angle of 70 degrees). 21 shows (a) to (c) SEM images ((a) 30x, (b) 500x, (c) 2000x; (b) and (c) correspond to the enlarged SEM image in the circled area in (a)) of the substrate surface in Example 5 (a substrate was used in which the main surface facing the electrode was plastically deformed by pressing chips obtained by previously grinding the main surface with a metal file against the main surface). 22 shows (d) Raman spectra.22 shows (a) to (c) SEM images ((a) 30x, (b) 500x, (c) 2000x; (b) and (c) correspond to the enlarged SEM images of the circled region in (a)) of the substrate surface in Comparative Example 4 (when a substrate with an untreated main surface facing the electrode portion was used) and (d) Raman spectrum. Fig. 23 is a graph showing the relationship between the α value and the β value in Examples 3 to 5 and Comparative Example 4.

[0010] [Diamond-forming device] A diamond-forming device according to one embodiment of the present invention will be described below with reference to the drawings.

[0011] (Basic configuration of diamond-forming device) First, before explaining the characteristic parts of the present invention, the basic configuration of the diamond-forming device will be explained. Fig. 1 is a cross-sectional view showing a diamond-forming device according to one embodiment of the present invention. As shown in Fig. 1, a diamond-forming device 100 according to one embodiment of the present invention comprises a reaction vessel 30 in which a raw material liquid 10 containing a carbon source is held and in which a substrate 20 is placed in the raw material liquid 10, and an electrode unit 40 capable of generating plasma in the raw material liquid 10.

[0012] For example, an alcohol solution can be used as the raw material liquid 10 containing a carbon source. As an example of the alcohol solution, a combination of methanol and ethanol can be used. Although not particularly limited, 70 to 99% by volume or more of methanol and 1 to 30% by volume of ethanol can be used.

[0013] Substrate 20 is a member that serves as a base for forming diamond on its surface (mainly the main surface), and is held by a substrate holder inside reaction vessel 30. This substrate holder is disposed so as to extend from the top (or upper lid) of reaction vessel 30 to the inside. As will be described later, substrate 20 that can be used in the present invention can be steel (i.e., alloy steel) that contains a certain amount or more of alloy elements other than iron and carbon.

[0014] A quartz vessel, for example, can be used as the reaction vessel 30. The reaction vessel 30 can be in a sealed state. The sealed reaction vessel 30 can be depressurized by a pressure reducer 91 via an adjustment valve 92 in order to reduce energy loss during diamond formation using plasma.

[0015] The electrode unit 40 has alumina, Teflon (registered trademark), or the like surrounding it as an insulating unit 60. The electrode unit 40 may be a metal (e.g., aluminum, tungsten, or the like) conductor, and is preferably composed of a pair of electrodes arranged to sandwich the substrate 20 in order to facilitate plasma generation.

[0016] In the electrode unit 40, one end of its longitudinal axis is on the source liquid side, and the other end is connected to the resonator 50. Microwaves or the like generated by an electromagnetic wave generator can be introduced into this resonator 50 from a waveguide 80 via a coupling window 70. The microwaves or the like generate heat at the tip of the metal conductor serving as the electrode unit 40, which forms bubbles, and high-temperature (approximately 3000°C) plasma can be generated within these bubbles.

[0017] After the plasma is generated, the raw material liquid 10 is partially vaporized between the generated plasma and the substrate 20 facing the plasma, generating a low-temperature gas containing the carbon source of the raw material liquid 10. This carbon source is deposited on the main surface of the substrate 20, thereby forming a predetermined diamond on the substrate 20 side.

[0018] From the viewpoint of facilitating the suitable supply of the carbon source necessary for diamond formation to the substrate 20 side by the plasma, the electrode unit 40 is positioned adjacent to and vertically below (or vertically above) the substrate 20 so as to be mutually opposed to the substrate 20. In this case, the distance L between the electrode unit 40 and the substrate 20 may be 0.5 mm to 3.0 mm, preferably 1.0 mm to 2.5 mm, and more preferably 1.5 mm to 2.0 mm, from the viewpoint of direct irradiation of the generated plasma onto the substrate 20.

[0019] (Common Technical Knowledge of Those Skilled in the Art) In conventional liquid plasma chemical vapor deposition processes, substrates containing iron as a primary component are commonly used. According to common technical knowledge of those skilled in the art, iron has the property of diffusing carbon atoms contained in the source solution into its interior, and it is known that carbon components do not remain on the surface of the substrate but tend to penetrate between the iron lattices within the substrate. For this reason, inclusions such as an intermediate layer composed of a bond between carbon and a metal component (transition metal elements such as chromium, titanium, vanadium, nickel, molybdenum, and tungsten) that is understood to be less oxidizable than iron and less likely to allow carbon to penetrate into the substrate, or microscopic diamond seeding particles, have been separately provided on the substrate. A carbon source has been deposited on these separately provided inclusions, such as an intermediate layer.

[0020] (The impetus for conceiving the present invention) In this regard, from the viewpoint of improving diamond production efficiency, it is desirable to form diamond without providing any additional inclusions such as intermediate layers, and the inventors of the present application have conducted extensive research into methods for forming diamond directly on substrate 20.

[0021] (Characteristics of the present invention) As a result of the investigation, the inventors of the present invention have newly found that, as shown in Fig. 2, when a liquid plasma chemical vapor deposition method is carried out using a substrate 20 having at least one recess 22 on the main surface 21 facing the electrode part 40, diamond C can be directly formed on the substrate 20 without providing any additional intervening material such as an intermediate layer (see Fig. 3 and Fig. 4). Such direct formation of diamond C on the substrate 20 is an epoch-making matter compared to the technical common sense of the above-mentioned person skilled in the art.

[0022] More specifically, it has been newly discovered that diamond C can be formed at least in the edge region 24 that forms the opening 23 of the recess 22. The term "recess" as used herein refers not to a through-hole that penetrates from one side to the other, but to a recess having an opening, such as a recess consisting of a bottom and a side extending from the bottom. Furthermore, the term "recess" as used herein refers to a recess formed by cutting, plastic deformation, or the like, regardless of its size (including diameter and depth) compared to a portion of the substrate surface where no recess is formed (i.e., a flat surface). Furthermore, the term "recess" as used herein does not include the conventional scratch-shaped grooves extending in one direction solely for embedding (seeding) diamond nuclei, but may include scratch-shaped grooves extending in one direction that contribute to direct diamond growth on the substrate without seeding. The term "edge region 24" as used herein refers to a region including not only the edge portion itself but also its peripheral portion (such as the portion extending from the edge portion into the recess formation region). Furthermore, it has been newly discovered that diamond C can also be formed on the main surface 21 of the substrate 20 extending from this edge region 24 .

[0023] (Mechanism for directly forming diamond C on substrate 20) The inventors of the present application believe that the direct formation of diamond C on substrate 20 when using substrate 20 with the recess 22 described above is achieved by the following possibility.

[0024] Specifically, first, the diamond-forming device 100 according to one embodiment of the present invention, which includes a substrate 20 with a recess 22, can be manufactured mainly through the following steps. Specifically, as shown in FIG. 5A, a cutting tool such as a drill is used to perform cutting (i.e., machining) on ​​the main surface 21A of a plate-shaped substrate 20A. The term "drill" as used herein refers to a drill with a point angle of 40 degrees or more and 160 degrees or less, for example, 90 degrees or more and 140 degrees or less, and may be, for example, a twist drill with a twisted tip. Furthermore, the term "drill" as used herein does not include a flat drill with a point angle of approximately 180 degrees.

[0025] In the present invention, the substrate used may be steel (i.e., alloy steel) containing a certain amount or more of alloying elements other than iron and carbon. Specifically, the substrate may contain a transition metal element. For example, the substrate may contain at least one element selected from the group consisting of iron, chromium, nickel, copper, molybdenum, and tungsten. As an example, the substrate may be stainless steel containing iron as the primary component and chromium as a secondary component, such as SUS403 or SUS430. As another example, the substrate may be stainless steel containing iron as the primary component and chromium / nickel as secondary components, such as SUS304.

[0026] By performing this cutting process, a substrate 20 having a recess 22 can be obtained. Since the drill used in this example does not include a flat drill with a point angle of approximately 180 degrees, the recess 22 after cutting process is tapered (i.e., tapered) toward the inside of the substrate 20 in cross-sectional view (see FIG. 4). Furthermore, the recess 22 may be rectangular, square, circular, elliptical, or polygonal in plan view (see FIG. 5B).

[0027] 5C, the substrate 20 with the recess 22 is placed in the reaction vessel 30 by being held by a substrate holder inside the reaction vessel 30. Specifically, the substrate 20 is placed so that the tip of the electrode unit 40 capable of generating plasma and at least the recess 22 of the substrate 20 are directly opposite each other. In this state, plasma is supplied to the substrate 20 according to the submerged plasma chemical vapor deposition method.

[0028] The inventors of the present application understand that the following state occurs during cutting: Specifically, when cutting using a drill or the like, cutting heat of about 100 to 300 degrees is generated, which may cause some of the minor components that make up the substrate 20 to melt and appear on the main surface 21 side, and the minor components that are exposed by subsequent cooling may be provided as a sintered body 25 on the main surface 21 of the substrate 20 (see FIG. 6).

[0029] In particular, when the substrate 20 contains carbon, chromium, and / or nickel as a secondary component, the chromium and / or nickel have the property of capturing and holding carbon atoms on their surface, while the iron has the property of diffusing carbon atoms into its interior. Therefore, as shown in FIG. 7, in the sintered body 25, it is understood that the carbon component 25B is likely to remain on the surface of the chromium and / or nickel component 25A as a secondary component.

[0030] In light of this, and without being bound by any particular theory, the inventors of the present invention believe that a bonded body (or sintered body) containing chromium and / or nickel and carbon attached to its surface can function as what is conventionally called an intermediate layer and / or a microscopic diamond seed. In other words, this sintered body can contain amorphous carbon as an intermediate layer, etc.

[0031] As a result, as described above, it is understood that diamond C can be finally formed directly on the substrate 20 without the need to separately form an intermediate layer or the like as in the past. The inventors of the present application understand that the sintered body containing this chromium and / or nickel and carbon attached to its surface is mainly located in the formation region of the recess 22 of the substrate 20 and on the periphery of this formation region. This is based on the fact that so-called cutting chips are scattered in the formation region of the recess 22 and on the periphery thereof at a high rate during cutting.

[0032] (Mechanism of diamond formation in the edge region that defines the opening of the recess (and on the substrate main surface extending from the edge region)) Furthermore, when a sintered body containing chromium and / or nickel and carbon attached to this surface is formed on main surface 21 of substrate 20 in this manner, and plasma P is supplied to main surface 21 of substrate 20 as shown in Figures 7 and 8, the carbon source of raw material liquid 10 located at least between plasma P and substrate 20 can be converted into low-temperature gas 27 by the heat of about 3000 degrees of plasma P. Specifically, as shown in Figure 8, low-temperature gas 27 derived from this carbon source can be composed of a relatively thin region 27A and relatively thick regions 27B and 27C between plasma P and substrate 20.

[0033] The present inventors have also found that when a sintered body containing chromium and / or nickel and carbon is formed, there is a difference in the thickness of the low-temperature gas 27 derived from the carbon source. More specifically, the sintered body containing chromium and / or nickel and carbon attached to its surface serves as an active nucleus, and diamond C is easily formed in the relatively thin low-temperature gas region 27A.

[0034] In this regard, the distance D1 between the interface between the relatively thin region 27A and the surface of the substrate 20 and the portion opposite the interface (or the distance between the interface and the high-temperature plasma P) is smaller than the distance D2 between the interface between the relatively thick regions 27B, 27C and the surface of the substrate 20 and the portion opposite the interface (or the distance between the interface and the high-temperature plasma P).

[0035] Without being bound by any particular theory, it is believed that this difference in distance is related to the difference in the thermal conductivity of the plasma P up to the interface between the local region of low-temperature gas and the surface of the substrate 20, and thereby to the location where the diamond C is ultimately formed.

[0036] From the above, as described above, it is possible to finally form diamond C at least in the edge region 24 that forms the opening portion 23 of the recess 22. Furthermore, it is also possible to finally form diamond C on the main surface 21 of the substrate 20 that extends from this edge region 24 (see FIGS. 3 and 4).

[0037] As mentioned above, the inventors of the present invention believe that the sintered body containing chromium and / or nickel and carbon attached to the surface, which may be formed by cutting the substrate 20, contributes to the final formation of the diamond.

[0038] However, without being limited to this, when a substrate 20 with a recess is manufactured in advance using a mold, die, or the like, it is possible that the difference in thickness of the low-temperature gas 27 derived from the carbon source of the raw material liquid is more important than the formation of a sintered body containing chromium and / or nickel and carbon attached to its surface by cutting processing itself.

[0039] More specifically, it is possible that the relatively thin low-temperature gas region 27A is more involved in contributing to the formation of diamond C than the formation of the sintered body itself containing chromium and / or nickel and carbon attached to its surface.

[0040] (Mechanism for the resistance of diamond C to peeling) In addition, during the diamond formation process, the substrate 20 is heated by plasma P until the opposite main surface side reaches approximately 600 to 700 degrees. In this regard, in the conventional mode, the expansion coefficient of iron, which is the main component of the substrate 20, is different from the expansion coefficient of diamond, so when the iron contracts during the temperature reduction process of the substrate 20 after the irradiation of plasma P is stopped, the diamond has difficulty following the contracting iron. As a result, the diamond is prone to peeling off from the substrate.

[0041] In contrast, in one embodiment of the present invention, a sintered body containing cobalt / nickel as a secondary component of the substrate is formed on the main surface 21 of the substrate 20, and the cobalt / nickel has the property of making it easier for the carbon source of diamond to adhere to its surface than iron (i.e., the cobalt / nickel and the carbon source have good bonding properties). Therefore, when the cobalt / nickel shrinks during the temperature drop of the substrate 20 after the irradiation of the plasma P is stopped, the diamond tends to follow the cobalt / nickel, which shrinks more than iron.

[0042] Furthermore, the region where the recess 22 is formed on the substrate 20 is a space region. Therefore, compared to a predetermined region of the substrate 20 without a recess, the region where the recess 22 is formed is understood to be a stress relaxation point in the substrate 20 and is relatively less likely to shrink. For these reasons, as shown in Figure 9, the diamond C is less likely to peel off from the substrate 20.

[0043] The above description has been given on the assumption that the number of recesses 22 in the substrate 20 is one. However, the number of recesses 22 may be two or more. In this case, as shown in Figures 10 and 11, at least a first recess 22XI and a second recess 22YI spaced apart from the first recess 22XI may be provided. In this case, in one embodiment of the present invention, a diamond extending along the main surface 21I of the substrate 20I may be formed between the first recess 22XI and the second recess 22YI (see Figure 18).

[0044] [Diamond-coated substrate] The following describes the configuration of the diamond-coated substrate formed using the diamond-forming device 100 having the above-described characteristic configuration. Note that, since the characteristic configuration of the substrate 20 has already been described above, the following description will be simplified.

[0045] As described above, it has been found that diamond C can be formed directly on the substrate 20 by performing the submerged plasma chemical vapor deposition method using the diamond-forming device 100 according to one embodiment of the present invention (see FIGS. 3 and 4). This allows the diamond-coated substrate to be removed from the reaction vessel 30 of the diamond-forming device 100 after performing the submerged plasma chemical vapor deposition method.

[0046] Specifically, this diamond-coated substrate comprises a substrate 20 having at least one recess 22 on its main surface 21, and a diamond C formed directly on the main surface 21 of the substrate 20 (see Figures 4, 16 and 18, etc.). Note that the term "diamond-coated substrate" as used herein refers to a substrate directly coated (or directly covered) with diamond, and can also be referred to as a "substrate with diamond," a "composite of diamond and substrate," and / or an "integrated product of diamond and substrate."

[0047] As previously mentioned, the substrate 20 and the recess 22 in the substrate 20, which are components of this diamond-coated substrate, have the following characteristics. In one embodiment, the recess 22 in the substrate 20 can be formed by cutting using a drill with a point angle of 40 degrees or more and 160 degrees or less (see FIGS. 5A, 12A, and 12B). When the recess is formed by cutting, the recess 22 in the substrate 20 can be tapered in cross-sectional view (see FIG. 4, etc.). In this case, the recess 22 in the substrate 20 can be rectangular, square, circular, elliptical, or polygonal in plan view (see FIG. 5B). The recess 22 in the substrate 20 can also be formed by plastic deformation of the main surface of the substrate 20. Diamonds C are formed in the edge region 24 that forms the opening 23 of the recess 22 in the substrate 20 (see FIGS. 3, 4, 16, and 17). Diamonds C are also formed on the main surface 21 of the substrate 20 extending from the edge region 24 (see FIGS. 3, 4, and 18). When at least a first recess 22XI and a second recess 22YI spaced apart from the first recess 22XI are provided, a diamond extending along the main surface 21I of the substrate 20I is formed between the first recess 22XI and the second recess 22YI (see FIGS. 10, 11, and 18). The substrate 20 includes a transition metal element material. The substrate 20 includes at least one element material selected from the group consisting of iron, chromium, nickel, copper, molybdenum, and tungsten. The substrate 20 is an alloy steel. The substrate 20 is stainless steel.

[0048] Although one embodiment of the present invention has been described above, it is merely a typical example within the scope of application of the present invention. Therefore, it will be readily understood by those skilled in the art that the present invention is not limited to this embodiment and that various modifications can be made.

[0049] Diamond was formed by the in-liquid plasma chemical vapor deposition method using the following device.

[0050] Examples 1 and 2 (Components) A diamond-forming device 100 comprising the following components was used. Raw material solution 10: Methanol solution (97% by volume) and ethanol solution (3% by volume). Substrate 20: A substrate made of stainless steel (SUS304) was used. A substrate with recesses 22 (opening diameter 0.5 mm, depth 0.01-0.1 mm) formed by cutting (machining) using a twist drill with a 118-degree point angle (see Figures 12A and 12B) was used. The number of recesses 22 was nine. The twist drill used was a NACHI Corporation SD (straight shank) 0.5 [blade diameter D: 0.5 mm, flute length (l): 7.5 mm, total length L: 30 mm]. Note that by using a drill with a 118-degree point angle, the cross-sectional shape of the recesses 22 formed in the substrate was tapered, and the planar shape of the recesses 22 was circular. The distance between the centers of the openings of each recess was 1.0 mm. The diamond that had been prepared was pressed into this recess 22 and used as a pedestal. ■ Reaction vessel 30: A cylindrical reactor vessel (inner diameter 94 mm, height 100 mm) made of quartz glass and a stainless steel flange, and airtight, was used. ■ Electrode part 40: A reactor vessel made of tungsten and consisting of an electrode with a diameter of 4 mm was used. ■ Insulating part 60 around the electrode part 40: PTFE (Teflon (registered trademark))

[0051] (Procedure) The electrode unit 40 was placed below the reaction vessel 30, and then the raw material solution 10 was poured into the reaction vessel 30. Then, a top cover, which constitutes part of the reaction vessel with a substrate holder holding the substrate 20, was installed, so that the substrate 20 was positioned facing the electrode unit 40 at a distance. The facing distance was adjusted to 1.5 mm. After the substrate 20 was placed, the pressure reducer (aspirator) was operated to reduce the pressure inside the reaction vessel 30. After reducing the pressure, 2.5 GHz microwaves were irradiated through the waveguide 80 (WRJ-2 type waveguide) to generate plasma between the recessed portion of the electrode unit 40 and the substrate 20. The diameter of the plasma was 4 to 6 mm. The pressure was then adjusted to 40 kPa using the adjustment valve 92.

[0052] Example 3 Plasma was generated under the same conditions as in Example 1. In this example, the opposing distance between the substrate 20 and the electrode portion was set to 2.0 mm, and microwaves of 2.45 GHz were used. Other conditions were the same as in Example 1.

[0053] Example 4 Unlike Example 1, a substrate with a recess was used, which was formed by pressing a cemented carbide alloy with a diameter of 4 mm and a tip angle of 70 degrees against the main surface of the substrate 20 facing the electrode portion, causing plastic deformation. In this example, the distance between the substrate 20 and the electrode portion was set to 2.0 mm, and microwaves of 2.45 GHz were used. Other conditions were the same as in Example 1.

[0054] Example 5 Unlike Example 1, the surface of the substrate 20 was previously scraped with a metal file to form chips, and the chip-bearing substrate 20 was then clamped in a vice to press the chips against the surface of the substrate 20 and adhere them. By pressing the chips against the substrate surface, the substrate surface was plastically deformed, forming recesses on the surface. This substrate with recesses was used in this example. In this example, the opposing distance between the substrate 20 and the electrode was set to 2.0 mm, and microwaves of 2.45 GHz were used. Other conditions were the same as in Example 1.

[0055] Comparative Example 1 The main surface of the substrate 20 facing the electrode portion was polished with sandpaper, and the polishing powder generated by the polishing was removed. The other conditions were the same as in Example 1.

[0056] Comparative Example 2 The main surface of the substrate 20 facing the electrode portion was polished with a metal file, and the polishing powder generated by the polishing was removed. The other conditions were the same as in Example 1.

[0057] The main surface of the substrate 20 facing the electrode portion was polished with a flat drill (diameter: 6 mm) having a tip angle of 180 degrees, and polishing powder generated by polishing was removed. The other conditions were the same as those in Example 1.

[0058] Comparative Example 4: An untreated substrate was used, which had not been subjected to machining or other processing. In this comparative example, the opposing distance between the substrate 20 and the electrode portion was set to 2.0 mm, and microwaves of 2.45 GHz were used. Other conditions were the same as in Example 1.

[0059] (Measurement details) After performing the submerged plasma chemical vapor deposition method, the deposits on the substrates in Examples 1 to 5 and Comparative Examples 1 to 4 were observed with a scanning electron microscope (SEM), and Raman spectra were measured. Scanning electron microscope (SEM) (manufactured by JEOL Ltd. / product name: JSM-6060) Micro-Raman spectroscopic analyzer (manufactured by RENISHAW / product name: inViaReflex, excitation light (150 mW), spot diameter: 1.4 μm, YAG laser wavelength: 532 nm)

[0060] During the measurement, the deposit (film) on the substrate surface was analyzed by Raman spectroscopy to detect the diamond peak (sp ３ 1333cm represents －１ The diamonds that showed the peak at 1000 .ANG. were evaluated as diamonds.

[0061] For Examples 3 to 5 and Comparative Example 4, the α value, which quantifies the deposition area of ​​the deposit on the substrate, and the β value, which quantifies the quality of the deposit (equivalent to diamond), were calculated.

[0062] The "α value" referred to here is a value obtained by cutting out a circle in the area where the plasma hits the SEM image, binarizing the image into black and white for each pixel using OpenCV (Open Source Computer Vision Library), and quantifying the proportion of white pixels (corresponding to the area of ​​the deposited portion of the deposit) out of the total pixels.

[0063] The "β value" here refers to the linear approximation of the fluorescence background of the Raman spectrum (1100 cm －１ ~1700cm －１ Based on the linear approximation, the diamond peak (1333 cm －１ ) and the distance to the G peak (1550 cm) for graphite －１ ) and the distance to the target point is calculated, and the ratio of the two values ​​is expressed as a numerical value.

[0064] (Measurement results) In Comparative Examples 1 to 3, low-quality diamonds were synthesized. The area on which diamonds formed was also small. When the experiment was performed multiple times under the same conditions, most of the deposits on the substrate were amorphous carbon. The probability of diamond formation was about 10% (see Figures 13 to 15).

[0065] In Examples 1 and 2, high-quality diamonds were formed over a wider area than in Comparative Examples 1 to 3. When experiments were performed multiple times under the same conditions, the probability of diamond formation was about 50%. In Example 1, diamonds were formed in the edge region that formed the opening of recess 22 in substrate 20 (see Figures 16 and 17). Furthermore, in Example 2, diamonds were also formed on main surface 21 of substrate 20 extending from this edge region (specifically, the portion between adjacent recesses that was not machined with a drill) (see Figure 18).

[0066] From the above, it was found that when the substrate surface is ground to form the recesses 22 in Examples 1 and 2, high-quality diamonds can be formed without the need for a separate intermediate layer or for seeding with minute diamonds, as in the past, compared to when the substrate surface is polished in Comparative Examples 1 to 3. As a result, after performing the submerged plasma chemical vapor deposition method, it was possible to remove from the reaction vessel of the diamond-forming device a diamond-coated substrate comprising a substrate having recesses on its main surface and diamonds formed directly on the main surface of the substrate.

[0067] Furthermore, in Examples 3 to 5 (see Figures 19 to 21) and Comparative Example 4 (see Figure 22), the measured α and β values ​​were as shown in Table 1 below (see Figure 23). In Example 3, diamonds were also formed in the edge region that formed the opening of the recess in the substrate and on the main surface of the substrate extending from this edge region (specifically, the portion between adjacent recesses that was not machined with a drill) (see Figure 19).

[0068] [Table 1]

[0069] 23, the α and β values ​​of the deposits obtained by generating plasma between the electrode part 40 and the recesses formed on the substrate surface in Examples 3 to 5 were both higher than the α and β values ​​of the deposits (diamonds) obtained by generating plasma between the electrode part 40 and the untreated substrate in Comparative Example 4. That is, it was found that the formation area of ​​the diamonds obtained in Examples 3 to 5 was larger than that in Comparative Example 4, and the quality of the diamonds obtained in Examples 3 to 5 was higher than that in Comparative Example 4. This shows that the substrate with recesses contributes to increasing the formation area of ​​the diamonds deposited on the substrate and improving their quality.

[0070] Without being bound by any particular theory, it is possible that the formation of recesses on the substrate surface by cutting or plastic deformation in Examples 3 to 5 exposed the Cr and Ni components contained in the constituent components of the substrate (SUS304) to the substrate surface. In Comparative Example 4, these Cr and Ni components were stable by bonding with O (oxygen) in the air on the surface of the untreated substrate. On the other hand, in Examples 3 to 5, scratches on the substrate surface due to plastic deformation or cutting treatment weakened the bonds between the Cr and Ni components and O (oxygen), potentially making the substrate unstable. In this unstable state, when the carbon (C) component in the raw material solution 10 is decomposed and supplied by plasma generation, the Cr and Ni components are able to abandon O (oxygen) and bond with the carbon component. It is believed that this bond functions as an intermediate layer, which allows diamond to grow in the edge region that forms the opening of the recesses in the substrate.

[0071] Comparing the α and β values ​​among Examples 3 to 5, it was found that the α value of Example 3 was approximately 0.53 and the β value was approximately 2.63, which means that the α and β values ​​were the highest among Examples 3 to 5. Furthermore, in Example 4, the α value was approximately 0.39 and the β value was approximately 1.77, while in Example 5, the α value was approximately 0.35 and the β value was approximately 1.74, which means that the α and β values ​​of Example 4 were slightly higher than those of Example 5.

[0072] While not being bound by any particular theory, it is believed that when recesses are formed by cutting, the Cr and Ni components contained in the constituents of the substrate (SUS304) are more likely to be exposed to the substrate surface due to the cutting process. This allows the combination of these components with the carbon component in raw material liquid 10 decomposed by plasma to function more effectively as an intermediate layer, thereby enabling more effective deposition of diamond.

[0073] Furthermore, in Example 5, compared to Comparative Example 4, chips previously cut with a metal file were found to adhere to the recesses formed on the surface of the substrate. The chips contained Cr and Ni components, which may be unstable due to weak bonds with O (oxygen) caused by the cutting process. Therefore, the Cr and Ni components contained in the chips adhered to the substrate surface may abandon this O (oxygen) and bond with the carbon (C) component in the raw material liquid 10 decomposed by the plasma, forming a bond. It is believed that this bond was the catalyst that enabled the growth of diamond at least in the edge region of the substrate.

[0074] Also, in Example 3, compared to Example 4, it is thought that chips resulting from the cutting process adhered to the recesses formed on the surface of the substrate due to the cutting process. Therefore, as in Example 5, it is thought that the Cr and Ni components contained in the chips adhering to the substrate surface abandoned this O (oxygen) and bonded with the carbon (C) component in raw material liquid 10 decomposed by the plasma, and that this bond became the catalyst for the growth of diamond.

[0075] In Examples 2, 3, and 5, diamonds were also formed on the main surface of the substrate extending from the edge region forming the opening of the recess in the substrate. This is thought to be because the bonds between Cr, Ni, and carbon components located in the edge region spread to the main surface of the substrate (corresponding to the flat region of the substrate) continuing to the edge region, and the Cr and Ni components that were bonded in a stabilized state with O (oxygen) on the main surface of the substrate abandoned the O (oxygen) component and bonded preferentially with the carbon component in the bonds, which made it possible for diamonds to grow on the flat region of the substrate as well.

[0076] Alternatively, it can be interpreted that the bond between the Cr, Ni components and the carbon component located in the edge region spreads to the main surface of the substrate (corresponding to the flat region of the substrate) continuous with the edge region, and the carbon component in this bond reduces the O (oxygen) component bound to the Cr, Ni components to CO, causing the Cr, Ni components to lose O (oxygen) and become unstable, which in turn causes these unstable Cr, Ni components to bond with the carbon (C) component in raw material liquid 10 decomposed by the plasma, making it possible for diamond to grow on the flat region of the substrate as well.

[0077] Each embodiment is merely an example, and the present invention is not limited to each embodiment. In addition, partial substitution or combination of the configurations shown in different embodiments is possible.

[0078] One embodiment of the present invention is as follows. <1> A diamond-forming device comprising: a reaction vessel in which a raw material liquid containing a carbon source is held and in which a substrate is placed in the raw material liquid; and an electrode unit capable of generating plasma in the raw material liquid, the substrate having at least one recessed portion on a main surface facing the electrode unit. <2> The diamond-forming device according to <1>, in which diamond can be formed directly on the main surface of the substrate. <3> The diamond-forming device according to <1> or <2>, in which diamond can be formed in an edge region that forms the opening of the recessed portion. <4> The diamond-forming device according to <3>, in which diamond can be further formed on the main surface of the substrate extending from the edge region. <5> The diamond-forming device according to <4>, in which the at least one recessed portion comprises a first recessed portion and a second recessed portion arranged at a distance from the first recessed portion, and the diamond extending along the main surface of the substrate is formed between the first recessed portion and the second recessed portion. <6> The diamond-forming device according to any one of <1> to <5>, wherein the substrate contains a material of a transition metal element. <7> The diamond-forming device according to <6>, wherein the substrate contains a material of at least one element selected from the group consisting of iron, chromium, nickel, copper, molybdenum, and tungsten. <8> The diamond-forming device according to any one of <1> to <7>, wherein the substrate is an alloy steel. <9> The diamond-forming device according to <8>, wherein the substrate is stainless steel. <10> The diamond-forming device according to any one of <1> to <9>, wherein the electrode portion and the recessed portion of the substrate can directly face each other. <11> The diamond-forming device according to any one of <1> to <10>, wherein the recessed portion is tapered in cross-sectional view. <12> The diamond-forming device according to any one of <1> to <11>, wherein the recessed portion is rectangular, square, circular, elliptical, or polygonal in plan view. <13> The diamond-forming device according to any one of <1> to <12>, wherein the substrate has the recess provided by cutting using a drill with a point angle of 40 degrees or more and 160 degrees or less.<14> The diamond-forming device according to any one of <1> to <10>, wherein the substrate has the recessed portion provided by plastic deformation of the main surface of the substrate. <15> A diamond-forming method using the diamond-forming device according to any one of <1> to <14>, wherein the plasma is supplied to the substrate with the electrode unit capable of generating plasma and at least the recessed portion of the substrate facing each other. <16> A diamond-coated substrate comprising a substrate having at least one recessed portion on its main surface, and a diamond formed directly on the main surface of the substrate. <17> The diamond-coated substrate according to <16>, wherein the substrate has the recessed portion provided by cutting using a drill with a point angle of 40 degrees or more and 160 degrees or less. <18> The diamond-coated substrate according to <16>, wherein the substrate has the recessed portion provided by plastic deformation of the main surface of the substrate. <19> The diamond-coated substrate according to any one of <16> to <18>, wherein the diamond is formed in an edge region that forms the opening of the recessed portion. <20> The diamond-coated substrate according to <19>, further comprising a diamond formed on the main surface of the substrate extending from the edge region. <21> The diamond-coated substrate according to <20>, wherein the at least one recess comprises a first recess and a second recess spaced apart from the first recess, and the diamond extending along the main surface of the substrate is formed between the first recess and the second recess. <22> The diamond-coated substrate according to any one of <16>, <17>, and <19> to <21>, wherein the recess is tapered in cross-sectional view. <23> The diamond-coated substrate according to any one of <16>, <17>, and <19> to <22>, wherein the recess is rectangular, square, circular, elliptical, or polygonal in plan view. <24> The diamond-coated substrate according to any one of <16> to <23>, wherein the substrate contains a material of a transition metal element.<25> The diamond-coated substrate according to <24>, wherein the substrate comprises a material of at least one element selected from the group consisting of iron, chromium, nickel, copper, molybdenum, and tungsten. <26> The diamond-coated substrate according to any one of <16> to <25>, wherein the substrate is a steel alloy. <27> The diamond-coated substrate according to <26>, wherein the substrate is a stainless steel.

[0079] A diamond-forming device according to an embodiment of the present invention allows for the formation of high-strength diamond-coated substrates (i.e., diamond-bearing substrates). CROSS-REFERENCE TO RELATED APPLICATIONS

[0080] This application claims priority under the Paris Convention of Japanese Patent Application No. 2021-192474 (filing date: November 26, 2021, title: "Diamond-forming device and diamond-coated substrate"), the entire contents of which are incorporated herein by reference.

[0081] 100 Diamond formation device 10 Raw material liquid 20, 20I Substrate (with recess) 20A Plate-shaped substrate (without recess) 21, 21I Main surface of substrate facing electrode portion 21A Main surface of plate-shaped substrate 22 Recess 22XI, 22YI Recess 23 Opening portion of recess 24 Edge region forming opening portion of recess 25 Sintered body 25A Chromium and / or nickel component, etc. 25B Carbon component 27 Low-temperature gas derived from carbon source of raw material liquid 27A Relatively thin region of low-temperature gas 27B Relatively thick region of low-temperature gas 27C Relatively thick region of low-temperature gas 30 Reaction vessel 40 Electrode portion 50 Resonator 60 Insulating portion 70 Coupling window 80 Waveguide 91 Pressure reducer 92 Adjusting valve C Diamond D1 D1: Distance between the interface between the relatively thin region of the low-temperature gas and the surface of the substrate and the opposite side of the interface D2: Distance between the interface between the relatively thick region of the low-temperature gas and the surface of the substrate and the opposite side of the interface P: Plasma L: Distance between the electrode and the substrate

Claims

1. a reaction vessel in which a raw material liquid containing a carbon source is held and a substrate is placed in the raw material liquid; and an electrode unit capable of generating plasma in the raw material liquid, The substrate has at least one recess on a main surface facing the electrode portion.

2. 2. The diamond forming device according to claim 1, wherein diamond can be formed directly on the main surface of the substrate.

3. 2. The diamond forming device according to claim 1, wherein diamonds can be formed on an edge region that defines the opening of the recess.

4. 4. The diamond forming device according to claim 3, further capable of forming diamond on a main surface of the substrate extending from the edge region.

5. 5. A diamond forming device as described in claim 4, wherein the at least one recess comprises a first recess and a second recess spaced apart from the first recess, and the diamond extending along the main surface of the substrate is formed between the first recess and the second recess.

6. The diamond-forming device of claim 1 , wherein the substrate comprises a material of a transition metal element.

7. 7. The diamond forming device of claim 6, wherein the substrate comprises a material of at least one element selected from the group consisting of iron, chromium, nickel, copper, molybdenum, and tungsten.

8. 10. The diamond forming device of claim 1, wherein the substrate is a steel alloy.

9. 9. The diamond forming device of claim 8, wherein the substrate is stainless steel.

10. 2. The diamond-forming device according to claim 1, wherein the electrode portion and the recessed portion of the substrate are directly opposite each other.

11. The diamond-forming device of claim 1 , wherein the recess is tapered in cross section.

12. The diamond-forming device according to claim 1 , wherein the recess is rectangular, square, circular, elliptical, or polygonal in plan view.

13. 2. The diamond-forming device according to claim 1, wherein the substrate has the recess provided by cutting using a drill having a point angle of 40 degrees or more and 160 degrees or less.

14. 2. The diamond forming device according to claim 1, wherein the substrate has the recess provided by plastic deformation of a main surface of the substrate.

15. A diamond-forming method using the diamond-forming device according to any one of claims 1 to 14, comprising: The method for forming diamond includes providing the plasma to the substrate in a state in which the electrode portion capable of generating the plasma and at least the recessed portion of the substrate face each other.

16. A diamond-coated substrate comprising: a substrate having at least one recess in a major surface thereof; and a diamond formed directly on the major surface of the substrate.

17. 17. The diamond-coated substrate according to claim 16, wherein the substrate has the recess provided by cutting using a drill with a point angle of 40 degrees or more and 160 degrees or less.

18. 17. The diamond-coated substrate according to claim 16, wherein the substrate has the recess provided by plastic deformation of a major surface of the substrate.

19. 17. The diamond-coated substrate according to claim 16, wherein the diamonds are formed in an edge region that defines an opening of the recess.

20. 20. The diamond-coated substrate of claim 19, further comprising diamond formed on a major surface of the substrate extending from the edge region.

21. 21. A diamond-coated substrate as described in claim 20, wherein the at least one recess comprises a first recess and a second recess spaced apart from the first recess, and the diamond extending along the major surface of the substrate is formed between the first recess and the second recess.

22. 17. The diamond-coated substrate of claim 16, wherein the recess is tapered in cross section.

23. 17. The diamond-coated substrate according to claim 16, wherein the recess is rectangular, square, circular, elliptical, or polygonal in plan view.

24. 17. The diamond-coated substrate of claim 16, wherein the substrate comprises a transition metal element material.

25. 25. The diamond-coated substrate of claim 24, wherein the substrate comprises a material of at least one element selected from the group consisting of iron, chromium, nickel, copper, molybdenum, and tungsten.

26. 17. The diamond-coated substrate of claim 16, wherein the substrate is a steel alloy.

27. 27. The diamond-coated substrate of claim 26, wherein the substrate is stainless steel.