Synthetic single crystal diamond

Abstract

A synthetic single crystal diamond which contains nitrogen atoms at a concentration of 200 ppm to 1500 ppm (inclusive) on the basis of the number of atoms, the Raman shift [lambda] 1 cm-1 of the peak in the primary Raman scattering spectrum of the synthetic single crystal diamond and the Raman shift [lambda] 2 cm-1 of the peak in the primary Raman scattering spectrum of the synthetic IIa type single crystal diamond having a nitrogen atom number-based concentration of 1 ppm or less show the relationship of formula A:-0.85 lt; formula A: [lambda] 1-[lambda] 2 < =-0.15.

Description

Technical Field

[0001] The present disclosure relates to a synthetic single crystal diamond. This application claims priority based on Japanese Patent Application No. 2023-002185 filed on January 11, 2023. The entire contents of the Japanese Patent Application are incorporated herein by reference. Background Art

[0002] Single crystal diamond is widely used in cutting tools, grinding tools, wear-resistant tools, etc. due to its high hardness. Single crystal diamond used for tools includes natural diamond and synthetic diamond.

[0003] Natural diamonds often contain clustered nitrogen atoms (type Ia) as impurities. These clustered nitrogen atoms within diamond crystals can inhibit the development of plastic deformation and cracks that occur when diamond is used in tools. Consequently, natural diamonds possess high mechanical strength. However, natural diamonds have significant quality variations and unstable supply, limiting their use in industrial applications.

[0004] On the other hand, synthetic diamonds are widely used in the industrial field because of their consistent quality and stable supply.

[0005] Conventional synthetic diamond contains isolated substitutional nitrogen atoms as impurities (Type Ib). The higher the concentration of isolated substitutional nitrogen atoms in a diamond crystal, the worse the mechanical properties of the diamond tend to be. Therefore, when Type Ib synthetic diamond is used in tools, it tends to cause wear and chipping of the cutting edge.

[0006] There is also synthetic diamond (Type IIa) that contains almost no nitrogen impurities. Type IIa synthetic diamond does not contain impurities or crystal defects that inhibit crack growth, so when used in tools, it tends to easily cause chipping of the cutting edge.

[0007] Therefore, research is underway to improve the wear resistance and defect resistance of synthetic diamond.

[0008] For example, Patent Document 1 (International Publication No. 2019 / 077888) discloses synthetic single-crystal diamond having high hardness and excellent defect resistance.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: International Publication No. 2019 / 077888 Summary of the Invention

[0012] The synthetic single-crystal diamond disclosed herein is a synthetic single-crystal diamond containing nitrogen atoms at a concentration of 200 ppm or more and 1500 ppm or less based on the number of atoms, wherein:

[0013] The Raman shift of the peak in the primary Raman scattering spectrum of the synthetic single crystal diamond is λ1 cm -1 The Raman shift λ2cm of the peak in the primary Raman scattering spectrum of synthetic type IIa single crystal diamond with a nitrogen atom concentration of 1 ppm or less based on the atomic number of nitrogen atoms is -1 The relationship of the following formula A is shown:

[0014] -0.85<λ1-λ2≤-0.15Formula A. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic cross-sectional view showing an example of a sample chamber structure for producing synthetic single-crystal diamond according to one embodiment of the present disclosure.

[0016] Figure 2 This is an overview diagram of the sliding test device. DETAILED DESCRIPTION

[0017] [Problems to be Solved by the Present Disclosure]

[0018] Conventional wire drawing dies, scribing tools, wire guides, polishing tools, and the like using synthetic diamond tend to wear rapidly if the workpiece is slid at a low load and high speed or for a long time.

[0019] Therefore, an object of the present disclosure is to provide a synthetic single-crystal diamond having excellent wear resistance, particularly in low-load and long-term sliding processing.

[0020] [Effects of the Present Disclosure]

[0021] According to the present disclosure, it is possible to provide synthetic single-crystal diamond having excellent wear resistance even in processing under low load and for a long time.

[0022] [Description of Embodiments of the Present Disclosure]

[0023] First, embodiments of the present disclosure will be described below.

[0024] (1) The synthetic single-crystal diamond disclosed herein is a synthetic single-crystal diamond containing nitrogen atoms at a concentration of 200 ppm to 1500 ppm based on the number of atoms, wherein:

[0025] The Raman shift of the peak in the primary Raman scattering spectrum of the synthetic single crystal diamond is λ1 cm -1The Raman shift λ2cm of the peak in the primary Raman scattering spectrum of synthetic type IIa single crystal diamond with a nitrogen atom concentration of 1 ppm or less based on the atomic number of nitrogen atoms is -1 The relationship of the following formula A is shown:

[0026] -0.85<λ1-λ2≤-0.15Formula A.

[0027] According to the present disclosure, it is possible to provide synthetic single-crystal diamond having excellent wear resistance even in processing under low load and for a long time.

[0028] (2) In the above (1), the half-value width W of the peak in the primary Raman scattering spectrum of the synthetic single crystal diamond may be 2.7 cm -1 Above and 4.5cm -1 Therefore, when the synthetic single crystal diamond is used as a material for a wear-resistant tool such as a mold, the tool can have excellent wear resistance for a long period of time.

[0029] (3) In the above (1) or (2), in the infrared absorption spectrum of the synthetic single crystal diamond measured by Fourier transform infrared spectroscopy, at a wave number of 2680 cm -1 Above 2695cm -1 An absorption peak exists in the following range. Synthetic single crystal diamond having this absorption peak has further improved sliding properties.

[0030] (4) In any one of the above (1) to (3), in the infrared absorption spectrum of the synthetic single crystal diamond measured by Fourier transform infrared spectroscopy, the wave number 2680 cm -1 Above 2695cm -1 The maximum absorption intensity IA of the absorption peak in the following range is at wave number 2160 cm -1 As a result, the sliding properties of the synthetic single crystal diamond are further improved.

[0031] (5) In any one of the above (1) to (4), the {001} plane of the synthetic single crystal diamond may be <100> The Knoop hardness in the {001} direction is 65 GPa or more and 90 GPa or less. Here, the Knoop hardness is measured in accordance with JIS Z 2251:2009 at a temperature of 23°C ± 5°C and a test load of 4.9 N. <100> The Knoop hardness is 65 GPa or more, which is much harder than metal materials. Therefore, it is suitable for use in processing metal materials such as SUS, Ni alloy, and Ti alloy.

[0032] (6) In any of (1) to (5) above, the synthetic single crystal diamond may have no absorption peaks derived from aggregates of nitrogen atoms in its infrared absorption spectrum measured by Fourier transform infrared spectroscopy. Thus, the majority of nitrogen atoms in the synthetic single crystal diamond exist as isolated substitutional nitrogen atoms, and thus tensile stress is likely to increase, thereby enhancing the effect of suppressing abrasive wear.

[0033] [Details of the embodiments of the present disclosure]

[0034] <Existing Forms of Nitrogen Atoms in Diamond Crystals>

[0035] First, in order to deepen understanding of the synthetic single crystal diamond disclosed herein, the existence form of nitrogen atoms present as impurities in the crystal, which is one of the main factors determining the properties of diamond, will be described.

[0036] Nitrogen atoms in diamond crystals can be classified into isolated substitutional nitrogen atoms, aggregated nitrogen atoms, etc. according to their existence form.

[0037] An isolated substitutional nitrogen atom (C center) refers to a position in a diamond crystal where a nitrogen atom is substituted in a unit of one atom for a carbon atom.

[0038] The synthetic single crystal diamond containing isolated substitutional nitrogen atoms has a wavelength of 1130 cm-1 in the infrared absorption spectrum measured by Fourier transform infrared spectroscopy. -1 Near (i.e., wave number 1130±2cm -1 ) shows the absorption peak.

[0039] Because synthetic single-crystal diamond containing isolated substitutional nitrogen atoms has unpaired electrons from the nitrogen atoms, the concentration of these atoms can be measured using ESR (Electron Spin Resonance) analysis. ESR detects signals from crystal defects with unpaired electrons, in addition to isolated substitutional nitrogen atoms. In this case, isolated substitutional nitrogen atoms can be isolated and detected based on the g-value or signal relaxation time.

[0040] Aggregated nitrogen atoms refer to nitrogen atoms that exist in a diamond crystal as a result of the aggregation of two or more nitrogen atoms.

[0041] Aggregated nitrogen atoms exist in A centers (nitrogen 2-atom pairs), B centers (nitrogen 4-atom aggregations), B' centers (platelets), H3 centers (nitrogen 2-atom aggregations), N3 centers (nitrogen 3-atom aggregations), etc.

[0042] A center (nitrogen 2-atom pair) refers to an aggregate composed of two nitrogen atoms that form a covalent bond, and each nitrogen atom is substituted with a carbon atom that constitutes the diamond crystal. Diamonds containing A centers (nitrogen 2-atom pairs) are called type IaA. Synthetic single crystal diamond containing A centers (nitrogen 2-atom pairs) has an infrared absorption spectrum measured by Fourier transform infrared spectroscopy at a wave number of 1282 cm -1 Nearby (e.g., wave number 1282±2cm -1 ) shows the absorption peak.

[0043] A B center (nitrogen four-atom cluster) is an aggregate consisting of a vacancy and four nitrogen atoms adjacent to the vacancy, and each nitrogen atom is substituted for a carbon atom constituting a diamond crystal.

[0044] Diamonds containing four nitrogen atoms are called type IaB. Synthetic single crystal diamonds containing four nitrogen atoms have an infrared absorption spectrum measured by Fourier transform infrared spectroscopy at a wave number of 1175 cm -1 Near (e.g., wave number 1175±2cm -1 ) shows the absorption peak.

[0045] B' centers (also called platelets) are plate-like aggregates composed of five or more nitrogen atoms and interstitial carbon, and are incorporated into the crystal as inclusions.

[0046] Diamonds containing B' centers (platelets) are called IaB' type. Synthetic single crystal diamonds containing B' centers (platelets) have an infrared absorption spectrum measured by Fourier transform infrared spectroscopy at a wave number of 1358 cm -1 Above 1385cm -1 The absorption peaks are shown below.

[0047] An H3 center (nitrogen 2 atom cluster) is an aggregate consisting of a vacancy and two nitrogen atoms adjacent to the vacancy, each of which replaces a carbon atom that constitutes a diamond crystal. In this specification, "a nitrogen atom adjacent to a vacancy" refers to the nitrogen atom with the shortest interatomic distance to the carbon atom (i.e., the nearest neighbor) when a carbon atom is assumed to be present at the vacancy position. This is also the same meaning in the N3 center and B center described below.

[0048] Synthetic single crystal diamond containing H3 centers (aggregation of nitrogen 2 atoms) shows a fluorescence peak near a fluorescence wavelength of 503 nm (for example, a fluorescence wavelength of 503±2 nm) in the fluorescence spectrum obtained by irradiating excitation light shorter than about 500 nm, for example, excitation light with a wavelength of 325 nm.

[0049] An N3 center (nitrogen 3-atom cluster) is an aggregate consisting of a vacancy and three nitrogen atoms adjacent to the vacancy, each nitrogen atom being substituted for a carbon atom constituting a diamond crystal.

[0050] In the fluorescence spectrum obtained by irradiating synthetic single crystal diamond containing N3 centers (aggregation of 3 nitrogen atoms) with excitation light shorter than about 410 nm, for example, excitation light with a wavelength of 325 nm, the fluorescence peak is shown in one or both of the ranges near the fluorescence wavelength of 415 nm (for example, the fluorescence wavelength of 415±2 nm) and above the fluorescence wavelength of 420 nm and below 470 nm.

[0051] First, the inventors of the present invention studied the wear morphology of conventional synthetic single-crystal diamonds during low-load, long-term sliding processing. They concluded that the wear produced during low-load, long-term sliding processing is not wear caused by mechanical damage (accumulation of microscopic cleavage), but rather attrition wear caused by atomic shedding due to the accumulation of fatigue caused by long-term sliding under low load.

[0052] As a result of intensive research, the inventors of the present invention have discovered that the occurrence of abrasive wear is suppressed when synthetic single crystal diamond contains a large amount of nitrogen (200 to 1500 ppm) as isolated substitutional nitrogen atoms in the crystal, thereby completing the present disclosure.

[0053] The following describes specific examples of synthetic single-crystal diamond according to the present disclosure. In the drawings of this disclosure, identical reference numerals represent identical or equivalent parts. Dimensional relationships, such as length, width, thickness, and depth, have been modified for clarity and simplicity in the drawings and do not necessarily represent actual dimensional relationships.

[0054] In this specification, expressions in the form of “A to B” mean that A is greater than or equal to B. When A does not have a unit and only B has a unit, the unit of A is the same as that of B.

[0055] In the present disclosure, when one or more numerical values ​​are described as the lower limit and the upper limit of a numerical range, a combination of any one numerical value described as the lower limit and any one numerical value described as the upper limit is also disclosed.

[0056] [Embodiment 1: Synthetic Single Crystal Diamond]

[0057] A synthetic single-crystal diamond according to one embodiment of the present disclosure (hereinafter also referred to as "this embodiment") is a synthetic single-crystal diamond containing nitrogen atoms at a concentration of 200 ppm to 1500 ppm based on the number of atoms, wherein:

[0058] The Raman shift of the peak in the primary Raman scattering spectrum of the synthetic single crystal diamond is λ1 cm -1 The Raman shift λ2cm of the peak in the primary Raman scattering spectrum of synthetic type IIa single crystal diamond with a nitrogen atom concentration of 1 ppm or less based on the atomic number of nitrogen atoms is -1 The relationship of the following formula A is shown:

[0059] -0.85<λ1-λ2≤-0.15Formula A.

[0060] The synthetic single crystal diamond of this embodiment can have excellent wear resistance even in processing under low load and for a long time. The reason for this is not clear, but it is presumed to be the following (i) and (ii).

[0061] (i) The synthetic single crystal diamond of this embodiment contains nitrogen atoms at a concentration of 200 ppm to 1500 ppm based on the number of atoms. Furthermore, the Raman shift of the peak in the primary Raman scattering spectrum of the synthetic single crystal diamond of this embodiment is λ1 cm -1 The Raman shift λ2cm of the peak in the primary Raman scattering spectrum of synthetic type IIa single crystal diamond with a nitrogen atom concentration of 1 ppm or less based on the atomic number of nitrogen atoms is -1 The relationship of the following formula A is shown:

[0062] -0.85<λ1-λ2≤-0.15Formula A.

[0063] In the synthetic single-crystal diamond of this embodiment, a large number of nitrogen atoms exist as isolated substitutional nitrogen atoms. This generates strong tensile stress within the crystal lattice of the synthetic single-crystal diamond. This tensile stress is presumably responsible for suppressing wear caused by abrasive loss due to accumulated fatigue. Details regarding the relationship between the above-mentioned formula A, the form of nitrogen atoms in the synthetic single-crystal diamond, and the internal stress of the synthetic single-crystal diamond will be described later.

[0064] (ii) It is speculated that the synthetic single-crystal diamond of this embodiment contains a large amount of nitrogen, which changes the electronic state of the surface of the synthetic single-crystal diamond, improves the sliding properties, and reduces the friction coefficient.

[0065] When single-crystal diamond contains isolated substitutional nitrogen atoms, local tensile stresses are generated in the crystal lattice surrounding them. Consequently, these isolated substitutional nitrogen atoms become the starting point for plastic deformation and failure, reducing hardness and significantly degrading mechanical properties such as wear resistance and defect resistance. Consequently, treatments to increase the presence of large numbers of isolated substitutional nitrogen atoms in single-crystal diamond have not been performed. In contrast, the inventors of the present invention have discovered that single-crystal diamond containing large numbers of isolated substitutional nitrogen atoms exhibits excellent sliding properties and wear resistance in tool applications involving low-load, long-duration sliding processes.

[0066] <Nitrogen Atomic Concentration>

[0067] The synthetic single crystal diamond of this embodiment contains nitrogen atoms at a concentration of 200 ppm or more and 1500 ppm or less (hereinafter also referred to as "nitrogen atom concentration") on an atomic number basis. From the perspective of improving sliding properties, the lower limit of the nitrogen atom concentration of the synthetic single crystal diamond is 200 ppm or more, and may be 300 ppm or more, or 400 ppm or more. From the perspective of improving wear resistance, the upper limit of the nitrogen atom concentration of the synthetic single crystal diamond is 1500 ppm or less, and may be 1400 ppm or less, or may be 1300 ppm or less. The nitrogen atom concentration in the synthetic single crystal diamond may be 200 ppm or more and 1500 ppm or less, 300 ppm or more and 1400 ppm or less, or 400 ppm or more and 1300 ppm or less.

[0068] The nitrogen atomic concentration N (ppm) of synthetic single crystal diamond is determined by Fourier transform infrared spectroscopy at a wave number of 1130 cm -1 Absorption coefficient A(cm -1 ), calculated by the following formula 1:

[0069] N(ppm)=25·A(cm -1 )Formula 1.

[0070] <Primary Raman scattering spectrum>

[0071] The Raman shift of the peak in the primary Raman scattering spectrum of the synthetic single crystal diamond of this embodiment is λ1 cm -1 The Raman shift λ2cm of the peak in the primary Raman scattering spectrum of synthetic type IIa single crystal diamond with a nitrogen atom concentration of 1 ppm or less based on the atomic number of nitrogen atoms is -1 The relationship of the following formula A is shown:

[0072] -0.85<λ1-λ2≤-0.15Formula A.

[0073] The internal stress state of synthetic single crystal diamond can be determined by calculating the Raman shift of the peak in the primary Raman scattering spectrum of synthetic single crystal diamond by λ1cm. -1 The Raman shift λ2 cm of the peak in the primary Raman scattering spectrum of a synthetic type IIa single crystal diamond (hereinafter also referred to as a standard sample or synthetic type IIa single crystal diamond) having a nitrogen atom number-based concentration of 1 ppm or less is -1Specifically, the internal stress state of the synthetic single crystal diamond can be evaluated by the magnitude of the peak position shift represented by the difference between λ1 and λ2 (λ1-λ2). The reason for this is described below.

[0074] The synthetic type IIa single crystal diamond used as a standard sample refers to a single crystal diamond that is high-purity and free of lattice defects and internal strain, synthesized by a temperature difference method under high temperature and high pressure. For example, it is commercially available as a high-purity type IIa single crystal diamond manufactured by Sumitomo Electric Co., Ltd. The concentration of nitrogen atoms in the synthetic type IIa single crystal diamond is less than 1 ppm based on the atomic number, and it contains almost no nitrogen atoms, so there is no internal stress in the diamond crystal. In addition, the synthetic type IIa single crystal diamond shows a sharp and strong peak in the primary Raman scattering spectrum. Generally, the Raman shift of this peak appears at 1332 cm -1 to 1333cm -1 The Raman shift value varies depending on the temperature of the environment during measurement. In this specification, the Raman shift is a value measured at room temperature (20°C or higher and 25°C or lower).

[0075] If isolated substitutional nitrogen atoms are present within a diamond crystal, the Raman shift shifts toward lower frequencies compared to synthetic type IIa single-crystal diamond. In this case, tensile stress is generated within the diamond crystal due to the isolated substitutional nitrogen atoms. On the other hand, if clustered nitrogen atoms are present instead of isolated substitutional nitrogen atoms, the Raman shift shifts toward higher frequencies compared to synthetic type IIa single-crystal diamond. In this case, tensile stress is either absent or compressive stress is generated within the diamond crystal.

[0076] Thus, by comparing the Raman shift λ1cm in synthetic single crystal diamond -1 Compared with the Raman shift of synthetic type IIa single crystal diamond λ2cm -1 The value of can be used to evaluate the state of internal stress in synthetic single crystal diamond.

[0077] Based on the above insights, the inventors of the present invention have made a -1 and λ2cm -1 Difference (λ1-λ2)(cm -1 ) and the wear resistance of synthetic single crystal diamond in low load and long time processing. -1 ) shows the relationship shown in the following formula A, the synthetic single crystal diamond has excellent sliding characteristics and shows excellent wear resistance.

[0078] -0.85<λ1-λ2≤-0.15Formula A

[0079] If (λ1-λ2) satisfies the relationship of the above-mentioned formula A, the amount of isolated substitutional nitrogen atoms in the synthetic single-crystal diamond is sufficiently large, and the synthetic single-crystal diamond can have excellent sliding properties and excellent wear resistance. From the perspective of improving wear resistance, the lower limit of (λ1-λ2) is greater than -0.85, and can be greater than -0.83, greater than -0.76, or greater than -0.68. From the perspective of improving sliding properties, the upper limit of (λ1-λ2) is less than -0.15, less than -0.20, or less than -0.25. (λ1-λ2) is greater than -0.85 and less than -0.15, greater than -0.83 and less than -0.15, greater than -0.76 and less than -0.20, or greater than -0.68 and less than -0.25.

[0080] The half-value width W of the peak in the primary Raman scattering spectrum of the synthetic single-crystal diamond of this embodiment can be 2.7 cm -1 Above and 4.5cm -1 Here, the half-value width refers to the full width at half maximum (FWHM). It is speculated that since the synthetic single-crystal diamond of this embodiment contains a large number of isolated substitutional nitrogen atoms, lattice strain is generated by these isolated substitutional nitrogen atoms, and the half-value width W of the peak becomes wider.

[0081] The large number of isolated substitutional nitrogen atoms in the synthetic single-crystal diamond of this embodiment generates tensile stress in the carbon atoms on the diamond surface, suppressing the frequency of atomic shedding caused by prolonged sliding and thus inhibiting wear due to fatigue. Therefore, when the synthetic single-crystal diamond of this embodiment is used as a material for wear-resistant tools such as molds, the tools can exhibit excellent wear resistance over a long period of time.

[0082] From the perspective of improving wear resistance, the lower limit of the half-value width W may be 2.7 cm. -1 Above, can also be 2.9cm -1 Above, can also be 3.1cm -1 From the perspective of improving sliding properties, the upper limit of the half-value width W can be 4.5 cm -1 Below, can also be 4.3cm -1 Below, can also be 4.2cm -1 Below. The half-value width W can be 2.7 cm -1 Above and 4.5cm -1 Below, can also be 2.9cm -1 Above and 4.3cm -1 Below, can also be 3.1cm -1Above and 4.2cm -1 the following.

[0083] The Raman shift and half-value width of the peaks in the primary Raman scattering spectra of synthetic single-crystal diamond and standard samples were measured using a micro-Raman spectrometer. Measurements were performed at room temperature (20°C to 25°C) using a 532nm laser as the excitation light. Temperature fluctuations in the detector and optical system of the Raman spectrometer were kept to within ±1°C during measurement.

[0084] An arbitrary surface of synthetic single crystal diamond is polished, and the Raman shift of the peak in the primary Raman scattering spectrum of the polished surface is λ1cm -1 An arbitrary surface of a synthetic type IIa single crystal diamond as a standard sample was polished, and the Raman shift of the peak in the primary Raman scattering spectrum of the polished surface was measured by λ2cm. -1 Perform the measurement.

[0085] λ1 and λ2 are the wave numbers where the primary Raman scattering spectrum signal is the strongest. The peak shape is evaluated by peak fitting with a Lorentzian function or a Gaussian function. Based on the peak shape after peak fitting, (λ1-λ2) cm is calculated. -1 Based on this peak shape, the half-value width W of the peak in the primary Raman scattering spectrum of the synthetic single-crystal diamond is obtained.

[0086] <Infrared absorption spectrum>

[0087] In the infrared absorption spectrum of the synthetic single crystal diamond of this embodiment measured by Fourier transform infrared spectroscopy, the wavelength of the synthetic single crystal diamond is 2680 cm -1 Above 2695cm -1 An absorption peak exists in the following range. Synthetic single crystal diamond with this absorption peak exhibits further improved sliding properties. The mechanism for this is not yet clear, but the inventors speculate that the electronic state of isolated substitutional nitrogen atoms within the crystal lattice is the preferred state for improving sliding properties.

[0088] In the present disclosure, in the infrared absorption spectrum at wave number 2680 cm -1 Above 2695cm -1 The absorption peak in the following range refers to the absorption spectrum at wave number 2680cm -1 Above 2695cm -1 In the following range, a maximum value exists in a graph created by subtracting the baseline, and the shape of the peak including the maximum value is a substantially bilaterally symmetrical mountain-shaped figure.

[0089] In the infrared absorption spectrum of the synthetic single crystal diamond of this embodiment measured by Fourier transform infrared spectroscopy, the wave number is 2680 cm -1Above 2695cm -1 The maximum absorption intensity IA of the absorption peak in the following range can be 2160 cm -1 The absorption intensity IB under the condition of 1.0% or more. As a result, the sliding characteristics of the synthetic single crystal diamond are further improved. Here, the wave number 2160cm -1 The absorption intensity IB below refers to the absorption intensity of the absorption caused by phonons from diamond.

[0090] The lower limit of the percentage of the maximum absorption intensity IA to the absorption intensity IB (IA / IB) × 100 can be 1.0% or greater, 1.5% or greater, or 2.0% or greater. The upper limit of the percentage (IA / IB) × 100 is not particularly limited and can be, for example, 30% or less. The percentage (IA / IB) × 100 can be 1.0% or greater and 30% or less, 1.5% or greater and 0% or less, or 2.0% or greater and 30% or less.

[0091] The synthetic single-crystal diamond of this embodiment may not exhibit absorption peaks derived from nitrogen atom aggregates in its infrared absorption spectrum, as measured by Fourier transform infrared spectroscopy. The nitrogen atom aggregates exhibiting absorption peaks in the infrared absorption spectrum are A centers, B centers, and B' centers. In other words, the synthetic single-crystal diamond of this embodiment may not contain A centers, B centers, or B' centers. Consequently, the majority of nitrogen atoms in the synthetic single-crystal diamond exist as isolated substitutional nitrogen atoms, thus facilitating an increase in tensile stress and improving the effect of suppressing abrasive wear.

[0092] In the case of synthetic single crystal diamond containing A centers, in the infrared absorption spectrum, at wave number 1280 cm -1 Over 1284cm -1 There is an absorption peak A below. In the case of synthetic single crystal diamond containing B center, in the infrared absorption spectrum, at wave number 1173cm -1 Over 1177cm -1 There is an absorption peak B below. In the case of synthetic single crystal diamond containing B' center, in the infrared absorption spectrum, at wave number 1358cm -1 Above 1385cm -1 The presence of absorption peak C is shown below. When at least one of absorption peak A, absorption peak B, and absorption peak C is present in the infrared absorption spectrum of synthetic single-crystal diamond, it is determined that an absorption peak derived from aggregates of nitrogen atoms is present in the infrared absorption spectrum. When none of absorption peak A, absorption peak B, and absorption peak C are present in the infrared absorption spectrum of synthetic single-crystal diamond, it is determined that an absorption peak derived from aggregates of nitrogen atoms is absent in the infrared absorption spectrum.

[0093] Examples of possible nitrogen atom forms in the synthetic single-crystal diamond of this embodiment include NV centers, which are nitrogen atoms bonded to vacancies, and H3 centers, which are composed of two nitrogen atoms and a vacancy. Their presence cannot be confirmed by infrared absorption spectroscopy, but can be confirmed by luminescence.

[0094] The infrared absorption spectrum of synthetic single-crystal diamond is obtained by processing the synthetic single-crystal diamond into a plate approximately 1 mm thick, polishing both light-transmitting surfaces to a mirror finish, and measuring the absorbance in the infrared region using Fourier transform infrared spectroscopy. Measurements are performed at room temperature (20°C to 25°C). Temperature fluctuations of the measuring equipment and sample during measurement are kept to within ±1°C.

[0095] <{001} <100> Knoop hardness>

[0096] The {001} plane of the synthetic single crystal diamond of this embodiment <100> Knoop hardness in the direction (also referred to as "{001} <100> Knoop hardness”) can be 65 GPa or more and 90 GPa or less. In the present disclosure, {} represents a plane orientation that is a general term including plane orientations that are equivalent in crystal geometry, and <> represents a direction that is a general term including directions that are equivalent in crystal geometry. In the {001} plane of a typical Ib-type single crystal diamond (nitrogen atom number-based concentration of 50 to 200 ppm), <100> The hardness of the {001} direction is about 100 GPa. The synthetic single crystal diamond of this embodiment can be lower than this. <100> The Knoop hardness is 65 GPa or more, which is much harder than metal materials. Therefore, it is suitable for use in processing metal materials such as SUS, Ni alloy, and Ti alloy.

[0097] The above {001} <100> The lower limit of the Knoop hardness may be 65 GPa or more, 73 GPa or more, or 77 GPa or more. <100> The upper limit of the Knoop hardness may be 90 GPa or less, 87 GPa or less, or 85 GPa or less. <100> The Knoop hardness may be 65 GPa or more and 90 GPa or less, 73 GPa or more and 87 GPa or less, or 77 GPa or more and 85 GPa or less.

[0098] {001} <100> Knoop hardness (hereinafter also referred to as HK, unit is GPa) is measured in accordance with JIS Z 2251:2009 at a temperature of 23°C ± 5°C and a test load of 4.9 N. First, the {001} plane of the synthetic single crystal diamond is <100> The indentation was made in the direction with a load of 4.9 N. The diagonal length a (μm) of the obtained indentation was measured and the {001} <100> Knoop hardness (HK).

[0099] {001} <100> Knoop hardness (HK) = 14229 × 4.9 / a 2 Formula 2

[0100] [Embodiment 2: Method for producing synthetic single-crystal diamond]

[0101] Hereinafter, an example of a method for producing a synthetic single crystal diamond according to the first embodiment will be described. The synthetic single crystal diamond according to the first embodiment may be produced using, for example, Figure 1 The sample chamber having the structure shown was produced by the temperature difference method.

[0102] like Figure 1 As shown, in a sample chamber 10 for producing synthetic single crystal diamond 1, an insulator 2, a carbon source 3, a solvent metal 4, and a seed crystal 5 are arranged in a space surrounded by a graphite heater 7, and a pressure medium 6 is arranged outside the graphite heater 7. The temperature difference method is a synthesis method in which a longitudinal temperature gradient is set inside the sample chamber 10, and a temperature gradient is formed in the high temperature portion (T high ) configure carbon source 3, in the low temperature part (T low ) A diamond seed crystal 5 is configured, a solvent metal 4 is configured between the carbon source 3 and the seed crystal 5, and the conditions are maintained above the temperature at which the solvent metal 4 dissolves and above the pressure at which the diamond becomes thermally stable, so that a synthetic single crystal diamond 1 grows on the seed crystal 5.

[0103] Diamond powder is preferably used as the carbon source 3. Alternatively, graphite or pyrolytic carbon may be used.

[0104] As the solvent metal 4, one or more metals selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), and manganese (Mn), or alloys containing these metals can be used. The solvent metal 4 may further include one or more elements selected from the group consisting of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), hafnium (Hf), tantalum (Ta), tungsten (W), osmium (Os), iridium (Ir), and platinum (Pt).

[0105] Nitrides such as iron nitride (Fe2N, Fe3N), aluminum nitride (AlN), phosphorus nitride (P3N4), silicon nitride (Si3N4), and organic nitrogen compounds such as melamine and sodium azide can be added to the carbon source 3 or solvent metal 4 as nitrogen sources, either alone or as a mixture. Diamond or graphite, which contain a large amount of nitrogen, can also be added as nitrogen sources. Thus, the synthesized synthetic single crystal diamond 1 contains nitrogen atoms. In this case, the nitrogen atoms in the synthetic single crystal diamond 1 are primarily present as isolated substitutional nitrogen atoms.

[0106] The content of the nitrogen supply source in the carbon source 3 or the metal solvent 4 is adjusted so that the concentration of nitrogen atoms in the synthesized diamond single crystal is 200 ppm or more and 1500 ppm or less. For example, when the solvent metal is an alloy composed of iron, cobalt, and nickel and the nitrogen supply source is iron nitride (Fe3N), the concentration of iron nitride (Fe3N) in the solvent metal can be set to 0.01 to 0.15 mass%.

[0107] During the synthesis of synthetic single crystal diamond 1, an ultra-high pressure generator is used to control the pressure and temperature to predetermined conditions. Specifically, the temperature of the low temperature portion is first raised to 1350-1400°C. Then, the pressure is raised to 5.5 GPa while maintaining the temperature constant (hereinafter also referred to as the "first step"). Next, in order to be able to lower the temperature of the low temperature portion to 1300°C ± 10°C while maintaining the pressure at 5.5 GPa, the power input to the ultra-high pressure generator is gradually reduced over 60 hours (hereinafter also referred to as the "second step"). In this way, the synthetic single crystal diamond of embodiment 1 can be obtained. By making the pressure and temperature conditions during synthesis the same as those in the first and second steps, the synthetic single crystal diamond obtained can contain a large number of isolated substitutional nitrogen atoms. Such synthesis conditions are newly discovered by the inventors of the present invention.

[0108] Furthermore, in conventional methods for producing synthetic single-crystal diamond using the temperature difference method, the pressure and temperature during synthesis are kept constant to maintain stable crystal growth. Under these conditions, nitrogen atoms in the synthetic single-crystal diamond tend to exist not only as isolated substitutional nitrogen atoms but also as aggregated nitrogen atoms. Consequently, conventional temperature difference methods have been unable to achieve synthetic single-crystal diamond in which λ1 and λ2 satisfy the relationship in Equation A.

[0109] Example

[0110] This embodiment will be described in more detail with reference to examples, but this embodiment is not limited to these examples.

[0111] [Production of synthetic single crystal diamond]

[0112] Use with Figure 1 In the sample chamber having the structure shown, diamond single crystals of various samples were synthesized by a temperature difference method using a solvent metal.

[0113] An alloy composed of iron, cobalt, and nickel was prepared as a solvent metal, to which iron nitride (Fe3N) powder was added as a nitrogen source. The concentration of iron nitride in the solvent metal is shown in the "Iron Nitride Concentration (Mass%)" column under "Production Conditions" in Table 1. For example, in Sample 2, the concentration of iron nitride in the solvent metal was 0.01% by mass.

[0114] Diamond powder was used as the carbon source, and about 0.5 mg of diamond single crystal was used as the seed crystal. The temperature in the sample chamber was adjusted by a heater to create a temperature difference of several tens of degrees between the high-temperature area containing the carbon source and the low-temperature area containing the seed crystal.

[0115] Using an ultra-high pressure generator, first raise the temperature of the low temperature portion to the temperature recorded in the "Temperature °C" column of the "First Step" of the "Manufacturing Conditions" in Table 1. Then, while maintaining the temperature constant, increase the pressure to 5.5 GPa (first step). Next, in the samples recorded as "Yes" in the "Second Step Power Adjustment" column of Table 1, in order to be able to lower the temperature of the low temperature portion to 1300°C ± 10°C while maintaining the pressure at 5.5 GPa, the power input to the ultra-high pressure generator was gradually reduced over 60 hours (second step). In the samples recorded as "No" in the "Second Step Power Adjustment" column of Table 1, the second step was not performed, and the temperature and pressure in the first step were maintained for 60 hours. Through the above-mentioned steps, synthetic single crystal diamonds of each sample were obtained.

[0116]

[0117] [evaluate]

[0118] The obtained synthetic single crystal diamond was subjected to nitrogen atomic concentration measurement, Raman spectroscopy, infrared spectroscopy, Knoop hardness measurement, and sliding test.

[0119] <Measurement of Nitrogen Atom Concentration>

[0120] The nitrogen atomic concentration of the synthetic single crystal diamond of each sample was measured. The specific measurement method is described in Embodiment 1, so its description will not be repeated. The results are shown in the "Nitrogen Atomic Concentration ppm" column of "Synthetic Single Crystal Diamond" in Table 1.

[0121] <Raman spectroscopy>

[0122] A primary Raman scattering spectrum of synthetic single crystal diamond was prepared for each sample, and the value of (λ1-λ2) and the half-value width W of the peak were measured. The specific measurement method is described in Embodiment 1, so its description will not be repeated. The results are shown in the "λ1-λ2 cm" of the "Raman spectrum" of "Synthetic single crystal diamond" in Table 1. -1 " and "half-value width W cm -1 ” column.

[0123] <Infrared Spectroscopy>

[0124] Infrared absorption spectra of synthetic single crystal diamonds used to prepare each sample, at wave number 2680 cm -1 Above 2695cm -1 The presence or absence of absorption peaks in the following ranges, wave number 2680cm -1 Above 2695cm -1 The maximum absorption intensity IA of the absorption peak in the following range is relative to the wave number 2160 cm -1 The percentage of the absorption intensity IB under (IA / IB) × 100 and the presence or absence of the absorption peak from the aggregate of nitrogen atoms are confirmed or measured. The specific confirmation and measurement method is described in Implementation Example 1, so its description is not repeated. The results are shown in Table 1 "Synthetic Single Crystal Diamond" "Wave Number 2680cm -1 -2695cm -1 Absorption peak", "(IA / IB)×100%" column.

[0125] <{001} <100> Knoop hardness>

[0126] The {001} <100> The Knoop hardness was measured. The specific confirmation and measurement method is described in the first embodiment, so the description thereof will not be repeated. The results are shown in the "{001} <100> Knoop hardness GPa" column.

[0127] <Sliding test>

[0128] use Figure 2The sliding test apparatus 80 shown performs a sliding test on the synthetic single crystal diamond of each sample. The sliding test apparatus 80 includes a machining center 60 and a sample holding unit 70. The machining center 60 includes a spindle 61 and a fixing screw 62 for fixing a SUS wheel 63 to the spindle 61. The sample holding unit 70 includes: a clamp 76 for holding the synthetic single crystal diamond 1 of each sample to be measured; a cylinder 71 for moving the clamp 76 toward the SUS wheel 63; and a linear guide 72 arranged around the cylinder 71. The SUS wheel 63 is a circular plate with a diameter of 10 mm and a thickness of 2 mm, and the blade tip is a U-shaped blade with a blade tip radius of 1 mm. The synthetic single crystal diamond 1 of each sample is in the form of a plate, and the first surface 77 pressed by the SUS wheel 63 is ground by a diamond grinder. The first surface of the synthetic single crystal diamond 1 is a (100) surface.

[0129] The conditions for the sliding test are as follows: The following conditions correspond to a low-load and long-term sliding process.

[0130] Load: 0.5N

[0131] Circumferential speed: 150m / min

[0132] Test time: 200 minutes

[0133] At the end of the test (after 200 minutes), the depth of the sliding wear scar formed on the surface of the synthetic single-crystal diamond 1 of each sample was measured. The results are shown in the "Sliding Wear Scar Depth μm" column under "Sliding Test" in Table 1. A smaller sliding wear scar depth indicates better sliding properties and wear resistance of the synthetic single-crystal diamond.

[0134] [Investigation]

[0135] Samples 3 to 16 correspond to Examples. Samples 1, 2, and 17 correspond to Comparative Examples. It was confirmed that Samples 3 to 16 (Examples) exhibited smaller sliding wear scar depths in the sliding test than Samples 1, 2, and 17 (Comparative Examples), demonstrating superior wear resistance even during low-load, long-term sliding processing.

[0136] As described above, the embodiments and examples of the present disclosure have been described. However, it is anticipated from the outset that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways.

[0137] The embodiments and examples disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated not by the embodiments and examples described above but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0138] Description of Reference Numerals

[0139] 1: synthetic single crystal diamond; 2: insulator; 3: carbon source; 4: solvent metal; 5: seed crystal; 6: pressure medium; 7: graphite heater; 10: sample chamber; 60: machining center; 61: spindle; 62: fixing screw; 63: SUS wheel; 70: sample holding part; 71: cylinder; 72: linear guide; 76: fixture; 77: first surface; 80: sliding test device.

Claims

1. A synthetic single-crystal diamond comprising nitrogen atoms at a concentration of 200 ppm to 1500 ppm based on the number of atoms, wherein: The Raman shift of the peak in the primary Raman scattering spectrum of the synthetic single crystal diamond is λ1 cm -1 The Raman shift λ2cm of the peak in the primary Raman scattering spectrum of synthetic type IIa single crystal diamond with a nitrogen atom concentration of 1 ppm or less based on the atomic number of nitrogen atoms is -1 The relationship of the following formula A is shown: -0.85<λ1-λ2≤-0.15Formula A.

2. The synthetic single crystal diamond according to claim 1, wherein The half-value width W of the peak in the primary Raman scattering spectrum of the synthetic single crystal diamond is 2.7 cm -1 Above and 4.5cm -1 the following.

3. The synthetic single crystal diamond according to claim 1 or 2, wherein: In the infrared absorption spectrum of the synthetic single crystal diamond measured by Fourier transform infrared spectroscopy, at the wave number 2680 cm -1 Above 2695cm -1 There is an absorption peak in the following range.

4. The synthetic single crystal diamond according to any one of claims 1 to 3, wherein In the infrared absorption spectrum of the synthetic single crystal diamond measured by Fourier transform infrared spectroscopy, the wave number is 2680 cm -1 Above 2695cm -1 The maximum absorption intensity IA of the absorption peak in the following range is at wave number 2160 cm -1 The absorption intensity IB is more than 1.0%.

5. The synthetic single crystal diamond according to any one of claims 1 to 4, wherein The {001} plane of the synthetic single crystal diamond <100> The Knoop hardness in the direction is 65 GPa or more and 90 GPa or less. The Knoop hardness is measured in accordance with JIS Z 2251:2009 at a temperature of 23° C.±5° C. and a test load of 4.9 N.

6. The synthetic single crystal diamond according to any one of claims 1 to 5, wherein In the infrared absorption spectrum of the synthetic single crystal diamond measured by Fourier transform infrared spectroscopy, there is no absorption peak derived from aggregates of nitrogen atoms.

Images