Synthetic single crystal diamond and its manufacturing method

Abstract

A synthetic single crystal diamond containing 100-1500 ppm inclusive of nitrogen atoms, said synthetic single crystal diamond containing an aggregate consisting of a single pore and one of two to four nitrogen atoms existing adjacent to the pore, wherein the ratio b / a [wherein a stands for the length of the longer diagonal line and b stands for the length of the shorter diagonal line between the diagonal lines of a Knoop indentation along the direction <110> in the plane {001} of the synthetic single crystal diamond] is 0.08 or less, said Knoop indentation having been formed by measuring the Knoop hardness along the direction <100> in the plane {001} of the synthetic single crystal diamond in accordance with JIS Z 2251:2009 at a temperature of 23°C±5°C under a test load of 4.9 N.

Description

[Technical Field]

[0001] This disclosure relates to synthetic single crystal diamonds and methods for producing the same. This application claims priority to Japanese Patent Application No. 2020-113054, filed on June 30, 2020. The entire contents of said Japanese Patent Application are incorporated herein by reference. [Background technology]

[0002] Due to its high hardness, single crystal diamond is widely used in tools such as cutting tools, grinding tools, and wear-resistant tools. The single crystal diamonds used in tools include natural diamonds and synthetic diamonds.

[0003] Most natural diamonds contain agglomerated nitrogen atoms (type Ia) as impurities. The agglomerated nitrogen atoms in diamond crystals can prevent plastic deformation and crack propagation that occurs when diamonds are used in tools. This gives natural diamonds high mechanical strength. However, natural diamonds vary widely in quality and their supply is unstable, limiting their use in industrial applications.

[0004] On the other hand, synthetic diamonds are widely used in industrial fields because they have consistent quality and can be supplied stably.

[0005] Ordinary synthetic diamonds contain isolated substitutional nitrogen atoms (type Ib) as impurities. The higher the concentration of isolated substitutional nitrogen atoms in a diamond crystal, the more likely the mechanical properties of the diamond tend to deteriorate. Therefore, when type Ib synthetic diamonds are used in tools, they tend to be prone to wear and chipping of the cutting edge.

[0006] There are also synthetic diamonds (type IIa) that contain almost no nitrogen impurities. Type IIa synthetic diamonds do not contain impurities or crystal defects that prevent cracks from progressing, so when used in tools, they tend to chip the cutting edge.

[0007] Therefore, research is being conducted into techniques for improving the wear resistance and chipping resistance of synthetic diamonds.

[0008] For example, Patent Document 1 (WO 2019 / 077888) discloses a synthetic single crystal diamond that has high hardness and excellent chipping resistance. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2019 / 077888 Summary of the Invention

[0010] The synthetic single crystal diamond of the present disclosure is a synthetic single crystal diamond containing nitrogen atoms in an amount of 100 ppm or more and 1500 ppm or less, the synthetic single crystal diamond comprises an aggregate consisting of one vacancy and any one of two to four nitrogen atoms adjacent to the vacancy; The synthetic single crystal diamond has a {001} plane. <110> the ratio b / a of the length b of the shorter diagonal line of the Knoop indentation in the direction to the length a of the longer diagonal line is 0.08 or less, The Knoop indentation is in the {001} plane of the synthetic single crystal diamond. <100> This is a synthetic single crystal diamond formed by measuring the Knoop hardness in the direction in accordance with JIS Z 2251:2009 at a temperature of 23°C ± 5°C and a test load of 4.9N.

[0011] The method for producing a synthetic single crystal diamond according to the present disclosure is a method for producing the above-described synthetic single crystal diamond, comprising the steps of: A first step of synthesizing a diamond single crystal containing nitrogen atoms at a concentration of 100 ppm to 1500 ppm (based on the atomic number) by a temperature difference method using a solvent metal; a second step of irradiating the diamond single crystal with one or both of an electron beam and a particle beam imparting an energy of 100 MGy or more and 1000 MGy or less; This is a method for producing synthetic single crystal diamond, which includes a third step in which the diamond single crystal after the second step is subjected to a pressure of 5 GPa or more and a temperature of 2300°C to 2600°C for 1 minute to 3600 minutes to obtain a synthetic single crystal diamond. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram for explaining the Knoop indentation. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an example of a sample chamber configuration used in producing synthetic single crystal diamond according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Problem to be solved by this disclosure] Due to the recent demand for longer tool life, there is a demand for synthetic single crystal diamonds with even better wear resistance and chipping resistance.

[0014] Therefore, an object of the present invention is to provide a synthetic single crystal diamond that has high hardness, a large elastic recovery rate, and excellent chipping resistance. [Effects of this disclosure]

[0015] According to the present disclosure, it is possible to provide a synthetic single crystal diamond that has high hardness, a large elastic recovery rate, and excellent chipping resistance.

[0016] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) The synthetic single crystal diamond of the present disclosure is a synthetic single crystal diamond containing 100 ppm or more and 1500 ppm or less of nitrogen atoms, the synthetic single crystal diamond comprises an aggregate consisting of one vacancy and any one of two to four nitrogen atoms adjacent to the vacancy; The synthetic single crystal diamond has a {001} plane. <110> the ratio b / a of the length b of the shorter diagonal line of the Knoop indentation in the direction to the length a of the longer diagonal line is 0.08 or less, The Knoop indentation is in the {001} plane of the synthetic single crystal diamond. <100> This is a synthetic single crystal diamond formed by measuring the Knoop hardness in the direction in accordance with JIS Z 2251:2009 at a temperature of 23°C ± 5°C and a test load of 4.9N.

[0017] The synthetic single crystal diamond of the present disclosure has high hardness, high elastic recovery, and excellent chipping resistance.

[0018] (2) In the infrared absorption spectrum of the synthetic single crystal diamond, the wave number is 1175±2 cm -1 It is preferable that the absorption peak is within the range of

[0019] According to this, synthetic single crystal diamond can have high hardness, a large elastic recovery rate, and excellent chipping resistance.

[0020] (3) In the fluorescence spectrum of the synthetic single crystal diamond, it is preferable that an emission peak exists in either or both of the fluorescence wavelength range of 503±2 nm and the fluorescence wavelength range of 510 nm or more and 530 nm or less.

[0021] According to this, synthetic single crystal diamond can have high hardness, a large elastic recovery rate, and excellent chipping resistance.

[0022] (4) In the fluorescence spectrum of the synthetic single crystal diamond, it is preferable that an emission peak exists in either or both of the fluorescence wavelength range of 415±2 nm and the fluorescence wavelength range of 420 nm to 470 nm.

[0023] According to this, synthetic single crystal diamond can have high hardness, a large elastic recovery rate, and excellent chipping resistance.

[0024] (5) In the infrared absorption spectrum of the synthetic single crystal diamond, the wave number is 1282±2 cm -1 It is preferable that the absorption peak is within the range of

[0025] According to this, synthetic single crystal diamond can have high hardness, a large elastic recovery rate, and excellent chipping resistance.

[0026] (6) In the infrared absorption spectrum of the synthetic single crystal diamond, the wave number is 1370 cm -1 Over 1385cm -1 It is preferable that the absorption peak is within the following range:

[0027] According to this, synthetic single crystal diamond can have high hardness, a large elastic recovery rate, and excellent chipping resistance.

[0028] (7) The {001} plane of the synthetic single crystal diamond <100> The Knoop hardness in the direction is preferably 100 GPa or more.

[0029] This allows synthetic single crystal diamond to have excellent wear resistance.

[0030] (8) In a fracture strength test in which a spherical diamond indenter with a tip radius of 50 μm is pressed against the surface of the synthetic single crystal diamond at a load rate of 100 N / min, the crack initiation load is preferably 17 N or more.

[0031] This allows synthetic single crystal diamond to have excellent chipping resistance.

[0032] (9) The method for producing a synthetic single crystal diamond according to the present disclosure includes: The method for producing the synthetic single crystal diamond described above comprises: A first step of synthesizing a diamond single crystal containing nitrogen atoms at a concentration of 100 ppm to 1500 ppm (based on the atomic number) by a temperature difference method using a solvent metal; a second step of irradiating the diamond single crystal with one or both of an electron beam and a particle beam imparting an energy of 100 MGy or more and 1000 MGy or less; This is a method for producing synthetic single crystal diamond, which includes a third step in which the diamond single crystal after the second step is subjected to a pressure of 5 GPa or more and a temperature of 2300°C to 2600°C for 1 minute to 3600 minutes to obtain a synthetic single crystal diamond.

[0033] This makes it possible to obtain a synthetic single crystal diamond that has high hardness, a large elastic recovery rate, and excellent chipping resistance.

[0034] [Details of the embodiments of the present disclosure] <Form of nitrogen atoms in diamond crystals> First, to deepen understanding of the synthetic single crystal diamond of the present disclosure, we will explain nitrogen atoms present as impurities in the crystal, which is one of the main factors that determine the performance of diamond.

[0035] Nitrogen atoms in a diamond crystal can be classified into isolated substitutional nitrogen atoms, aggregated nitrogen atoms, and the like depending on their state of existence.

[0036] An isolated substitutional nitrogen atom (C center) is one in which a nitrogen atom replaces a carbon atom in a diamond crystal.

[0037] The present inventors have newly hypothesized that when an isolated substitutional nitrogen atom is contained in a diamond crystal, local tensile stress is generated in the crystal lattice around it, which becomes the starting point for plastic deformation and fracture, reducing hardness and reducing wear resistance and chipping resistance.

[0038] Synthetic single-crystal diamond containing isolated substitutional nitrogen atoms exhibits an infrared absorption spectrum measured by Fourier transform infrared spectroscopy at a wavenumber of 1130 cm-1 (i.e., wavenumber 1130±2cm -1 ) shows the absorption peak.

[0039] In synthetic single-crystal diamonds containing isolated substitutional nitrogen atoms, the presence of unpaired electrons originating from the nitrogen atoms allows the concentration of isolated substitutional nitrogen atoms to be measured by ESR analysis (ESR: Electron Spin Resonance). In addition to isolated substitutional nitrogen atoms, ESR also detects signals from crystal defects and other sources that have unpaired electrons. In this case, isolated substitutional nitrogen atoms can be isolated and detected by measuring the g-value or the relaxation time of the signal.

[0040] Agglomerated nitrogen atoms are those in which two or more nitrogen atoms are aggregated together in a diamond crystal.

[0041] The present inventors have newly assumed that the aggregated nitrogen atoms in diamond crystals can suppress the plastic deformation and crack growth that occur when a load is applied to the diamond crystals.The present inventors have newly assumed that when diamond crystals contain aggregated nitrogen atoms, the hardness of the diamond crystals increases, the elastic deformability increases, and the fracture resistance improves.

[0042] The agglomerated nitrogen atoms are classified into A center (two nitrogen atom pair), H3 center (two nitrogen atom agglomeration), N3 center (three nitrogen atom agglomeration), and B center (four nitrogen atom agglomeration). collection ) and B' centers (platelets), etc.

[0043] The A center (nitrogen diatomic pair) is an aggregate consisting of two nitrogen atoms, which are covalently bonded and each nitrogen atom is substituted for a carbon atom that constitutes a diamond crystal. Diamonds containing the A center (nitrogen diatomic pair) are called IaA type. Synthetic single crystal diamonds containing the A center (nitrogen diatomic pair) have a wavenumber of 1282 cm in the infrared absorption spectrum measured by Fourier transform infrared spectroscopy. -1 (e.g., wave number 1282±2 cm -1) shows the absorption peak.

[0044] The H3 center (diatomic nitrogen agglomerate) is an agglomerate consisting of one vacancy and two nitrogen atoms adjacent to the vacancy, and each nitrogen atom is substituted for a carbon atom constituting a diamond crystal. In this specification, "nitrogen atom adjacent to the vacancy" means the nitrogen atom with the shortest interatomic distance to the carbon atom (i.e., nearest neighbor atom) when a carbon atom is assumed to exist at the position of the vacancy. This also applies to the N3 center and B center described below.

[0045] Synthetic single crystal diamond containing an H3 center (agglomeration of two nitrogen atoms) has a fluorescence spectrum obtained by irradiating it with excitation light shorter than approximately 500 nm, for example, excitation light with a wavelength of 325 nm, in which an emission peak exists near a fluorescence wavelength of 503 nm (for example, a fluorescence wavelength of 503±2 nm) and / or within the fluorescence wavelength range of 510 nm or more and 530 nm or less.

[0046] An N3 center (agglomeration of three nitrogen atoms) is an aggregate consisting of one vacancy and three nitrogen atoms adjacent to the vacancy, and each nitrogen atom replaces a carbon atom that makes up the diamond crystal.

[0047] Synthetic single crystal diamond containing an N3 center (agglomeration of three nitrogen atoms) has a fluorescence spectrum obtained by irradiating it with excitation light shorter than approximately 410 nm, for example, excitation light with a wavelength of 325 nm, in which an emission peak exists near a fluorescence wavelength of 415 nm (for example, a fluorescence wavelength of 415±2 nm) and / or within the fluorescence wavelength range of 420 nm or more and 470 nm or less.

[0048] B center (4 nitrogen atoms) collection ) is an aggregate consisting of one vacancy and four nitrogen atoms adjacent to the vacancy, each of which replaces a carbon atom that makes up the diamond crystal.

[0049] Diamonds containing B centers (four nitrogen atoms aggregated) are called IaB type. Synthetic single crystal diamonds containing four nitrogen atoms aggregated have a wavenumber of 1175 cm in the infrared absorption spectrum measured by Fourier transform infrared spectroscopy. -1 (e.g., wave number 1175±2cm -1 ) shows the absorption peak.

[0050] B' centers (also called platelets) are plate-shaped aggregates consisting of five or more nitrogen atoms and interstitial carbon atoms, and are incorporated as inclusions within the crystal.

[0051] Diamonds containing B' centers (platelets) are called IaB' type. Synthetic single crystal diamonds containing B' centers (platelets) have a wavenumber of 1358 cm in the infrared absorption spectrum measured by Fourier transform infrared spectroscopy. -1 Over 1385cm -1 The absorption peaks are shown below.

[0052] The present inventors have conducted extensive research into aggregated nitrogen atoms that can improve the properties of synthetic single crystal diamond, and have newly discovered that the B center, H3 center, and N3 center have little crystal distortion and a stable structure.The present inventors have also newly discovered that by forming at least one of the B center, H3 center, and N3 center in synthetic single crystal diamond, it is possible to further improve the mechanical properties of the synthetic single crystal diamond, such as hardness, elastic deformability, and fracture resistance, and have completed the present disclosure.

[0053] The specific example of the synthetic single crystal diamond and its manufacturing method of the present disclosure will be described below with reference to the drawings.In the drawings of the present disclosure, the same reference numerals represent the same parts or corresponding parts.In addition, the dimensional relationships of length, width, thickness, depth, etc. are appropriately changed for the purpose of clarifying and simplifying the drawings, and do not necessarily represent the actual dimensional relationships.

[0054] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0055] In this specification, a generic plane orientation including crystal geometrically equivalent plane orientations is indicated by {}, and a generic direction including crystal geometrically equivalent directions is indicated by < >.

[0056] [Embodiment 1: Synthetic single crystal diamond] The synthetic single crystal diamond of this embodiment is a synthetic single crystal diamond containing 100 ppm or more and 1500 ppm or less of nitrogen atoms, and the synthetic single crystal diamond includes an aggregate consisting of one vacancy and any one of two to four nitrogen atoms present adjacent to the vacancy, and in the {001} plane of the synthetic single crystal diamond <110> The ratio b / a of the length of the shorter diagonal line b to the length of the longer diagonal line a of the Knoop indentation in the direction is 0.08 or less, and the Knoop indentation is formed in the {001} plane of the synthetic single crystal diamond. <100> This is a synthetic single crystal diamond formed by measuring the Knoop hardness in the direction in accordance with JIS Z 2251:2009 at a temperature of 23°C ± 5°C and a test load of 4.9N.

[0057] The synthetic single crystal diamond of this embodiment has high hardness, a large elastic recovery rate, and excellent chipping resistance. The reasons for this are not clear, but are presumed to be as follows (i) to (iii).

[0058] (i) The synthetic single crystal diamond of this embodiment contains nitrogen atoms at a concentration of 100 ppm or more and 1500 ppm or less based on the number of atoms. This makes it easy for the nitrogen atoms in the synthetic single crystal diamond to aggregate together. Therefore, the synthetic single crystal diamond is easy to contain aggregated nitrogen atoms, has large elastic deformation properties, and improves fracture resistance.

[0059] (ii) The synthetic single crystal diamond of this embodiment contains an aggregate consisting of one vacancy and two to four nitrogen atoms adjacent to the vacancy, and therefore has high hardness, large elastic deformability, and improved fracture resistance.

[0060] (iii) In the synthetic single crystal diamond of this embodiment, the ratio b / a of the diagonals of the Knoop indentation is 0.08 or less. Therefore, the synthetic single crystal diamond has high elastic deformability. The relationship between the Knoop indentation and elastic deformability will be described later.

[0061] <Nitrogen atom concentration> The synthetic single crystal diamond of this embodiment contains nitrogen atoms at a concentration of 100 ppm or more and 1500 ppm or less based on the number of atoms (hereinafter also referred to as "nitrogen atom concentration"). If the nitrogen atom concentration is 100 ppm or more, the nitrogen atoms in the synthetic single crystal diamond tend to form aggregated nitrogen atoms. If the nitrogen atom concentration is 1500 ppm or less, the synthetic single crystal diamond can have high hardness and excellent chipping resistance.

[0062] The lower limit of the nitrogen atom concentration in synthetic single crystal diamond can be 100 ppm or more, 200 ppm or more, or 300 ppm or more.The upper limit of the nitrogen atom concentration in synthetic single crystal diamond can be 1500 ppm or less, 1400 ppm or less, or 1300 ppm or less.The nitrogen atom concentration in synthetic single crystal diamond can be 100 ppm or more and 1500 ppm or less, 100 ppm or more and 1400 ppm or less, 100 ppm or more and 1300 ppm or less, 200 ppm or more and 1500 ppm or less, 200 ppm or more and 1400 ppm or less, 200 ppm or more and 1300 ppm or less, 300 ppm or more and 1500 ppm or less, 300 ppm or more and 1400 ppm or less, or 300 ppm or more and 1300 ppm or less.

[0063] The nitrogen atom concentration in synthetic single crystal diamond can be measured by secondary ion mass spectrometry (SIMS).

[0064] <Agglomerated nitrogen atoms> The synthetic single crystal diamond of this embodiment includes an aggregate consisting of one vacancy and two to four nitrogen atoms adjacent to the vacancy. An example of an aggregate consisting of one vacancy and two nitrogen atoms adjacent to the vacancy is the H3 center (agglomeration of two nitrogen atoms). An example of an aggregate consisting of one vacancy and three nitrogen atoms adjacent to the vacancy is the N3 center (agglomeration of three nitrogen atoms). An example of an aggregate consisting of one vacancy and four nitrogen atoms adjacent to the vacancy is the B center (agglomeration of four nitrogen atoms).

[0065] The B center, H3 center, and N3 center have little crystal distortion and a stable structure. The synthetic single crystal diamond of this embodiment contains at least one of the B center, H3 center, and N3 center, and therefore has high hardness, large elastic deformability, and excellent chipping resistance.

[0066] (Center B) The synthetic single crystal diamond of this embodiment preferably contains an aggregate (B center (agglomerate of four nitrogen atoms)) consisting of one vacancy and four nitrogen atoms adjacent to the vacancy. The presence of a B center in a synthetic single crystal diamond can be confirmed by an infrared absorption spectrum measured by Fourier transform infrared spectroscopy. Specifically, in the infrared absorption spectrum, a B center at a wave number of 1175 cm -1 (e.g., wave number 1175±2cm -1 ) is present, the synthetic single crystal diamond is judged to contain a B center.

[0067] (H3 Center) The synthetic single crystal diamond of this embodiment preferably contains an aggregate (H3 center (diatomic nitrogen aggregate)) consisting of one vacancy and two nitrogen atoms present adjacent to the vacancy. The presence of an H3 center in a synthetic single crystal diamond can be confirmed by a fluorescence spectrum obtained by irradiating the synthetic single crystal diamond with excitation light of a wavelength of 325 nm. Specifically, if the fluorescence spectrum obtained by irradiating the synthetic single crystal diamond with excitation light of a wavelength of 325 nm contains an emission peak in either or both of the fluorescence wavelength range of 503±2 nm and the fluorescence wavelength range of 510 nm or more and 530 nm or less, the synthetic single crystal diamond is judged to contain an H3 center.

[0068] The peak in the fluorescence wavelength range of 503±2 nm is an emission peak corresponding to the zero-phonon line of the H3 center, and the emission peak in the fluorescence wavelength range of 510 nm to 530 nm is an emission peak corresponding to the subband (phonon sideband) of the H3 center. The emission peak in the fluorescence wavelength range of 510 nm to 530 nm is observed as one or more mountain-shaped peaks within that range. At least one of the mountain-shaped peaks exhibits the maximum intensity within that range.

[0069] (N3 Center) The synthetic single crystal diamond of this embodiment preferably contains an aggregate (N3 center (agglomeration of three nitrogen atoms)) consisting of one vacancy and three nitrogen atoms present adjacent to the vacancy. Whether a synthetic single crystal diamond contains an N3 center can be confirmed by the fluorescence spectrum obtained by irradiating the synthetic single crystal diamond with excitation light of a wavelength of 325 nm. Specifically, if the fluorescence spectrum obtained by irradiating the synthetic single crystal diamond with excitation light of a wavelength of 325 nm contains an emission peak in either or both of the fluorescence wavelength range of 415±2 nm and the fluorescence wavelength range of 420 nm or more and 470 nm or less, the synthetic single crystal diamond is judged to contain an N3 center.

[0070] The peak in the fluorescence wavelength range of 415±2 nm is an emission peak corresponding to the zero-phonon line of the N3 center, and the emission peak in the fluorescence wavelength range of 420 nm to 470 nm is an emission peak corresponding to the subband (phonon sideband) of the N3 center. The emission peak in the fluorescence wavelength range of 420 nm to 470 nm is observed as one or more mountain-shaped peaks within that range. At least one of the mountain-shaped peaks exhibits the maximum intensity within that range.

[0071] (A center (two nitrogen atom pair)) The synthetic single crystal diamond of this embodiment preferably contains an A center (a pair of two nitrogen atoms). The A center in the synthetic single crystal diamond can suppress the propagation of cracks. Therefore, the synthetic single crystal diamond can have excellent chipping resistance.

[0072] The presence of an A center in a synthetic single crystal diamond can be confirmed by an infrared absorption spectrum measured by Fourier transform infrared spectroscopy. Specifically, in the infrared absorption spectrum, the A center at a wave number of 1282 cm -1 Near (e.g., 1282±2 cm -1 ) is present, the synthetic single crystal diamond is judged to contain an A center.

[0073] (B' center (platelet)) The synthetic single crystal diamond of this embodiment has an infrared absorption spectrum with a wave number of 1370 cm -1 Over 1385cm -1 It is preferable that the absorption peak is present within the following range: The absorption peak is derived from the B' center (platelet) in the synthetic single crystal diamond.

[0074] In the infrared absorption spectrum of synthetic single crystal diamond, the wavenumber is 1370 cm -1 Over 1385cm -1If the absorption peak is within the range below, the size of the nitrogen atom aggregates contained in the B' center (platelet) is appropriate, which can prevent plastic deformation and crack propagation and is less likely to become the starting point of fracture. Therefore, the synthetic single crystal diamond can have high hardness and excellent strength.

[0075] Generally, synthetic single crystal diamonds containing B' centers (platelets) have a wave number of 1358 cm in the infrared absorption spectrum. -1 Over 1385cm -1 The absorption peak is shown below. However, the wave number is 1370 cm -1 Smaller range (wavenumber 1358 cm -1 wave number 1370cm or more -1 If there is an absorption peak at a wavenumber of 1358 cm or less, the B' center (platelet) aggregates within the crystal are too large and can become the starting point for fracture, which is undesirable. Therefore, in the infrared absorption spectrum of synthetic single crystal diamond, -1 wave number 1370cm or more -1 It is preferred that there be no absorption peaks within the range of less than 1000 nm.

[0076] (Other agglomerated nitrogen atoms) Aggregated nitrogen atoms other than the H3 center, N3 center, B center, and B' center do not have a significant effect on the mechanical properties of synthetic single crystal diamond. Therefore, the synthetic single crystal diamond of this embodiment may contain aggregated nitrogen atoms other than the H3 center, N3 center, B center, and B' center.

[0077] <Lone-substituted nitrogen atom> The synthetic single crystal diamond of this embodiment preferably does not contain isolated substitutional nitrogen atoms (C centers), which allows the synthetic single crystal diamond of this embodiment to have high hardness and excellent chipping resistance.

[0078] The absence of isolated substitutional nitrogen atoms in synthetic single crystal diamonds can be determined by the infrared absorption spectrum measured by Fourier transform infrared spectroscopy. Single crystal diamonds containing isolated substitutional nitrogen atoms have a wavelength of 1130 cm in the infrared absorption spectrum measured by Fourier transform infrared spectroscopy. -1 (i.e., wavenumber 1130±2cm -1 ) in the infrared absorption spectrum of synthetic single crystal diamond. -1 By confirming that no absorption peaks due to isolated substitutional nitrogen atoms are present in the range, it can be determined that no isolated substitutional nitrogen atoms are present.

[0079] In the infrared absorption spectrum, the wave number is 1130±2 cm -1 In the range, there is a shoulder in the absorption spectrum of aggregated nitrogen atoms other than isolated substitutional nitrogen atoms, and if it is unclear whether the shoulder is an absorption peak derived from isolated substitutional nitrogen atoms, the presence or absence of isolated substitutional nitrogen atoms can be determined by ESR analysis. If there are no isolated substitutional nitrogen atoms in a synthetic single crystal diamond, there are no unpaired electrons in the synthetic single crystal diamond. Therefore, when ESR analysis is performed on such a synthetic single crystal diamond, no signal is detected. This confirms that there are no isolated substitutional nitrogen atoms in the synthetic single crystal diamond.

[0080] <Infrared absorption spectrum> When a diamond crystal contains C centers, A centers, B centers, and B' centers (platelets), absorption peaks originating from each center are observed in the infrared absorption spectrum of the diamond crystal measured by Fourier transform infrared spectroscopy. Because the waveforms of each center overlap, the presence or amount of each center cannot be determined solely from the intensity value at each wavenumber. However, by considering the approximate waveform of each center through a relative comparison of the intensity at each wavenumber, it is possible to determine the presence or absence of each center and qualitatively evaluate the content ratio of each center.

[0081] <Ratio of diagonals of Knoop indentation b / a> In the {001} plane of the synthetic single crystal diamond of this embodiment <110> The ratio b / a of the length of the shorter diagonal line b to the length of the longer diagonal line a of the Knoop indentation in the direction is 0.08 or less, and the Knoop indentation is formed in the {001} plane of the synthetic single crystal diamond. <100> The Knoop hardness in the direction is measured in accordance with JIS Z 2251:2009 at a temperature of 23°C ± 5°C and a test load of 4.9N.

[0082] The measurement of the Knoop hardness is known as one of the scales for expressing the hardness of industrial materials, as specified in JIS Z2251:2009, and involves pressing a Knoop indenter against the material to be measured at a predetermined temperature and with a predetermined load (test load) to determine the hardness of the material.

[0083] Here, the Knoop indenter is a diamond indenter in the shape of a quadrangular prism with a diamond-shaped base. The diamond-shaped base has a ratio b' / a' of the length b' of the shorter diagonal to the length a' of the longer diagonal. The Knoop indentation refers to a mark left at the point where the Knoop indenter is released immediately after being pressed against the material to be measured (synthetic single crystal diamond in this embodiment) at the above temperature and test load. In this embodiment, the indentation is made by pressing the Knoop indenter against the {001} plane of the synthetic single crystal diamond. <100> In accordance with JIS Z 2251:2009, an indentation (Knoop indentation) is made in the direction of the sample at a temperature of 23°C ± 5°C and a test load of 4.9N.

[0084] One of the features of the synthetic single crystal diamond of this embodiment is that the ratio b / a of the diagonal lines of the Knoop indentation is 0.08 or less, which is smaller than the ratio b' / a' (0.141) of the original Knoop indenter. This is because the material to be measured (i.e., the synthetic single crystal diamond in this embodiment) behaves elastically, causing the indentation to elastically return to its original shape (elastic recovery).

[0085] The above phenomenon will be explained using Figure 1, which conceptually shows a Knoop indentation. For example, if the material being measured does not exhibit any elastic recovery, the cross section of the Knoop indenter and the Knoop indentation will have the same shape (the part shown as "original Knoop indentation" in Figure 1). On the other hand, the synthetic single crystal diamond of this embodiment is prone to elastic deformation in the direction of the arrow in the figure, so the Knoop indentation will be rhombic, as shown by the solid line in the figure. In other words, the greater the return in the direction of the arrow in the figure, the smaller the value of the ratio b / a. The smaller the value of the ratio b / a, the greater the elastic deformability.

[0086] The synthetic single crystal diamond of this embodiment has a diagonal ratio b / a of the Knoop indentation of 0.08 or less, and therefore has large elastic deformability. Large elastic deformation results in high toughness, resulting in a tough synthetic single crystal diamond.

[0087] The upper limit of the ratio b / a of the diagonal lines of the Knoop indentation is 0.08 or less, and can be 0.075 or less, 0.07 or less, 0.065 or less, or 0.06 or less. The smaller the ratio b / a of the diagonal lines of the Knoop indentation, the greater the elastic deformability, so there is no particular need to set a lower limit. There are cases where no plastic deformation or fracture occurs at all, in which case b / a is 0, and the Knoop indentation consists only of the longer diagonal line. Therefore, the lower limit of the ratio b / a of the diagonal lines of the Knoop indentation can be 0 or more. The ratio b / a of the diagonal lines of the Knoop indentation can be 0 or more, 0 or more to 0.08 or 0 or more to 0.075 or 0 or more to 0.06 or less. 0.07 Hereinafter, it can be set to 0 or more and 0.065 or less, or 0 or more and 0.06 or less.

[0088] <Knoop hardness> The synthetic single crystal diamond according to this embodiment has a {001} plane. <100> Knoop hardness in the {001} direction (hereinafter referred to as <100> The Knoop hardness (also referred to as "hardness") is preferably 100 GPa or more. <100> Synthetic single crystal diamonds, which have a Knoop hardness of 100 GPa or more, are harder and more wear-resistant than natural diamonds, which contain nitrogen.

[0089] {001} of synthetic single crystal diamond <100> The lower limit of the Knoop hardness can be 105GPa or more, 110GPa or more, or 115GPa or more. <100> The upper limit of the Knoop hardness is not particularly limited, but from the viewpoint of manufacturing, it can be set to, for example, 150 GPa or less. <100> The Knoop hardness can be 100 GPa or more and 150 GPa or less, 105 GPa or more and 150 GPa or less, 110 GPa or more and 150 GPa or less, or 115 GPa or more and 150 GPa or less.

[0090] {001} of synthetic single crystal diamond <100> The method for evaluating the Knoop hardness (hereinafter also referred to as HK, unit is GPa) will be explained. First, the Knoop hardness in the {001} plane of synthetic single crystal diamond <100> In accordance with JIS Z 2251:2009, an indentation is made in the direction perpendicular to the specimen at a temperature of 23°C ± 5°C and a test load of 4.9 N. The diagonal line a (μm) on the longer side of the indentation is measured, and the Knoop hardness (HK) is calculated using the following formula A.

[0091] HK=14229×4.9 / a 2 Formula A

[0092] <Crack initiation load> The synthetic single crystal diamond of this embodiment preferably has a crack initiation load of 15 N or more in a fracture strength test in which a spherical diamond indenter with a tip radius (R) of 50 μm is pressed against the surface of the synthetic single crystal diamond at a load rate of 100 N / min. If the crack initiation load is 15 N or more, the synthetic single crystal diamond has excellent fracture strength and fracture resistance, and when used as a tool material, chipping of the cutting edge is unlikely to occur.

[0093] The lower limit of the crack initiation load of synthetic single crystal diamond can be 17N or more, 20N or more, 25N or more, 30N or more.The upper limit of the crack initiation load is not particularly limited, but from the viewpoint of manufacturing, it is, for example, 50N or less.The crack initiation load of synthetic single crystal diamond can be 15N or more and 50N or less, 17N or more and 50N or less, 20N or more and 50N or less, 25N or more and 50N or less, 30N or more and 50N or less.

[0094] The specific method for the fracture strength test is as follows: A spherical diamond indenter with a tip radius (R) of 50 μm is pressed against the sample, and a load is applied to the sample at a loading rate of 100 N / min, and the load at the moment when a crack appears in the sample (crack initiation load) is measured. The moment when a crack appears is measured with an AE sensor. A higher crack initiation load indicates a higher sample strength and better fracture resistance.

[0095] If an indenter with a tip radius (R) smaller than 50 μm is used as the measurement indenter, the sample will undergo plastic deformation before a crack occurs, making it impossible to accurately measure the strength of the crack. While measurements are possible using an indenter with a tip radius (R) larger than 50 μm, this increases the load required for crack occurrence and the contact area between the indenter and the sample, resulting in problems such as the effect of sample surface imperfections on measurement accuracy and the significant influence of the single crystal's crystal orientation. Therefore, it is preferable to use an indenter with a tip radius (R) of 50 μm for fracture strength testing of synthetic single crystal diamonds.

[0096] <Application> The synthetic single crystal diamond of this embodiment can be used for cutting tools such as precision cutting bits and woodworking cutters, wear-resistant tools such as grinding wheel dressers, wire drawing dies, scribing tools, water jet orifices, and wire guides, as well as tools for a wide range of applications.

[0097] [Embodiment 2: Method for producing synthetic single crystal diamond] The following describes an example of a method for producing the synthetic single crystal diamond of embodiment 1. The synthetic single crystal diamond of embodiment 1 is not limited to those produced by the following production method, and may be those produced by other production methods.

[0098] The method for producing synthetic single crystal diamond of the present disclosure is the method for producing synthetic single crystal diamond of embodiment 1, and comprises the following steps: a first step of synthesizing a diamond single crystal containing nitrogen atoms at a concentration of 100 ppm or more and 1500 ppm or less, based on the number of atoms, by a temperature difference method using a solvent metal; a second step of irradiating the diamond single crystal with one or both of an electron beam and a particle beam that imparts an energy of 100 MGy or more and 1000 MGy or less; and a third step of applying a pressure of 5 GPa or more and a temperature of 2300°C or more and 2600°C or less for 1 minute or more and 3600 minutes or less to the diamond single crystal after the second step, thereby obtaining a synthetic single crystal diamond.

[0099] (1st step) Diamond single crystals can be produced by the temperature difference method using a sample chamber having the configuration shown in FIG. 2, for example.

[0100] As shown in Figure 2, in a sample chamber 10 used to produce a diamond single crystal 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 method in which a vertical temperature gradient is created inside the sample chamber 10, and a high-temperature section (T high ) carbon source 3, low temperature part (T low ) and a solvent metal 4 is placed between the carbon source 3 and the seed crystal 5, and the temperature is maintained at or above the temperature at which the solvent metal 4 dissolves and at or above the pressure at which the diamond becomes thermally stable, thereby growing a diamond single crystal 1 on the seed crystal 5.

[0101] Diamond powder is preferably used as the carbon source 3. Graphite or pyrolytic carbon can also be used. The solvent metal 4 can be one or more metals selected from iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), etc., or an alloy containing these metals.

[0102] Nitrogen sources such as nitrides such as iron nitride (FeN, FeN), aluminum nitride (AlN), phosphorus nitride (PN), and silicon nitride (SiN) or organic nitrogen compounds such as melamine and sodium azide can be added to the carbon source 3 or solvent metal 4, either singly or as a mixture. Diamond or graphite containing a large amount of nitrogen can also be added as a nitrogen source. This allows nitrogen atoms to be contained in the synthesized diamond single crystal. At this time, the nitrogen atoms in the diamond single crystal are mainly present as isolated substitutional nitrogen atoms.

[0103] The content of the nitrogen source in the carbon source 3 or the solvent metal 4 is adjusted so that the nitrogen atom concentration in the synthesized diamond single crystal is 100 ppm or more and 1500 ppm or less.For example, in the carbon source, the content of nitrogen atoms derived from the nitrogen source can be 200 ppm or more and 3000 ppm or less.In addition, in the solvent metal, for example, when the solvent metal is an alloy made of iron-cobalt-nickel and the nitrogen source is Fe3N, the content of the nitrogen source can be 0.01 mass % or more and 0.2 mass % or less.

[0104] The solvent metal 4 may further contain 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] (2nd process) The resulting diamond single crystal is then irradiated with either or both of an electron beam and a particle beam imparting an energy of 100 MGy to 1000 MGy, which introduces lattice defects into the diamond single crystal and forms vacancies.

[0106] If the irradiation energy amount is less than 100MGy, the introduction of lattice defects may be insufficient. On the other hand, if the energy amount exceeds 1000MGy, excessive vacancies may be generated, which may significantly reduce the crystallinity. Therefore, the energy amount is preferably 100MGy or more and 1000MGy or less.

[0107] As the particle beam, a neutron beam or a proton beam can be used. The irradiation conditions are not particularly limited as long as the diamond single crystal can be given an energy of 100MGy or more and 1000MGy or less. For example, when using an electron beam, the irradiation energy can be 4.6MeV or more and 4.8MeV or less, the current can be 2mA or more and 5mA or less, and the irradiation time can be 30 hours or more and 45 hours or less.

[0108] (3rd step) Next, the diamond single crystal after the second step is subjected to a pressure of 5 GPa or more and a temperature of 2300°C to 2600°C for 1 minute to 3600 minutes to obtain a synthetic single crystal diamond. As a result, isolated substitutional nitrogen atoms in the diamond single crystal move through the vacancies and aggregate to become aggregated nitrogen atoms.

[0109] By setting the temperature of the third step to 2300°C or higher, the movement of nitrogen atoms in the diamond single crystal is promoted, and the formation of aggregates consisting of one vacancy and two to four substitutional nitrogen atoms present around the vacancy is promoted. If the temperature of the third step is less than 2300°C, it is difficult to form these aggregates. From the viewpoint of cost and productivity, the upper limit of the temperature of the third step is preferably 2600°C or less.

[0110] On the other hand, when a diamond single crystal is heated to 2300°C or higher under normal pressure, the diamond single crystal is graphitized. As a result of intensive research, the inventors have newly discovered that by subjecting a diamond single crystal to a temperature of 2300°C or higher and 2600°C or lower for 1 minute or longer and 3600 minutes or shorter under a high pressure of 5GPa or higher, the diamond single crystal is not graphitized, and the migration of nitrogen atoms in the diamond single crystal can be promoted.

[0111] The time for which the diamond single crystal is subjected to a temperature of 2300°C to 2600°C under a high pressure of 5 GPa or more is from 1 minute to 3600 minutes. The time for which the diamond single crystal is subjected to a temperature of 2300°C to 2600°C under a high pressure of 5 GPa or more can be from 60 minutes to 360 minutes. The pressure at this time can be from 5 GPa to 20 GPa.

[0112] The second and third steps can be repeated two or more times, with each being performed once as one cycle, thereby promoting the aggregation of isolated substitutional nitrogen atoms within the diamond single crystal.

[0113] [Appendix 1] The synthetic single crystal diamond of the present disclosure may include an aggregate (B center (aggregate of four nitrogen atoms)) consisting of one vacancy and four nitrogen atoms adjacent to the vacancy.

[0114] [Appendix 2] The synthetic single crystal diamond of the present disclosure may include an aggregate (H3 center (agglomeration of two nitrogen atoms)) consisting of one vacancy and two nitrogen atoms adjacent to the vacancy.

[0115] [Appendix 3] The synthetic single crystal diamond of the present disclosure may include an aggregate (N3 center (aggregate of three nitrogen atoms)) consisting of one vacancy and three nitrogen atoms adjacent to the vacancy.

[0116] [Appendix 4] The synthetic single crystal diamond of the present disclosure may include a B center and an H3 center.

[0117] [Appendix 5] The synthetic single crystal diamond of the present disclosure may include a B center and an N3 center.

[0118] [Appendix 6] The synthetic single crystal diamond of the present disclosure may include a B center, an H3 center, and an N3 center.

[0119] [Appendix 7] The synthetic single crystal diamond of the present disclosure preferably does not contain isolated substitutional nitrogen atoms (C centers), which further improves the hardness and fracture resistance of the synthetic single crystal diamond.

[0120] [Appendix 8] In the infrared absorption spectrum of the synthetic single crystal diamond of the present disclosure, the wave number is 1130±2 cm -1 It is preferable that there is no absorption peak due to the C center within this range. This further improves the hardness and chipping resistance of the synthetic single crystal diamond. -1 Within this range, there is also absorption by A and B centers.

[0121] [Appendix 9] In the infrared absorption spectrum of the synthetic single crystal diamond of the present disclosure, the wave number is 1358 cm -1 wave number 1370cm or more -1 Preferably, there is no absorption peak within the range of less than 1000 nm, which further improves the hardness and chipping resistance of the synthetic single crystal diamond.

[0122] [Appendix 10] The nitrogen atom concentration in the synthetic single crystal diamond of the present disclosure can be 100 ppm or more and 1400 ppm or less. The nitrogen atom concentration in the synthetic single crystal diamond of the present disclosure can be 100 ppm or more and 1300 ppm or less. The nitrogen atom concentration in the synthetic single crystal diamond of the present disclosure can be 200 ppm or more and 1500 ppm or less. The nitrogen atom concentration in the synthetic single crystal diamond of the present disclosure can be 200 ppm or more and 1400 ppm or less. The nitrogen atom concentration in the synthetic single crystal diamond of the present disclosure can be 200 ppm or more and 1300 ppm or less. The nitrogen atom concentration in the synthetic single crystal diamond of the present disclosure can be 300 ppm or more and 1500 ppm or less. The nitrogen atom concentration in the synthetic single crystal diamond of the present disclosure can be 300 ppm or more and 1400 ppm or less. The nitrogen atom concentration in the synthetic single crystal diamond of the present disclosure can be 300 ppm or more and 1300 ppm or less.

[0123] [Appendix 11] The ratio b / a of the diagonals of the Knoop indentation of the synthetic single crystal diamond of the present disclosure may be 0 or greater and 0.08 or less. The ratio b / a of the diagonals of the Knoop indentation of the synthetic single crystal diamond of the present disclosure may be 0 or greater and 0.075 or less. The ratio b / a of the diagonals of the Knoop indentation of the synthetic single crystal diamond of the present disclosure is 0 or more 0.07 It can be as follows: The ratio b / a of the diagonals of the Knoop indentation of the synthetic single crystal diamond of the present disclosure may be 0 or greater and 0.065 or less. The ratio b / a of the diagonals of the Knoop indentation of the synthetic single crystal diamond of the present disclosure may be 0 or greater and 0.06 or less.

[0124] [Appendix 12] The {001} of the synthetic single crystal diamond of the present disclosure <100> The Knoop hardness can be 100 GPa or more and 150 GPa or less. The {001} of the synthetic single crystal diamond of the present disclosure <100> The Knoop hardness can be 105 GPa or more and 150 GPa or less. The {001} of the synthetic single crystal diamond of the present disclosure <100> The Knoop hardness can be 110 GPa or more and 150 GPa or less. The {001} of the synthetic single crystal diamond of the present disclosure <100> The Knoop hardness can be 115 GPa or more and 150 GPa or less.

[0125] [Appendix 13] The crack initiation load of the synthetic single crystal diamond of the present disclosure may be 15N or more and 50N or less. The crack initiation load of the synthetic single crystal diamond of the present disclosure may be 17N or more and 50N or less. The crack initiation load of the synthetic single crystal diamond of the present disclosure may be 20N or more and 50N or less. The crack initiation load of the synthetic single crystal diamond of the present disclosure may be 25N or more and 50N or less. The crack initiation load of the synthetic single crystal diamond of the present disclosure may be 30N or more and 50N or less. [Example]

[0126] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0127] [Production of synthetic single crystal diamond] <Sample 2, Sample 4 to Sample 8> (1st step) Using the sample chamber configured as shown in Figure 2, single-crystal diamond is synthesized by the temperature gradient method using a solvent metal.

[0128] An alloy consisting of iron, cobalt and nickel was prepared as the solvent metal. nitrogen Iron nitride (FeN) powder is added as an element source. The concentration of iron nitride in the solvent metal is shown in the "Iron nitride concentration in solvent metal (mass%)" column under "Manufacturing conditions" in Table 1. For example, in Sample 2, the concentration of iron nitride in the solvent metal is 0.02 mass%.

[0129] Diamond powder is used as the carbon source, and approximately 0.5 mg of diamond single crystal is used as the seed crystal. The temperature in the sample chamber is adjusted using a heater so that there is a temperature difference of several tens of degrees between the high-temperature section where the carbon source is located and the low-temperature section where the seed crystal is located. Using an ultra-high-pressure generator, the pressure is set to 5.5 GPa, and the temperature in the low-temperature section is controlled within the range of 1370°C ± 10°C (1360°C to 1380°C), and maintained for 60 hours, synthesizing diamond single crystal on the seed crystal.

[0130] (2nd process) Next, the resulting diamond single crystal is irradiated with an electron beam. The irradiation conditions are: irradiation energy 4.6 MeV, current 2 mA, and irradiation time 30 hours. These irradiation conditions give the diamond single crystal an energy of 100 MGy.

[0131] (3rd step) Next, the diamond single crystal after electron beam irradiation is subjected to a high pressure of 6 GPa or more (listed as "high pressure" in Table 1) for 60 minutes at the temperature listed in the "Third step (60 minutes)" column under "Manufacturing conditions" in Table 1 to obtain a synthetic single crystal diamond. For example, in sample 2, the diamond single crystal is subjected to a pressure of 6 GPa or more (high pressure) and a temperature of 2350°C for 60 minutes.

[0132] <Sample 1> For sample 1, a diamond single crystal is synthesized by the same first step as for sample 2. For sample 1, the second and third steps are not performed.

[0133] <Sample 3> For sample 3, a diamond single crystal is synthesized by the same first step as for sample 4. For sample 1, the second and third steps are not performed.

[0134] [Table 1]

[0135] <Evaluation> The synthetic single crystal diamonds of Samples 2 and 4 to 8, and the diamond single crystals of Samples 1 and 3 (hereinafter also referred to as "synthetic single crystal diamonds / diamond single crystals") were subjected to nitrogen concentration measurement, fluorescence spectrum measurement, infrared spectroscopic analysis, and {001} <100> The Knoop hardness is measured, the ratio of the diagonal lines of the Knoop indentation (b / a) is measured, and a breaking strength test is performed.

[0136] (Measurement of nitrogen atom concentration) The nitrogen atom concentration in each sample of synthetic single crystal diamond / diamond single crystal was determined by SIMS analysis. The results are shown in the "Nitrogen atom concentration (ppm)" column of "Synthetic single crystal diamond / diamond single crystal" in Table 2.

[0137] (Fluorescence spectrum) After mirror-polishing the surface of each synthetic single crystal diamond / diamond single crystal sample, the fluorescence spectrum is measured by irradiating it with excitation light of 325 nm wavelength.

[0138] In the fluorescence spectrum, the presence or absence of an emission peak within the ranges (a) to (d) below is confirmed. (a) Fluorescence wavelength range: 415±2nm (b) Fluorescence wavelength in the range of 420 nm to 470 nm (c) Fluorescence wavelength within the range of 503±2 nm (d) Fluorescence wavelength in the range of 510 nm to 530 nm The results are shown in Table 2 under the columns "Emission peak within 415±2 nm range," "420-470 nm subband," "Emission peak within 503±2 nm range," and "510-530 nm subband" in the "Fluorescence spectrum" of "Synthetic single crystal diamond / diamond single crystal."

[0139] If an emission peak exists in either or both of (a) the fluorescence wavelength range of 415±2 nm and (b) the fluorescence wavelength range of 420 nm to 470 nm, the N3 center is considered to be "present," and if an emission peak does not exist in either range, the N3 center is considered to be "absent." The results are shown in the "N3 center" column of "Fluorescence spectrum" for "Synthetic single crystal diamond / diamond single crystal" in Table 2.

[0140] If an emission peak exists in either or both of (c) the fluorescence wavelength range of 503±2 nm and (d) the fluorescence wavelength range of 510 nm to 530 nm, the H3 center is deemed to be "present," and if an emission peak does not exist in either range, the H3 center is deemed to be "absent." The results are shown in the "H3 center" column of "Fluorescence spectrum" for "Synthetic single crystal diamond / diamond single crystal" in Table 2.

[0141] (Infrared spectroscopy) Each synthetic single crystal diamond / diamond single crystal sample was processed into a plate approximately 1 mm thick, and the two light-transmitting surfaces were polished to a mirror finish. After that, absorbance in the infrared region was measured using Fourier transform infrared spectroscopy, and an infrared absorption spectrum was created.

[0142] In the infrared absorption spectrum, excluding absorption by other centers, the wavenumber is 1282 ± 2 cm -1 If there is an absorption peak at the wavenumber of 1282±2 cm, the A center is considered to be "present." -1 If there is no absorption peak in the A center, it is considered to be "absent." The results are shown in the "A center" column of "Infrared absorption spectrum" for "Synthetic single crystal diamond / Diamond single crystal" in Table 2.

[0143] In the infrared absorption spectrum, excluding absorption by other centers, the wavenumber is 1175±2 cm -1 If there is an absorption peak at the wavenumber of 1175±2cm, the B center is considered to be "present." -1 If there is no absorption peak in this range, the B center is considered to be "absent." The results are shown in the "B center" column of "Infrared absorption spectrum" for "Synthetic single crystal diamond / Diamond single crystal" in Table 2.

[0144] In the infrared absorption spectrum, excluding absorption by other centers, the wavenumber is 1130±2 cm -1 If there is an absorption peak at the wavenumber of 1130±2cm, the C center is considered to be "present." -1 If there is no absorption peak in this range, the C center is considered to be "absent." The results are shown in the "C center" column of "Infrared absorption spectrum" for "Synthetic single crystal diamond / Diamond single crystal" in Table 2.

[0145] In the infrared absorption spectrum, excluding absorption by other centers, the wavenumber is 1370 to 1385 cm -1 If there is an absorption peak at wavenumber 1370-1385cm, the B' center (platelet) is considered to be present. -1 If there is no absorption peak in this spectrum, the B' center (platelet) is deemed to be "absent." The results are shown in the "B' center / platelet" column of "Infrared absorption spectrum" for "Synthetic single crystal diamond / Diamond single crystal" in Table 2.

[0146] In addition, synthetic single crystal diamond containing B' center (platelet) has a wave number of 1358 cm in the infrared absorption spectrum. -1 Over 1385cm -1 The absorption peak is shown below. However, the wave number is 1370 cm -1 Smaller range (wavenumber 1358 cm -1 wave number 1370cm or more -1 If an absorption peak is present at a wavenumber of 1358 cm or less, the B' center (platelet) aggregates in the crystal are too large and can become the starting point for fracture, which is undesirable. -1 wave number 1370cm or more -1 There is no absorption peak below this.

[0147] For reference, the wave number 2160 cm is the absorption by phonons in diamond. -1 When the absorbance is set to 1, the wave number is 1282 cm -1 (A center) absorbance value, wavenumber 1175 cm -1(B center) absorbance value, wavenumber 1130 cm -1 (C center) absorbance value, wavenumber 1370 cm -1 Over 1385 cm -1 The absorbance value of the following peaks, wavenumber 1358 cm -1 Wave number 1370 or more cm -1 The absorbance value of the peak less than this is calculated. The results are shown in the "I(1282) / I(2160)", "I(1175) / I(2160)", "I(1130) / I(2160)", "I(1370-1385) / I(2160)", and "I(1358-1370) / I(2160)" columns of the "Infrared Absorption Spectra" of "Synthetic Single Crystal Diamond / Diamond Single Crystal" in Table 2.

[0148] Regarding I(1175) / I(2160), the value of I(1175) / I(2160) is larger for sample 3 without the B center than for sample 2 with the B center. This is because sample 3 has a large amount of nitrogen in the C center, and the wavenumber 1175 cm originating from the shoulder of the absorption spectrum of this C center is -1 This is because the absorption is strong at 1000 nm, and does not indicate that Sample 3 contains a B center.

[0149] Regarding I(1130) / I(2160), Samples 4 to 8, which do not have a C center, have a larger I(1130) / I(2160) value than Sample 1, which has a C center. This is because Samples 4 to 8 have a large amount of nitrogen in the A and B centers, and the wavenumber 1130 cm originates from the shoulders in the absorption spectra of these A and B centers. -1 This is because the absorption is strong at 1000 nm, and does not indicate that Samples 4 to 8 contain a C center.

[0150] (Knoop hardness measurement) Synthetic single crystal diamond / diamond single crystal {001} plane of each sample <100> An indentation was made in the direction of the diamond with a load of 4.9 N. The length a (μm) of the longer diagonal of the resulting Knoop indentation was measured, and the Knoop hardness (HK) was calculated using the following formula A. The specific measurement method is described in embodiment 1, so the description will not be repeated. The results are shown in Table 2 under "Synthetic single crystal diamond / diamond single crystal" in the "{001} <100> The values are shown in the "Knoop hardness" column. HK=14229×4.9 / a 2 Formula A

[0151] (Measurement of Knoop indentation (b / a)) For the Knoop indentation obtained by the above Knoop hardness measurement, the length a of the longer diagonal line and the length b of the shorter diagonal line are measured, and the ratio b / a is calculated. The results are shown in Table 2 under "synthetic single crystal diamond / single crystal diamond" and "b / a{001} <110> The smaller the ratio b / a, the greater the elastic deformability.

[0152] (Breaking strength test) A spherical diamond indenter with a radius of 50 μm was prepared, and a load was applied to each sample of synthetic single crystal diamond / diamond single crystal at a loading rate of 100 N / min at room temperature (23°C), and the load (crack initiation load) at the moment when a crack occurred in the sample was measured. The specific measurement method is described in embodiment 1, so the description will not be repeated. The higher the crack initiation load, the higher the strength of the sample and the better its fracture resistance. The results are shown in the "Crack initiation load" column of "Synthetic single crystal diamond / diamond single crystal" in Table 2.

[0153] [Table 2]

[0154] <Consideration> Sample 2 and samples 4 to 8 correspond to Examples. Sample 1 and sample 3 correspond to Comparative Examples. It was confirmed that Sample 2 and samples 4 to 8 (Examples) have higher hardness, greater elastic deformability, and superior chipping resistance than Sample 1 and sample 3 (Comparative Example).

[0155] Although the embodiments and examples of the present disclosure have been described above, it is originally intended that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0156] 1 Diamond single crystal, 2 Insulator, 3 Carbon source, 4 Solvent metal, 5 Seed crystal, 6 Pressure medium, 7 Graphite heater, 10 Sample chamber

Claims

1. A synthetic single crystal diamond containing 100 ppm to 1500 ppm of nitrogen atoms, the synthetic single crystal diamond comprises an aggregate consisting of one vacancy and any of two to four nitrogen atoms present adjacent to the vacancy; the ratio b / a of the length b of the shorter diagonal of the Knoop indentation in the <110> direction on the {001} face of said synthetic single crystal diamond to the length a of the longer diagonal is 0.08 or less; The Knoop indentation is formed by measuring the Knoop hardness of the synthetic single crystal diamond in the <100> direction within the {001} plane in accordance with JIS Z 2251:2009 at a temperature of 23°C ± 5°C and a test load of 4.9 N.

2. In the infrared absorption spectrum of the synthetic single crystal diamond, the wave number is 1175±2 cm －１ 2. The synthetic single crystal diamond of claim 1, wherein the diamond has an absorption peak within the range of

3. 3. A synthetic single crystal diamond according to claim 1 or claim 2, wherein in the fluorescence spectrum of the synthetic single crystal diamond, an emission peak exists in one or both of a fluorescence wavelength range of 503±2 nm and a fluorescence wavelength range of 510 nm or more and 530 nm or less.

4. 4. A synthetic single crystal diamond according to any one of claims 1 to 3, wherein in the fluorescence spectrum of the synthetic single crystal diamond, an emission peak exists in one or both of a fluorescence wavelength range of 415±2 nm and a fluorescence wavelength range of 420 nm or more and 470 nm or less.

5. In the infrared absorption spectrum of the synthetic single crystal diamond, the wave number is 1282±2 cm －１ 5. The synthetic single crystal diamond according to claim 1, wherein the diamond has an absorption peak within the range of

6. In the infrared absorption spectrum of the synthetic single crystal diamond, the wave number is 1370 cm －１ Over 1385cm －１ A synthetic single crystal diamond according to any one of claims 1 to 5, which has an absorption peak within the following range:

7. 7. A synthetic single crystal diamond according to any one of claims 1 to 6, wherein the Knoop hardness in the <100> direction of the {001} plane of said synthetic single crystal diamond is 100 GPa or more.

8. 8. A synthetic single crystal diamond according to any one of claims 1 to 7, wherein in a fracture strength test in which a spherical diamond indenter with a tip radius of 50 μm is pressed against the surface of the synthetic single crystal diamond at a load rate of 100 N / min, the crack initiation load is 17 N or more.

9. A method for producing a synthetic single crystal diamond according to any one of claims 1 to 8, comprising: A first step of synthesizing a diamond single crystal containing nitrogen atoms at a concentration of 100 ppm to 1500 ppm (based on the atomic number) by a temperature difference method using a solvent metal; a second step of irradiating the diamond single crystal with one or both of an electron beam and a particle beam imparting an energy of 100 MGy to 1000 MGy; a third step of applying a pressure of 5 GPa or more and a temperature of 2300°C to 2600°C for 1 minute to 3600 minutes to the diamond single crystal after the second step to obtain a synthetic single crystal diamond.

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