A method for regulating the surface structure of a large-size boron-doped diamond single crystal

Abstract

The present application relates to a kind of methods for regulating the surface structure of large-size boron-doped diamond single crystal, comprising constructing reaction system, using high temperature and high pressure temperature gradient method to synthesize large-size boron-doped diamond single crystal;TiB2 regulates the nitrogen concentration in the crystal, adding 0-5wt.% TiB2 to synthesize hexagonal-octahedral diamond crystal from yellow, light yellow, light yellow-light blue to black;TiB2 regulates the growth characteristics and morphology of diamond, adding 0-50wt.% TiB2 to synthesize diamond crystal from hexagonal-octahedral to octahedral.The present application grows a batch of boron-containing diamond single crystal by introducing TiB2 in FeNi-C system under high temperature and high pressure conditions, which can directly regulate the defect size, depth and density of the surface of large-size boron-containing diamond single crystal by adjusting the doping amount of TiB2, providing a new idea for the surface treatment of boron-containing diamond.

Description

Technical Field

[0001] This invention belongs to the field of diamond single crystal growth technology in crystal growth, specifically relating to a method for controlling the surface structure of large-size boron-doped diamond single crystals. Background Technology

[0002] Boron-containing diamond crystals exhibit superior heat resistance, chemical inertness, and compressive strength compared to conventional diamonds. Furthermore, boron-containing diamonds possess excellent semiconductor properties, enabling the fabrication of power electronic devices that operate normally under extreme temperatures and harsh environments, making them a promising high-temperature, high-power semiconductor material. The surface structure of boron-containing diamonds differs fundamentally from that of conventional diamonds. Boron forms a new boron-carbon structure with the carbon atoms on the diamond surface, achieving a stable state and making it an excellent adsorbent, catalytic, and filtration material, as well as an electrode for wastewater treatment. To meet the numerous new and potential applications of boron-containing diamond materials, it is necessary to create structures with specific morphologies and roughness on its surface, thereby improving the flexibility, high surface area-to-volume ratio, and self-sharpening properties of the boron-containing diamond surface.

[0003] Currently, most research focuses on the oxidation resistance, wear resistance, and electrical properties of boron-containing diamond, with fewer reports on the influence of boron on the growth and surface morphology of large-size diamond single crystals. The morphology of a crystal is correlated with its internal structure, and the surface morphology of a crystal, as a trace left over from the crystal growth process, can, to some extent, aid in the study of the crystal growth mechanism. Therefore, the study of both surface and microscopic morphology of materials is equally important. Gong Jianhong et al., through their research on the surface morphology of boron-containing diamond, discovered various surface morphologies, including pits, spherical particle clusters, parallel steps, petal-shaped growth mounds, and triangular spiral steps. Blank VD et al. studied the structural characteristics of BDD, proving the presence of boron in the diamond lattice distortion region. ZHANG JQ et al. proposed the "bald spot" model to explain the differences in crystal growth rate and the generation of surface defects in boron-containing diamond. However, the above studies all involved diamond crystals grown in environments with high nitrogen impurities; the surface defect structure and morphological characteristics of large boron-containing diamond single crystals grown in low-nitrogen environments remain unclear. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling the surface structure of large-size boron-doped diamond single crystals, so as to solve the problem of controlling the surface defect structure and morphological characteristics of boron-containing diamond single crystals grown in a low-nitrogen environment.

[0005] The objective of this invention is achieved through the following technical solution: A method for controlling the surface structure of large-size boron-doped diamond single crystals includes the following steps: A. Constructing the reaction system Large-size boron-doped diamond single crystals were synthesized using a high-temperature, high-pressure temperature gradient method. From the high-temperature end to the low-temperature end of the cavity, carbon source 11, catalyst 5, seed crystal 6, and MgO+ZrO2 crystal bed 13 were arranged sequentially. Carbon source 11 was formed by mixing and pressing high-purity graphite powder and high-purity TiB2 powder. Catalyst 5 was an FeNi alloy, and the {111} facet of seed crystal 6 was the growth surface. The center temperature of the cavity was 1300℃-1400℃, and the high pressure was 5.6 GPa. B. Regulation of nitrogen concentration in crystals by TiB2 In step A, high-purity TiB2 powder was added to the FeNi-C system. The amount of high-purity TiB2 powder added was 1-5 wt.% of the weight of high-purity graphite powder. Then, hexahedral diamond crystals ranging from light yellow and light yellow-light blue to black were synthesized. The center temperature of the cavity was 1340 ℃ and the reaction time was 12 h. C and TiB2's effects on diamond growth characteristics and morphology In step A, high-purity TiB2 powder is added to the FeNi-C system. The amount of high-purity TiB2 powder added is 10-50 wt.% of the weight of high-purity graphite powder. Then, diamond crystals ranging from hexahedral to octahedral are synthesized. The center temperature of the cavity is 1360 ℃ and the growth time is 24 h.

[0006] Further, in step A, the size of the seed crystal 6 is 0.8mm-1mm.

[0007] Further, in step A, the pressed carbon source 11 is assembled in the synthesis chamber, and each sample assembly block is dried at 120°C for half an hour before high-pressure synthesis.

[0008] Further, in step B, the diamond crystals produced when the amount of high-purity TiB2 powder added is 1 wt.% are light yellow, when the amount of high-purity TiB2 powder added is 2 wt.% or 3 wt.% are light yellow to blue, when the amount of high-purity TiB2 powder added is 4 wt.% are light yellow to blue, and when the amount of high-purity TiB2 powder added is 5 wt.% are black.

[0009] Further, in step C, when the amount of high-purity TiB2 powder added is 10 wt.% or 20 wt.%, the diamond crystal produced is hexahedral; when the amount of high-purity TiB2 powder added is 30 wt.%, 40 wt.%, or 50 wt.%, the diamond crystal produced is transformed into an octahedron.

[0010] Furthermore, in step C, when the amount of high-purity TiB2 powder added is greater than 20 wt.%, a large number of triangular pit defects appear on the diamond surface, including dot bottom, eccentric dot bottom and surface bottom features.

[0011] Furthermore, when the amount of high-purity TiB2 powder added was adjusted from 30 wt.% to 50 wt.%, the side length of the triangular pit defect decreased from 2.85 μm to 1.09 μm, the depth decreased from 590 nm to 50 nm, and the surface roughness Rq of the crystal also decreased from 145.302 nm to 6.896 nm.

[0012] Compared with the prior art, the beneficial effects of the present invention are: This invention introduces TiB2 into the FeNi-C system to grow a batch of large boron-containing diamond single crystals under high temperature and high pressure conditions. The properties and characteristics of the synthesized crystals, such as the concentration of boron and nitrogen impurities, crystal quality, surface morphology, and crystal defects, were studied in detail. By adjusting the amount of TiB2 doping, the size, depth, and density of defects on the surface of large-size boron-containing diamond single crystals can be directly controlled, providing a new approach to the surface treatment of boron-containing diamonds. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the assembly of the composite block; Figure 2 Optical diagrams of crystals in the FeNi-C system with TiB2 addition of 0-5 wt.%. Figure 2 a- Figure 2 f: 0-50wt.%; Figure 3 Optical images of crystals in the FeNi-C system with TiB2 addition of 0-50 wt.% Figure 2 a- Figure 2 f: 0-50wt.%; Figure 4 Raman spectra of crystals with TiB2 content of 0-50 wt.% in the FeNi-C system; Figure 5 The following are surface scan images of crystals in the FeNi-C system with TiB2 addition of 0-50 wt.%, (M-1)-(M-6): 0-50 wt.%; Figure 6 A three-dimensional AFM image of the crystal surface in the FeNi-C system with TiB2 addition of 20-50 wt.%; Figure 7 AFM data of the crystal surface in the FeNi-C system with TiB2 addition of 20-50 wt.%; Figure 8 This is a schematic diagram of the pits on the surface of a diamond. Figure 8 awei1 point bottom, Figure 8 b is the eccentric point base. Figure 8 c represents the face and the base; Figure 9 (Ⅰ) Infrared absorption spectra of crystals with TiB2 addition of 0-5 wt.% in the FeNi-C system; Figure 9 (II) is the 1000-1400cm² region in the infrared spectrum. -1 Enlarged views of the parts, (a)-(f): 0-5wt.%.

[0015] In the figure: 1. Pyrophyllite 2. Dolomite 3. NaCl+ZrO2 liner 4. MgO+Al2O3 insulating tube 5. Catalyst 6. Seed crystal 7. Heating graphite tube 8. Dolomite 9. Conductive steel ring 10. MgO+Al2O3 plug 11. Carbon source 12. Crystal sample 13. MgO+ZrO2 crystal bed 14. Graphite sheet. Detailed Implementation

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0017] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0018] This invention discloses a method for controlling the surface structure of large-size boron-doped diamond single crystals. The method employs a high-temperature, high-pressure temperature gradient approach to synthesize TiB2-doped diamond in a FeNi-C system. Specifically, high-purity TiB2 powder (0-50 wt.%) is mixed with high-purity graphite powder and pressed into carbon sources of uniform size. FeNi alloy is used as the growth catalyst, and the {111} facet of the seed crystal is used as the growth surface. Large-size heavy boron-doped diamond single crystals are synthesized using the high-temperature, high-pressure temperature gradient approach.

[0019] The present invention provides a method for controlling the surface structure of large-size boron-doped diamond single crystals, comprising the following steps: A. Constructing the reaction system Assemble the cavity; the assembled cavity structure is as follows: Figure 1 As shown. The pyrophyllite block 1 is used for pressure transmission and sealing; the dolomite ring 2 is used for pressure transmission and heat preservation; the NaCl+ZrO2 liner 3 is used for pressure transmission; the MgO+Al2O3 insulating tube 4 is used for pressure transmission and insulation; the metal catalyst 5 acts as a catalyst for diamond growth; the seed crystal 6 serves as the substrate for growing large single diamond crystals; the heated graphite tube 7 generates high-temperature conditions in the synthesis chamber; the dolomite 8 in the conductive steel ring is used for pressure transmission and heat preservation; the conductive steel ring 9 is used for conductivity; the MgO+Al2O3 plug 10 is used for pressure transmission and insulation; the high-purity graphite carbon source 11 is used as the source of carbon atoms required for crystal growth; the crystal sample 12 is the diamond crystal obtained after growth; the MgO+ZrO2 crystal bed 13 is used for pressure transmission, insulation, and seed crystal placement; and the graphite sheet 14 is used for conductivity and heating.

[0020] Large-size boron-doped diamond single crystals were synthesized using a high-temperature, high-pressure temperature gradient method. From the high-temperature end to the low-temperature end of the cavity, a carbon source 11, a catalyst 5, a seed crystal 6, and an MgO+ZrO2 crystal bed 13 were arranged sequentially. The carbon source 11 was formed by mixing and pressing high-purity graphite powder and high-purity TiB2 powder. The catalyst 5 was an FeNi alloy, and the {111} facet of the seed crystal 6 was the growth surface. The center temperature of the cavity was 1300-1400℃, and the high pressure was 5.6 GPa. The size of the seed crystal 6 was 0.8 mm-1 mm.

[0021] B. Regulation of nitrogen concentration in crystals by TiB2 In step A, high-purity TiB2 powder was added to the FeNi-C system. The amount of high-purity TiB2 powder added was 1-5 wt.% of the weight of high-purity graphite powder. Then, hexahedral diamond crystals ranging from light yellow and light yellow-light blue to black were synthesized. The center temperature of the cavity was 1340 ℃ and the reaction time was 12 h.

[0022] Specifically, in step A, high-purity TiB2 powder is added to the FeNi-C system. The amount of high-purity TiB2 powder added is 10-50 wt.% of the weight of high-purity graphite powder. Then, diamond crystals ranging from hexahedral to octahedral are synthesized. The center temperature of the chamber is 1360 ℃, and the growth time is 24 h. In step A, the pressed carbon source 11 is assembled in the synthesis chamber. Each sample assembly block is dried at 120 ℃ for half an hour before high-pressure synthesis.

[0023] When the amount of high-purity TiB2 powder added is 1 wt.%, the diamond crystals are light yellow; when the amount of high-purity TiB2 powder added is 2 wt.% or 3 wt.%, the diamond crystals are light yellow to blue; when the amount of high-purity TiB2 powder added is 4 wt.%, the diamond crystals are light yellow to blue; and when the amount of high-purity TiB2 powder added is 5 wt.%, the diamond crystals are black.

[0024] C and TiB2's effects on diamond growth characteristics and morphology When the addition of high-purity TiB2 powder is 10 wt.% or 20 wt.%, the diamond crystals produced are hexahedral, while when the weight ratio is 30 wt.%, 40 wt.%, or 50 wt.%, the diamond crystals produced are octahedral.

[0025] When the addition of high-purity TiB2 powder exceeds 20 wt.%, numerous triangular pit defects appear on the diamond surface, including point-bottom, eccentric point-bottom, and face-bottom features. When the addition of high-purity TiB2 powder is adjusted from 30 wt.% to 50 wt.%, the side length of the triangular pit defects decreases from 2.85 μm to 1.09 μm, the depth decreases from 590 nm to 50 nm, and the crystal surface roughness Rq also decreases from 145.302 nm to 6.896 nm. Example

[0026] 1. Synthesis of TiB2-doped diamond in the FeNi-C system like Figure 1 As shown, the synthesis of TiB2-doped diamond in the FeNi−C system was carried out using the temperature gradient method on a domestically produced hinged six-sided press (SPD-6×1400).

[0027] The high-quality seed crystals 6 used in the experiment had a size of 0.8mm-1mm. Since boron impurities are not uniformly distributed in diamond single crystals, the {111} growth region typically has a higher impurity concentration. To further improve the uniformity of boron impurity concentration and distribution in the crystal, the {111} plane was selected as the growth plane for seed crystal 6 in this experiment, and growth was carried out at temperatures between 1300℃ and 1400℃, specifically 1340℃ and 1360℃, to synthesize crystals where the {111} growth region constituted the majority. High-purity graphite powder (99.99%) was used as the carbon source, FeNi alloy as the growth catalyst, and high-purity TiB2 (99.999%) as an additive. Graphite and TiB2 powders were uniformly mixed in different weight ratios and pressed into carbon sources of uniform size. The pressed carbon sources were then assembled in the synthesis cavity. Before the synthesis experiment, to avoid the influence of moisture adsorbed by the sample assembly materials on the experimental results, each sample assembly block (the same assembly, different TiB2 addition amounts, and the assembled blocks) was placed in a 120℃ drying oven for half an hour. Then, the assembly blocks were removed and placed on the high-pressure equipment for the synthesis experiment. The temperature inside the chamber was calibrated according to the relationship curve between input power and temperature measured by double platinum-rhodium (Pt-30%RH / Pt-6%RH) thermocouples. The synthesis pressure was calibrated according to the calibration curve between oil pressure and internal chamber pressure established based on the high-pressure phase transition points of bismuth (Bi), barium (Ba), and thallium (Tl).

[0028] The synthesized product was heat-treated in a dilute nitric acid solution to separate the crystals from the metal catalyst 5. The separated crystals were then placed in a hot mixed solution of sulfuric acid and nitric acid (volume ratio 3:1) to remove residual graphite from the crystal surface. The treated diamond crystals were observed for crystal quality and surface morphology using a stereomicroscope (OM), scanning electron microscope (SEM), and atomic force microscope (AFM). Infrared spectroscopy was performed using a Bruker VERTEX 70V Fourier transform infrared spectrometer (FTIR) with a spectral range of 400 cm⁻¹. -1 -4000 cm -1 The resolution is 2 cm. -1 The Raman spectra were measured using a Renishaw InVia laser micro Raman spectrometer with a laser wavelength of 532 nm.

[0029] 2. Effect of TiB2 on nitrogen concentration in crystals Nitrogen, the most common impurity element in diamond, has high solubility and readily enters the crystal lattice during diamond growth, thus inhibiting boron entry into the diamond lattice. Furthermore, nitrogen, as a deep-level donor, readily compensates for boron acceptors in diamond. Therefore, when synthesizing boron-doped diamond, researchers strive to minimize the concentration of nitrogen impurities in the crystal. To investigate the effect of TiB2 on the nitrogen impurity concentration in the synthesized crystal, this invention synthesized a batch of low-doped diamond crystals by adding 0-5 wt.% TiB2 to the FeNi-C system. The experimental conditions and results are summarized in Table 1.

[0030] Table 1 Experimental conditions and results of adding 0-5 wt.% TiB2 to the FeNi-C system

[0031] like Figure 2 As shown, at low doping concentrations, the crystals are all hexahedral. With increasing TiB2 doping concentration, the diamond color changes from yellow → light yellow → light yellow → blue → black, which is due to the incorporation of boron into the diamond lattice. The distribution of boron in the diamond lattice is not uniform, preferentially entering the {111} crystal planes. Simultaneously, the yellow color caused by nitrogen in the diamond also shows a weakening trend, indicating that TiB2 doping plays a certain role in nitrogen removal. To more intuitively observe whether the nitrogen content in the diamond lattice decreases, this invention further performed infrared spectroscopy on diamonds with low doping concentrations.

[0032] from Figure 9 In (II), it can be seen that compared with the infrared spectrum of 0 wt.%, as the TiB2 doping content increases, the C-core nitrogen corresponding to 1130 cm⁻¹ increases. -1 and 1344 cm -1 The peak gradually weakens at 1050 cm⁻¹, indicating that the concentration of nitrogen in the core of the synthesized diamond crystal decreases continuously with increasing doping concentration. (The peak at 1050 cm⁻¹ is shown in the figure.) -1 1265 cm -1 1332 cm -1 The peak at that point and the N in the diamond crystal + It depends on the concentration. Figure 9 (Ⅰ) is located at 2460 cm -1 and 2800 cm -1 The two peaks are related to boron atoms in diamond. Figure 9 (I) There are almost no 2460 cm⁻¹ lines in the bd spectrum. -1 and 2800 cm -1The presence of absorption peaks related to electrically neutral boron impurities indicates that there are relatively few electrically neutral boron impurities in diamond, with most of the boron acceptors being compensated by nitrogen. As the TiB2 doping content further increases, these two peaks become more prominent, indicating that boron atoms have entered the diamond lattice and their content continues to rise.

[0033] To more intuitively reflect the nitrogen content in diamond, the 1130 cm⁻¹ infrared spectrum was used as a reference. -1 Absorption peak per 1 cm -1 The absorption coefficient corresponds to (25±2) ppm of C-core nitrogen, 1332 cm⁻¹ -1 Absorption peak per 1 cm -1 The absorption coefficient corresponds to (5.5 ± 1) ppm N. + The correspondence between impurities can be used to roughly calculate the concentration of nitrogen impurities in the diamond lattice. The specific calculation formula and data are as follows:

[0034] Table 2. Nitrogen impurity concentrations in crystals with TiB2 addition of 0-5 wt.% in the FeNi-C system.

[0035] Table 2 shows the data calculated from Table 1. It can be seen that as the doping concentration increases, the C-core nitrogen concentration in the crystal continuously decreases and eventually disappears, decreasing from 161 ppm in undoped TiB2 to 58 ppm with a 3 wt% doping level. When the TiB2 addition reaches 4 wt.%, no C-core nitrogen-related peaks can be detected. + The concentration initially increases and then decreases. This is because as the concentration of B acceptors in the TiB2-doped crystal increases, more nitrogen atoms undergo charge compensation interactions to produce N2. + Subsequently, as the amount of carbon-core nitrogen entering the crystal decreases, the charge compensation effect weakens, and N... + The concentration decreased. The total nitrogen content in the crystal gradually decreased and disappeared, indicating that TiB2 can effectively remove N impurities from the diamond lattice.

[0036] 3. The effect of TiB2 on diamond growth characteristics To investigate the effect of TiB2 on diamond growth characteristics in more detail, this invention further increases the amount of TiB2 added. FeNi alloy was selected as the growth catalyst 5, the {111} facet of the seed crystal was used as the growth surface, and high-purity TiB2 was used as the additive. Large-size boron-doped diamond single crystals were synthesized and studied using a high-temperature, high-pressure temperature gradient method. The results of the synthesis experiments are shown in Table 3.

[0037] Table 3. Experimental results of diamond crystal synthesis in the FeNi-C system with the addition of TiB2.

[0038] After acid washing and ultrasonic cleaning, the synthesized crystals were observed for surface morphology using a Leica stereo microscope. The resulting optical photographs are shown below. Figure 3 As shown.

[0039] from Figure 3 As can be seen, the undoped TiB2 crystal is yellow, hexahedral, and a standard type Ib diamond. Keeping the growth conditions constant, when the TiB2 addition amount is increased to 10 wt.%, the crystal becomes an opaque black hexahedral. When the addition amount reaches 20 wt.%, the {110} facets disappear, and the development of the {311} facets weakens. When the TiB2 addition amount continues to increase, such as... Figure 2 d- Figure 2 As shown in f, all other crystal faces in the crystal disappear completely, leaving only the {111} face, and the crystal form changes from hexahedron to octahedron.

[0040] 4. Raman spectroscopy analysis of heavily doped crystals Raman spectroscopy is suitable for analyzing the internal structure, impurity content, and crystal quality variations of diamond crystals. Raman spectroscopy tests were performed on samples M1-M6, and the results are as follows: Figure 4 As shown, compared to the undoped TiB2 crystal M1, the full width at half maximum (FWHM) of the Raman spectrum gradually increases, indicating that the crystal quality deteriorates with increasing TiB2 content. The diamond Raman peaks of samples M2-M6 all exhibit asymmetry; this line shape is called the Fano line shape, caused by Fano resonance resulting from the interference of optical phonons with the Raman continuum. This phenomenon can only be observed in boron-doped diamonds with high impurity concentrations and is an important phenomenon in the Raman spectrum of boron-doped diamonds. Unlike other impurity elements in diamond, boron impurities, when reaching a certain concentration, will produce a series of additional peaks in the Raman spectrum. From... Figure 4 It can be seen that when the doping concentration is 10 wt.%, the M2 Raman peak in the crystal appears at 590 cm⁻¹. -1 900 cm -1 And 1042 cm -1 The peak at 590 cm⁻¹, believed to be related to changes in the phonon density of states in diamond caused by boron impurities, only appears in the Raman spectra of diamonds with high boron concentrations. With further increases in doping concentration, the peak at 590 cm⁻¹ in samples M3-M5... -1 900 cm -1 and 1042 cm -1 The peak disappears at 500 cm, but reappears at 500 cm. -1 and 1225 cm -1 The nearby Raman Peak. Located at 500 cm. -1The nearby peaks are correlated with boron atom pairs, and the presence of these two peaks indicates that the boron content in the diamond reaches 10. 20 cm -3 This indicates that the diamond testing area has reached a heavily doped level.

[0041] 5. The effect of TiB2 on crystal surface morphology To more clearly observe the morphological characteristics and crystal defect structure of synthetic diamonds, this invention performed SEM characterization on diamonds from M1 to M6. The electron scanning images are shown below. Figure 5 As shown. Figure 5 Under 500x magnification, M1-1 showed no obvious defects on the {111} face of the undoped diamond crystal, and the crystal surface was smooth and flat. Figure 5 In M2-1, the TiB2 doped crystal with a doping concentration of 10 wt.% showed some growth striations on the {111} facet, but no other obvious defects were observed. When the doping concentration was increased to 20 wt.%, a large number of equilateral triangular defects appeared on the {111} facet of sample M3. The vertices of these triangles pointed towards the edge direction of the {111} facet. At a magnification of 1000x ( Figure 5 In M3-2, it can still be observed that most of the triangular defects remain independent, and the triangles are relatively uniform in size. Magnified observation of the {311} surface of sample M3 (circled area in Figure M3), as shown in Figure M3-3, reveals a large number of identical triangular defects on the {311} surface at 1000x magnification, with most of these defects exhibiting a "dot-base" shape. When the doping concentration is 30 wt.%, from... Figure 5 In M4-1, we can observe that the sharp corners of some triangular defects have become rounded, and the triangular defects have become more disordered. Magnification ( Figure 5 M4-2) revealed smaller triangular defects in certain areas, indicating a non-uniformity in the size of these defects. Simultaneously, the triangular defects began to transform into a "flat-bottomed" shape, and their size decreased, as shown when magnified. Figure 5 As shown in M4-3, the morphological features of the M5 crystal surface are no longer observable at 500x magnification. However, when the magnification is increased to 2000x (…),… Figure 5 In M5-1, numerous defects were observed, indicating that the size of the triangular defects had further decreased. Most of the defect sharp corners were further rounded, transforming from triangles to hexagons, and some defects overlapped with each other. At 3000x magnification (Figure M6-1), it was observed that the surface of crystal M6, except for a few pits, was generally corroded. This was due to the defects becoming smaller and denser, eventually overlapping and corroding away a layer of the diamond surface.

[0042] Table 4. Crystal surface defect parameters under atomic force microscopy

[0043] To more intuitively observe the defects on the sample surface, this invention performed atomic force microscopy tests on samples M3-M6. From Figure 6 It can be seen that the triangular defects on the surface of crystal M3 remain relatively independent, and the pits have point bases. Other samples show varying degrees of overlap, consistent with the observed phenomena during scanning. In the image, the point base of the pit on the surface of crystal M4 does not coincide with the centroid of the pit triangle boundary, as shown... Figure 8 As shown in b, the dot bottom is eccentric relative to the boundary of the etched pit. Compared with M3 and M4, the triangular pits on the M5 surface change from being predominantly dot-bottom to being predominantly surface-bottom. With increasing TiB2 doping concentration, more triangular defects are observed within the same test area. Table 3 shows that the side length of the triangular defects decreases from 2.85 μm to 1.09 μm. The pit depth decreases from 590 nm to 65.54 nm, and the crystal surface roughness Rq also decreases from 145.302 nm to 6.896 nm. This indicates that with increasing TiB2 doping concentration, the size of triangular defects on the diamond surface gradually decreases, the density gradually increases, and the depth gradually decreases.

[0044] In a diamond lattice, a carbon atom forms covalent bonds with four surrounding carbon atoms, while a boron atom, with only three electrons in its outermost shell, can only form covalent bonds with three carbon atoms. This makes the diamond lattice more prone to distortion, and lattice defects increase with increasing boron content. Under appropriate etching conditions, the CC atoms at diamond vacancies break first and continuously expand outwards, macroscopically manifesting as triangular corrosion pits on the {111} plane of the diamond surface. Line defects in diamond can be considered as being composed of many point defects, with triangular defects nucleating at each point defect and stacking together. When the line defect is parallel to the diamond cleavage plane, agglomeration occurs. If the line defect is perpendicular to the diamond cleavage plane, with prolonged etching, the pit will remain at the bottom until the bottom of the pit reaches the end of the line defect, at which point the pit will gradually transform into a flat-bottomed type. The depth of the pit depends on the length of the line defect in the crystal; when the linear defect forms an angle with the cleavage plane, the pit will exhibit an off-center appearance. If the etching rate is slow, the resulting pits have straight edges, while if the etching rate is fast, the corners of the pits are rounded. As the TiB2 doping level increases, the nitrogen content in diamond decreases, and more boron atoms replace carbon atoms in the diamond lattice, leading to an increase in defects. The defect density increases, and the density of triangular defects also increases, eventually overlapping to create the corrosion pattern shown in Figure M5-1.

[0045] This invention employs a temperature gradient method to synthesize large diamond single crystals in a Fe-Ni-C system by adding different amounts of TiB2 (0-50 wt.%) at 5.6 GPa, 1340 ℃, and 1360 ℃. It was found that TiB2 affects the concentration of boron and nitrogen impurities and surface defects in the diamond. With increasing TiB2 content, when the TiB2 content is between 0-5 wt.%, the nitrogen content of the crystal gradually decreases, and the diamond color changes from yellow → light yellow → light yellow → blue → black, with the crystal form changing from hexahedral to octahedral. When the TiB2 content reaches 10-50 wt.%, the crystal exhibits a black color and an octahedral morphology dominated by {111} faces. Furthermore, numerous triangular pit defects begin to appear on the crystal surface. The side length of the triangular pit defect decreased from 2.85 μm to 1.09 μm, the depth decreased from 590 nm to 50 nm, and the surface roughness Rq of the crystal also decreased from 145.302 nm to 6.896 nm.

[0046] Raman spectroscopy analysis showed that boron successfully entered the diamond lattice and the boron content in the tested area reached 1020 cm⁻¹. -1 Infrared spectroscopy results show that TiB2 can effectively remove nitrogen impurities from the diamond lattice.

[0047] Scanning electron microscopy and atomic force microscopy revealed numerous triangular defects on the diamond surface when the TiB2 content exceeded 20 wt.%. The shapes of these triangular pits varied depending on the TiB2 content, exhibiting characteristics such as "dot bottom," "eccentric dot bottom," and "surface bottom," which are related to the numerous defects generated by boron atoms entering the diamond. With increasing TiB2 doping concentration, the triangular defects showed a trend of decreasing size, increasing density, and decreasing depth.

[0048] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for controlling the surface structure of large-size boron-doped diamond single crystals, characterized in that, Includes the following steps: A. Constructing the reaction system Large-size boron-doped diamond single crystals were synthesized using a high-temperature, high-pressure temperature gradient method. From the high-temperature end to the low-temperature end of the chamber, a carbon source 11, a catalyst 5, a seed crystal 6, and an MgO+ZrO2 crystal bed 13 were arranged sequentially. The carbon source 11 was formed by mixing and pressing high-purity graphite powder and high-purity TiB2 powder. The catalyst 5 was an FeNi alloy, and the {111} facet of the seed crystal 6 was the growth surface. The center temperature of the chamber was 1300-1400℃, and the high pressure was 5.6 GPa. The size of the seed crystal 6 was 0.8 mm-1 mm. The pressed carbon source 11 was assembled in the synthesis chamber. Each sample assembly was dried at 120℃ for half an hour before high-pressure synthesis. B. Regulation of nitrogen concentration in crystals by TiB2 In step A, high-purity TiB2 powder was added to the FeNi-C system. The amount of high-purity TiB2 powder added was 1-5 wt.% of the weight of high-purity graphite powder. Then, hexahedral diamond crystals ranging from light yellow and light yellow-light blue to black were synthesized. The center temperature of the cavity was 1340 ℃ and the reaction time was 12 h. C and TiB2's effects on diamond growth characteristics and morphology In step A, high-purity TiB2 powder is added to the FeNi-C system. The amount of high-purity TiB2 powder added is 10-50 wt.% of the weight of high-purity graphite powder. Then, diamond crystals ranging from hexahedral to octahedral are synthesized. The center temperature of the cavity is 1360 ℃ and the growth time is 24 h.

2. The method for controlling the surface structure of large-size boron-doped diamond single crystals according to claim 1, characterized in that: In step B, when the amount of high-purity TiB2 powder added is 1 wt.%, the diamond crystal is light yellow; when the amount of high-purity TiB2 powder added is 2 wt.% or 3 wt.%, the diamond crystal is light yellow to blue; when the amount of high-purity TiB2 powder added is 4 wt.%, the diamond crystal is light yellow to blue; and when the amount of high-purity TiB2 powder added is 5 wt.%, the diamond crystal is black.

3. The method for controlling the surface structure of large-size boron-doped diamond single crystals according to claim 1, characterized in that: In step C, when the amount of high-purity TiB2 powder added is 10 wt.% or 20 wt.%, the diamond crystal produced is hexahedral; when the amount of high-purity TiB2 powder added is 30 wt.%, 40 wt.%, or 50 wt.%, the diamond crystal produced is transformed into octahedral.

4. The method for controlling the surface structure of large-size boron-doped diamond single crystals according to claim 3, characterized in that: In step C, when the amount of high-purity TiB2 powder added is greater than 20 wt.%, a large number of triangular pit defects appear on the diamond surface, including dot bottom, eccentric dot bottom and surface bottom features.

5. The method for controlling the surface structure of large-size boron-doped diamond single crystals according to claim 4, characterized in that: When the amount of high-purity TiB2 powder added was adjusted from 30 wt.% to 50 wt.%, the side length of the triangular pit defect decreased from 2.85 μm to 1.09 μm, the depth decreased from 590 nm to 50 nm, and the surface roughness Rq of the crystal also decreased from 145.302 nm to 6.896 nm.

Images