Synthetic Diamond Crystals Research Articles

The mechanical properties of various chemical vapor deposition diamond structures compared to the ideal single crystal

The structural and electronic properties of the diamond lattice, leading to its outstanding mechanical properties, are discussed. These include the highest elastic moduli and fracture strength of any known material. Its extreme hardness is strongly connected with the extreme shear modulus, which even exceeds the large bulk modulus, revealing that diamond is more resistant to shear deformation than to volume changes. These unique features protect the ideal diamond lattice also against mechanical failure and fracture. Besides fast heat conduction, the fast vibrational movement of carbon atoms results in an extreme speed of sound and propagation of crack tips with comparable velocity. The ideal mechanical properties are compared with those of real diamond films, plates, and crystals, such as ultrananocrystalline (UNC), nanocrystalline, microcrystalline, and homo- and heteroepitaxial single-crystal chemical vapor deposition (CVD) diamond, produced by metastable synthesis using CVD. Ultrasonic methods have played and continue to play a dominant role in the determination of the linear elastic properties, such as elastic moduli of crystals or the Young’s modulus of thin films with substantially varying impurity levels and morphologies. A surprising result of these extensive measurements is that even UNC diamond may approach the extreme Young’s modulus of single-crystal diamond under optimized deposition conditions. The physical reasons for why the stiffness often deviates by no more than a factor of two from the ideal value are discussed, keeping in mind the large variety of diamond materials grown by various deposition conditions. Diamond is also known for its extreme hardness and fracture strength, despite its brittle nature. However, even for the best natural and synthetic diamond crystals, the measured critical fracture stress is one to two orders of magnitude smaller than the ideal value obtained by ab initio calculations for the ideal cubic lattice. Currently, fracture is studied mainly by indentation or mechanical breaking of freestanding films, e.g., by bending or bursting. It is very difficult to study the fracture mechanism, discriminating between tensile, shear, and tearing stress components (mode I–III fracture) with these partly semiquantitative methods. A novel ultrasonic laser-based technique using short nonlinear surface acoustic wave pulses, developing shock fronts during propagation, has recently been employed to study mode-resolved fractures of single-crystal silicon. This method allows the generation of finite cracks and the evaluation of the fracture strength for well-defined crystallographic configurations. Laser ultrasonics reaches the critical stress at which real diamond fails and therefore can be employed as a new tool for mechanistic studies of the fracture behavior of CVD diamond in the future.

TEM and DSC Studies on the Synthetic Diamond Grown from Fe-Ni-C-B System under HPHT

Transmission Electron Microscope (TEM) and Different Scanning Calorimetry (DSC) Methods Were Used to Investigate the Diamonds Grown with Different Boron Content Alloy Catalysts under High-Pressure High-Temperature (HPHT). Experimental Results Demonstrated the Microstructure and Composition of Boride Compounds in Synthetic Diamond, such as (FeNi)23(CB)6 ,(Fe, Ni)3(C,B), (Fe,Ni)B and B4C, Whose Formation Process Was Analyzed. the Thermal Stability of Diamond Depends on Boron Concentration in Catalyst According to DSC Studies. we Analyzed the Reason of Diamond Oxidation.The Work Offers Valuable Information for Improving the Thermal Stability of Synthetic Diamond Crystals by Adjusting Boron Content in the Fe-Ni Based Catalyst.

Interaction of diamond with ultrafine Fe powders prepared by different procedures

We have studied the interaction of synthetic diamond crystals with ultrafine Fe powders during catalytic diamond gasification in a hydrogen atmosphere at 900°C. The Fe powders were prepared by three procedures: reduction of Fe2O3 nanopowder; evaporation using an ELV-6 electron accelerator, followed by condensation; and reduction of ferric chloride. The surface-processed diamond crystals were examined by electron microscopy. The results indicate that ultrafine powders produced by the first two procedures cause predominantly lateral etching of diamond. The Fe particles prepared by the third procedure penetrate into the bulk of diamond crystals and produce etch pits and “tunnels,” thereby markedly increasing the specific surface area of the crystals.

Synthesis and characterization of p-type boron-doped IIb diamond large single crystals

High-quality p-type boron-doped IIb diamond large single crystals are successfully synthesized by the temperature gradient method in a china-type cubic anvil high-pressure apparatus at about 5.5 GPa and 1600 K. The morphologies and surface textures of the synthetic diamond crystals with different boron additive quantities are characterized by using an optical microscope and a scanning electron microscope respectively. The impurities of nitrogen and boron in diamonds are detected by micro Fourier transform infrared technique. The electrical properties including resistivities, Hall coefficients, Hall mobilities and carrier densities of the synthesized samples are measured by a four-point probe and the Hall effect method. The results show that large p-type boron-doped diamond single crystals with few nitrogen impurities have been synthesized. With the increase of quantity of additive boron, some high-index crystal faces such as {113} gradually disappear, and some stripes and triangle pits occur on the crystal surface. This work is helpful for the further research and application of boron-doped semiconductor diamond.

High average power diamond Raman laser

We report a pulsed Raman laser at 1193 nm based on synthetic diamond crystals with a record output power of 24.5 W and a slope efficiency of 57%. We compared the performance of an anti-reflection coated crystal at normal incidence with a Brewster cut sample. Raman oscillation was achieved at both room temperature and under cryogenic operation at 77 K. Modeling of these experiments allowed us to confirm the value of Raman gain coefficient of diamond, which was found to be 13.5 ± 2.0 cm/GW for a pump wavelength of 1030 nm.

Diamond Islands Wafer for Super LED Manufacture

Diamond's (111) face can grow epitaxial GaN with wurtzite structure. Better still, single crystal AlN can be deposited directly on such diamond surface. Boron doped diamond has the highest mobility of holes, and silicon doped AlN can boost electron mobility. The AlN on diamond is capable to emit ultraviolet (UV) light with high intensity. Such UV light can excite phosphors for the emission of different colors, including white light with balanced RGB distribution. There are many possibilities of making super LED with diamond. Unfortunately, diamond wafers are not available commercially. However, synthetic diamond crystals can be made cheaply by a noval seeding technology (DiaCan{trade mark, serif}). These diamond crystals are embedded in a ceramic matrix to form diamond islands wafer (DIW). DIW is the enabling substrate for making super LED in the near future.

UV detectors based on epitaxial diamond films grown on single-crystal diamond substrates by vapor-phase synthesis

The prospects for use of CVD-technology for epitaxial growth of single-crystal diamond films of instrumental quality in UHF plasma for the production of optoelectronic devices are discussed. A technology for processing diamond single crystals that provides a perfect surface crystal structure with roughness less than 0.5 nm was developed. It was demonstrated that selective UV detectors based on synthetic single-crystal diamond substrates coated with single-crystal films can be produced. A criterion for selecting clean and structurally perfect single crystals of synthetic diamond was developed for the epitaxial growth technology.

Acoustic Emission Study of Growth Process of Diamond Crystals under HPHT

The growth process of synthetic diamond single crystals under high-pressure and high-temperature (HPHT) was investigated using acoustic emission (AE) technique. And AE parameters corresponding to growth process were analyzed. However, the AE features of diamond growth are relativelyweak and easily obscured by other AE sources. So the fast Fourier transformation (FFT) was used to calculate the frequency spectra of AE signals for identifying different AE sources. The results showed that the variation of AE counts and energy is in a good agreement with the formation process of synthetic diamond crystals. And the AE signals pronounced from diamond growth are concentrated in the frequency range from 100 to 250 kHz. Thus, AE technique is an effective way to monitor and study the diamond growth, and the frequency analysis can be a useful way to identify different AE sources.

Synthesis and characterization of strip-shape diamonds from Fe-based alloy and graphite system under high pressure and high temperature

The unusual strip-shape diamond crystals were successfully synthesized in the system of Fe-based powder alloy and graphite under pressures of 5.6–5.8 GPa and temperatures of 1600–1650 K in a cubic anvil high pressure high temperature (HPHT) apparatus (SPD-6×1200). The synthetic diamond crystals have a strip-shape with light green color. The lengths of the crystals are 0.6–0.8 mm with length to diameter ratios around 2.0–2.5. SEM photographs reveal that the crystals have two main kinds of shapes: one elongated along the (1 0 0) and the other along the (1 1 1) directions. The FTIR spectra of the diamond synthesized indicate that its nitrogen concentration is higher than the normal diamond crystal.

Strength and elastic deformation of natural and synthetic diamond crystals shock compressed along [100

Plane shock wave experiments were conducted to determine the strength and elastic response of natural and synthetic diamond single crystals shocked along [100] to peak elastic stresses of ∼90 and ∼120 GPa. Velocity interferometry was used to measure particle velocity histories and shock velocities in the diamond samples. The maximum elastic wave amplitudes (89±3 GPa) for both crystal types were comparable. This value corresponds to shear stresses of 30 and 35 GPa (∼G/15) for the (111) [11¯0] and (111) [21¯1¯] slip systems, respectively. Surprisingly, the elastic limit (57±3 GPa) was lower for the higher peak stress. The elastic constant C111 was experimentally determined to be −7804±653 GPa.

Synthesis of high quality type-Ib diamond crystals in carats grade

High quality type-Ib tower-shape gem-diamond crystals in carats grade were synthesized in cubic anvil high pressure apparatus (SPD-6×1200) at 5.4 GPa and 1250–1450°C. The relationship between the growth time and the weight of growth diamond has been gained. The faces of {110} and {113} were found in the synthetic diamond crystals frequently. We found that the relative growth rate of {113} face was descending with the increase of growth temperature, and that of {110} face had no obvious change with the increase of the growth temperatures and the growth time. In the work, the crystal defects were studied carefully, and the reasons for the appearance of the defects were also obtained. Some diamond crystals have been polished into the anvil of DAC (Diamond Anvil Cell) and the diamond jewelry. Compared with natural diamond crystal, synthetic diamond crystal has the merits such as small grinding quantity, low cost, etc., so it can be widely used in super high pressure field and gemstone industry.

Thermal Expansion of Diamond at Low Temperatures

Temperature variation of a lattice parameter of a synthetic diamond crystal (type IIa) was measured using high-energy-resolution x-ray Bragg diffraction in backscattering. A 2 order of magnitude improvement in the measurement accuracy allowed us to directly probe the linear thermal expansion coefficient at temperatures below 100 K. The lowest value measured was 2x10{-9} K-1. It was found that the coefficient deviates from the expected Debye law (T3) while no negative thermal expansion was observed. The anomalous behavior might be attributed to tunneling states due to low concentration impurities.

High-reflectivity high-resolution X-ray crystal optics with diamonds

Hard-X-ray mirrors usually rely on total external reflection at grazing incidence, owing to the high-penetration and low X-ray reflectivity of most materials. A demonstration of the almost perfect reflectance of hard X-rays from diamond at near-normal incidence could allow the development an entirely new class of X-ray optics. Owing to the depth to which hard X-rays penetrate into most materials, it is commonly accepted that the only way to realize hard-X-ray mirrors with near 100% reflectance is under conditions of total external reflection at grazing incidence to a surface. At angles away from grazing incidence, substantial reflectance of hard X-rays occurs only as a result of constructive interference of the waves scattered from periodically ordered atomic planes in crystals (Bragg diffraction). Theory predicts that even at normal incidence the reflection of X-rays from diamond under the Bragg condition should approach 100%—substantially higher than from any other crystal. Here we demonstrate that commercially produced synthetic diamond crystals do indeed show an unprecedented reflecting power at normal incidence and millielectronvolt-narrow reflection bandwidths for hard X-rays. Bragg diffraction measurements of reflectivity and the energy bandwidth show remarkable agreement with theory. Such properties are valuable to the development of hard-X-ray optics, and could greatly assist the realization of fully coherent X-ray sources, such as X-ray free-electron laser oscillators1,2,3.

Optical and paramagnetic properties of synthetic diamond crystals irradiated with electrons and annealed

The optical and paramagnetic properties of single crystals of synthetic diamond grown by the temperature-gradient method in high-pressure apparatuses with the systems of catalytic solvents (Co, Fe) and (Ni, Fe) are studied at room temperature. The optical absorption spectra (in the wavelength range λ = 400–800 nm) and the spectra of electron spin resonance are registered for the initial diamond crystals, the crystals irradiated with 6 MeV electrons (the fluence 1.5 × 1018 cm−2), and the irradiated diamonds subjected to isochronous thermal annealing in vacuum (for 60 min). It is shown that, with such treatment, the diamond crystals synthesized with different metal catalysts (Co or Ni) exhibit similar optical properties, but different paramagnetic properties. The data obtained by infrared spectroscopy and electron spin resonance spectroscopy are coincident for radiation defects and different for nitrogen centers (the P1 centers and exchange-coupled pairs of nitrogen atoms). The spectra of the electron spin resonance of the samples annealed at temperatures below 1273 K (in the case of the Co-containing catalyst) and 1073 K (in the case of Ni-containing catalyst) exhibited broad lines produced by residual impurities of the catalyst metal and were accompanied by a distortion of the spectrum of paramagnetic nitrogen in the form of a tilt of the ESR spectra with respect to the zero line.

Effects of NaN3 Added in Fe—C System on Inclusion and Impurity of Diamond Synthesized at High Pressure and High Temperature

Effects of NaN3 added in Fe—C system to synthesize nitric diamond at high pressure and high temperature are investigated. Diamond crystals with high nitrogen concentration are synthesized by the system of Fe—C and NaN3 additive at pressure 5.8 GPa and at temperatures 1750–1780K for 15 min. The synthetic diamond crystals have a cubo-octahedral or octahedral shape with yellowish green or green colour. Some disfigurements are observed on the surfaces of most diamond crystals. The composition and content of inclusions formed by iron in diamond are changed and iron nitride is detected in diamond crystals synthesized with Fe–C–NaN3 additive. As the amount of NaN3 additive increases, Fe3 C decreases and iron nitride increases with α-Fe being nearly constant. Moreover, the nitrogen concentrations in diamond crystals synthesized with 1.5wt% NaN3 additive is up to 2250 ppm in substitutional form.

Recent Advances in High Pressure Apparatus for Diamond Synthesis

Recent progress of the technology of large-scale high pressure apparatus have permitted us to produce synthetic diamond powders in larger quantities at a lower cost. The advances in high-pressure and high-temperature control technique have enabled the commercialization of high-purity large synthetic diamond crystals. In this article, recent advances and future prospects in the high-pressure apparatus technology for synthetic diamonds are described.

Plastic deformation and optical behavior of high-purity synthetic diamond crystal subjected to high stress load at room temperature

The optical behavior around the culet of a diamond anvil made of high-purity and defect-free synthetic diamond crystal, which was plastically deformed at room temperature, was investigated by cathodoluminescence spectroscopy. It was found that the free exciton peaks weaken while the A-band and 2BD bands appear at the culet center where plastic deformation occurred. It was demonstrated that the free exciton peaks near the edge of the culet shift to the long wavelength side, indicating that the band structure of the peripheral areas of the culet changes because of residual strain caused by the plastic deformation in the culet center.

Monitoring diamond crystal growth, a combined experimental and SIMS study

Detailed ion microprobe measurements have been made on two synthetic diamond crystals in order to investigate how variations in chemical and isotopic compositions are related to growth sectors and overall growth history. The crystals were grown by the metal catalyst technique under identical T - P conditions of 1450 °C and 5.5 GPa, but with different source nitrogen abundances. Measurements for carbon and nitrogen isotope compositions and nitrogen abundance were made in traverses across the crystal sectors, which included cubic sectors and octahedral sectors of both relatively rapid and relatively slow growth. In both crystals an early phase of growth dominated by falling δ 13 C and rising of N ppm is followed by an extensive phase of growth with moderately constant δ 13 C and gradually descending N ppm . The change from falling to stable δ 13 C ratios has been numerically modelled on the basis of the carbon isotope fractionation between the carbon solution in metal melt and the growing diamond in closed system; the stabilization of the diamond carbon isotope composition is achieved once a steady state is attained and diamond grows with the same carbon isotope composition as the graphite source. The decreasing N ppm values appear to be a product of Rayleigh fractionation. Carbon isotope compositions show little difference between different growth sectors, and δ 15 N values in any given sector show no change with time of growth. However, the nitrogen isotope compositions show major differences of ca. 30 ‰ between octahedral and cubic sectors. These differences are not related to growth rate or time of growth and appear to represent a consistent difference in N isotope adhesion between the two faces.

Dependence of Crystal Quality and β Value on Synthesis Temperature in Growing Gem Diamond Crystals

High quality Ib gem diamond single crystals were synthesized in cubic anvil high-pressure apparatus (SPD-6 × 1200) under 5.4 GPa and 1230°C-1280°C. The (100) face of seed crystal was used as growth face, and Ni70Mn25Co5 alloy was used as solvent/catalyst. The dependence of crystal quality and β value (the ratio of height to diameter of diamond crystal) on synthesis temperature was studied. When the synthesis temperature is between 1230°C and 1280°C, the β value of the synthetic high-quality gem diamond crystals is between 0.4 and 0.6. The results show that when the β value is between 0.4 and 0.45, the synthetic diamonds are sheet-shape crystals; however, when the β value is between 0.45 and 0.6, the synthetic diamonds are tower-shape crystals. In addition, when the β value is less than 0.4, skeleton crystals will appear. When the β value is more than 0.6, most of the synthetic diamond crystals are inferior crystals.

The effect of HPHT treatment on the spectroscopic features of type IIb synthetic diamonds

The effect of high pressure high temperature treatment on the spectroscopic features of boron-doped type IIb synthetic diamonds has been studied. Synthetic HPHT diamond crystals with different concentrations of boron acceptors were annealed at temperatures in the range 1800–2650 °C under a stabilizing pressure of 7–7.5 GPa. Fourier-transform infra-red absorption spectroscopy and cathodoluminescence were applied to study the effect of the annealing. We found that for annealing temperatures up to 2650 °C, the IR absorption features related to neutral boron acceptors did not change in intensity, demonstrating that single substitutional boron was not affected by the treatment. This finding is in good agreement with the recent first-principle calculations of Goss and Briddon (Phys. Rev. B 73 (2006) 085207) predicting very high activation energies for migration of substitutional boron in the diamond lattice. For diamonds with boron concentration of about 1 ppm, it was found that annealing at 2650 °C for 1 h produced an intense CL emission band peaking at 2.85 eV, which is known to be related to dislocations. It was suggested that dislocations in the studied boron-doped diamonds were formed due to plastic deformation occurred during anneals.