Effects of additive NaN_3 on the HPHT synthesis of large single crystal diamond grown by TGM

In this paper,large single crystal diamond with perfect shape and high nitrogen concentration approximately 1671-1742 ppm was successfully synthesized by temperature gradient method (TGM) under high pressure and high temperature (HPHT).The HPHT synthesis conditions were about 5.5 GPa and 1500-1550 K.Sodium azide (NaN3) with different amount was added as the source of nitrogen into the synthesis system of high pure graphite and kovar alloy.The effects of additive NaN3 on crystal growth habit were investigated in detail.The crystal morphology,nitrogen concentration and existing form in synthetic diamond were characterized by means of scanning electron microscope (SEM) and infrared (IR) absorption spectra,respectively.The results show that with an increase of the content of NaN3 added in the synthesis system,the region of synthesis temperature for high-quality diamond becomes narrow,and crystal growth rate is restricted,whereas the nitrogen concentration in synthetic diamond increases.Nitrogen exists in diamond mainly in dispersed form (C-centers) and partially aggregated form (A-centers).The defects occur more frequently on crystal surface when excessive NaN3 is added in the synthesis system.

Energy beam-based direct and assisted polishing techniques for diamond:A review

Diamond is a highly valuable material with diverse industrial applications,particularly in the fields of semiconductor,optics,and high-power electronics.However,its high hardness and chemical stability make it difficult to realize high-efficiency and ultra-low damage machining of diamond.To address these challenges,several polishing methods have been developed for both single crystal diamond(SCD)and polycrystalline diamond(PCD),including mechanical,chemical,laser,and ion beam processing methods.In this review,the characteristics and application scope of various polishing technologies for SCD and PCD are highlighted.Specifically,various energy beam-based direct and assisted polishing technologies,such as laser polishing,ion beam polishing,plasma-assisted polishing,and laser-assisted polishing,are summarized.The current research progress,material removal mechanism,and infuencing factors of each polishing technology are analyzed.Although some of these methods can achieve high material removal rates or reduce surface roughness,no single method can meet all the requirements.Finally,the future development prospects and application directions of different polishing technologies are presented.

Effect of surface modification on the radiation stability of diamond ohmic contacts

The ohmic contact interface between diamond and metal is essential for the application of diamond detectors.Surface modification can significantly affect the contact performance and eliminate the interface polarization effect.However,the radiation stability of a diamond detector is also sensitive to surface modification.In this work,the influence of surface modification technology on a diamond ohmic contact under high-energy radiation was investigated.Before radiation,the specific contact resistivities(ρc)between Ti/Pt/Au-hydrogen-terminated diamond(H-diamond)and Ti/Pt/Au-oxygenterminated diamond(O-diamond)were 2.0×10^(-4)W·cm^(2) and 4.3×10^(-3)Wcm^(2),respectively.After 10 MeV electron radiation,the ρc of Ti/Pt/Au H-diamond and Ti/Pt/Au O-diamond were 5.3×10^(-3)W·cm^(2)and 9.1×10^(-3)W·cm^(2),respectively.The rates of change of ρc of H-diamond and O-diamond after radiation were 2550%and 112%,respectively.The electron radiation promotes bond reconstruction of the diamond surface,resulting in an increase in ρc.

Research on the hydrogen terminated single crystal diamond MOSFET with MoO_3 dielectric and gold gate metal

The single crystal diamond with maximum width about 10 mm has been grown by using microwave plasma chemical vapor deposition equipment. The quality of the grown diamond was characterized using an X-ray diffractometer. The FWHM of the（004） rocking curve is 37.91 arcsec, which is comparable to the result of the electronic grade single crystal diamond commercially obtained from Element Six Ltd. The hydrogen terminated diamond field effect transistors with Au/Mo03 gates were fabricated based on our CVD diamond and the characteristics of the device were compared with the prototype Al/MoO3 gate. The device with the Au/MoO3 gate shows lower on-resistance and higher gate leakage current. The detailed analysis indicates the presence of aluminum oxide at the Al/MoO3 interface, which has been directly demonstrated by characterizing the interface between A1 and MoO3 by X-ray photoelectron spectroscopy. In addition, there should be a surface transfer doping effect of the MoO3 layer on H-diamond even with the atmospheric-adsorbate induced 2 DHG preserved after MoO3 deposition.

B-C Bond in Diamond Single Crystal Synthesized with h-BN Additive at High Pressure and High Temperature

The synthesis of diamond single crystal in the Fe64Ni36-C system with h-BN additive is investigated at pressure 6.5 GPa and temperature range of 1300-1400℃. The color of the obtained diamond crystals translates from yellow to dark green with increasing the h-BN addition. Fourier-transform infrared （FTIR） results indicate that sp2 hybridization B-N-B and B-N structures generate when the additive content reaches a certain value in the system. The two peaks are located at 745 and 1425cm-1, respectively. Fhrthermore, the FTIR characteristic peak resulting from nitrogen pairs is noticed and it tends to vanish when the h-BN addition reaches 1.1 wt%. Furthermore, Raman peak of the synthesized diamond shifts down to a lower wavenumber with increasing the h-BN ~ddition content in the synthesis system.

Structural Imperfections Associated with Supersaturated Vacancies in an HPHT-Grown Diamond Single Crystal

A diamond single crystal, which was synthesized at a high temperature of 1570 K and a high pressure of 5.5 GPa in a Fe-Ni-C system, was directly and systematically examined by transmission electron microscopy (TEM). It is proposed that there exists a variety of imperfections such as dislocation loops, stacking faults, twins and stacking-fault tetrahedral in the diamond, which may be derived from the supersaturated vacancies generated during rapid cooling from high temperature. The formation process of the imperfections is discussed briefly.

Laser Processing Mechanism of Monocrystalline Diamond

When a Nd：YAG laser, the wavelength of which is permeable for diamond, is focused on the surface of a diamond sample, a layer of surface material is ablated. Therefore, diamond can be cut by repetitive irradiation. In this study, the processing mechanism of ablation for a single crystal diamond was examined using a heat conduction analysis, considering laser absorption at the surface or the temperature dependence of absorption coefficient. When the laser beam is absorbed at the surface layer, the surface layer is ablated during an early period in the laser pulse. Once the absorption surface layer is ablated, the laser beam penetrates the base material and ablation stops. On the other hand, if the authors assume that single crystal diamond has the temperature dependence of absorption coefficient which is about equal to that of CVD （chemical vapor deposition） diamond, the temperature rise is not enough to ablate the material. However, it became clear that the diamond is ablated deeply when the authors consider both absorption at the surface layer and the temperature dependence of the absorption coefficient. It can be considered that the surface is transformed to graphite and becomes the absorption layer during the repetitive irradiation. It is estimated that the phase change to graphite is very small and its volume fraction is a few percent at most.

FEM simulations and experimental studies of the temperature field in a large diamond crystal growth cell

We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method （TGM） at high pressure and high temperature （HPHT）. We employ both the finite element method （FEM） and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.