Nano-polycrystalline diamond synthesized through the decomposition of stearic acid

ABSTRACT

Here we report a novel route for synthesizing nano-polycrystalline diamond (NPD) using stearic acid (C₁₈H₃₆O₂) as a starting material under high pressure and high temperature. The obtained NPD shows a transparent dark-yellowish color similar to the standard NPD synthesized from graphite and consists of extremely fine diamond grains (～10?nm). The temperature required for the present synthesis of pure transparent NPD is as low as 1000°C at 13 and 17?GPa, which is surprisingly lower than that for conventional NPD synthesis (1800–2000°C). The amorphous-like, extremely poorly crystalline graphite produced by the thermal decomposition of stearic acid likely provides preferential nucleation sites for diamond and significantly lower the activation energy. The removal of volatile components such as H₂O generated through the decomposition from the system is a key to obtain pore-free transparent NPD. Magnesite, MgCO₃ and periclase, MgO can be used as an efficient H₂O remover through the hydration reaction.     

Origin,characteristics, and suppression of residual nitrogen in MPCVD diamond growth reactor

Unintentional nitrogen incorporation has been observed in a set of microwave plasma chemical vapor deposition (MPCVD)-grown samples. No abnormality has been detected on the apparatus especially the base pressure and feeding gas purity. By a comprehensive investigation including the analysis of the plasma composition, we found that a minor leakage of the system could be significantly magnified by the thermal effect, resulting in a considerable residual nitrogen in the diamond material. Moreover, the doping mechanism of leaked air is different to pure nitrogen doping. The dosage of several ppm of pure nitrogen can lead to efficient nitrogen incorporation in diamond, while at least thousands ppm of leaked air is required for detecting obvious residual nitrogen. The difference of the dosage has been ascribed to the suppression effect of oxygen that consumes nitrogen. As the unintentional impurity is basically detrimental to the controllable fabrication of diamond for electronic application, we have provided an effective way to suppress the residual nitrogen in a slightly leaked system by modifying the susceptor geometry. This study indicates that even if a normal base pressure can be reached, the nitrogen residing in the chamber can be "activated" by the thermal effect and thus be incorporated in diamond material grown by a MPCVD reactor.     

Effect of the codoping of N—H—O on the growth characteristics and defects of diamonds under high temperature and high pressure

Diamond crystals were synthesized with different doping proportions of N—H—O at 5.5 GPa—7.1 GPa and 1370 °C—1450 °C. With the increase in the N—H—O doping ratio, the crystal growth rate decreased, the temperature and pressure conditions required for diamond nucleation became increasingly stringent, and the diamond crystallization process was affected. [111] became the dominant plane of diamonds; surface morphology became block-like; and growth texture, stacking faults, and etch pits increased. The diamond crystals had a two-dimensional growth habit. Increasing the doping concentration also increased the amount of N that entered the diamond crystals as confirmed via Fourier transform infrared spectroscopy. However, crystal quality gradually deteriorated as verified by the red-shifting of Raman peak positions and the widening of the Raman full width at half maximum. With the increase in the doping ratio, the photoluminescence property of the diamond crystals also drastically changed. The intensity of the N vacancy center of the diamond crystals changed, and several Ni-related defect centers, such as the NE1 and NE3 centers, appeared. Diamond synthesis in N—H—O-bearing fluid provides important information for deepening our understanding of the growth characteristics of diamonds in complex systems and the formation mechanism of natural diamonds, which are almost always N-rich and full of various defect centers. Meanwhile, this study proved that the type of defect centers in diamond crystals could be regulated by controlling the N—H—O impurity contents of the synthesis system.     

Application of polymeric drilling fluids for reducing wearing of drill bit

The drill bit or cutting tool is a very important part of the rock drilling operation, it is directly associated with the rate of penetration. Bit wearing has significant involvement of time, labor, and wealth. By identifying the effect of various machine and rock parameters on bit wearing, the optimum working condition can be adopted to achieve high drilling efficiency. In this experimental work, the rate of penetration and parameters of drilling fluids (i.e. type, additives, and concentration, etc.) were optimized to identify their respective impact on the bit wearing of impregnated core diamond bit. The study has been conducted on a laboratory rotary drilling setup. The role of aqueous solutions of carboxymethyl cellulose (CMC), guar gum (GG), and polyacrylamide (PAM) has been examined as polymeric drilling fluid additives on sandstone rock samples and compared with the results of tap water alone as drilling fluid. A significant decrement in bit wearing has been noticed with all additives and the maximum reduction of 70.02% was achieved with CMC fluid additive.     

A critical review on the electrochemical production and use of peroxo-compounds

Peroxosulfates, peroxocarbonates and peroxophosphates form a group of powerful oxidants that can be synthesized electrochemically and used for the treatment of refractory compounds. Based on the latest studies in the bibliography, this critical review presents the potentialities and also the current limits of the electrosynthesis of these peroxo compounds coupled to their reactions with target compounds. The main parameters such as electrode material, use of additives, cell geometry, temperature and pH affecting the efficiency of the process will be discussed. To conclude, the new challenges and research perspectives in this theme to be performed will be presented before development at an industrial scale.     

Effect of laser fluence on c‐axis orientation of LiNbO3 piezoelectric films on nanocrystalline diamond by pulsed laser deposition

Completely c‐axis oriented LiNbO₃ piezoelectric films have been deposited on nanocrystalline diamond (NCD)/Si substrates with SiO₂ buffer layer by pulsed laser deposition. The amorphous SiO₂ buffer layer was formed on NCD/Si substrates by sol‐gel method. The c‐axis orientation and crystallinity of LiNbO₃ films are strongly dependent on the laser fluence, and the laser fluence 3.6 J/cm² is found to be the optimal value for the growth of oriented LiNbO₃ film, which has a smooth surface with composed of a large mount of uniform grains. The average surface roughness of LiNbO₃ films is about 6.7 nm.     

A synthetic diamond probe for both low-energy mammography X-rays and high-energy electron therapy beams

Although diamond has been studied for dosimetry principally due to its near-tissue equivalence, its use in both low-energy X-rays and high-energy electron beams has not been reported. This report is based on dosimetric studies of a synthetic diamond probe when subjected to diagnostic mammography X-ray photons and megavoltage electron therapy beams. The probe, constructed using entirely tissue-equivalent Perspex body, was configured for radiation dose measurement in either ‘edge-on’ or ‘flat-on’ exposure geometry without having first to re-orient the diamond within the body of the detector, and it was designed to be compatible with commercial electrometer systems. The radiation response of the diamond tested showed negligible energy dependence; its minimal background signal, high sensitivity (547.52 nC Gy⁻¹ mm⁻³) and suitability for measurements in small radiation fields of steep dose gradients due to its small size make it suitable for clinical dosimetry. The presented probe has the potential advantage of replacing conventional radiation dosimeters.     

White electroluminescence of n-ZnO：Al/p-diamond heterostructure devices

An n-ZnO：A1/p-boron-doped diamond heterostructure electroluminescent device is produced, and a rectifying be- havior can be observed. The electroluminescence spectrum at room temperature exhibits two visible bands centred at 450 nm-485 nm （blue emission） and 570 nm-640 nm （yellow emission）. Light emission with a luminance of 15 cd/m2 is observed from the electroluminescent device at a forward applied voltage of 85 V, which is distinguished from white light by the naked eye.     

Magnetic transition of ferromagnetic material at high pressure using a novel system

A system for the investigation of the magnetic properties of materials under high pressure is fabricated based on diamond anvil cell （DAC） technology. The system is designed with an improved coil arranged around the diamond of a non-magnetic DAC. Using this system, the magnetic transition of ferromagnetic （Fe） sample under increasing pressure can be observed. We successfully obtain the evolution of magnetic properties as a function of applied pressure reaching 26.9 GPa in the Fe sample. A magnetic transition is observed at approximately 13 GPa, which is consistent with the theoretical prediction.     

冲击波实验用铝楔形靶加工技术

采用单点金刚石车削技术制备加工铝楔形靶,发现金刚石车削加工楔形靶实际轮廓为圆锥面。通过Veeco NT1100白光干涉仪对表面轮廓及粗糙度进行了测量,结果表明平面部分表面粗糙度小于50 nm,最大峰谷值小于100 nm,斜面部分表面粗糙度小于200 nm。分析认为斜面部分粗糙度测量数值较大是由刀具工作角度变化导致的,而测量轮廓线非圆锥体母线又导致粗糙度测量结果大于实际值。