Papers by Keyword: Diamond

Abstract: In this study, we propose a simple and effective approach to enhance (110) orientation in diamond films grown on (100) Si substrates by microwave plasma chemical vapor deposition. It is found that the crystalline structure of diamond films strongly rely on the CH₄ concentration in the nucleation stage. Under the same growth condition, when the CH₄ concentration is less than 7% (7%) in the nucleation stage, the diamond films exhibit randomly oriented structure; once the value exceeds 7%, the deposited films are strongly (110) oriented. It could be verified by experiments that the formation of (110) orientation in diamond films are related to the high nucleation density and high fraction of diamond-like carbon existing in nucleation samples.

Abstract: Lateral gate depletion expansion towards drain contact has been analyzed on p-type diamond metal-semiconductor field effect transistor by electron beam induced current. The investigation was restricted to a closed channel to simplify the study and to directly observe the expansion of the lateral depletion region. The experimental data agreed with the theoretical model given in the literature.

Abstract: Several studies have been carried out regarding the influence of dislocations on device characteristics; however, most of them had been limited to pseudo-vertical structures using high pressure high temperature (HPHT) insulating material as the substrate. In this study, we have investigated the influence of dislocations to the devices using vertical structure SBD on p+ HPHT substrate. SBDs were selectively fabricated on specific dislocation areas. The SBD fabricated on the threading dislocation area indicated fatal influence of the dislocation on the device characteristics.

Abstract: The dislocation of a p⁺ high-temperature, high-pressure (HPHT) seed crystal is analyzed by X-ray topography using a SR light source, and compared with that of an insulating HPHT seed crystal. The dislocation density of the typical insulating HPHT substrate is around 250 cm^-2. Over several years, significant progress has been achieved in reducing the dislocation density of the typical insulating HPHT substrate from the order of 10⁴–10⁵ cm^-2 to 10² cm^-2. The p⁺ HPHT seed crystal has unique properties, especially in terms of the number of stacking faults (SFs), and very clear growth sector boundaries with dislocation densities of up to 3000 cm^-2. As most research activities have been focused on the “insulating substrate” in HPHT growth technology for a long time, several challenges need to be overcome with respect to the growth of a p⁺ HPHT crystal.

Abstract: Currently, novel method to synthesize diamond film on material substrate called as in-liquid microwave plasma CVD (IL-MPCVD) has been achieved. It has been studied and improved in addition expected as new method instead of conventional gas phase microwave plasma CVD (MPCVD). The purpose of this study is to synthesize single crystal diamond using IL-MPCVD in high speed deposition. The experimental conditions, methanol was poured in to the reactor. Each of diamond particles (100) and (111) was embedded on the stainless steel substrates (SUS632J2). It was mounted to the substrate holder of in-liquid plasma equipment and installed on the top cover. The distance between the tip of the electrode and the substrate was kept to 1.5mm. A microwave of 2.45GHz was irradiated into the quartz glass tube reactor from the rectangular cavity resonator with 4 mm diameter tungsten electrode and the plasma was generated at its tip. The microwave was adjusted in appropriate power to maintain a certain substrate temperature. Diamond films were evaluated by Raman spectroscopy, Scanning Electron Microscope (SEM) and Laser Microscope (LM). As a result, the best orientation for epitaxial growth was found to be (100) which have film growth gradually and smooth surface. Whereas (111) face has polycrystalline film with irregularity growth and rough surface. The remaining H and C after CO synthesis satisfying H/C>20 is necessary to synthesized diamond using IL-MPCVD. The deposition rate was about 32 μm/h when both single crystal and polycrystalline diamond film were synthesized.

Abstract: To meet the need of high-performance thermal management materials in the field of electronic applications, heat sink materials reinforced with synthetic diamonds have been prepared via powder metallurgy. A matrix of a silver alloy with a silicon content of 0.45 wt.% was chosen out of the prediction of the thickness of a final carbide layer of about 180 nm. The volume content of the diamonds and the diamond size were kept constant. The mixed powders were consolidated by Spark Plasma Sintering (SPS) using different sintering temperatures between 800 and 870 °C with a holding time of 30 min. The maximum thermal conductivity of 680 W/(mK) measured at room temperature and 620 W/(mK) at 275 °C was obtained at 810 °C sintering temperature. The degradation of the most promising sample after one thermal cycle up to 275 °C was determined below 1 percent of the value after sintering.

Abstract: Boron doped diamond coatings are used in electrochemistry, due to the high overvoltage for oxygen generation. Niobium is often used as bulk material, but also diamond deposition on titanium was demonstrated. For metallic bulk materials corrosion can take place in case of defects in the diamond coating. This problem can be avoided by using carbon based substrates. Diamond deposition on carbon substrates is difficult, because atomic Hydrogen needed for diamond growth attacks graphitic and amorphous carbon. These reactions have the effects that carbon in the substrate is etched and the amount of atomic hydrogen needed for diamond growth is reduced. To reduce the carbon etching on the substrate, the duration till diamond layer formation should be short. By controlling the diamond deposition conditions, boron addition and seeding with diamond prior to deposition, the formation of diamond coatings on carbon fibre composites (CFC) is possible. Electrochemical measurements of the boron doped diamond coatings verified the excellent electrochemical properties of the samples, e.g. good electrical conductivity, high overvoltage for oxygen and hydrogen but also chemical inertness.

Abstract: The long-term reliability of Schottky pn diodes (SPNDs) on diamond having widely used Ti/Pt/Au electrodes was investigated at 500°C in order to identify degradation phenomena at higher temperatures. A vital degradation event was observed after the passage of about 100 hours in that both forward and reverse currents were progressively reduced. AES depth profiling and X-STEM-EELS analyses revealed that this occurred because the Ti contact material changed to insulating (or semiconductive) TiO₂, causing large series resistance.

Abstract: This paper describes the application of Cold Spray to the deposition of a diamond grade pre-coated with Cu and Ni. Diamond powders are therefore used as the sole feedstock without the addition of separate binders (ductile phases) in cold spraying. The experimental results showed that it was possible to manufacture thick metal-diamond composite coatings with high diamond fraction in the coating but without phase change or graphitization. Results presented in this paper demonstrate the feasibility of a new methodology for the deposition of metal-diamond/ceramic composite coating with the cold spray technique.

Abstract: Recently, diamonds have been utilized gradually for sliding parts and wear-resistant parts because of their excellent properties. The shape of diamond applied to these parts is not only plane but also arc-shaped inner surface. Therefore, development of diamond polishing technology is required. In this study, ultraviolet assisted polishing was thought to develop to polish polycrystalline diamond (PCD) on arc-shaped inner surface. The authors investigated effect of ultraviolet radiation on polishing efficiency and surface roughness. As a result, the surface roughness Ra of PCD showed less than 15 nanometers. In addition, polishing efficiency was improved about 30 percent due to ultraviolet assisted polishing.