Toshimi Abe

Formation of 250‐μm‐diameter diamond crystals by combustion flame method: Effects of preformation of molybdenum oxide on the substrate

Combustion flame method using acetylene and oxygen has recently proved itself to be a powerful tool to obtain qualified diamond microcrystals with excellent easiness of the performance. Analysis on the spatial variation of the morphology of the deposited film by this method indicates that both the carbon‐bearing radicals from the inner flame and the molybdenum oxide formed by the outer flame are the essence of the growth. The latter aspect has therefore been more definitely incorporated into the process by forming an oxide film prior to the deposition. This preoxidation, together with the simultaneous application of a magnetic field proposed recently by the authors, has led to a drastic suppression of the graphite formation and an excellent increase of the deposited area and of the microcrystal diameter of the diamond. Especially, crystals as large as 250 μm have been successfully grown.

MoO2 Hollow Fiber with Rectangular Cross Sections

Molybdenum oxide hollow fiber with rectangular cross sections has been discovered. The fibers grow on a Mo substrate heated with an acetylene-oxygen combustion flame from the backside. The edge length of the cross-sectional rectangle ranges from ~0.1 to 10 µm. The material, as determined from the X-ray photoelectron spectroscopy and X-ray diffraction, is of monoclinic MoO2.

Microcrystalline diamond deposition using a combustion flame of acetylene and oxygen with a magnetic field

Microcrystalline diamonds were successfully deposited on an abraded molybdenum surface under a magnetic field using a combustion flame of acetylene (C2H2) and oxygen (O2) gases. The deposition rate was about 1 μm/min, which is an order larger than that obtained by conventional chemical‐vapor‐deposition methods. The magnetic field led to an increase of the deposited area and of the microcrystal diameter. The microcrystals show good crystallinity as observed from scanning electron microscopy, reflective electron diffraction, and x‐ray diffraction measurements.

Thin-Film Deposition of Silicon-Incorporated Diamond-Like Carbon by Plasma-Enhanced Chemical Vapor Deposition Using Monomethylsilane as a Silicon Source

We have deposited Si-incorporated diamond-like carbon (DLC) films by radio-frequency plasma-enhanced chemical vapor deposition using methane, argon, and monomethylsilane (MMS; CH3SiH3) as a silicon source, and have investigated the structural and mechanical properties of the films. The deposition rate and Si atomic fraction [Si/(Si+C)] in the DLC films increased with increasing MMS flow ratio. The Si fraction was approximately 13% at a MMS flow ratio [MMS/(MMS+CH4)] of 3%, showing that the deposition using a combination of CH4 and MMS produces films with high Si content compared with those deposited using conventional C and Si sources. The Si fraction was also found to increase with a decrease in Ar flow rate under a constant MMS flow ratio. Many particles composed mainly of Si, whose size was 0.3–1 µm in diameter, were observed on the surface when deposition was carried out at MMS flow ratios of 15 and 30%. Compressive internal stress in the films decreased with the MMS flow ratio and/or with the Ar flow rate. The decrease in internal stress is probably due to the relaxation of a three-dimensional rigid network by the formation of Si–C and Si–H bonds in the films as well as Ar+ ion bombardment.

Formation of highly uniform and dense diamond microcrystal thin films using a combustion flame surrounded by an inert‐gas flow

An inert‐gas curtain method, in which a combustion flame of oxygen/acetylene mixture is protected from the air by a surrounding inert‐gas flow, has been developed for the deposition of microcrystalline diamond films. As a result, highly uniform and highly dense microcrystal films of diamonds possessing the quality of natural diamond were successfully prepared. The inert‐gas flow allows the hydrocarbon radicals in the flame to be varied for preferential deposition of diamonds.

Effects of Silicon Source Gas and Substrate Bias on the Film Properties of Si-Incorporated Diamond-Like Carbon by Radio-Frequency Plasma-Enhanced Chemical Vapor Deposition

We have deposited Si-incorporated diamond-like carbon (DLC) films by radio-frequency plasma-enhanced chemical vapor deposition using methane, argon, and organosilanes, and investigated the effects of Si source gas (monomethylsilane, dimethylsilane) and substrate bias (negative dc bias, negative pulse bias) on the structure and the mechanical and tribological properties of the films. The Si-DLC films deposited using monomethylsilane as a Si source gas tended to have a higher Si atomic fraction ratio [Si/(Si+C)] than the films deposited using dimethylsilane. Friction coefficient and internal stress decreased by the incorporation of Si into the films. However, many particles composed mainly of Si were observed on the film surfaces when deposition using a dc bias was carried out at higher monomethylsilane or dimethylsilane flow ratios. It was found that for both the Si source gases, the use of a pulse bias was effective in suppressing the formation of particles and further decreasing friction coefficient and internal stress. Additionally, the pulse-biased Si-DLC films were found to have a higher wear resistance than the dc-biased Si-DLC films.

Characteristics of Silicon/Nitrogen-Incorporated Diamond-Like Carbon Films Prepared by Plasma-Enhanced Chemical Vapor Deposition

We have deposited silicon/nitrogen-incorporated diamond-like carbon (Si–N-DLC) films by radio-frequency plasma-enhanced chemical vapor deposition (PECVD) using methane (CH4), argon (Ar), and hexamethyldisilazane [(CH3)3Si]2NH as the Si and N source, and investigated the structure and the mechanical and tribological properties of the films. We compared the properties of the Si–N-DLC films with those of the Si-incorporated DLC (Si-DLC) films prepared by PECVD using monomethylsilane (CH3SiH3) as the Si source. It was found that the N incorporation together with Si into DLC was effective in further decreasing the internal stress and increasing the adhesion strength. The friction coefficients of the Si–N-DLC films containing 4.0% N or less were as low as those of the Si-DLC films. We also found that the Si–N-DLC film containing 10.0% Si and 4.0% N had a higher wear resistance than the Si-DLC film containing 10.8% Si. The wear rate was comparable to that of the undoped DLC film.

Formation of Nanoparticles by Control of Electron Temperature in Hollow-Typed Magnetron Radio Frequency CH4/H2 Plasma

In this study, we investigate the effects of electron temperature Te on the production of nanoparticles by using the grid-biasing method in hollow-typed magnetron radio frequency (RF) CH4/H2 plasma. We find that nanoparticles are produced in low-Te plasma. On the other hand, thin film depositions, such as nanowalls, are mainly observed and almost no nanoparticles are created in high-Te plasma. This implies that a reduction in the CH2/CH3 radical ratio is important for producing nanoparticles, together with a reduction in sheath potential in front of the substrate. The change in electron temperature in plasma has a marked effect on film quality.

Autocatalytic reaction model: a phenomenology for nucleation-coalescence-growth of thin films

In many thin film growth systems, the surface morphology develops via nucleation of two-dimensional clusters, their growth and coalescence. When desorption of surface adsorbate is thermally activated, time evolution of the films coverage becomes a delicate function of both the temperature and pressure of the growth. The autocatalytic reaction (ACR) model, a rate equation known in chemical kinetics, is a powerful tool to describe such complicated temporal behaviors, and is successfully applied to analysis of dry oxidation at Si(001)-2×1 surfaces. Monte Carlo simulation indicates that the physics behind the ACR model lies in its effective inclusion of nucleation, growth, and coalescence processes.

Microcrystalline diamond deposition using inert-gas curtain combustion-flame method

Abstract Inert-gas curtain combustion-flame method, in which a combustion flame of oxygen/acetylene mixture is surrounded by an inert-gas (Ar and/or He) flow to prevent mixing oxygen from the air, has been developed for the deposition of microcrystalline diamond thin films. The emission spectra from the combustion flame showed reduction in the ultraviolet region with increasing inert-gas flow, indicating a suppression of the outer flame by the curtain. Highly uniform and highly dense microcrystalline films of diamonds were successfully prepared, which is understood to be caused by realization of a combustion flame with optimum radical concentrations. Morphological variations due to the choice of the inert gas have also been found.