Yoshikatsu Namba

Attempt to grow diamond phase carbon films from an organic solution

Diamond phase carbon films have been grown on silicon substrates at temperatures of less than 50 °C by using an organic solution. Substrates were negatively biased with sufficient dc potential to simulate ionized deposition conditions used in physical vapor deposition. The surface morphology, crystal structure, and some physical properties of the films were examined by scanning electron microscopy, transmission electron microscopy, x‐ray photoemission spectroscopy. It was confirmed that the film is composed of small grains of diamond phase or diamondlike structure.

Crystal structure of diamondlike carbon films prepared by ionized deposition from methane gas

Diamondlike carbon films have been prepared by ionized deposition from methane gas. The film structures were examined by transmission electron microscopy, electron diffraction, and electron spectroscopy for chemical analysis techniques. It was found that the structure of the carbon films could be classified into three types: (i) amorphous, (ii) graphite, and (iii) cubic. These types depended mainly on the deposition conditions. Usually crystalline carbon films were diamond mixed with graphite showing an average grain size of several hundred angstroms. Very hard films were composed of diamond crystallites distributed in amorphous matrix.

Size effects appearing in the Raman spectra of polycrystalline diamonds

Various spectra of Raman for different grain sizes of diamond powder have been studied. The spectra are also correlated to the results of transmission electron diffraction, transmission electron microscopy, scanning electron microscopy, and x‐ray photoelectron spectroscopy. When the Raman peak intensity was decreased, the spectra broadened and shifted to a lower frequency in accordance with the decrease of the grain size. Finally, in the region of a few hundred angstroms, the detected signals were almost comparable to the noise level. While unchanged, lattice spacings for transmission electron diffraction patterns and constant peak heights for x‐ray photoelectron spectroscopy analysis were observed for different grain sizes.

Structural study of the diamond phase carbon films produced by ionized deposition

Diamond phase carbon films have been prepared with the aid of an ionized deposition technique. The structures of these films were examined by transmis‐ sion electron microscopy and transmission electron diffraction. It was found that the crystal structure of these films depends strongly on the deposition conditions, especially on the substrate potential. For a negatively biased substrate potential, a film having a halo or diamond pattern was obtained, while the graphite patterns were observed for a positively biased potential. These structures were confirmed by directly comparing them with those of diamond or graphite powder. The observed average grain size of the diamond film was several hundred angstroms and was much smaller than that of graphite. Finally, we discuss the formation process of diamond phase carbon films.

Friction and wear properties of thin films of carbon with diamond structure prepared by ionized deposition

The friction and wear properties for thin films of carbon with diamond structure, prepared by ionized deposition, slid with copper have been examined in a pressure range of 5×10−4 to 105 Pa. The friction coefficient shows a tendency to decrease with the increase of pressure and it is <0.2 because the surfaces of thin films of carbon with diamond structure are very smooth. The specific wear rate of copper sliders decreases as the pressure becomes lower. However, no wear is detected on thin films of carbon with diamond structure.

Large grain size thin films of carbon with diamond structure

Diamond thin films were formed by deflecting the flow of CH+4 using a magnetic field. The possibility of involvement of neutral particles and their effects on film formation were examined. The results show (i) the estimated amount of the neutral particle involved during the ionized deposition was nearly 30%, (ii) the surface morphology of the film prepared by the deposition of the deflecting ion was very smooth when it was examined by scanning electron microscopy, and (iii) transmission electron diffraction and transmission electron microscopy indicated relatively large grain polycrystalline diamond films.

Cross−sectional structure of Bi films and its phenomenological analysis

The cross−sectional structure of evaporated Bi films has been investigated using electron microscopy and a replica technique. The conditions of films formation were varied by using a range of substrate temperatures and deposition rates. It was found that a critical stage in the growth process is reached when the film becomes continuous. Whether the surface structure existing at this stage is maintained or becomes smooth during further growth is determined principally by the deposition rate. Based on these results a phenomenological analysis was made, assuming that changes in the surface roughness occur as a result of the surface diffusion of adatoms. It has been shown that this theoretical description of surface roughness as a function of temperature and deposition rate agrees well with the experimental observations.

Deposition of diamond phase carbon films on surface pretreated stainless steel substrate

The deposition of diamond phase carbon films on stainless steel substrates by an ionized deposition technique has been studied. A molybdenum grid used during argon ion sputtering had a decisive role in improving the morphology and adhesion ability of the substrate surface. The chemical composition of the surface was obtained by x-ray photoelectron spectroscopy, indicating the reduction of oxygen, carbon, and other contamination, while the surface morphology of the substrate obtained by scanning electron microscopy showed less roughness with a partially smooth surface. Attempts to extract the deposited films from the pretreated substrate surface by a superadhesive agent with an adhesion of 250 kg/cm 2 failed, yielding a much stronger adhesion for the pretreated surface. This fact was also supported by examining the surface morphology, hardness, and the resistivity of the films deposited on the same substrates. As for the crystal structure of diamond phase carbon films on stainless steel, selected area diffraction patterns obtained from transmission electron microscopy suggested a mixture of amorphous carbon and polycrystalline diamond components.

Raman observation of diamond phase carbon films prepared by ionized deposition

Abstract The crystal structure of ion-deposited diamond phase carbon films was examined using transmission electron microscopy, transmission electron diffraction, X-ray photoelectron spectroscopy and Raman scattering. The Raman spectra of these films indicated a broad pattern including the amorphous or graphitic structure, while the diffraction pattern, hardness and resistivity suggested diamond material. The experimental data showed that the disagreement between these structural characterizations is caused by large differences in Raman scattering cross-sections for graphite and diamond, since the intrinsic Raman intensity of the graphite spectrum is 50 times that of the diamond spectrum. Thus the ion-deposited carbon films are believed to be composed of microcrystalline diamond.

Study of the abrasion property of diamondlike films synthesized on iron

The iron materials coated by the diamondlike carbon (DLC) films are expected to have a wide range of application, however, for these substrate materials some difficulties are still remained compared to that of Si. Hard, flat, and strong adhesive DLC films can be synthesized on Mo coated iron substrates by the ionized deposition technique with the aid of the pretreatment of Ar ion bombardment. The DLC films on iron indicate Vickers hardness of more than 5000 kg/mm2. The abrasion test using B4C powder shows that no corrosion can be observed on the DLC films coated on iron materials. The surface properties of the strongly adhering DLC coated substrates are almost the same as those of the DLC films and these properties are independent of the base materials of the substrates.