Akimitsu Hatta

Comparative Study on Chemical Vapor Deposition of Diamond-Like Carbon Films from Methane and Acetylene Using RF Plasma

Diamond-like carbon films (DLC) were prepared by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at a frequency of 13.56 MHz using methane (CH4) and acetylene (C2H2) at different RF powers. Optical emission spectroscopy (OES) was carried out to investigate plasma chemistry. The intensity of Hα in the C2H2 plasma was about one-half that in the CH4 plasma, whereas in both cases, the intensities of CH radicals were similar. The resistivity of the deposited films decreased with an increase in RF power, whereas growth rate increased with RF power. CH4-based films were found to be more insulating than C2H2-based films at high RF powers. The high resistivity of the films was obtained from both CH4 and C2H2 at low RF powers. The insulating property was due to the hydrogenation of sp2 bonds in the films.

Pulsed Microplasma Using Carbon Nanotubes for Cathode

Using carbon nanotubes (CNTs) or a flat Pt film for the cathode, microplasma was produced in a scanning electron microscope (SEM) chamber containing Ar gas at nearly atmospheric pressure, with gap lengths from 10 to 800 µm. Field electron emission measurements were carried out in the SEM chamber, and gas discharges were conducted at the same configuration in a gas cell installed in the SEM chamber. The ignition voltages using the CNT cathode were much lower than those using the flat Pt cathode under the same conditions, because of the field electron emission. The ignition of gas discharge using the CNT cathode was reproducible every time, because of the ensured supply of primary electrons. It was suggested that the pulse discharge using the CNT cathode was a convolution of the discrete electron avalanche originating from the field emission.

Microplasma Discharge Using Carbon Nanotubes for Cathode

Microplasma has been studied with gaps from 10 to 1000 mum at near atmospheric pressure in a scanning electron microscope (SEM) chamber using CNTs for cathode. The field emission and gas discharge experiments were carried out at the same configuration. It was confirmed that field electron emission effectively provided primary electrons into the gap, which ignited discharge easily. In the case of gas discharge using carbon nanotubes for cathode, the cathode surface was not damaged even if the discharge current was more than 150 mA

Comparison of properties of diamond nanowhiskers obtained by etching diamond films with different metal coatings in radio frequency plasma

The properties of diamond nanowhiskers fabricated from uncoated and oxidizable metals coated diamond film surfaces were compared. Whiskers with average diameter of 50 nm were obtained from all of samples. Iron was found to be the easiest etching metal among the metals used. Metal coatings reduce the number density of whiskers and inhibit etching rate as masks. The lowest density (about 20 µm-2) is obtained by the whiskers fabricated on Mo-coated diamond films. Raman spectroscopy measurement illustrates that a diamond bonding sp3 structure is uninfluenced by the etching process. It is also confirmed that the obtained whiskers show a good field emission behavior. The highest emission current density (10-5 A/µm2) was obtained on the sample with the lowest number density.

Synthesis of carbon nanomaterials by atmospheric microplasma

Atmospheric microplasma was produced in a scanning electron microscope (SEM) chamber for synthesizing carbon nanomaterials. The SEM observation is convenient for both adjusting the gap length and observing the electrode surface before and after experiments. After adjusting the gap length, the electrodes were housed in a small removable gas cell equipped in the SEM chamber and CH4 discharge gas was introduced into the gas cell. It was found that the discharge was pulsated automatically due to slow discharge through a large ballast resistor and fast discharge through gas breakdown even though a DC voltage was applied. The peak pulse current density was almost 60 kA/cm2, the peak power density in the microplasma volume was approximately 555 MW/cm3, and the pulse width was 10 ns typically. Spherical and nanotube like carbon nanomaterials was found on the cathode surface after the microplasma discharging for 1-5 seconds. With the discharge time increases, the spherical substance changes into nanotube like carbon nanomaterials.

Effect of Thin Aluminum Layer on Fabricating Silicon Micro Cone Structures

A unique technique of the fabricating sub micron sized silicon (Si) cones structure has been found. (Yoshimura, 2002) The technique consists of two processes: 1) depositing fine metal particles or layer, 2) etching in microwave plasma with negatively bias. A size distribution of unevenness on the surface of deposited aluminum (Al) layer was observed from samples after several minutes etching. A similar distribution of the cone shaped products were observed from 60 minutes etched samples also. The change of shape of the unevenness and cone shaped products under varied etching time was observed by using FE-SEM. The EDX spectrum of Al vs. Si was observed. In this paper, the relationship of distribution between the unevenness on Al layer and size of the cone products will be presented