M. Kitajima

Growth of silicon oxide on silicon in the thin film region in an oxygen plasma

The time dependence of silicon oxide growth in a radio frequency oxygen plasma is studied by using in situ rapid ellipsometry. An extremum in the change of the ellipsometric parameter Δ versus discharge time is observed in the thin films region and is explained by a change in the refractive index value accompanying the oxide film growth.

Observation of relaxation processes of disorder in ion-irradiated graphite using Raman spectroscopy

Abstract Real-time Raman measurement has been applied to monitor the thermal relaxation processes in graphite at 411–463 K under 5 keV deuterium ion irradiation. The observed time dependence of density of defects revealed that the thermal relaxation process consists of three distinct stages. Dominant processes have been discussed for each stage.

Reduction in Raman intensity of Si(1 1 1) due to defect formation during ion irradiation

Abstract Real-time Raman measurements have been performed on a Si(1 1 1) surface while under irradiation by 5 keV He+, Ar+, and Kr+ ions. The intensity of the optical phonon peak at 521 cm−1 has been seen to decrease with increasing ion fluence. The reduction rate of the intensity increase with increasing ion mass. The reduction of the phonon line intensity is interpreted as being dominated by the total number of the vacancies within the optical penetration depth.

Real-time observation of thermal relaxation of initial damage in graphite under ion irradiation

Abstract Real-time Raman measurements are conducted for graphite during and after helium ion and deuterium ion irradiation at the sample temperatures from 393 to 473 K. A transient behavior is observed in the thermal relaxation of lattice disorder. Results indicate that two processes exist for the restoration of the phonon correlation length by thermal relaxation. The fast process is suggested to be a recombination of vacancies and interstitials, and the activation energies have similar values: 0.89 ± 0.10 eV for helium ion irradiation and 1.0 ± 0.10 eV for deuterium ion irradiation. The slow process suggests a chemical effect; the activation energy for deuterium ion irradiation (0.36 ± 0.25 eV) is smaller than that for helium ion irradiation (1.8 ± 0.30 eV).

Silicon wafer orientation dependence in the initial plasma oxidation processes

Abstract The change in the optical characteristics of Si oxide in plasma oxidation processes on Si(1 0 0) and Si(1 1 1) has been investigated by rapid ellipsometry in order to study the effects of silicon wafer orientation on a very thin oxide film. The result shows that the oxidation rate on Si(1 1 1) is larger than that on Si(1 0 0) in the plasma oxidation.

Raman study of the phase separation in ZrO2-12 mol% CeO2 ceramic

Abstract We present Raman spectra of the ZrO2-12 mol% CeO2 ceramic heat- treated at 1000°C, 1200 °C and 1420 °C in the flowing mixture gas of H2+Ar. Raman spectra reveal the tetragonal to monoclinic phase transition and three Raman bands are observed at 279 cm-1, 410 cm-1 and 456 cm-1 at temperatures above 1200 °C; it turned out that these Raman bands are assigned to neither of the monoclinic phase nor the tetragonal phase. It is suggested that the starting ceramic undergoes phase separation in the heat-treatments in the mixture gas of H2+Ar; the phase separation probably takes place as a result of the valence change of Ce during the heat-treatments, which leads to destabilization of the original tetragonal phase.

Study of raman spectroscopy on carbon materials irradiated with a high current density electron beam

Abstract Micro Raman spectroscopy analysis has been performed on the eroded surfaces of Isotropie graphite and C/C composite materials irradiated with a high current density electron beam (HCDE). The results show that no amorphous structure has been produced in either materials by HCDE beam irradiation, and the growth of graphite microcrystallites is due to annealing induced by electron beam heating. Furthermore, irradiation has induced no great change in the spectrum of carbon fibers in the C/C composite. The shift of the peaks in Raman spectra has also been reported and discussed.

Numerical calculation on deuterium absorption in palladium under high pressure D2 gas at low temperatures

Abstract Numerical calculation has been performed for the deuterium absorption behaviour in Pd under high pressure D2 gas at low temperatures. Present calculation shows that the absorption is dominated by the surface process rather than diffusion.