Papers by Author: Wataru Minami

Abstract: The characteristics, such as electron temperature and the electron density, of CF4/Ar discharge in 2.45GHz microwave has been investigated by using a Langmuir probe with the microwave power and position. The results showed that the electron temperature and the electron density decrease with increasing distance from the plasma source. Increasing power enhances the dissociation and ionization of gas, and increases the electron densities. The electron temperature was decreased by reducing the mean free path of electrons with increasing microwave power. The electron temperature is 7.63 ~ 2.49 eV, and the electron density is 0.85×1011 ~ 4.3×1011 cm-3. From obtained electron energy distribution function, we known that high energy electron decreased with increasing microwave power and distance from the plasma source. The generated plasma by developed our system has good quality as results of Debye length λD = 35.8 ~ 67.3 μm, and Ln(ND) = 33.4 ~ 35.2.

Abstract: The decomposition characteristics of CF4 with Argon or oxygen in 2.45GHz microwave has been investigated by using a Langmuir probe with variation of the microwave power and chamber pressure. For CF4/Ar and CF4/O2/Ar discharges, the ion density and the electron density decrease with increasing microwave power. The electron temperature was decreased by reducing the mean free path of electrons with increasing microwave power. Also with increasing pressure, the electron temperature increase, and ion and electron density decrease by increase of inelastic collision frequency and of collision with the walls in the chamber. The electron temperature is 13.6 ~ 5.9 [eV], the electron density is 4.4×1010 ~ 2.2×1010 [cm-3] and ion density is 5.2×1011 ~ 4×1010 [cm-3]. According as add oxygen, ion and electron density increased relatively comparing to CF4/Ar discharge. The electron temperature is 8.5 ~ 6.2 [eV], the electron and ion density is 5.1×1010 ~ 2.1×1010 [cm-3] and 3.7×1011 ~ 7.3×1010 [cm-3], respectively.

Abstract: In order to fabricate an alumina ceramics with high density at low sintering temperature, nanosized γ–Al2O3 powders with average size of 9.7 nm were added to microsized γ–Al2O3 powders with 2 #m and they were well mixed. Its sintering behavior was studied in the temperature range of 1000oC to 1300oC and in holding time from 1 hour to 10 hours. Compacted samples with a different mixed ratio of nanosized and microsized Al2O3 powders (N/M ratio) were prepared and pressured at 1 GPa in a uniaxial direction. The phase transformation from γ–Al2O3 to α–Al2O3 takes place at 1100oC for 1hour sintering in all compacted samples. This rate is increased with increasing N/M ratio. The relative density varied from 70% to 95% depending on temperature and N/M ratio. With increasing sintering temperature from 1000oC to 1300oC, it was changed from 70% to 93%. Especially, the relative density was enhanced about 9% higher than that of only microsized sample by only 10 wt% addition of nanosized powders.