Hiroshi Kuwahata

Inactivation of Escherichia coli using atmospheric-pressure plasma jet

An atmospheric-pressure argon (Ar) plasma jet was applied to the inactivation of Escherichia coli. The Ar plasma jet was generated at a frequency of 10 kHz, an applied voltage of 10 kV, and an Ar gas flow rate of 10 L/min at atmospheric pressure. E. coli cells seeded on an agar medium in a Petri dish were inactivated by Ar plasma jet irradiation for 1 s. Scanning electron microscopy (SEM) revealed that E. coli cells were killed because their cell wall and membrane were disrupted. To determine the causes of the disruption of the cell wall and membrane of E. coli, we performed the following experiments: the measurement of the surface temperature of an agar medium using a thermograph, the analysis of an emission spectrum of a plasma jet obtained using a multichannel spectrometer, and the determination of the distribution of the concentration of hydrogen peroxide (H2O2) generated on an agar medium by plasma jet irradiation using semiquantitative test strips. Moreover, H2O2 solutions of different concentrations were dropped onto an agar medium seeded with E. coli cells to examine the contribution of H2O2 to the death of E. coli. The results of these experiments showed that the cell wall and membrane of E. coli were disrupted by electrons in the plasma jet, as well as by electroneutral excited nitrogen molecules (N2) and hydroxyl (OH) radicals in the periphery of the plasma jet.

Carrier Concentration Dependence of Photoacoustic Spectra of Silicon by a Piezoelectric Transducer Method

Photoacoustic (PA) spectra near the energy gap (Eg) of n- and p-type silicon (Si) were observed at various carrier concentrations using a piezoelectric transducer method. With increasing carrier concentration, the PA signal intensity at energies slightly higher than Eg decreased for n-type samples and increased for p-type samples. The decrease and the increase were considered to be due to the increase in free electrons at the bottom of the conduction band and to the increase in holes at the top of the valence band, respectively. The PA spectra were not observed for either type of sample above a carrier concentration of 1017 cm-3.

Carrier Concentration Dependence of Photoacoustic Signal Intensity of Silicon.

Photoacoustic (PA) spectra near the energy gap of n- and p-type silicon were investigated at various carrier concentrations. The PA signal intensity at energies lower than the energy gap increased with increasing carrier concentration for both types. The increase is considered to be due to the increase in the heat generated in the samples following free carrier absorption and nonradiative relaxation processes. The PA signal intensity increased drastically above a carrier concentration of 1017 cm-3 for n-type and above that of 1016 cm-3 for p-type silicon.

INVESTIGATION OF THE ANNEALING BEHAVIOR OF DAMAGE IN SI IMPLANTED INP BY PHOTOACOUSTIC AND RAMAN SPECTROSCOPY

Abstract The annealing behavior of damage in InP implanted with 200 keV Si ions at doses of 1012–1016 ions/cm2 was investigated by photoacoustic spectroscopy (PAS) using a microphone as a detector and Raman spectroscopy. Band tails were observed in the photoacoustic (PA) spectra of implanted samples at energies lower than the bandgap energy. The PA intensity at the band tails increased with increasing implantation dose and reached a critical value at a dose of 1014 ions/cm2 indicating that the implanted layers were completely amorphized. The isochronal (15 min) annealing curves of the PA intensity for the amorphized samples can be classified into four temperature regions: region I below 200°C, region II at 200–300°C, region III at 300–600°C and region IV above 600°C. The results of PA and Raman measurements indicated that the implanted layers were in an amorphous state in region I, the implanted layers transformed from an amorphous state to a mono-crystalline state including complicated defects in region II, the defects decreased slightly in region III and defects with the dissociation of phosphorus from the sample surface were generated in region IV.

Comparison of annealing behavior in photoacoustic signal intensity of Si+ implanted InP by microphone and piezoelectric transducer methods

The damage produced with the Si+-implantation in InP generated the heat and the photoacoustic (PA) signal intensity at energies lower than Eg increased in the microphone method, while the damage suppressed the generation and the propagation of the elastic wave and the PA intensity at energies higher than Eg decreased in the piezoelectric transducer method. The carrier activated with the annealing also suppressed the generation of the elastic wave and the PA intensity at energies higher than Eg decreased in the piezoelectric transducer method.

Comparison of annealing behavior in photoacoustic signal intensity of Si+implanted InP by microphone and piezoelectric transducer methods

The damage produced with the Si+-implantation in InP generated the heat and the photoacoustic (PA) signal intensity at energies lower than Eg increased in the microphone method, while the damage suppressed the generation and the propagation of the elastic wave and the PA intensity at energies higher than Eg decreased in the piezoelectric transducer method. The carrier activated with the annealing also suppressed the generation of the elastic wave and the PA intensity at energies higher than Eg decreased in the piezoelectric transducer method.

Comparison of annealing behavior in photoacoustic signal intensity of

The damage produced with the Si+-implantation in InP generated the heat and the photoacoustic (PA) signal intensity at energies lower than Eg increased in the microphone method, while the damage suppressed the generation and the propagation of the elastic wave and the PA intensity at energies higher than Eg decreased in the piezoelectric transducer method. The carrier activated with the annealing also suppressed the generation of the elastic wave and the PA intensity at energies higher than Eg decreased in the piezoelectric transducer method.