Tae Hun Chung

Bacterial inactivation using atmospheric pressure single pin electrode microplasma jet with a ground ring

Bacterial inactivation experiment was performed using atmospheric pressure microplasma jets driven by radio-frequency wave of 13.56 MHz and by low frequency wave of several kilohertz. With addition of a ground ring electrode, the discharge current, the optical emission intensities from reactive radicals, and the sterilization efficiency were enhanced significantly. When oxygen gas was added to helium at the flow rate of 5 SCCM, the sterilization efficiency was enhanced. From the survival curve of Escherichia coli, the primary role in the inactivation was played by reactive species with minor aid from heat, UV photons, charged particles, and electric fields.

Ultralarge capacitance-voltage hysteresis and charge retention characteristics in metal oxide semiconductor structure containing nanocrystals deposited by ion-beam-assisted electron beam deposition

Amorphous silicon films are deposited by ion-beam-assisted electron beam deposition and subsequently oxidized by a rapid thermal oxidation process. The oxidized film contains a large density of nanocrystals specifically localized at a certain depth from the Si/SiOx interface, whereas no evidence of nanocrystals is found for oxidized films deposited without ion beam assistance. Such a marked contrast resulted from the enhancement of nucleation rate by ion beam irradiation. The metal-oxide-semiconductor structure utilizing the film shows an ultralarge capacitance–voltage hysteresis whose width is over 20 V. In addition capacitance–time measurement shows a characteristic capacitance transient indicating nondispersive carrier relaxation. The retention time shows a dependence on applied bias and the maximum time of ∼70 s is obtained near midgap voltage. The retention time dependence on applied bias and large capacitance–voltage hysteresis are attributed to direct tunneling of trapped charges in the deep traps ...

Charge retention characteristics in a metal–insulator–semiconductor capacitor containing Ge nanocrystals

We investigate the charge retention characteristics in a metal–insulator–semiconductor capacitor containing Ge nanocrystals (~3 nm in diameter) using capacitance–voltage measurements with various gate bias sweep rates. The metal–insulator–semiconductor capacitor is fabricated by pulsed laser deposition and rapid thermal oxidation. The capacitance–voltage curve shows the strong hysteresis indicating charging/discharging of carriers during the gate bias sweeping. The stored charge densities, evaluated from the flat band voltage shifts, show the non-dispersive carrier relaxation, which is a characteristic property for nanocrystals arranged in a layer. In addition, we observe an interesting capacitance ledge during forward bias sweeping. From the trap distribution determination by the Terman method, the capacitance ledge is due to an energetically localized trap at 0.33 eV + Ev. The energetic position of the trap is in agreement with the ground-state hole energy level in the Ge nanocrystals. This suggests the possibility that the trap level is related to the fact that the stored charges initially tunnel out at the ground-state hole energy level.

Plasma enhanced chemical vapor deposition of silicon oxide films using TMOS/O2 gas and plasma diagnostics

Thin oxide films are deposited from tetramethoxysilane in an inductively coupled oxygen glow discharge supplied with radio frequency power. The deposition rate and the chemical bonding states of deposited films are analyzed by ellipsometry and by Fourier transform infrared spectroscopy, respectively, and the intensities of light emission from molecules and radicals in the plasma are measured by optical emission spectroscopy. Langmuir probe is employed to estimate the plasma density and electron temperature. With these tools, the effects of parameters such as r.f. power of inductive coupling, substrate bias power, oxygen partial pressure ratio, total pressure on the properties of the film and of the plasma are investigated. The correlation between the properties of the film and the characteristics of the plasma are explained wherever possible.

Plasma effects on the generation of reactive oxygen and nitrogen species in cancer cells in-vitro exposed by atmospheric pressure pulsed plasma jets

Atmospheric pressure pulsed helium plasma jets are utilized for plasma-cell interactions. The effect of operating parameters such as applied voltage, pulse repetition frequency, and duty ratio on the generation of specific reactive oxygen and nitrogen species in gas and liquid phases and within cells is investigated. The apoptotic changes detected by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling assay in cells caused by plasma exposure are observed to correlate well with the levels of extracellular and intracellular reactive oxygen and nitrogen species.

Formation of luminescent Si nanocrystals by high-temperature rapid thermal chemical vapor deposition

We observe a completely different growth regime of silicon-rich oxide (SRO) layers by rapid thermal chemical vapor deposition for the formation of luminescent nanocrystals. The growth regime is characterized by low [N2O]/[SiH4] ratios ( 700 °C). High-resolution cross-sectional transmission electron microscopy (XTEM) shows the bimodal distribution of large polycrystals and nanocrystals after post-deposition annealing. The luminescence is attributed to the nanocrystals. Fourier transform infrared spectroscopy in conjunction with XTEM and energy-dispersive x-ray studies show the phase separation and bonding reconfiguration in as-deposited SRO layers. The effectively increased oxygen content in the oxide matrix by phase separation and bonding reconfiguration reduces the diffusion coefficient of Si in the matrix, resulting in the formation of nanocrystals during post-deposition annealing.

Charge retention effect in metal–oxide–semiconductor structure containing Si nanocrystals prepared by ion-beam-assisted electron beam deposition

An amorphous Si layer prepared by ion-beam-assisted electron beam deposition (IBAED) method is oxidized by a rapid thermal oxidation technique. We observe a nanocrystal band located at about 4 nm from the Si/SiOx interface by cross-sectional transmission electron microscope observation. The metal–oxide–semiconductor (MOS) structure employing the oxide layer with the nanocrystal band exhibits a large capacitance–voltage hysteresis indicative of trapping of electrons/holes. In contrast, a relatively small capacitance–voltage hysteresis is found for the MOS diode prepared by conventional electron beam deposition (EBD) without ion-beam assistance. Such a marked difference shows that the ion-beam irradiation plays an important role in the formation of nuclei, which would grow to nanocrystals during subsequent rapid thermal oxidation process. Interestingly, the MOS prepared by IBAED shows a characteristic capacitance transient behavior, indicative of non-dispersive carrier relaxation. In addition, the charge retention times shows a bias dependence and a maximum of 72 s near the mid-gap voltage. Such a bias-dependent retention time is interpreted in terms of the tunneling of trapped charges in nanocrystals through empty interface states.

Area-selective formation of Si nanocrystals by assisted ion-beam irradiation during dual-ion-beam deposition

We investigate the effect of Ar-ion-beam irradiation during the deposition of SiOx films by dual-ion-beam deposition system. Ion-beam irradiation effectively increases the oxygen content, x, in SiOx films indicative of the preferential sputtering of Si phase as compared to SiO2 phase in SiOx films. We observe the intense photoluminescence from nonirradiated sample after postdeposition annealing at 1100°C indicating the formation of Si nanocrystals as shown by a cross-sectional transmission electron microscope. However, the increased oxygen content in ion-beam-irradiated sample results in small optical volume of small Si nanocrystals not sufficient for yielding appreciable photoluminescence intensity after postdeposition annealing. The property is utilized for achieving the area-selective formation of Si nanocrytals by inserting a shadow mask in assist ion beam during deposition.