Ken Cho

Investigations on Plasma-Biomolecules Interactions as Fundamental Process for Plasma Medicine

Investigations on plasma-biomolecules interactions have been carried out as fundamental process for plasma applications in medical science and biological treatments. In this study, plasma interactions with L-alanine which are amino acids: the building blocks of proteins have been investigated in terms of physical effects. Effect of ion and photon irradiation on degradation of L-alanine has been studied via x-ray photoelectron spectroscopy (XPS) analysis of chemical bonding states. The XPS results showed that the decrease in the -CH3 bond, >C(NH2)COOH bond, and -COOH bond peaks of main component of the L-alanine with increasing ion energy, ion dose and photon energy. The L-alanine degraded by ions and photons with energy over 6eV.

Low-temperature formation of amorphous InGaZnOx films with inductively coupled plasma-enhanced reactive sputter deposition

A plasma-enhanced sputter deposition system has been developed via enhancement of target sputter discharge with inductively coupled RF plasma (ICP) driven by multiple inner-type low-inductance antennas (LIAs). The advantage of fine control of reactivity during the deposition is of great significance for the deposition of a transparent amorphous oxide semiconductor films, amorphous InGaZnOx (a-IGZO), whose electrical properties are significantly sensitive to the reactivity of the films with oxidation species during the film deposition. The characteristics of thin-film transistors (TFTs) fabricated with an a-IGZO film using the plasma-enhanced magnetron sputter deposition system have been investigated. The a-IGZO channel TFTs fabricated using the plasma-enhanced reactive sputtering system at a substrate temperature as low as or lower than 150 °C exhibited a good performance of μFE = 18.5 cm2 V−1 s−1.

Combinatorial Analysis of Plasma–Surface Interactions of Poly(ethylene terephthalate) with X-ray Photoelectron Spectroscopy

Combinatorial analysis has been demonstrated for the examination of plasma–surface interactions of poly(ethylene terephthalate) (PET) in terms of chemical bonding state, with X-ray photoelectron spectroscopy (XPS). The chemical bonding states have been investigated for PET films exposed to an argon–oxygen mixture plasma with a density gradient sustained with RF power of 88, 175, and 350 W. The XPS results obtained from three batches of experiments showed a slight increase in the bond peaks caused by the oxidation of which PET with an increase in the product of (ion saturation current) × (plasma exposure time), corresponds to ion dose.

Large-area and low-damage processes for hybrid flexible device fabrications with reactive high-density plasmas driven by multiple low-inductance antenna modules

Plasma generation and control technologies for meters-scale ultra-large-area plasma sources have been developed with multiple low-inductance antenna (LIA) modules, as a promising candidate of ultra-large-area and high-density plasma sources for next-generation processing of hybrid flexible devices. Properties of argon-oxygen mixture plasmas sustained with multiple LIA units have been investigated and surface modifications of polymer substrates using the plasmas have been performed. Ion energy distribution at the sheath edge of the argon-oxygen mixture plasmas showed considerable suppression of ion energies as small as or less than 10 eV. We have examined effect of plasma exposure on surface modification and/or degradation of polymer. Surface analysis of polytetrafluoroethylene (PTFE) exhibited nano-surface modification of the polymer surface without suffering degradation of molecular structures beneath the nano- surface layer.

Effects of Irradiation with Ions and Photons in Ultraviolet–Vacuum Ultraviolet Regions on Nano-Surface Properties of Polymers Exposed to Plasmas

The interactions of ions and photons in ultraviolet (UV) and vacuum ultraviolet (VUV) regions from argon plasmas with polymer surfaces were investigated by of depth analysis of chemical bonding states in the nano-surface layer of poly(ethylene terephthalate) (PET) films via conventional X-ray photoelectron spectroscopy (XPS) and hard X-ray photoelectron spectroscopy (HXPES). The PET films were exposed to argon plasmas by covering the PET films with MgF2 and quartz windows as optical filters to compare the irradiation effects with ions and photons. The conventional XPS results indicated that oxygen functionalities (the C–O bond and the O=C–O bond) were degraded by ion bombardment in the shallower region up to about 10 nm from the surface, whereas the effect of photoirradiation in the UV and VUV regions was insignificant. The HXPES analysis showed that irradiation with ions and photons did not cause serious damage in chemical bonding states in the deeper region up to about 50 nm from the surface.