Jun-Woo Park

Effect of Ga∕In ratio on the optical and electrical properties of GaInZnO thin films grown on SiO2∕Si substrates

Amorphous GaInZnO and polycrystalline ZnO thin films are grown by rf magnetron sputtering. Their optical properties are investigated by spectroscopic ellipsometry. The optical gap of the GaInZnO film increases with the increase of Ga content and by annealing. These are attributed to the large band-gap energy of Ga2O3 and the structural relaxation after annealing, respectively. The changes in optical properties show a strong correlation to the device characteristics of GaInZnO thin film transistors: The turn-on voltage increases as the optical gap increases with increasing Ga∕In ratio. This study shows that the GaInZnO thin films are as excellent as transparent oxide semiconductors.

Optical properties of thermally annealed hafnium oxide and their correlation with structural change

We studied the optical properties of hafnium oxide as its structure changed. The shoulderlike feature that appears in crystalline HfO2 near the energy trough of the optical absorption edge after thermal anneal was found to have a direct correlation with the crystallization of the film. A luminescence feature near 4.1 eV could also be observed for some of the crystallized hafnium oxide films, but it did not have a direct correlation with crystallization or the shoulderlike feature. Our experimental results do not support the recently proposed self-trapped exciton (STE) model, where the shoulderlike absorption and the UV luminescence features are both attributed to STE. Simultaneous measurements of structural and optical properties of thermally annealed hafnium oxide films revealed that the shoulderlike feature is not related to defects, but rather is intrinsic to crystallized hafnium oxides. We discuss some possible origins of the shoulderlike feature based on our experimental results. Nevertheless, the UV...

Microstructure, optical property, and electronic band structure of cuprous oxide thin films

Cuprous oxide (Cu2O) thin films were grown via radio frequency sputtering deposition at various temperatures. The dielectric functions and luminescence properties of the Cu2O thin films were measured using spectroscopic ellipsometry and photoluminescence, respectively. High-energy peaks were observed in the photoluminescence spectra. Several critical points (CPs) were found using second derivative spectra of the dielectric functions and the standard critical point model. The electronic band structure and the dielectric functions were calculated using density functional theory, and the CP energies were estimated to compare with the experimental data. We identified the high-energy photoluminescence peaks to quasi-direct transitions which arose from the granular structures of the Cu2O thin films.

Optical properties of (GeTe, Sb2Te3) pseudobinary thin films studied with spectroscopic ellipsometry

The authors measure the dielectric functions of (GeTe, Sb2Te3) pseudobinary thin films by using spectroscopic ellipsometry. By using standard critical point model, they obtained the optical transition (critical point) energies of the amorphous (crystalline) thin films. The optical (indirect band) gap energies of the amorphous (crystalline) phase are estimated from the linear extrapolation of the absorption coefficients. The band structure calculations show that GeTe, Ge2Sb2Te5, and Ge1Sb2Te4 have indirect gap whereas Ge1Sb4Te7 and Sb2Te3 have direct gap. The measured indirect band gap energies match well with electronic band structure calculations.

Optical properties of amorphous and crystalline Sb-doped SnO2 thin films studied with spectroscopic ellipsometry: Optical gap energy and effective mass

We investigated the optical properties of amorphous and crystalline antimony (Sb)-doped tin dioxide (SnO2) thin films grown using the co-sputtering deposition method at room temperature. We used undoped and Sb-doped (8 wt. %) SnO2 targets. Varying the relative power ratio of the two targets, we controlled the Sb-composition of the SnO2:Sb thin films up to 2.3 at. % of Sb contents. Through annealing, the as-grown amorphous SnO2:Sb thin films were transformed to crystalline thin films. Dielectric functions were obtained from the measured ellipsometry angles, Ψ and Δ, using the Drude and parametric optical constant models. We determined the absorption coefficients and optical gap energies of the SnO2:Sb thin films from the dielectric functions. We found increasing optical gap energy with increasing Sb composition. Increases in the Drude tail amplitudes, a signature of free carrier concentrations, were found in annealed, crystalline thin films with increasing Sb composition. The increase in the optical gap en...

Transition from a nanocrystalline phase to an amorphous phase in In-Si-O thin films: The correlation between the microstructure and the optical properties

We investigated the structural and optical properties of In-Si-O thin films as the phase abruptly changes from nanocrystalline (nc) to amorphous (a) with increasing Si content. In-Si-O thin films were deposited on Si substrate using a co-sputtering deposition method. The RF power of the In2O3 target was fixed at 100 W, while the power applied to the SiO2 target was varied between 0 W and 60 W. At the Si = 2.8 at. %, i.e., at the onset of amorphous phase, the optical properties, including the dielectric functions, optical gap energies, and phonon modes, changed abruptly which were triggered by changes in the crystallinity and surface morphology. X-ray diffraction (XRD) spectra showed crystalline (c-) In2O3-like peaks below Si = 2.2%. Additionally, a broad peak associated with an amorphous (a-) In2O3 phase appeared above 2.8%. However, the Raman spectra of In-Si-O showed very weak peaks associated with c-In2O3 below 2.2%, and then showed a strong Raman peak associated with a-In-Si-O above 2.8%. X-ray photoe...

Oral administration of Lactobacillus casei variety rhamnosus partially alleviates TMA‐induced atopic dermatitis in mice through improving intestinal microbiota

The purpose of this study was to investigate the effect of Lactobacillus casei variety rhamnosus (LCR35) on Atopic dermatitis (AD)‐like symptoms in mice.

Investigation of the Structural and Optical Properties of Ge-doped SbTe Films with Various Sb:Te Ratios

In this study, we investigated the structural and optical properties of Ge-doped SbTe Ge–ST thin films with three differing compositions: Ge0.06Sb0.77Te0.17 Ge–STH ,G e 0.05Sb0.70Te0.25 Ge–STM, and Ge0.05Sb0.64Te0.31 Ge–STL, grown on Si substrate by radio-frequency sputtering method. The films were annealed at 250°C for crystallization and their crystal structures were examined by X-ray diffraction. Compared to the X-ray diffraction spectra of the undoped SbTe, the Ge–ST thin films had a hexagonal structure with large stacking periods. Using Raman spectroscopy, we investigated the shift of the phonon mode frequencies A1g and Eg of the films with varying Sb:Te ratios. We compared the dependence of the phonon frequencies of Ge–ST on the Sb content to those of the corresponding undoped SbTe. The composition dependence of the A1g phonon frequency could be explained in terms of the linear extrapolation of Sb and Sb2Te3 crystals. By using spectroscopic ellipsometry, we measured the dielectric function of the thin films in the near-IR, visible, and ultraviolet spectral regions. The optical energy gaps and bandgaps of the amorphous and crystalline phases, respectively, were determined using linear extrapolation of the absorption coefficient. The optical gap energies of the amorphous Ge–ST films were determined to be about 0.5–0.6 eV, whereas the indirect bandgap energies of the crystalline films shrank substantially to about 0.15–0.2 eV.

Joint Cooling does not Hinder Athletic Performance during High-intensity Intermittent Exercise

We examined the effects of ankle and knee joint cooling on 20-m sprint times and maximal vertical jump heights during high-intensity intermittent exercise. 21 healthy collegiate male basketball (n=14) and handball players (n=7) underwent 3 experimental sessions. Each session consisted of four 15-min quarters of high-intensity intermittent exercises including various intensities of 20-m shuttle running and jumping. A 20-min bilateral joint cooling (ankle, knee, or control-no cooling: in a counterbalanced order) was applied before quarters 1 and 3. After joint cooling, no warm-up activity other than the exercise protocol was given. The 20-m sprint times and maximal vertical jump heights in each experimental session were recorded at baseline (prior to quarter-1) and during each quarter. To test joint cooling effects over time, we performed 3×5 mixed model ANOVAs. Neither ankle nor knee joint cooling changed 20-m sprint times (F8,280=1.45; p=0.18) or maximal vertical jump heights (F8,280=0.76; p=0.64). However, a trend was observed in which joint cooling immediately decreased (quarters 1 and 3) but active warm-up for approximately 20 min improved 20-min sprint times (quarters 2 and 4). Our study suggests that athletic performance such as sprinting and jumping are not altered by joint cooling applied prior to or during high-intensity intermittent exercise.

Mean-Field Theoretical Structure of He and Be Isotopes

The intrinsic structures of He and Be even-even neutron-rich isotopes are investigated using an axially symmetric Hartree-Fock (HF) approach with a Skyrme mean-fleld potential. In these HF calculations, the He and Be isotopes appear to be prolate in their ground states, and the Be isotopes have oblate-shaped isomeric states, except for 12 Be, which has a spherical ground state and a prolate isomeric state. Protons are bound stronger in the isotope with more neutrons while neutron levels are somewhat insensitive to the number of neutrons. The neutron magic number 6, the intruder state 1/2 + in the ground states of 9 He and 11 Be, and the relatively large neutron rms radius of 6 He were shown to originate from the large deformation of the neutron distribution rather than from the halo structure. The most probable candidate for a halo nucleus here is the excited oblate state of 16 Be, which has a large neutron skin with a relatively small quadrupole moment.