Journal of the Korean Physical Society

Characteristics of ZnO:Ga (GZO) thin films fabricated by RF magnetron sputtering using chamber pressure have been investigated. Low chamber pressure results in low resistivity due to high mobility and carrier concentration. Result is ascribed to minimizing the influence of residual gases in the chamber, which promotes stoichiometric composition, increases Ga concentration and reduces grain boundary scattering. The average transmittance of all deposited films is over 85%. Therefore, controlling the chamber pressure is a critical parameter in the characterization of GZO thin films and a valuable method for obtaining films with better characteristics.

In the present paper, we study the entropy analysis of boundary layer flow over a slender stretching sheet under the action of a non uniform magnetic field that is acting perpendicular to the flow direction. The effects of viscous dissipation and Joule heating are included in the energy equation. Using similarity transformation technique the momentum and thermal boundary layer equations to a system of nonlinear differential equations. Numerical solutions are obtained using the shooting and fourth-order Runge-Kutta method. The expressions for the entropy generation number and Bejan number are also obtained using a suggested similarity transformation. The main objective of this article is to investigate the effects of different governing parameters such as the magnetic parameter (M2), Prandtl number (Pr), Eckert number (Ec), velocity index parameter (m), wall thickness parameter (α), temperature difference parameter (Ω), entropy generation number (Ns) and Bejan number (Be). All these effects are portrayed graphically and discussed in detail. The analysis reveals that entropy generation reduces with decreasing wall thickness parameter and increasing temperature difference between the stretching sheet and the fluid outside the boundary layer. The viscous and magnetic irreversibilities are dominant in the vicinity of the stretching surface.

In this work, a new current model of the MgZnO/ZnO high electron mobility transistors (HEMTs) has been developed considering the exact velocity-field characteristics of electrons in ZnO. The drain current of the device has been studied with reference to different applied potentials. The other device parameters, such as drain conductance, mutual conductance, cut-off frequency, and maximum operating frequency, are also calculated and their variations with different device parameters are studied. In addition, the variation of drain current with respect to ambient temperature and mole fraction of MgZnO have been studied and the results are reported. It has been noticed from our study that device characteristics depend significantly on the shift of temperature as well as the mole fraction of MgZnO. Finally, the theoretical results are compared with the experimental data reported earlier to crosscheck the validity of this model.

First-principles calculations based on density functional theory for a new Heusler compound Ti2FeSn have been performed using the self-consistent full-potential linearized augmented plane wave method. The results showed that the Ti2FeSn Heusler alloy was a half-metallic ferrimagnet. The obtained total magnetic moment of Ti2FeSn was 2 μ B per formula unit for the equilibrium lattice parameter, which is in agreement with the Slater-Pauling rule (M tot = Z tot - 18). The calculated minority spin and spin-flip gaps were 0.79 eV and 0.38 eV, respectively. In addition, the band structure and the density of states were studied, and the reason for the appearance of a minority band gap is discussed. The Ti2FeSn alloy kept a 100% spin polarization at the Fermi level and had a half-metallic characteristic for lattice constants from 5.5 to 6.7 Å showing that it is an interesting material in the field of spintronics.

A gas electron multiplier (GEM) detector with a gadolinium cathode has been developed to explore its potential application as a neutron detector. It consists of three standard-sized (10 × 10 cm2) GEM foils and a thin gadolinium plate as the cathode, which is used as a neutron converter. The neutron detection efficiencies were measured for two different cathode setups and for two different drift gaps. The thermal neutron source at the Korea Research Institute of Standards and Science (KRISS) was used to measure the neutron detection efficiency. Based on the neutron flux measured by KRISS, the neutron detection efficiency of our gadolinium GEM detector was 4.630 ± 0.034(stat.) ± 0.279(syst.)%.

Block copolymers were used to achieve nanoscale patterning. Block copolymers, particularly polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA), produce patterns from which one block polymer may be selectively etched. However, the selective wet etching of PMMA with acetic acid can induce the remaining PS structures to collapse due to capillary forces between adjacent PS domains during drying. This study presents an alternative approach to the formation of nanoscale patterns by using an atmospheric UV-ozone (AP-UVO, λ = 365 nm) exposure system. Compared with the general etching system, AP-UVO exposure is relatively low cost, can potentially be scaled up, and proceeds via a simple process. In addition, we demonstrate that the line and space (L/S) sizes of the block copolymer pattern can be controlled by using the AP-UVO etch time. Also, we were able to obtain well-ordered patterns from the combining the AP-UVO exposure process with a control process of block copolymers conditions. These results suggest that the AP-UVO exposure method with block copolymers may be used to form etch masks, particularly for the fabrication of graphene nanoribbons, quantum dots, nano grid wires, and nanopores.

We report the pseudodielectric functions and the critical points of GaAsxSb1−x ternary alloy films. Data were obtained by performing spectroscopic ellipsometry on 1-μm-thick films grown on (001) GaAs by using molecular beam epitaxy. Artifacts from surface contaminants, including oxide overlayers, were minimized by using in-situ chemical cleaning, leading to accurate representations of the bulk dielectric responses of these materials. We determined the energies of the E1, E1+Δ1, E′0, E′0+Δ′0, E2, E′2, and E′1 critical points from numerically calculated second energy derivatives, as well as their compositional dependences by using lineshape fitting.

Treatment planning system calculations in inhomogeneous regions may present significant inaccuracies due to loss of electronic equilibrium. In this study, three different dose calculation algorithms, pencil beam (PB), collapsed cone (CC), and Monte-Carlo (MC), provided by our planning system were compared to assess their impact on the three-dimensional planning of lung and breast cases. A total of five breast and five lung cases were calculated by using the PB, CC, and MC algorithms. Planning treatment volume (PTV) and organs at risk (OARs) delineations were performed according to our institution’s protocols on the Oncentra MasterPlan image registration module, on 0.3–0.5 cm computed tomography (CT) slices taken under normal respiration conditions. Intensitymodulated radiation therapy (IMRT) plans were calculated for the three algorithm for each patient. The plans were conducted on the Oncentra MasterPlan (PB and CC) and CMS Monaco (MC) treatment planning systems for 6 MV. The plans were compared in terms of the dose distribution in target, the OAR volumes, and the monitor units (MUs). Furthermore, absolute dosimetry was measured using a three-dimensional diode array detector (ArcCHECK) to evaluate the dose differences in a homogeneous phantom. Comparing the dose distributions planned by using the PB, CC, and MC algorithms, the PB algorithm provided adequate coverage of the PTV. The MUs calculated using the PB algorithm were less than those calculated by using. The MC algorithm showed the highest accuracy in terms of the absolute dosimetry. Differences were found when comparing the calculation algorithms. The PB algorithm estimated higher doses for the target than the CC and the MC algorithms. The PB algorithm actually overestimated the dose compared with those calculated by using the CC and the MC algorithms. The MC algorithm showed better accuracy than the other algorithms.