中野 武雄

Abstract A helium collisional-radiative (CR) model, coupled with a chemical kinetics model incorporating dominant processes of nitrogen, oxygen, and trace humidity ( ), is developed for the diagnostic analysis of emission spectra in the visible range (300–900 nm). The CR model accounts for excitation, de-excitation, ionization, and association processes induced by neutral helium atoms, which are essential at atmospheric pressure. Neutral and singly ionized nitrogen molecules, and atomic oxygen are treated as independent states with detailed kinetic pathways to trace the emission lines of their respective species. The developed model enables the inverse determination of effective electron density, effective electron temperature, and impurity concentrations by fitting selected helium, nitrogen, and oxygen lines. The model was applied to evaluate emission spectra from a dielectric barrier discharge and an atmospheric-pressure helium plasma jet containing minor air impurities. The results indicate that the axial impurity distributions can be appropriately diagnosed, and the calculated plasma parameters exhibit reasonable physical self-consistency under the investigated conditions.

In this study, the direct growth of graphene on insulating substrates was performed at low temperatures (500–700 °C) using hydrogen-assisted sputter deposition with an Ar/H2 gas mixture and a graphite target. Using this approach, few-layer {002}-oriented graphene was formed on SiO2/Si substrates without the use of catalysts or transfer processes. The resulting film exhibited an electrical conductivity of 123 S cm−1 (sheet resistance of 4.07 × 104 Ω/□), hole mobility of 24.5 cm2 V−1 s−1, and carrier concentration of 3.14 × 1019 cm−3. By systematically varying the substrate temperature and hydrogen gas fraction, four distinct regions were identified, corresponding to graphene growth, carbon nanowalls, amorphous carbon, and no film deposition. The study findings suggested that the generation of CHx species by chemical sputtering of the graphite target played an important role in graphene growth, and that the growth mechanism was governed by the balance between the surface decomposition of CHx on the heated substrate and the hydrogen-induced etching of unstable carbon atoms. This approach therefore represents a simple and scalable route for transfer-free graphene integration on insulators at reduced temperatures.

Abstract The effects of sputtering gas on particle transport in DC magnetron sputtering have been studied. Using argon or krypton as sputtering gas, Al, Ti, Cu, or Mo targets were sputtered at gas pressures ranging from 0.5 to 20 Pa. The deposition rates at the front face were almost constant at low gas pressures, then decreased above a certain pressure. The thickness uniformity deteriorated with increasing gas pressure, and the backside deposition reached its maximum at the boundary pressure. The dependence of these behaviors on the gas and target materials was examined using thermalization behavior evaluated by Monte Carlo simulation.

Mode transitions in reactive sputtering of metal (Ti, V) oxides are studied. Under a controlled Ar gas pressure at a flow rate of 10 sccm, direct current sputtering plasma was generated. The oxygen flow rate Q and discharge power P were changed in two ways (Q was varied at fixed P, and vice versa), and the mode transitions were monitored using the state jump in the discharge voltage. When the transition points (P, Q) were plotted as two-dimensional (2D) maps, the metal-to-oxide and oxide-to-metal transition points were found to be located on two corresponding straight lines that passed through the origin, irrespective of how the parameters were varied. The origin of this behavior is discussed and ascribed to the linear relationship between the input power and the sputter etching rate of the target. These results also suggest that the metal-mode, hysteresis, and oxide-mode regions of the 2D map can be determined by a few pilot experiments. By depositing vanadium oxide films under conditions in the oxide-mode region, near its boundary, films with very similar optical properties could be obtained.

Transparent conductive Al-doped Zinc oxide thin films were deposited on glass substrates by conventional radio frequency magnetron sputtering (C-RFMS) and inductively coupled plasma-assisted radio frequency magnetron sputtering (ICP-RFMS) methods. The structural and electrical properties of films were studied as a function of the radial position (r) of the substrate in both methods. A good thickness uniformity was obtained in ICP-RFMS, while a significant decrease in film thickness was observed at r=30 mm (erosion zone) in C-RFMS. The c-axis orientation was achieved in all positions in ICP-RFMS, while crystallinity was degraded at r≧25 mm in C-RFMS. Low resistivity ρ of the order of 10^-4 Ω cm was obtained at all positions in ICP-RFMS, while ρ was rapidly increased at r≧30 mm in C-RFMS. In ICP-RFMS, high-energy ion bombardment is suppressed due to the modified plasma density profile and lower space potential. As for transparency, the sample prepared at r=0 mm in ICP-RFMS showed an average visible transmittance of 81%, higher than that in C-RFMS. Throughout the study, it was demonstrated that ICP-RFMS method was promising to improve the radial distribution of structural, electrical, and optical properties of Al-doped ZnO thin films.