Tomohiro Kobayashi

Spatial Redistribution of Oxygen Ions in Oxide Resistance Switching Device after Forming Process

The change in the spatial distribution of oxygen ions after an initial voltage application called the forming process was investigated for oxide resistance switching devices by secondary ion mass spectrometry mapping. To track the motion of oxygen ions, tracer 18O ions were implanted in a planar Pt/CuO/Pt device. We found clear evidence for the oxygen reduction in the conductive bridge structure formed between two electrodes. In addition, the oxygen ions in the bridge structure drift to the anode, implying the oxygen diffusion (migration) induced by high electric field and/or current density. We discuss those results in terms of a filament model.

Rapid Recrystallization of Amorphous Silicon Utilizing Very-High-Frequency Microplasma Jet at Atmospheric Pressure

The rapid recrystallization of amorphous silicon (a-Si) utilizing a very-high-frequency (VHF) plasma jet of argon (Ar) at atmospheric pressure is investigated. A highly crystallized polycrystalline Si film is synthesized by optimizing the translating velocity of the substrate stage and the flow rate of argon. The temperature of the plasma exposure area reaches 1350±300 °C and the recrystallization of a-Si proceeded with time constants of 30–50 ms. The effects of the translating velocity of the substrate stage and the flow rate of argon on the rapid recrystallization of a-Si are demonstrated along with its mechanism.

Synthesis of Well-Aligned Carbon Nanotubes Using a High-Density RF Inductive Coupling Plasma

Growth of vertically well-aligned carbon nanotubes was demonstrated utilizing high-density rf inductive coupling plasma-enhanced chemical vapor deposition of methane. A sufficient supply of CH4-related precursors as well as a rapid large number of dangling bonds at the top surface due to a negative substrate dc bias are essential for promoting the deposition rate of vertically well-aligned carbon nanotubes. Rapid deposition at 60 A/s of vertically well-aligned multi-walled carbon nanotubes was achieved using pure methane (50 sccm) by adjusting the plasma conditions.

SPINS AND CARRIERS IN OXIDE SUPERCONDUCTORS STUDIED BY RAMAN SCATTERING

The spin and doped charge states in copper oxide superconductors were investigated by Raman spectroscopy. The anomalous magnon scattering in the antiferromagnetic insulator phases, such as the second peaks near 4J (J is the two-spin superexchange energy) in the B1g spectra and the large scattering intensities in the A1g spectra, suggests the existence of four-spin cyclic exchange interactions. When carriers are doped, the A1g spectra show non-“normal Fermi liquid” behavior. The imaginary part of the experimentally obtained susceptibility have ω-proportional part from ω~0. The gradient increases, on cooling, as in the case of the marginal Fermi liquid.

Two-spin superexchange and four-spin cyclic exchange interactions in high Tc superconducting cuprates and isostructural La2NiO4

Raman spectra in the antiferromagnetic insulator phases of s = 1/2 high T c superconducting cuprates were compared with s = 1 La 2 NiO 4 . The anomalous magnon spectra in cuprates suggest that the four-spin cyclic exchange interactions are very large. The doped carriers in cuprates show non-Fermi liquid behavior.