Takaya Kawabe

Electron-stimulated surface stress relaxation of Si

We have observed the nonthermal relaxation of surface stress in Si induced by electron irradiation at room temperature. An atomically thin disordered layer was introduced by Ar ion bombardment. The surface stress change during ion bombardment and the following electron irradiation of Si(100) was measured by means of an optical microcantilever technique. We have found that the compressive stress in the Si surface due to disorder induced by ion bombardment was completely relaxed by electron irradiation at low energy. The criterion for complete relaxation is found not to be total energy deposition, but the number of irradiated electrons.

Effects of surface disorder on the surface stress of Si 100 during oxidation

We have studied the effects of disorder on surface stress during oxidation. The surface stress change during ion bombardment and the following plasma oxidation on Si(100) was measured by means of an optical microcantilever technique. We have found compressive stress on Si surface due to disorder induced by ion bombardment and determined it quantitatively in terms of the number of defects. This disorder-induced compressive stress was completely relaxed by the plasma oxidation processes. The initial evolution of the surface stress during oxidation on bombarded surfaces is quite different from that on unbombarded Si(100) surfaces.

Plasma density dependence of the oxidation rate of Si by in situ during process rapid ellipsometry

Oxidation of silicon in a radio frequency discharge oxygen plasma was studied using in situ during process rapid ellipsometry (1 s resolution and interval). Plasma characteristics were also determined by the Langmuir probe method and emission spectroscopy. From the measurement of in situ during process rapid ellipsometry, oxidized film thickness of silicon increased steeply right after starting rf discharge and slowly after ≊3000 s. It was found that thickness change rate measured by in situ during process rapid ellipsometry immediately after starting the rf discharge was strongly proportional to O2+ ions density.

Experimental observation of the ambipolar potential in a tandem mirror by use of negative ion beam

A negative ion beam probe is described. Advantages of this method for the potential measurement of the plasma in a minimum‐B magnetic field are discussed and the method is applied to measure the potential difference between the plug and the central cell in a GAMMA‐6 tandem mirror.

Observation of relaxation processes of disorder in ion-irradiated graphite using Raman spectroscopy

Abstract Real-time Raman measurement has been applied to monitor the thermal relaxation processes in graphite at 411–463 K under 5 keV deuterium ion irradiation. The observed time dependence of density of defects revealed that the thermal relaxation process consists of three distinct stages. Dominant processes have been discussed for each stage.

Translational Energy Distribution of CO Produced in Infrared-Laser-Assisted Reaction of O2 with a Graphite Surface

Infrared-laser-assisted reactions of O2 with a graphite surface were studied with laser-ionization mass spectroscopy. CO was observed as a reaction product of O2 and graphite. A time profile of CO was measured for the first time, and the mean translational temperature of CO was measured to be 790±80 K. The translational temperatures of carbon clusters of C, C2 and C3 evaporated from the surface were also measured.

GeO Desorption in Reactive Scattering of an Oxygen Molecular Beam with a Ge(100) Surface

Reactive scattering of O2 with a Ge(100) surface has been studied using resonance enhanced multiphoton ionization (REMPI) at substrate temperatures between 870 and 1020 K. The first observation of the (2+1) REMPI of GeO is performed at around 297 nm. The desorption rate constant of GeO is determined by analyzing the GeO waveforms, and is estimated to be k=1017.6±0.4 exp (-2.4±0.1 eV/k BT) [ s-1], and the large pre-exponential factor is well reproduced using a transition state theory calculation. The angular distribution of the GeO is found to be isotropic on the virgin surface and deformed on the highly etched surface.

Initial plasma oxidation kinetics of silicon: DC bias effects

The effects of applied bias on initial plasma oxidation of silicon was studied using real-time ellipsometry and Langmuir probe measurements. In the ultra-thin oxide regime, the plasma oxidation is enhanced by both positive bias and negative bias. The enhancement of the growth rate of oxide is explained mainly by the collision of electrons with adsorbed oxygen species, caused by positive bias, and by the collision of positive ions with the surface, caused by negative bias.

Neutron and plasma irradiations of fusion reactor materials using fusion plasma neutron sources

Abstract A compact and steady-state DT plasma with parameters relevant to a fusion-reactor, the FEF (fusion engineering facility), has been considered as a neutron source for the development of fusion reactor materials providing both. (1) 14 MeV fusion neutron irradiation testing, and (2) high charged particle flux for testing of plasma-facing materials during neutron irradiation. The 14 MeV neutron wall loading is about 1–2 MW/m 2 , with a test section area of 1 m 2 . One version of the test section is near the edge of the plasma in the vacuum chamber. Another is for high heat flux testing of plasma facing materials, where the charged particle flux leads to heat loads of several 10 kW/cm 2 . New versions of FEF, with localized high neutron fluxes, are also proposed by introducing a sloshing ion distribution into the plasma.

II.10.3. Open-ended fusion devices and reactors

Conceptual design studies on fusion reactors based upon open-ended confinement schemes, such as the tandem mirror and rf plugged cusp, have been carried out in Japan. These studies may be classified into two categories: near-term devices (Fusion Engineering Test Facility), and long-term fusion power recators. In the first category, a two-component cusp neutron source was proposed. In the second category, the GAMMA-R, a tandem-mirror power reactor, and the RFC-R, an axisymetric mirror and cusp, reactor studies are being conducted at the University of Tsukuba and the Institute of Plasma Physics. Mirror Fusion Engineering Facility parameters and a schematic are shown. The GAMMA-R central-cell design schematic is also shown.