Mayumi Tode

Effect of the Soft X-rays on Highly Hydrogenated Diamond-Like Carbon Films

The effect of soft X-ray irradiation of diamond-like carbon films in vacuum was investigated using synchrotron radiation (SR). Etching and the desorption of hydrogen upon SR exposure in vacuum occurred in highly hydrogenated diamond-like carbon (H-DLC) films; these processes were not observed in the irradiation of a low-hydrogenated DLC film. The extent of decrease in hydrogen content due to SR exposure was found to decrease with increasing the etching ratio of the H-DLC film. This indicates that hydrogen desorption from the H-DLC films competed with the etching process. Namely, the modified surface, in which hydrogen content was decreased by SR exposure, was immediately removed from the H-DLC film that had a high etching rate.

Growth of β-FeSi2 Thin Films on Silicon Substrates by Pulsed Laser Deposition Using ε-FeSi Alloy Targets

The growth of highly oriented β-FeSi2 thin films on Si substrates was successfully demonstrated by pulsed laser deposition using e-FeSi alloy targets. In our method, Si atoms are supplied from the substrate and a surface reaction occurs to form the β-FeSi2 layer. This growth process produces a sharp interface between the film and the substrate.

Eutectic α-Fe2Si5 and ε-FeSi Formed in an Arc Furnace Showed a Three-Layer Structure

We melted stiochiometrically mixed (FeSi2) Fe and Si powders in a tri-arc furnace in an argon atmosphere and allowed them to cool naturally to room temperature and obtained a eutectic crystal of e-phase embedded in α-phase of iron silicide. We determined three kinds of layers: the grain size of e-phase was more than 100 µm, about 50 µm and less than 1 µm. Only the first layer did not contain α-phase. The interfaces between the layers were so definite that the grain size was changed abruptly between the layers. When the crystal was annealed in vacuum at 1150 K for 70 h, the last two layers were transformed to β-FeSi2 but the bottom layer containing only e-phase was not changed by the thermal treatment.

Hydrogen Removal from Hydrogenated Diamond-Like Carbon Films by Exposure to Photon and Energetic Atomic Oxygen Beams

Stability of hydrogen in diamond-like carbon (DLC) film under simulated space environment, i.e., hyperthermal atomic oxygen, vacuum ultraviolet (VUV) and soft X-ray exposures has been studied. Hydrogen in DLC was released by exposure to low-energy atomic oxygen beam, whereas the gasification reaction of carbon atom needed collision energy above 3 eV. The desorption process in the deep region required a higher collision energy. The density of hydrogen decreased 11% by atomic oxygen exposure, and was independent of the collision energy. Photon exposure also releases hydrogen from DLC. High-energy photons in soft x-ray promote the hydrogen desorption even from deeper region with high efficiency. It was considered that soft x-ray could release bonded hydrogen which is not released by VUV or atomic oxygen exposures.

A chemical-state specific study of the composition of the natural oxide layer of V25Cr40Ti35

Angle-resolved photoelectron spectroscopy is an established technique for obtaining information on the depth dependence of the concentration of elements within a sample. When synchrotron radiation is used as the X-ray source, the high flux and high energy resolution allow chemical-state-specific information to be obtained – an area where the technique has advantages over more quantitative techniques with higher depth resolution. Here, we describe the application of the technique at the surface chemistry end-station at BL-23SU, SPring-8, where thin films can be analysed in situ. The technique is applied to studying the natural oxide surface layer of V25Cr40Ti35, a hydrogen-storage material.

Growth of -FeSi2 Thin Films on Silicon Substrates by Pulsed Laser Deposition Using "-FeSi Alloy Targets

The growth of highly oriented β-FeSi2 thin films on Si substrates was successfully demonstrated by pulsed laser deposition using e-FeSi alloy targets. In our method, Si atoms are supplied from the substrate and a surface reaction occurs to form the β-FeSi2 layer. This growth process produces a sharp interface between the film and the substrate.

Growth of β-FeSi2Thin Films on Silicon Substrates by Pulsed Laser Deposition Usingε-FeSi Alloy Targets

The growth of highly oriented β-FeSi2 thin films on Si substrates was successfully demonstrated by pulsed laser deposition using e-FeSi alloy targets. In our method, Si atoms are supplied from the substrate and a surface reaction occurs to form the β-FeSi2 layer. This growth process produces a sharp interface between the film and the substrate.

Eutectic α-Fe2Si5 and ε-FeSi Grown by the Czochralski Method from Arc Melt

We have grown eutectic bulk crystals of α-Fe2Si5 and e-FeSi by means of the Czochralski method from an arc melt with a tungsten rod. This method has the advantages of a one-step growth process and of the possible control of the crystal size. We obtained a crystal whose diameter was as large as 5 mm. Obtained crystals have a fibrous structure of e-FeSi in an α-Fe2Si5 matrix. The e-phase forms into fine rods of 1.2 µm width, which were densely distributed in the α-phase. The microstructure can be transformed in single-phase β-FeSi2 upon thermal annealing. The X-ray diffraction pattern of the obtained β-phase was also presented.