Mamoru Mohri

SiC coatings for first-wall candidate materials by R.F. sputtering

Abstract The r.f. sputtering technique was applied to form SiC coating films on first-wall candidate materials such as molybdenum, stainless steel and pyrolytic carbon at various temperatures. The coating films were examined by means of scanning electron microscopy, X-ray diffraction, Auger electron spectroscopy and roughness factor (RF) measurements. It was found that the coating films consisted of α-SiC and grew at relatively low temperatures, namely 300 °C, 600 °C and 800 °C on molybdenum, 304 stainless steel and pyrolytic carbon surfaces, respectively. The surfaces of α-SiC films grown above these temperatures were relatively smooth with small RFs in comparison with those prepared at lower temperatures. Lower temperature deposition gave rise to amorphous and rough coating films with considerably larger RFs.

Sputtering process of a silicon carbide surface with energetic ions by means of an AES-SIMS-FDS combined system

Abstract Surface phenomena on silicon carbide following interaction with energetic hydrogen ions and argon ions have been studied by means of simultaneous, in situ measurements with a combined system of AES-SIMS-FDS (Flash Desorption Spectroscopy). Bombardment by 0.7 and 1.5 keV argon ions was observed to sputter the surface atoms, both silicon and carbon, with the same sputtering yields. In the case of bombardment by hydrogen ions, on the other hand, silicon atoms were sputtered out preferentially through chemical sputtering to form silicon hydrides at room temperature. In-depth composition profiles of silicon carbide irradiated by 100-keV D + ions were also examined by the combined system.

Isomerization of 1-butene catalyzed by strontium oxide

Abstract The nature of the isomerization of 1-butene over SrO has been investigated. The isomerization rate and selectivity ( cis -2-butene/ trans -2-butene) depended strongly on the pretreatment temperature of the catalyst. The activity appeared on pretreating in vacuo at 650 °C or higher temperature and reached a maximum at 1000 °C. The selectivity gradually decreased with the rise of pretreatment temperature. The degree of the removal of CO 2 correlated with the change in the activity and the selectivity. n -Butylamine and ammonia poisoned preferentially the formation of trans -2butene. Hydrogen treatment of the surface at high temperature resulted in the retardation of the formation of cis -2-butene, while the trans -2-butene formation was retarded by oxygen treatment. The isomerization, both the formation of trans - and cis -2-butene, may occur on acid-base pair sites. The acid sites, presumably surface Sr 2+ , largely contribute to the formation of trans -2-butene, whereas basic sites, presumably surface O 2− , do to the formation of cis -2-butene.

Analysis of the plasma-wall interaction in the Heliotron E device

The plasma-wall interaction (PWI) of the currentless plasmas with temperature To, Tio ≤ 1.1 keV, density Ne = (2–10)× 1013/cm3, and volume-averaged beta value of β

Investigation of environmental problems caused by studded tires of automobiles using PIXE

≤ 2% was investigated. We have observed that PWI took place mainly where the divertor field line intersected the chamber wall (called divertor traces). Boundary plasmas were measured with electrostatic probes, which showed the presence of the divertor region with the parameters in the range of Ned = 1010–1011/cm3 and Ted = 10–50 eV. Surface analysis techniques (ESCA, AES, and RBS) were applied to analyze the surface probes (Si, graphite and stainless steel) and the test pieces (SiC, TiC, and stainless steel), which were irradiated by plasmas for short and long times respectively.

Changes in surface composition of low-Z compound materials with ion bombardment and heat treatment

Abstract The PIXE technique has been successfully applied to investigate the environmental problems caused by the studded tire of automobiles. The dust samples were collected on stacked filters in Sapporo and some other cities in Japan and Europe. PIXE measurements were performed using a 2 MeV proton beam. The results were compared with those of different cities. The main components of dust particulates were Al, Si, Ca, Fe and so on. The vertical distribution of dust concentration in the city of Sapporo was determined by PIXE in April and June. The concentration in April decreases exponentially with height from the ground. The effect of dust particulates due to studded tires is observed up to an altitude 60 m. On the other hand in June, the concentration on the ground is one-tenth of that in April, and it is almost unchanged with the distance in the vertical direction. The concentration of Ca in the dust particulates in the area where the studded tires are used increases by a factor of 2 to 4 in comparison with that in the ordinary soil.

Changes in the roughness factors of 304 stainless steel, pyrolytic carbon and silicon carbide surfaces with energetic ion irradiation

Abstract Changes in the composition of the well defined surface of low-Z carbides have been studied with the use of Auger electron spectroscopy. Polycrystalline B4C with a stoichiometric bulk composition and single crystals of TiC with a (001) plane and SiC with a (0001) plane were used as the samples for quantitative surface analysis. Comparisons in surface properties of these materials were made by various surface treatments such as ion bombardment with argon (3 keV, 8 μA/cm2) and heating up to 1000°C under ultra-high vacuum. In the case of B4C, carbon atoms segregated on the surface with the increase of temperature while with the argon ion bombardment a segregation of boron atoms took place. The surface composition ratios B/C examined at 1000°C were 2.6 and 4.4 with and without the ion bombardment, respectively. The TiC surface, on the other hand, was very stable against the heat treatment and no surface segregation was observed even at 1000°C. However, with the argon ion bombardment carbon atoms segregated slightly to the surface with the atomic ratio Ti/C of 0.87. In the case of SiC, a significant surface segregation of carbon was observed with the atomic ratio Si/C less than 0.3 at 1000°C and this tendency was retarded by the argon ion bombardment to 0.6 at the same temperature.

Quantitative measurement of surface roughness of graphite, silicon carbide and molybdenum irradiated with energetic deuterons

A new apparatus for rapid and precise measurement of very small surface area with high energetic particle irradiation has been developed for the purpose of “in situ” examination in connection with a torus plasma device(JIPPT-II at Nagoya University, Japan). The minimum detectable surface area by xenon adsorption at liquid nitrogen temperature was less than 2cm2 within the reproducibility in the determination estimated to be 5% or less. This apparatus was applied to the surfaces of type 304 stainless steel(304SS), pyrolytic carbon and SiC-coated carbon with the irradiation of D+, He+ and Ar+ ions. The roughness factor of 304SS increased greatly with the Ar+ irradiation from 1.37 to 7.65. The roughness factor of the pyrolytic carbon surface decreased with the irradiation of D+, He+ as well as Ar+ from 13 to 15. The roughness factor of SiC surface coated onto carbon at 1000°C was observed to be 21 – 23 and was not changed by the irradiation.

An Auger electron spectroscopy-secondary ion mass spectrometry study of layers of Cu-Ni and Ag-Au alloys modified by ion bombardment☆

Abstract On the basis of the BET method with xenon adsorption, an appartus for rapid and quantitative measurement of very small surface area (minimum detectable area, 10 cm 2 ) to estimate roughness factor (ratio of real surface area to geometrical surface area) of solid surfaces has been developed. By using the apparatus, changes in roughness factors of pyrolytic carbon, SiC and Mo with the irradiation of energetic deuterons were examined. The surface of pyrolytic carbon has a very large roughness factor of 433. After mechanical polishing it was 134, which was increased again 2.5 times by deuteron bombardment. On the other hand, SiC has a much smaller roughness factor of 47 and was found to be very stable against deuteron irradiation which caused no change in the roughness factor. From the comparison of the roughness factor values with some morphological observations by scanning electron microscopy and surface profilometry, fine structure of material surfaces has been proposed.

AES-SIMS(IMA)study of physical and chemical sputtering processesof low-Z materials by energetic ions

Abstract The effects of argon ion bombardment on the surface layers of Cu-Ni and Ag-Au alloys were studied. Mechanisms considered were preferential sputtering, enhanced diffusion and thermodynamic segregation. An Auger electron spectroscopy-secondary ion mass spectrometry combined system was used to determine the composition-depth profiles from several tens of angstroms below the surface. The variation of the depth profile in the layer modified as a result of ion bombardment revealed that above room temperature the outermost layer was always enriched with copper or silver for the respective alloys compared with the second and the third layers. The results indicated that thermodynamic segregation played an important role in determining the depth profile of the altered layer as well as preferential sputtering and enhanced diffusion.