Kuniaki Watanabe

A quantitative analysis of surface segregation and in-depth profile of copper-nickel alloys

Abstract By utilizing the difference in escape length of the Auger electrons with different energies, a calculation of the in-depth distribution of atomic concentration at the surface is presented on the basis of Palmbergs physical mechanism. Experimental results on clean surfaces of Cu-Ni alloys over the entire composition region with Auger spectroscopy were performed to make the in-depth profile of surface composition caused by annealing. The alloy composition of the first atomic layer at the surface was plotted against the bulk composition, showing significant enric enrichment of Cu atoms in that layer. The results indicated that the segregation takes place in about four atomic layers at the surface.

An AES study of surface segregation of AgAu alloys with ion bombardment and annealing

Abstract Equilibrium segregation and selective sputtering in the surface of AgAu alloys have been investigated systematically with argon ion bombardment and with annealing by means of AES measurements. Slight enrichment of Ag was observed on the alloy surfaces after the annealing of the alloys at 550°C, while relatively large enrichment of Au was observed on the ion-bombarded surfaces with the use of Au (240 eV) and Ag (300 eV) Auger electrons. With the aid of other Auger electrons with different escape lengths, it was found that the concentration varies with distance from the surface within the sampling depth of the Auger electrons. On the basis of the above facts, the depth profiles were proposed for the annealed and the ion-bombarded surfaces. The uppermost surface layer is enriched more with Ag than the apparent AES observations on both the ion-bombarded and the annealed surfaces. The proposed depth profiles on both the surface layers were compared with previous results by different authors.

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.

Oxide layers on GaAs prepared by thermal, anodic and plasma oxidation: In-depth profiles and annealing effects

Abstract The in-depth profiles of oxide layers prepared by thermal, anodic or plasma oxidation were investigated by means of simultaneous Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS) measurements. With the AES measurements it was found that the oxides grown by thermal oxidation consisted only of Ga2O3; a large pile-up of arsenic was found near the interface between the oxide layer and the substrate. In contrast, oxides formed by anodic and plasma oxidation contained both Ga2O3 and As2O3 and showed a much smaller pile-up of arsenic. The annealing of as-grown oxide layers at relatively low temperatures (around 300°C) caused the oxide composition to become more uniform with depth and made the interface thinner. Annealing at relatively higher temperatures gave rise to a deficiency of arsenic in the oxide and created a pile-up of arsenic near the interface. Preliminary X-ray photoelectron spectroscopy measurements revealed the presence of unoxidized arsenic in the sputterer surfaces of anodic and plasma oxides. The SIMS measurements revealed that the relative intensity of the secondary ions varied in a complicated way in the oxide and near the interface, where no appreciable changes in composition were observed by AES. The SIMS results suggest the existence of different oxides having different physiochemical properties; these differences probably alter the ionization yield and/or the process of emission of the secondary ions.

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

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.

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

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.

Changes in roughness factors of 304 and 316 L + N stainless steels with ion bombardment and discharge cleaning

The effect of ion bombardment on the roughness factor and morphology of 304 and 316 L + N stainless steels was measured by means of xenon adsorption and scanning electron microscopy. The roughness factor or real surface area was determined with the aid of the BET equation. The 304 stainless steel was bombarded with argon ions in a conventional r.f. sputtering apparatus, while the 316 L + N stainless steel was bombarded with argon ions or a mixture of ions generated in 90% Ar-10% O2 using glow discharge cleaning equipment. Morphological observation revealed that r.f. sputtering of 304 stainless steel gave rise to cone formation. The size and density of the cones increased with prolonged argon ion bombardment. Adsorption measurements revealed that the roughness factor increased with argon ion bombardment to reach a constant value around 7 after prolonged bombardment. The 316 L + N stainless steel used in the present study had a large roughness factor of about 15. Discharge cleaning by the mixture of ions did not change the morphology or the roughness factor, while discharge cleaning by argon ions alone gave rise to morphological changes which increased the roughness factor.

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

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.

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

Abstract Interactions of energetic ions with surfaces of silicon carbide have been studied under ultrahigh vacuum conditions in terms of physical and chemical sputtering processes by means of AES-SIMS(IMA) combined systems. The sputtering yield of silicon carbide with hydrogen, helium and argon ions was measured by a volumetric method as a function of target temperature. The sputtering yield was found to have a maximum at around 700° C for hydrogen ions, while it increased monotonically with temperature for helium and argon ions. The differing temperature dependency can be attributed to different sputtering processes.