Gas sorption by oxide layers on aluminium

Gas sorption by oxide layers on aluminium

Classified abstracts 1248--1259 a low n u m b e r (less than 1 per cent of the surface sites) of active sites for EID of H, + and a preferential filli...

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Classified abstracts 1248--1259 a low n u m b e r (less than 1 per cent of the surface sites) of active sites for EID of H, + and a preferential filling of these sites by surface diffusion. W P Gilbreath and D E Wilson, J Vae Sei Technol, 8 ( 1), Jan~Feb 197 I, 45 48. 16 1248. Coadsorption of hydrogen and carbon monoxide on (111) platinum. (USA) T h e c o a d s o r p t i o n of hydrogen and carbon m o n o x i d e on the (111) face of a platinum single crystal has been studied by a c o m b i n a t i o n of thermal flash desorption a n d electron impact desorption (EID) techniques in ultrahigh v a c u u m . Several c o m p o s i t i o n s over the range from 0 per cent-100 per cent C O have been studied, over a total pressure range from 5 × 10 9 to 5 × 10 7 torr. T h e observed adsorption behaviour is complex, indicating multiple binding sites for both gases. In addition, the EID studies show the f o r m a t i o n of a surface species containing both H a n d C O . This s a m e species h a s also been observed when f o r m a l d e h y d e was adsorbed directly from the vapour. V H Baldwin and J B Hudson, J Vac Sci Teehnol, 8 ( 1), Jan/Feb 1971, 53 56. 16 ! 249. Extended Hiickle calculations of relative chemisorption energies. (USA) T h e relative energies of c h e m i s o r p t i o n of molecules on a clean lead surface have been c o m p u t e d with an extended Htickel molecular orbital m e t h o d . T h e calculations were carried out with several organic molecules in order to investigate the f o r m a t i o n of m o n o molecular layers a n d their possible use as thin (10-20 ,~) insulating J o s e p h s o n t u n n e l i n g barriers. Calculating the adsorption energy at various locations on the Pb surface yields a m e a s u r e o f the surface coverage and the most suitable organics for f o r m i n g the monolayer. Nonoxidative adsorbates are found not to c h e m i s o r b on Pb while those which are oxidative do bond. T h e b o n d i n g energy of the acetoxy radical is f o u n d to be 4 eV and the ethyl radical energy is 0.6 eV. J C Robertson and C W Wilmsen, J Vac Sci Teehnol, 8 (1), Jan/Feb 1971, 53-56. 16 1250. Metal surfaces and their changes by chemisorption. (USA) New experimental evidence (field-ion-emission microscopy, fieldelectron-emission microscopy, ion-neutralization spectroscopy) has been found s u p p o r t i n g the idea that the properties of a surface a t o m in the m o m e n t of the interaction can be roughly a p p r o x i m a t e d by the properties of an individual atom. T h e type of a p p r o a c h which should be used in a particular case d e p e n d s both on the experimental m e t h o d a n d on the problems in which we are interested. Z Knor, J Vat' Sei Technal, 8 (1), Jan~Feb 1971,63-68. 16 1251. Interactions between chemisorbed species: H2 and N2 on (I00) tungsten. (USA) The interactions between h y d r o g e n a n d nitrogen adsorbed species on a (100) t u n g s t e n crystal have been investigated by flash desorption methods. W h e n the crystal covered with a m o n o l a y e r of hydrogen is exposed to gaseous N~, the nitrogen slowly replaces the two chemisorbed h y d r o g e n / 3 states by m e a n s o f a slight lowering of the hydrogen desorption energy. This displacement process occurs via slow thermal desorption of hydrogen in the presence of gaseous N= when the surface t e m p e r a t u r e is ~ 3 0 0 K , no such replacement is observed at 273 K. J T Yates and T E Madey, J Vac Sci Technol, 8 ( I ), Jan~Feb 1971,63 68. 16 1252. Surface structures formed during the interaction of sulphur compounds with the (111) face of nickel. (USA) T h e interaction of hydrogen sulphide, n-propyl mercaptan, a n d dimethyl disulphide with the (111) a n d (100) faces o f nickel has been studied by L E E D at t e m p e r a t u r e s up to 700 K. D u r i n g interaction a n d subsequent annealing, in vaeuo below l0 ~ torr at temperatures up to 1200 K, series of diffraction patterns were observed. F o u r of the patterns on (1 II) have been attributed to coincidence nets arising from structures which involve r e a r r a n g e m e n t a n d reorientation to (100) type layers. The patterns are described and the interpretations discussed. T Edmonds et al, J Vac Sci Technol, 8 ( 1), Jan/Feb 1971, 68- 74. 558

16 1253. Calcium fluoride vapour condensation and crystallization in vacuum. (France) A study of the c o n d e n s a t i o n of calcitml fluoride in clean, ultrahigh v a c u u m , shows that the c o n d e n s a t i o n occurs in two stages: first, the gaseous phase is adsorbed on the substrate or on already condensed material : and second, the solidification of the adsorbed phase. F Porreca et al, Le VMe, 26 (151), Jan Feb 1971, 15 18 (in t~'ench). 16 1254. L E E D studies on the initial oxidation of copper. (Japan) T h e initial oxidation of the ( l l 0 ) , (l l 1), a n d (100) copper surfaces with varying oxygen pressure and temperature was studied by L E E D techniques. T h e oxygen interaction differed on each surface. C u 2 0 was formed on the (111) and (100) faces but not observed on the (110) face in the L E E D pattern. Crystallographic relationships between C u 2 0 and substrate were determined. T h e results are discussed. K O k a d a et al, J Vae Soc Japan, 13 ( l I ), 1970, 371-376 (in Japanese). 16 1255. Physical adsorption of mixed gases at very low pressure. (Japan) A d s o r p t i o n of the mixed gases, N.,--CO, C O CO2, and K r - C O , on a Pyrex glass surface was observed in the pressure range l0 -~ to 10 ~ torr at 77.4°K. T h e a m o u n t of a c o m p o n e n t gas adsorbed was determined by thermal desorption for various cooling times of the adsorbent. T h e results show that gas c o m p o n e n t s with higher activation energy of desorption replace those with lower activation energy. T h e replacement of gases physisorbed at low temperature and at lowcoverage suggests the heterogeneous nature of the Pyrex glass surface. Y Tuzi and M Kobayashl, J Vac Sot" Japan, 14 (3), 1971, 8 3 88 (in Japanese). 16 1256. Interaction of oxygen with hot tungsten filament: effect of the w a l l o f t h e measuring cell. (Japan) T h e interaction of oxygen with a hot ttmgsten filament was studied by the technique of isotopic mixing. T h e tungsten filament, at the centre of a spherical glass cell, was flashed in isotopic oxygen at l0 6 tort. T h e cell wall was kept at several constant temperatures during the flashing. T h e results indicate that carbon monoxide and dioxide are produced by the surface of the glass cell rather than by oxygen interaction with the hot tungsten, with the exception of the initial stage, within the first 30 minutes. N Hayashi and J Watanabe, J Vac Soc Japan, 14 (3), 1971, 89-93 (in Japanese). 16 1257. Many-band radical-recombination luminescence of boron nitride. (USSR) Spectral-kinetic regularities o f radical-recombination luminescence o f b o r o n nitride are investigated in a d y n a m i c v a c u u m system at hydrogen partial pressure of 2.5 ~ 10 '~' torr and that of nitrogen of 5 y 10 -~torr. It is f o u n d that luminescence characteristics depend on the m a n n e r o f BN preparation, conditions of preliminary t r e a t m e n t and impurity concentrations on the sample surface. Yu M Naslednikov et al, Izv VUZ Fi=. No 2, 1971, 2 4 29 (in Russian). 16 1258. Influence of oxygen adsorption on kinetics of radical-recumbinationluminescenceoferystal-phospbors. (USSR) Influence of preliminary oxygen adsorption at pressure up to 0.3 torr on kinetics of radical-recombination luminescence of crystalp h o s p h o r s is investigated. Experimental results are discussed. Yu A Sivov et al, lzv VUZ Fiz, No 9, 1970, 124 126 (it! Russian). 16 1259. Gas sorption by oxide layers on aluminium. (USSR) Sorption of air, nitrogen, argon, hydrogen, neon a n d helium by an oxide layer on a l u m i n i u m is investigated in the pressure range 10 " to l0 ¢ torr with liquid nitrogen cooling, and sorption of helium in the pressure range 10 ~a to 10 ~' tort with liquid helium cooling. T h e experimental a r r a n g e m e n t is described. Anodic oxide layers with thicknesses of 20 and 100 /ml were examined. T h e pressure in the sorption cell was measured with the aid of an inverted m a g n e t r o n and ionization gauges. It is found that the isotherms of gas sorption obey the Freundlich equation. A five-fold increase in oxide layer thickness results in a 10- to 20-fold increase in the gas sorption capability. It is d e m o n s t r a t e d that for thin-layer sorbent type oxide layers on alum i n i u m it is not a d v a n t a g e o u s to use temperatures lower t h a n the condensation temperature of the sorbed gas. T h e oxide layer on a l u m i n i u m appears to be an efficient sorbent, it possesses m a n y