On the anisotropy of electron backscattering and of the sticking coefficient of gases on single crystal surfaces

A370 231

Surface Science 121 (1982) 231-242 North-Holland Pubhshmg Company

ON THE ANISOTROPY OF ELECTRON BACKSCATTERING OF THE STICKING COEFFICIENT OF GASES ON SINGLE CRYSTAL SURFACES T.M. GARDINER*. H.M. KRAMER** and E. BAUER

AND

Phvsdmlrsches Inmtut. Techmrche Umuersirar Clausthul. Lerbm:wasse 4, D-3392 Cirusthol- Zellerfeld. und Sonderforsthungsbererch 126 Gotlrngen -Cluusthul, D-3392 Cluurthol- Zellerfeld. Fed Rep of Germun~ Received

22 May 1982, accepted

for pubhcatlon

7 July 1982

The Influence of the amsotropy of backscattermg of electrons wth energies above the core hole lomzatlon energy of selected Auger processes on the amsotropy of the Auger electron emlwon IS studled usmg a cylmdrlcal W smgle crystal After the determmatlon of the amsotropy of the elastic backscattermg Its contrlbutlon to the amsotropy of Auger electron emlwon from adsorptlon layers IS obtamed by postulatmg that all other amsotropy causer are neghglble When apphed to an adsorbate wth orrentatlon-Independent coverage such as Fe this leads to an orlentatlon-dependent backscattermg correctlon term which may be apphed to adsorbates with orlentatlon-dependent stxkrng coefflclents such as 0, In this manner Auger ,lgnals may be converted mto true relative cocerages (corrected for backscattermg anrsotropy) In the case of oxygen adsorptlon this correctlon IS slgmfxant and leads to an orlentatlon-Independent lmtlal stlckmg coeffwent (of I) over most of the (I 10) zone except m the nelghbourhood of the {I IO) planes where It reaches It\ mimmum value of 0 28

Surface Science I21 (1982) 243-248 North-Holland Pubhshmg Company

TPD-NMR Rh/TiO, Thomas

STUDY

M. APPLE

243

OF HYDROGEN

IRREVERSIBLY

I March

ON

and Cecil DYBOWSKI

Department of Chemlyfyv and Center for Catalytic Screme and Tethnologv. Newark. Delaware 1971 I, USA Received

ADSORBED

1982, accepted

for pubhcatlon

Umver~rrv ot Delunure.

22 June 1982

TPD-NMR studies are demonstrated which reveal the presence of three lrreverslbly bound hydrogen species on Rh/TlO,. two asslgned to species produced when rhodium metal 1s present on the surface and one to surface hydroxyl groups The two surface species dependent on the presence of Rh desorb wth maxima at around 120 and 27O’C. while the remammg species (assigned to hydroxyl groups) desorbs around 550°C