Helium scattering as a probe of the clean and adsorbate covered Pt(111) surface

Al92 metals is obtained. Assuming that the surface Rayleigh phonons are dominant excitations in the energy transfer leads to distribution over the azimuthal angle which are somewhat than those observed. We also present an outline of a theory of the trapping-desorption based on the .master equation approach.

Surface Science 117 (1982) 53-59 North-Holland Publishing Company

involved narrower fraction,

53

STICKING AND INELASTIC SCATTERING AT METAL SURFACES: THE ELECTRON-HOLE PAIR MECHANISM K. SCHONHAMMER 1. Institut and

fiir

Theoretische Ph_vsik, Universittit

Humburg,

D-2000

Humburg,

Fed. Rep. OJ Germutly

0. GUNNARSSON Mu*-Pimck-Institut

Received

Jiir FestkiirperJorschuq.

14 September

I98

I ; accepted

D-7000

for publication

Stuttgurt.

Fed. Rep.

29 October

of Germut1.v

19X1

We present calculations of the contribution of the electron-hole pair creation to the inelastic scattering probability and the sticking coefficient of atoms or molecules on metal surfaces. For light chemically reactive adsorbates this mechanism can be very important. The total inelastic scattering probability for thermal He atoms on a copper surface due to e-h pairs on the other hand is only 10w5, i.e. for rare gas atoms the phonon mechanism is the dominating one.

60

Surface Science 117 (1982) 60-66 North-Holland Publishing Company

HELIUM SCATTERING AS A PROBE OF THE CLEAN AND ADSORBATE COVERED Pt(ll1) SURFACE Bene POELSEMA, Robert L. PALMER, Giinter MECHTERSHEIMER and George lnstitut fiir GrenzfliehenJorschung

und Vukuumphysrk.

COMSA Kernforschu,lgscr,s/rrge Jiilich.

D-51 70 Jiiltch,

Fed. Rep. of Germany

Received

14 September

1981; accepted

for publication

30 September

I981

Thermal energy (16-165 meV) helium nozzle beam scattering has been used as a probe of the physical structure of the nominal Pt(lll) surface and for the consequential effects of the adsorption of gases including CO, H,, 0, and C,H,. By careful crystal alignment and polishing techniques a Pt( 1 II) surface with terrace widths greater than 3000 A was achieved as judged by the helium scattering. The profile of the scattered peak was immeasurably affected by the presence of various adsorbates while the intensity decreases monotonically with coverage. The sensitivity of the scattered intensity to adsorbates is, in general, a function of the energy and angle of incidence of the helium beam. The scattering cross-section of the adsorbate can be, for some cases, much larger than its Van der Waals diameter and apparently increases with the degree of perfection of the surface.