Wesenberg, C.; Autzen, O.; Hasselbrink, Eckart:

Photodesorption from Ultra-Thin Metal Films - A Comparison of SO₂ and NO₂ on Ag/Si(100)

In: Applied Physics A: Materials Science & Processing, Jg. 88 (2007) ; Nr. 3, pp. 559-569
ISSN: 0947-8396
Zeitschriftenaufsatz / Fach: Chemie
The photochem. of SO₂ on thin epitaxial Ag films (5-60 nm) deposited on Si(100) has been studied using laser light with the wavelengths of 266, 355, and 532 nm. SO₂ desorbs with cross sections of 1.7*10⁻¹⁹,1.7*10⁻²⁰ and 2.9*10⁻²¹ cm², resp. The av. translation energy, {Etrans/2k}, is 440 K for 266 and 355 nm light, and 270 K for 532 nm light. Cross sections for a 60 nm thick Ag film are practically identical to the ones for Ag(111) as the substrate. An increase by a factor of ~3.5 is obsd. when the film thickness is reduced to 5 nm for 266 and 355 nm light. No significant change is obsd. for 532 nm excitation. The film thickness has no significant influence on the translational energy of the photodesorbed mols. The data are discussed in connection with the change of absorptivity of the metal film-semiconductor system. A model is put forward which takes into account the light absorption in the Si substrate and the reduced relaxation of excited electrons in Si. Modeling indicates that electrons excited in the Si substrate with energies and parallel momenta not allowed in Ag contribute to the surface chem. after crossing the gap in the projected band structure of Ag(111).