Photochemistry on ultrathin metal films: strongly enhanced cross sections for NO2 on Ag/Si(100).

The surface photochemistry of NO(2) on ultrathin Ag(111) films (5-60 nm) on Si(100) substrates has been studied. NO(2), forming N(2)O(4) on the surface, dissociates to release NO and NO(2) into the gas phase with translational energies exceeding the equivalent of the sample temperature. An increase of the photodesorption cross section is observed for 266 nm light when the film thickness is decreased below 30 nm despite the fact that the optical absorptivity decreases.

Photochemistry on thin metal films: probe of electron dynamics in metal-semiconductor heterosystems.

The surface photochemistry of on ultrathin epitaxial Ag films on Si(100) substrates has been studied with the goal to employ it as a tool to unravel the electron dynamics in such films. An increase of the photodesorption cross section is observed--a factor of 5 for 266 nm light and 12 nm film thickness--when the film thickness is decreased, despite the fact that the optical absorbtivity decreases. The increased photodesorption cross section is interpreted to result from photon absorption in the Si substrate producing electrons at energies and parallel momenta which are not allowed in Ag.