Reflection of light from gas adsorbed thin metallic films and their electrical resistance

Abstract

The effects of chemisorption on the visible and near infrared light reflected from evaporated Ag films are discussed on the basis of the Maxwell equations. To calculate a surface electric current generated by the electric field of incident electromagnetic wave, the Fuchs form specularity parameter derived by Greene in the Boltzmann-Fuchs transport equation is evaluated from the scattering probabilities of the conduction electrons at the surface. The specularity parameter determines simultaneously the electrical resistance of the films. The metal surface is approximated by the jellium model with a step surface potential barrier and standing wave functions of the conduction electrons. Scattering potentials of neutral adatoms are assumed to be V(r) = (− z ∗e 2 r ) exp(− 2r r 0 ) , where z ∗ and r 0 are determined by Slater's rule. It is found that O, N and C chemisorbed on Ag films of 200 A thickness produce relative decreases, ΔR f R f = (2–3) × 10 −4 in the reflectance for the coverage, 0.4 × 10 15 atoms cm 2 . The changes are comparable with those produced by the adsorbed layers estimated by the Fresnel reflection coefficient. Relative increase of resistance ΔR R of the film is found to be 2.0–2.5%.