VARIATION OF THE DC-RESISTANCE OF SMOOTH AND ATOMICALLY ROUGH SILVER FILMS DURING EXPOSURE TO C2H6 AND C2H4

Adsorption of C2H4 and C2H6 on smooth silver films increases the DC resistivity R in a way which correlates with the adsorbate induced density of states at the Fermi energy epsilon(F). The strongest increase in the film resistivity is observed after formation of atomic scale roughness by submonolayer quantities of cold-deposited silver. In good agreement with theory we find that the DC cross section of a silver adatom on smooth silver is about 14 angstrom2. When atomically roughened films are gradually exposed to C2H4, R decreases first and eventually increases, as observed for smooth films. The decrease of R is explained by a decrease of the Ag adatom induced density of states at epsilon(F) by adatom-C2H4-bonding via the pi* orbital of C2H4 and the adatom 5s-resonance. The initial relatively strong increase of R of an atomically roughened silver film by adsorption of C2H6 is explained by counteracting the smoothening of the surface profile by the electrons (Smoluchowski effect), because electrons at epsilon(F) can hardly penetrate C2H6.