MODIFICATION OF THE ELECTRICAL-RESISTANCE OF THIN COBALT FILMS UPON THE ADSORPTION OF CARBON-MONOXIDE

Thin films of pure Co with thicknesses ranging between 10 and 50 nm we re produced in UHV conditions. The films were deposited onto mica subs trates with dimensions of 1 cm x 1 cm x 0.1 cm. Thin gold wires were a ttached to the ends of the films in order to monitor their electrical resistivity. The films were introduced into a UHV chamber which consis ts of a quadrupole mass spectrometer and an Ar-sputtering gun for clea ning. The films were exposed to 10(-6) torr of high-purity CO and the resistivity of the films was monitored during exposure. The resistivit y changed in a ''sawtooth'' fashion similar to the changes observed by Pick in the Nb/H-2 system. The aim of these studies is to correlate c hanges in resistivity of the film with well-characterized adsorption s tates of CO on the Co surface. Carbon monoxide desorption from the cob alt films was studied (using a mass spectrometric method in an ultrahi gh vacuum system) and two carbon monoxide desorption peaks were observ ed identical to prior work using Co foils. These two states correspond to molecular CO and presumably dissociated CO. Changes in resistivity of the thin Co films appear to be related only to the molecular CO ad sorbed on the Co surface.