THE INTERACTION OF OXYGEN WITH NB(110) AT 300, 80 AND 20 K

The adsorption of O-2 on Nb(110) at 300, 86 and 20 K has been studied using high-resolution electron energy loss spectroscopy (KREELS), low energy electron diffraction (LEED) and Auger electron spectroscopy (AE S). At 300 and SO K O-2 is dissociatively chemisorbed and thin Nb-oxid e (NbO+NbO2) layers are formed. At saturation, signature of Nb2O5 isla nds on top of NbO and NbO2 layers have been found. At 20 K and low exp osures (<2 L) oxygen is dissociatively adsorbed and Nb oxide layers gr ow on the surface. The oxidation features of Nb(110) at 20 K are very similar to those found at 80 and 300 K. But, after forming protective oxide layers on the surface, the O-2 molecules are physisorbed. The fr equency of the O-O stretching vibration of physisorbed O-2 is 193 meV, which is close to the Raman frequency of O-2 molecules in the gas pha se.