Water adsorption on the (001) plane of Fe 2O 3: An XPS, UPS, Auger, and TPD study

Abstract

Thermal programmed desorption, ultraviolet photoelectron spectroscopy, and X-ray photoelectron spectroscopy have been used to study the reaction of H 2O with stoichiometric and partially reduced single crystals of α-Fe 2O 3. On the stoichiometric surface only ice condensation below 200 K was observed. Oxygen deficient surfaces were prepared by Ar bombardment giving rise to a decrease in the work function of the crystal of up to 1 eV. On these surfaces OH species were formed as detected by UPS that were stable up to 320 K. Annealing the defective surfaces between 475 and 700 K increased the work function by values between 0.5 and 0.7 eV respectively. These surfaces contained reduced Fe 2+ species in subsurface layers as shown by UPS and XPS, but were inactive towards H 2O chemisorption. The Fe 2+ species were stable for long periods of time at temperatures of up to 775 K. Potassium deposited on the surface forms a strongly bound monolayer compound. With H 2O it produced a complex that resulted in H 2 evolution upon annealing.