Oxidation of Silver by Atomic Oxygen

Interaction of silver with atomic oxygen has been studied at low incident-flux conditions (1015–1017 atomsċcm−2sċ−1, corresponding to a pressure of about 10−7 Pa) over the temperature range of 373 to 673 K. The only product of surface oxidation observed for these conditions was silver (I) oxide Ag2O. The parabolic rate law was normally observed, and the parabolic constant increased linearly with the incident flux of oxygen atoms. The parabolic rate constant also shows an unusual temperature dependence. It increases with an activation energy of 33 kJ/mol between 423 and 523 K and reaches a maximum at about 573 K and then decreases until oxidation stops around 673 K. Thermodynamical analysis of chemical reactions between silver and atomic oxygen shows the possibility of a “recombinative reduction” of silver oxide to silver metal by atomic oxygen which offers an explanation of the unusual temperature dependence.