Formation of an ordered oxide on the CoGa(1 0 0) surface by room temperature oxidation and annealing
The preparation of an ordered Ga 2O 3 oxide on the CoGa(1 0 0) surface by exposing the surface to oxygen at room temperature and subsequent annealing has been studied by thermal energy helium atom scattering and Auger electron spectroscopy. During room temperature oxidation a disordered Ga 2O 3 layer forms. The oxidation process is studied with He scattering and the results are compared with previously reported scanning tunneling microscopy investigations. Upon annealing, it is found that ordering of the oxide layer proceeds very slowly. Even at a temperature of 800 K, 50 K below the temperature at which the oxide decomposes and disappears from the surface, the ordering process is not yet completed after 1000 s. It is concluded that a smooth oxide film can be prepared by room temperature exposure to oxygen and annealing at temperatures just below decomposition temperature of the oxide (850 K) which is very uniform with respect to thickness. However, the amount of oxygen adsorbing at 300 K is not sufficient to produce a continuous film. About 10-15% of the surface is not covered by the oxide after this preparation method. To prepare a continuous oxide layer several cycles of room temperature oxidation and annealing seem necessary.