SURFACE-PLASMONS IN NIGA AND COGA ALLOYS

Electron energy losses at the surface of Ga, NiGa and CoGa have been s tudied by X-ray photoemission spectroscopy (XPS). These features are i nterpreted as being due to surface plasmons. For Ga metal the experime ntal result is in good agreement with the surface plasmon energy obtai ned by a free-electron model. At the surface of Coca and NiCa alloys, the corresponding energy is about 1 eV higher than that of pure Ga met al. This result is discussed in the framework of a free-electron model as well.