PLASMONS IN AMORPHOUS CAAL ALLOYS DETERMINED FROM PHOTOEMISSION AND ELECTRON-ENERGY-LOSS SPECTROSCOPY

We have used electron spectroscopy to study amorphous CaAl alloys acro ss the entire composition range. Synchrotron radiation photoemission w as used to examine the region of the Al 2p core level, with the energy of plasmon loss features giving the electron density around the Al at oms, while energy loss spectroscopy excited by low energy electrons pr obed the average electron density in the alloys. The plasmon energy is found to vary continuously with composition. For alloys with low Ca c oncentrations (below similar to 20 at%) there is reasonable agreement with expectations for fi ee-electron-like plasmons with Ca and Al havi ng their elemental valencies. At higher Ca concentrations the Al plasm on energy is larger than expected. Although this would be consistent w ith an increased electron density in the vicinity of the Al atom, the plasmon energies ate affected because part of the oscillator strength of the electron gas is associated with one-electron excitations around the Ca atoms. We argue that there is little charge transfer in the al loys, a result which agrees with our studies of the Auger parameter.