Electron Transport and Photoemission Studies of Amorphous CaAl Thin Films

Amorphous alloys of the binary system CaAl are known to have highly unusual electron transport properties with resistivities up to 450μΣcm and a Hall coefficient that deviates from free electron values at Ca concentrations higher than 45 atomic percent. For amorphous CaMg alloys, on the other hand, the resistivity is very much less and this great difference between the two sets of alloys is not fully understood.We report on the correlation of photoemission and transport measurements made on two sets of amorphous CaAl and CaMg alloys prepared by magnetron sputtering in such a way that we could carry out both sets of measurements within the same UHV system. A special feature of the measurements was that the electrical resistivity was also measured in-situ using a specially designed 4-point probe to check for amorphicity and to compare with transport experiments carried out elsewhere.Photoemission studies were carried out in the energy range 15–50 eV with tuneable synchrotron radiation enabling us to examine the Ca 3p-3d photoemission resonance in detail. The main result from the present series of experiments was that whereas in the CaAl alloys the Fermi edge developed a shoulder at high concentrations of Al, this feature was completely absent in CaMg. At the same time the intensity of the Ca 3p-3d photoemission resonance revealed the presence of d-states in both sets of alloys, indicating that the presence of these dstates cannot, by itself, explain the high resistivity of CaAl.