INTERFACE EXAFS USING GLANCING ANGLES

Abstract
The use of glancing angles to obtain EXAFS signals from thin interfacial regions is described. The technique is applicable to the case of a light overlayer on a heavy substrate for which total external reflection can be caused to occur at the interface. In this case the penetration into the substrate is very small (~20-30 A in many cases). Data have been obtained on two systems : Al on Cu and Ag on Au. The Al on Cu samples had 1000 A of Al on Cu and measurements were made on the interface structure as a function of annealing temperature. For anneals above 140°C clear indication of the growth of CuAl₂ at the interface is observed. The interface sensitivity was then verified by varying the glancing angle to determine the CuAl₂ layer thickness. Even for CuAl₂ layers as thin as 100 A, the EXAFS signal is essentially pure CuAl₂ with little contamination from the underlying Cu. For Ag on Au there is no compound formation and these techniques were used to look at interdiffusion as a function of annealing. In particular the Au environment in Ag grain boundaries could be detected.