INTERFACE EXAFS USING GLANCING ANGLES

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 (similar to 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 degrees 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 inter-diffusion as a function of annealing. In particular the Au environment in Ag grain boundaries could be detected.