INTERFACE EXAFS USING GLANCING ANGLES

Abstract

The use of glancing angles t o o btain EXAFS signals from thin interfacial regions is described. The technique is applicable t o the case of a light overlayer on a heavy substrate for which total external reflection can be caused to occur at the interface. In t his case the p enetration into the substrate is very small (520-30 A in many cases). Data have been obtained on two systems: A1 on Cu and Ag on Au. The A1 on Cu samples had 1000 A of A1 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 CuAIZ at the interface is observed. The interface sensitivity was then verified by varying the glancing angle to determine the CuA12 layer thickness. Even for CuA12 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. Understanding the structure of solid state interfaces is important for studies of solid state reactions, t hin film adhesion and stability. Traditional probes such as Auger sputter p rofiling and Rutherford backscattering can provide compositional information but no detailed structural information, and for buried interfaces often have only limited depth resolution. For single crystal interfaces electron microscopy can provide beautiful images, but sample preparation can be tedious and many systems involve polycrystalline or amorphous interfaces. In this paper the applications of glancing angle x-rays to the study of buried interfaces are discussed with particular emphasis on interface extended x-ray absorption fine s tructure (ExAFS) measurements.