A combined experimental and theoretical approach to grain boundary structure and segregation

Recently, the scanning transmission electron microscope has become capable of forming electron probes of atomic dimensions. Through the technique of Z -contrast imaging, it is now possible to form atomic resolution images with high compositional sensitivity from which atomic column positions can be d irectly determined. An incoherent image of this nature also allows atomic r esolution chemical analysis to be performed, by locating the probe over par ticular columns or planes seen in the image while electron energy loss spec tra are collected. Such data represent either an ideal starting point for f irst-principles theoretical calculations or a test of theoretical predictio ns. We present several examples where theory and experiment together give a very complete and often surprising atomic scale view of complex materials. (C) 1999 Elsevier Science B.V. All rights reserved.