Compositional analysis based on electron holography and a chemically sensitive reflection

A method for compositional analysis of low-dimensional heterostructures is presented. The suggested procedure is based on electron holography and the exploitation of the chemically sensitive (0 0 2) reflection. We apply an of f-axis imaging condition with the (0 0 2) beam strongly excited and centere d on the optic axis. The first side band of the hologram is centered using an "empty" reference hologram obtained for a hole of the specimen. From the centered side band we use the phase of the central (0 0 0) and the amplitu de of the (0 0 2) reflections to evaluate the local composition and the loc al specimen thickness in an iterative and self-consistent way. Delocalizati on effects that lead to a shift of the spatial information of (0 0 0) and ( 0 0 2) reflections are taken into account. The application of the procedure is demonstrated with an AlAs/GaAs(0 0 1) superlattice with a period of 5 n m. The concentration profiles obtained are discussed in relation to segrega tion. The measured segregation efficiency is R = 0.51 +/- 0.02. (C) 2001 El sevier Science B.V. All rights reserved.