High-resolution electron microscopy of quasi-amorphous materials

Abstract

Conventional methods of interpretation of HREM images rely on structure modeling followed by image simulation. These methods are inapplicable to the interpretation of micrographs of amorphous materials because the atomic structure is unknown a-priori. Previous experimental work by the present authors had indicated that the cross-correlation of intensity fields of different regions of an HREM micrograph can identify regions of structural order in an apparently random matrix. The present paper confirms this initial result by reporting results of cross-correlations on computer-simulated HREM images. The images were generated from a “multislice” calculation of electron-wavefront propagation through a composite material consisting of a Si crystallite affixed to a relatively thick amorphous Si substrate. The cross-correlation technique is shown to be capable of retrieving the c-Si region where the simulated HREM images reveal to evidence of the crystallite. There is an optimum microscope defocus for which retrieval of the ordered structure is most efficacious. The cross-correlation technique is found to be superior to conventional Fourier filtering for identifying regions of atomic order.