Quantitative method of assessing the nature of local order from HREM images for SRO on crystalline sublattices

• Published in: Ultramicroscopy Vol. 52; no. 3; pp. 415 - 420
• Main Authors: Hytch, M.J., Chevalier, J.-P.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.12.1993; Elsevier Science
• Subjects: Electron, positron and ion microscopes, electron diffractometers and related techniques; Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Physics; Scanning probe microscopes, components, and techniques; High resolution; Crystals; Sublattices; Mullite; Short-range order; Experimental study; Electron microscopy
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/0304-3991(93)90055-3

We examine high resolution electron microscope (HREM) images of a silicon mullite using a quantitative technique of analysis previously proposed. The aim is to determine the nature of the short range order (SRO) of the oxygen atoms. The digitised images are Fourier-transformed and two images are reconstructed with masks which include areas of reciprocal space related by the symmetry of the assumed superstructure. We call these “pseudo-dark-field” images. These two images are cross-correlated, and we discuss how the value of the cross-correlation coefficient can be used as an objective criterion for assessing the information content of the image and the extent of the spatial localisation of the SRO. For the case studied, a high degree of correlation is obtained which is shown to be significant compared to that expected from random noise. We interpret this in terms of the structural models and discuss whether a microdomain-type model can be justified.