MICROANALYSIS AT ATOMIC-RESOLUTION

In this paper we discuss how the dedicated scanning transmission elect ron microscope can provide a microanalysis of crystalline materials at atomic resolution. The method requires the establishment of incoheren t conditions for a reference imaging signal as well as the spectroscop ic signal. The image can then be used to focus and locate the probe to atomic precision for microanalysis. The Z-contrast image provides the most convenient incoherent reference image, and X-ray and electron en ergy loss data may be acquired simultaneously. In zone axis crystals, strong columnar channelling delays the onset of beam broadening for se veral hundred Angstroms, so that atomic resolution microanalysis may b e achieved in materials specimens of significant thickness. This combi nation of signals provides a powerful means for studying interface str ucture and bonding, and avoids relying on preconceived model structure s.