The theory of the image formation in high-resolution transmission electron microscopes is summarized. Emphasis is placed on describing the phase state of electron waves at the formation of crystal structure images, on comparing with that of lattice images. A practical procedure for calculating high-resolution electron microscope images is given, relating directly to the theory of image formation.
The features of the high resolution STEM are discussed, and the advantages of the STEM over the CTEM are considered. Contamination problems in the STEM are discussed. The resolution of the STEM and visibility of single heavy atoms are considered. Images of platinum atoms are used to demonstrate the microscope's various output signals. Various STEM techniques and their application to biological macromolecules are shown. Particular attention is directed to STEM low dose imaging, unstained observation, optimal sampling, and digital image processing techniques.
The application of high voltage transmission electron microscopy is the most effective approach to the high resolution observation of crystal and molecular structures at atomic level when based on the many beam principle for image formation. The results should be interpreted in terms of theoretical images computer-simulated on the basis of, for instance, multislice calculation procedure to avoid the misinterpretations of false images. Some electron photomicrographs are reproduced to show molecular and crystal structures of organic compounds such as chlorinated copper phthalocyanine, metal-TCNQ complexes and DNA. For some compounds, the images were obtained by the use of minimum dose system to reduce the influence of radiation damage which has a certain effect on the ultimate resolution. The intrinsic necessity of high instrumental resolution is also discussed in view of the feasibility to determine the structures as accurate as possible.
The principle of electron energy loss spectroscopy (EELS) is discussed based on the dielectric function of solid specimen. Electron energy loss spectra in low (<50eV) and high energy loss regions (>50eV) are analysed for graphite and explained by its electronic band structure. Limitations of the spatial resolution and the detectable mass concentration by EELS in TEM are discussed from the point of view of local chemical analysis. The mapping techniques and images formed by characteristic energy losses of each element contained within the specimen are shown for some examples. In addition to EELS in TEM, other examples of EELS in SEM are shown for surface analysis of bulk specimen.
Surface micro-topographs and structures revealed by TEM and REM in UHV electron microscope of conventional optics are shown, confining the discussion to basic and methodological aspects of surface microscopy.