Abstract
Usually the quality of the vacuum in electron microscopes is insufficient to allow meaningful observations on surface structure to be made except in the case of a few specially favorable types of specimen. However increasingly sophisticated instruments for observing specimens prepared and maintained in ultra-high vacuum environments are appearing and possibilities are being demonstrated for the study of the structure of surfaces and the progress of surface reactions with near-atomic resolution. High resolution transmission electron microscopes can reveal atom-high surface steps in some cases. By use of the profile imaging method the arrangements of surface atoms can be viewed with resolutions of 2Å or better and rearrangements or chemical changes of surface structure can be recorded at TV rates. Reflection electron microscopy from surfaces of bulk crystals has revealed surface details of large areas with resolutions of 10Å or better. By application of the scanning transmission instruments similar imaging modes may be combined with microdiffraction and microanalysis of regions 10Å or less in diameter.
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