Scanning reflection electron microscopy and associated techniques for surface studies

A variety of signals generated by electron beam/specimen interactions has been utilized to give structural, topographical and chemical information about the sample of interest. Each technique has its unique advantages and disadvantages, but the combination of different techniques can give more and more reliable results. Monotomic surface steps and surface dislocations have been imaged with high contrast in scanning reflection electron microscopy (SREM) images. With the use of dynamic focusing compensation SREM images can be kept in focus over a large field of view. Surface step structures have been examined by collecting secondary electrons with an image resolution approaching the probe size used in dedicated scanning transmission electron microscopy (STEM) instruments. Auger electrons, carrying chemical information, have been used to form images of surface steps and small particles deposited on oxide substrates. Nanometer-resolution Auger electron images have been obtained in our UHV STEM instrument and small metal clusters containing as few as 15 atoms have been detected in Auger peak images. The combination of various imaging, diffraction and analytical techniques has proved very powerful for characterizing surface structures with high spatial resolution and chemical sensitivity.