Increasing Resolution and Versatility in Low Temperature Conventional and Field Emission Scanning Electron Microscopy

Studies were undertaken to expand the versatility and the resolution of low temperature conventional and field emission scanning electron microscopy (SEM). The results indicated that simple modified specimen holders, which could be used in conjunction with the commercial cryosystems, allowed one to store specimens for several weeks in liquid nitrogen, either before or after observation in a conventional SEM, without incurring degradation of the surface features. Other modified holders permitted one to move the specimen closer to the final lens or to use the upper secondary electron detector, which is available with some SEMs. Both of these procedures increased the resolution that was attainable with the standard holders. In conventional SEM (CSEM) and field emission SEM (FESEM), holders were also modified to allow one to obtain complementary images of fractured specimens. When a conventional vacuum evaporator equipped with a freeze-etch module was used in conjunction with these holders, specimens could be fractured, etched, shadowed with platinum and coated with carbon before the sample was transferred to the cryostage in the SEM. This procedure increased resolution beyond that obtained with the sputter units in two commercial cryosystems that were used on a CSEM and a FESEM, provided membrane particle resolution in the FESEM and produced a coating or replica that could be recovered and examined in a TEM. These results, which demonstrated how resolution of cryospecimens can be enhanced in CSEM and FESEM, indicated that coating specimens in a high vacuum evaporator provided an alternative procedure that could be used to obtain high resolution images in a FESEM