Design and Application of a High Voltage Transmission Scanning Electron Microscope

Abstract

A transmission scanning electron microscope operating at voltages up to 600 kV has been built in this laboratory. Initial tests of the performance have been encouraging although the optimum performance has not yet been achieved. Developments and modifications of the instrument are now in progress in order to extend its range of applications and improve its output.The high voltage power supply and electron accelerator have been described previously. A combination of insulating oil and solid dielectric i s used to decrease leakage. This allows the high voltage unit to be compact, highly stable and inexpensive. It has proved to be reliable and trouble-free in operation.

Advances and Applications of Atomic-Resolution Scanning Transmission Electron Microscopy

“…The success of Crewe's new STEM and the progressive improvement of image resolution in conventional TEM, from crystal lattice imaging (Menter, 1956;Dowell, 1963;Komoda, 1966;Allpress et al, 1969) to structural imaging (Iijima, 1971;Cowley & Iijima, 1972;Allpress & Sanders, 1973), clearly galvanized the excitement for developing high-voltage, high-resolution electron microscopes. Cowley and Strojnik started designing and building a 600-kV transmission scanning electron microscope and reported the initial results of their effort (Cowley & Strojnik, 1968, 1969Cowley, 1970;Cowley et al, 1970). In designing this high-voltage STEM, they used two lenses to form a small electron probe and added deflection systems to manipulate scattered electrons in order to obtain decent electron diffraction patterns and to direct the scattered electrons into the electron spectrometer for EELS analysis.…”

“…If the scanning electron probe was stopped at any point of interest, a diffraction pattern, originating from a region with an area equal to the resolution limit of the STEM, would be recorded. In addition to investigating various STEM imaging modes, Cowley and colleagues studied the dependence of electron diffraction from crystalline samples on the defocus of the electron probe and discussed the origin of the fine structures in the observed convergent beam electron diffraction disks (Cowley et al, 1970;Smith & Cowley, 1971), similar to, but not exactly the same as, those reported for convergent beam electron diffraction (CBED) in conventional TEM (Cockayne et al, 1967). Cowley reported that the nature of the observed diffraction patterns depended on the aperture size of the probeforming lens and that the lens aberrations (e.g., spherical and chromatic aberrations) had an effect on the observed fine structures in the wide-angle CBED patterns.…”

“…When the electron beam was out-of-focus shadow images of the specimen within the wide-angle CBED disks appeared. It is interesting to note that Cowley and colleagues, based on the high-penetration power of high-energy electrons and the fact that, in an STEM, no imaging lenses were needed after the sample, proposed designs for conducting electron microscopy imaging and diffraction experiments on samples that could be exposed to air or other types of gases (Cowley et al, 1970). Cowley and Strojnik did not seem to consider the use of an FEG as the electron source.…”