This dissertation is an account of the design and construction of an instrument which combines scanning and conventional transmission electron microscopy in a single column. The microscope incorporates a lanthanum hexaboride electron gun working at voltages up to 100kV, and was designed to be capable of examining the same specimen feature in either the scanning or the conventional transmission mode of operation, with a resolution of 10Å or better without realinement or adjustment of the specimen. A three lens electron optical column has been added to the projector lenses of an AEI EM6 electron microscope. All lenses were designed with the aid of Munro's finite element computer programs. Particular attention was paid to the objective lens, which is of the Riecke-Ruska saturating condenser objective type. Computations of the first order optical properties and the third order aberration coefficients were undertaken and are presented here in such a way as to enable the effects of changes in all the important design variables to be determined. The probe-forming properties of condenser objectives, including the limitations to field width arising from their off-axis aberrations, are considered and predictions made of the capabilities of the chosen design. Attention is paid to the particular problem of column layout in a microscope where the illumination and imaging optics are not independent. The difficulties of machining electron lenses with very small polepiece bores to high accuracy are examined and a method described which is capable of polishing 2mm bores to a roundness of 0.2 microns using simple apparatus. A quantitative theory of stigmator correction has been developed. Micrographic evidence is presented to show that the microscope is capable of a resolving power of 10Å in CTEM and of forming 10Å diameter STEM probes. The limitations to performance and possible improvements to the instrument are discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:596505 |
| Date | January 1979 |
| Creators | Beaumont, S. P. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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