Scanning Electron Microscopy

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Biological Samples •Biological samples are not conductive and are particularly vulnerable to beam damage and other heating effects when examined in an <strong>Electron</strong> Microscope. •The level of exposure is referred to as ‘<strong>Electron</strong> Dose’ and is a measure of the number of electrons per unit area (e/nm 2 ). •Samples are either stained with conductive materials (e.g. OsO 4 ) or coated with Au or C. •Samples are viewed under vacuum, so they are dried to remove all water. a) b) •a) SEM image of Pneumonia, and b) SEM image of Diatom (Pictures from University of Iowa) •Preparing the samples ‘fixes’, and alters them – need a way to look at samples whilst they are still ‘wet’. Analytical Workshop 2012
Variable Pressure SEM •Localised charging is removed by the presence of gas in the sample chamber, effectively allowing the examination of non conductive samples •In Low vacuum mode the chamber is isolated from the high vacuum system(A) and is instead pumped by the additional rotary pump system(B). Analytical Workshop 2012
Page 1 and 2: Scanning Electron Microscopy Field
Page 3 and 4: Improving Resolution • Firstly, t
Page 5 and 6: Layout of a Generic SEM Gun 1 Apert
Page 7 and 8: Thermionic Gun Filament Wehnelt cyl
Page 9 and 10: Comparison of Sources •W filament
Page 11 and 12: Scanning the Beam\Beam Interactions
Page 13: Signal Detection • The Everhard -
Page 17 and 18: Compositional Analysis - Back Scatt
Page 19 and 20: BackScattered Imaging • Back scat
Page 21 and 22: Examples Images Imaged using ET Det
Page 23: Conclusions •Scanning Electron Mi

Scanning Electron Microscopy

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