The selection of conditions for examination of specimens in a scanning electron microscope

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Abstract
SUMMARY: In the past not much attention has been paid to the use of the most desirable conditions for examining a particular kind of specimen in a scanning electron microscope (SEM). The various factors affecting resolution in the SEM, namely those of beam diameter, beam penetration, contrast, signal‐to‐noise ratio and depth of focus, are examined. It is not possible in practice to eliminate all detrimental effects and compromises have to be made in instrumental settings, such as gun potential, lens currents, etc. in order to obtain the best image for a given specimen. This paper deals with the problems involved in examining textile fibres, metal surfaces and thin films with particular emphasis being made on the choice of gun potential and the amount of image detail observed. Examples are shown comparing micrographs taken using gun potentials of 5 kV and 20 kV, showing that due to electron‐penetration effects much surface detail is lost at the high gun potential. It is, therefore, useful to examine specimens initially at different accelerating voltages to determine if any desirable information is being lost due to the penetration of the electron beam. Some operating conditions are also given for use as a guideline for working at low accelerating voltages.

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