This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, and managers.

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A change in spot size (probe current) changes the secondary electron to backscattered electron ratio, resulting Contrast changes. The emission of secondary electrons from a given spot size or probe current will remain relatively constant as the accelerating voltage changes. However as the accelerating voltage is increased the backscattered electron (BSE) influence increases, diminishing the contribution to the image from secondary electrons.