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

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Boersch effect originates primarily from the interactions between the electrons in the tip region of the electron source. The deviation of the energy distribution of electrons emitted from the cathode in the source is in the format of Maxwell distribution due to the distribution broadening caused by a space-charge region in front of the cathode. Note that a large emitting area reduces this effect.