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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Thermionic emission produces a flow of charged particles (electrons or ions) from a heated surface or over a hot potential-energy barrier. This emission process occurs because the thermal energy provided to the charged particles overcomes the binding potential (work function) of the materials (e.g. metals) or liquids. The emitted electrons or ions have especially been applied in electron microscopes (EMs), X-ray tubes, and focused ion beam (FIB) systems.