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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Fine structures in an EEL spectrum originate from the transition from a core level to unoccupied states under the dipole selection rule. For instance, for 3d transition metals and their alloys, L_2,3 edges of EELS are characterized by two sharp peaks, called “white lines”. These white lines are induced by the excitations of 2p_1/2 and 2p_3/2 core electrons to unoccupied d-like states near the Fermi level (dipole transitions).