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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The M_4,5 edges in EELS presents the transitions of the 3d core electrons to the unoccupied states of p- and f-like symmetry. The sharp M₅ and M₄ peaks near the edge onsets originate from the quasiatomic, dipole-allowed transitions from an initial 3d¹⁰4fⁿ state to final 3d⁹4fⁿ⁺¹ states. These transitions mask the much weaker 3d → p edge. The M₅ and M₄ edges originate from the two ways that the spin quantum number, s, couples to the orbital angular momentum, l, giving the total angular momentum, j = l + s: This coupling induces two peaks that are M₅ from the 3d_5/2 (j = 5/2) level and M₄ from the 3d_3/2 (j = 3/2) level. In the lanthanides, the 4f electrons lie inside the 5s- and 5p-closed shells and so are well screened by them.