Practical Electron Microscopy and Database

The two strong L₃ and L₂ white lines originate from the transition of electrons from the spin-orbit split levels 2p_3/2 and 2p_1/2 to unoccupied 3d states. The L₃/L₂ ratio increases as the oxidation states of transition metals decrease and thus can be used to determine the oxidation states of cations, for instance, in 3d transition metal-oxides. As an example, Figure 4337 shows the EELS profiles of ramsdellite, pyrolusite, cryptomelane (for different valence states), bixbyite, and manganite materials. Various methods can be performed to understand the chemical properties of the elements in compounds, based on analysis of EELS white lines.

Figure 4337. The EELS profiles of ramsdellite, pyrolusite, different cryptomelane (synthesized
by different methods for different valence states), bixbyite, and manganite materials. The numbers
beside the spectrum give the valence states of each material. Adapted from [1].

Edges shift

Figure 4337 shows that the two Mn L_2,3-edges shift to higher energy loss range with the increase of oxidation state.

Width of the edge of the white lines depending on valence states

Figure 4337 shows that the Mn L₃-edge structure of Mn³⁺ compounds is narrower than the edges for the Mn⁴⁺ valence states.

Width of the edge of the white lines depending on material structure

Indicated in Figure 4337, unlike Mn³⁺ compounds, different structural types of MnO₂ (Mn⁴⁺ valence states) produce different widths of the Mn L₃ edge. The main L₃ peak from ramsdellite is apparently narrower than that of pyrolusite [2] because various arrangements of Mn octahedra give rise to different shapes of their EELS spectra [3].

Symmetry of the white line edge

Figure 4337 shows that the Mn L₃-edge structure of Mn³⁺ compounds is more symmetric than the edges for the Mn⁴⁺ valence states.

Energy difference between the two peaks of the white lines

The inset (A) in Figure 4337 shows the energy difference (ΔE(L₂-L₃)) between the two peaks of L_2,3-edges, corresponding to the different valence states and indicating a linear trend but with large errors as a result of the Coster-Kronig Auger decay effect on the broadening of Mn L₂ edges.

Intensity ratio of the two peaks of the white lines

The inset (B) in Figure 4337 shows the integrated Mn L_2,3 white-line intensity ratios, I(L₃)/I(L₂), as a function of the Mn valence state. The white-line intensities were integrated over 4 eV windows centered at the L_2,3 peak maxima.

[1] Shouliang Zhang, Kenneth J.T. Livi, Anne-Claire Gaillot, Alan T. Stone, and David R. Veblen, Determination of manganese valence states in (Mn³⁺, Mn⁴⁺) minerals by electron energy-loss spectroscopy, American Mineralogist, 95(11-12) 1741-1746.
[2] Garvie, L.A.J. and Craven, A.J. (1994) High-resolution parallel electron energyloss spectroscopy of Mn L_2,3-edges in inorganic manganese compounds. Physics and Chemistry of Minerals, 21, 191–206.
[3] Manceau, A., Gorshkov, A.I., and Drits, V.A. (1992) Structural chemistry of Mn, Fe, Co, and Ni in manganese hydrous oxides: Part I. Information from XANES spectroscopy. American Mineralogist, 77, 1133–1143.