Extended energy-loss fine structure analysis of 3d transition metals using L ionization edges

The extended energy-loss fine structure (EXELFS) in electron-energy-loss spectroscopy has been compared experimentally with the extended X-ray absorption fine structure (EXAFS), for determining local structure around 3d transition metals. Since the EXELFS spectrum is acquired in an analytical transmission electron microscope, the probing beam can be focused to offer a lateral spatial resolution in the nanometre range, which is several orders of magnitude better than that of X-rays. Also, the microscope allows the area of interest to be imaged and analysed by other methods. However, difficulties in the analysis of EXELFS of 3d transition metals arise from the overlap of the edges in the accessible L series. EXELFS of L ionization edges of crystalline Ni and Cu were examined as test specimens. The overlapped L₁,L₂ and L₃ edges were separated and compared with the K-edge EXAFS of the same samples. The first- and second-nearest-neighbour distances from EXELFS are in agreement with those measured from EXAFS and X-ray diffraction. As a structural probe, however, the accuracy of quantitative analysis of EXAFS is still superior since the L-edge EXELFS decays more rapidly than K-edge EXAFS.