Soft x-ray emission spectroscopy and its application in dilute Al in MG and Lial alloys

A new soft x-ray emission spectrometer designed for use with photon excitation from synchrotron light sources is described and characterized. Special design features, including a close-spaced input slit, large toroidal gratings, and a two-dimensional charge-coupled-device, Si-array based detector system, provide measuring efficiency 10⁴ times greater than that of a conventional spectrometer in a 5-m Rowland circle design. Descriptions of the spectrometer's design and calibration procedures, and of the photon flux distribution through the beam line from the synchrotron light sources are emphasized.

Measurements of (1) the Mg double ionization L-satellite spectrum and the Al L_{2 , 3}spectra for dilute alloys of 0.5%, 1.0%, and 2.0% Al in Mg, and of (2) the Al L_{2 , 3} and Li K spectra for LiAl(50% - 50%) alloy have been made with greatly improved resolution. For dilute Al in Mg alloys, the spectra of the Mg satellite and of the Al impurity contain similar features associated with screening of the extra core hole, but are otherwise dissimilar. The threshold peak is broadended in both spectra. The L₃-L₁ intercore transition in doubly ionized Mg is observed. A second, weak, high energy satellite is observed that may be produced by transitions from the ¹S₀ state of the doubly ionized core levels.

For LiAl alloy, we have found extreme sensitivity of the spectral features for both Al L_{2 , 3} and Li K emission to the presence of pure Li on the surfaces. The reproducible spectra have been compared with p-partial density of state (PDOS) for Li K emission and with (s + d)-PDOS for A1 L_{2 , 3} emission calculated by Asada et al. The match of A1 L_{2 , 3} with theoretical results is good except a broad bump centered at -2.5 eV from Fermi edge which shows the features of p-PDOS. It may imply a breakdown of the selection rules for a disordered alloy system. The fit between Li K spectrum and p-PDOS is poorer than for Al L spectrum. We attribute this effect to a strong transition matrix element effect on a PDOS calculation.