Temperature dependence of the soft x-ray emission edges of simple metals

The widths and energy positions of the $M_{2,3}$-emission edge of potassium, $K$-emission edge of beryllium, and $L_{2,3}$-emission edges of aluminum and magnesium have been measured for temperatures between 80 and 600 °K. All band edges broaden ($\Delta \Gamma$) and shift in energy ($\Delta E$) with increasing temperatures for these materials. Similar results were reported earlier for the Li $K$-emission edge and Na $L_{2,3}$ edge. Lattice-relaxation processes and the phonon core-hole interaction are the dominant mechanisms affecting the core-level widths and the experimentally observed edge widths. The edge shifts are found to be proportional to the thermal expansion of the lattice, and are discussed in terms of the electron energy-level shifts which occur as the lattice dilates.