L-Shell Soft-X-Ray Appearance-Potential Spectra of the3dTransition Metals

We have obtained $L$-Shell appearance-potential spectra for clean surfaces of the $3d$ transition metals: Sc, Ti, V, Cr, Mn, Fe, Co, and Ni. Spin-orbit splittings determined from these spectra are in excellent agreement with tabulated x-ray values. In all cases, however, the absolute binding energies are lower than the tabulated values, presumably as a result of the reduced coordination for surface atoms. The $\frac{L_3}{L_2}$ intensity ratios show a systematic variation with $Z$, approaching the expected statistical weighting of 2 only for a nearly empty (Sc) or nearly filled (Co and Ni) $3d$ band. It is less than 2 for all intermediate $Z\text{'}\mathrm{s}$ with a minimum value of approximately 1 at Cr. The $L_3$, $L_2$ peak widths decrease with $Z$ corresponding to the filling of the $3d$ band. The $L_1$ width, which is determined primarily by Auger lifetime broadening rather than the density of conduction-band states, exhibits a systematic decrease for $Z>\mathrm{}24\mathrm{}$ in contrast to theoretical predictions.