Scientific Highlight 1

A comparison between theory and experiment for the KL$_{23}$V Auger spectra of Na/Al(111). For such a system, the different Na adsorption geometries, on changing the adatom fractional coverage and the substrate growth temperature, are known.

Panel (a): The Na (√3×√3) R30º phase (1/3 ML). Calculated (solid line) and measured (red circles) KL$_{23}$V Auger profiles. The calculated curve, normalized to the experimental data, is obtained convolving the Auger rate with a Lorentzian with half width equal to 0.42 eV for the core hole lifetime and a Gaussian for nominal instrumental broadening. The measured one is shown after background subtraction. Panel (b): the Na 2×2 phase (1/2 ML). Calculated (solid line) and measured (blue circles) KL$_{23}$V Auger profiles. The calculated curve is obtained as in panel(a), but summing the contributions from the two inequivalent Na atoms.

The experimental and theoretical KL$_{23}$V spectra show a remarkable agreement. For the 1/3 ML, in panel a), both theoretical and experimental spectra display a main feature of the same shape and intensity. On the other hand, to fit the experiments for the 1/2 ML phase, it is necessary to sum up the contributions of the two theoretical spectra obtained from the inner and outer inequivalent Na atoms. The best fit was obtained by shifting the Auger spectrum of the outer atom by -0.5 eV, and assigning a weight of 3/8 to the outer Na atom signal and 5/8 to the inner one. The weight ratio between the two Na components is in agreement with the analysis of the relative height of the XPS signal. It is interesting to note that this result suggests a different population for the Na atoms in the two inequivalent sites.(after M. I. Trioni, S. Caravati, G. P. Brivio, L. Floreano, F. Bruno, and A. Morgante , Physical Review Letters 93, 206802 (2004)