Two-hole Final State Research Articles

Shapes and shifts in the oxygen Auger spectra

The oxidation of silicon and platinum single crystal faces, of polycrystalline supported catalysts and of some alloy surfaces has been studied by AES and as far as possible by LEED. A comparison of the oxygen Auger spectra obtained during the oxidation process with those found on oxides has been made; it shows that the modification of the fine structure of the oxygen Auger peaks gives some information about the binding state of oxygen. Two different structures, which compete one with the other, are described. In one case, a spectrum where three lines dominate is obtained; in the other case, a “quasi-atomic” spectrum characterized by five features is observed: multiplet splitting in the two-hole final state is predominant. Besides these differences in the fine structure of the Auger spectra one can notice shifts of several eV for the main feature. They have been correlated with the various observed LEED patterns. Physisorption, chemisorption, solution of oxygen in the metal lattice, growth of ordered or amorphous oxides are the different possibilities which are discussed.

Electronic properties of adsorbed layers of nitrogen, oxygen, and sulfur on silver (111)

We have studied ordered layers of nitrogen, oxygen, and sulfur adsorbed on an Ag (111) surface. Ultraviolet photoemission spectra (UPS) imply that each of these adsorbates induces a set of virtual levels above the $d$ band of silver, at about 3.4-eV binding energy, and below the $d$ band at about 8-eV binding energy. X-ray photoemission spectra show that the $1s$ binding energies of the nitrogen and oxygen layers are 397.9 and 530.4 eV, respectively, and that the $2p$ binding energy in the sulfur layer is 161.8 eV. Auger spectra excited by each of these core holes may be interpreted as arising from transitions involving electronic states measured in the above UPS experiments. Good agreement with most features of the experimental Auger spectra has been obtained using measured and calculated data for the surface electronic binding energies. The results show that the difference between the hole-hole repulsion and excess relaxation energies in the Auger final state are small. This evidence points to the formation of a silver-adsorbate surface layer in which the UPS observed electronic states have a high local density of states at the adsorbate atom cores and in which the two-hole Auger final states considered are delocalized.

L2,3MM Auger processes in selenium

The complete L2MM and L2MM Auger spectra of selenium have been observed using an X-ray photoelectron spectrometer. The relative energies of all components are shown to be in agreement with calculations which use the binding energies of core levels and tables of atomic integrals, intermediate coupling being assumed for the two-hole final states. The total relaxation accompanying LMM Auger processes in solid Se is independent of the two-hole final state and has been found to be 23.8+or-2.0 eV. This includes a total atomic contribution estimated as 14.6+or-1.0 eV of which 7.4+or-0.2 eV arises from relaxation in the outer shell. The contribution from intra shell relaxation is deduced to be 7.2+or-1.2 eV and from extra-atomic processes as 9.2+or-3.0 eV. This analysis of the relaxation is supported by measurement of an Auger line from the L3MN series.