Spin-dependent on-site electron correlations and localization in itinerant ferromagnets

Spin selectivity in angle-resolved Auger photoelectron coincidence spectroscopy (AR-APECS) is used to probe electron correlation in ferromagnetic thin films. In particular, exploiting the AR-APECS capability to discriminate Auger electron emission events characterized by valence hole pairs created either in the high or in the low total spin state, a strong correlation effect in the Fe M(2,3)VV Auger line shape (measured in coincidence with the Fe 3p photoelectrons) of Fe/Cu(001) thin films is detected and ascribed to interactions within the majority spin subband. Such an assignment follows from a close comparison of the experimental AR-APECS line shapes with the predictions of a model based on spin polarized density functional theory and the Cini-Sawatzky approach.

Electron-induced interaction of selected hydrocarbons with TiO2 surfaces: the relevance to extreme ultraviolet lithography

The aim of this work is to characterize desorption induced by electronic transition processes that affect the reflectivity of TiO2-capped multilayer mirrors used in extreme ultraviolet (EUV) lithography. A low energy electron beam is employed to mimic excitations initiated by EUV radiation. Temperature programmed desorption, x-ray photoelectron spectroscopy, and low energy ion scattering are used to analyze the surface reactions. Carbon film growth on the TiO2(011) crystalline surface is measured during 10-100 eV electron bombardment in benzene or methyl methacrylate vapor over a wide range of pressures and temperatures near 300 K. Low energy secondary electrons excited by EUV photons contribute substantially to the carbon accumulation on clean TiO2 cap layers. For benzene on clean TiO2, secondary electron effects dominate in the initial stages of carbon accumulation, whereas for C-covered TiO2, direct excitations appear to dominate. We report on the adsorption energy, the steady-state coverage of the molecules on the surface and the cross sections for electron-stimulated dissociation: all key parameters for understanding and modeling the processes relating to the EUV lithography mirrors.

Direct evidence for dynamic broadening of the energy spectra associated with the later steps of an Auger cascade

Auger cascade decay processes are of critical importance in x-ray-induced biological damage, chemical reactions, and desorption. Here, we report the first measurements of the isolated energy spectra of electrons emitted during the later steps of an Auger cascade process in a solid (MnO). The large widths and energy gains observed in cascade-induced Mn MVV Auger spectra (as compared to the spectra resulting from direct photoexcitation of the M core hole) provide strong evidence that valence holes created in previous cascade steps participate dynamically in later cascade steps.

Giant Coster-Kronig transitions and intrinsic line shapes of the anomalous Pd M45VV Auger spectrum of Pd/Ag(100) dilute surface alloys

The Pd M4VV and M5VV Auger spectra of the 0.1 ML Pd/Ag(100) dilute surface alloy have been measured using Auger-photoelectron coincidence spectroscopy. The M4VV spectrum indicates that Pd 3d(3/2) core holes have a Coster-Kronig decay rate that is approximately 10 times that of Pd metal. Our calculations show that this giant enhancement arises from the local electronic structure of excited Pd atoms at the surface. Anomalous features in the Auger line shape are similar to those seen in dilute bulk PdAg alloys, and these features in the M5VV and M4VV lines are in good agreement with theoretical predictions.