Excited band densities, surface resonances, and overlayer Umklapp processes observed in secondary electron emission from Ir(111) and Ir(111)(2�1)O surfaces

Abstract

The Ir(111) surface shows well-defined structural features in the angle-resolved low energy secondary electron spectrum, and the angular dispersions of these features have been measured for the three principal azimuths. The spectra are interpreted principally as emission from excited bulk bands; the correlation with calculations by Noffke and Fritsche [10] is excellent. Features in the symmetric ΓLW azimuth can be interpreted simply in terms of densities of states, but in the asymmetric pair of azimuths ΓLU, ΓLK there are substantial asymmetries in the secondary electron spectra although the densities of states are symmetric; it is proposed that the asymmetry is due to group velocity effects. Some additional features are interpreted as surface resonances. The Ir(111)(2×1)O surface shows additional low energy features which are interpreted as surface Umklapp of bulk state emission and as folding back of a surface resonance at the new surface zone boundary.