Evidence for Direct Optical Interband Transitions in Isochromat Spectra from Pt Single-Crystal Surfaces

Bremsstrahlung isochromat spectra at $\hslash \omega \cong 9.7$ eV were recorded from well characterized, clean Pt(111), Pt(100)1×1, and Pt(210) surfaces. These spectra show intense emission peaks at the Fermi level as well as smaller peaks whose positions and intensities vary with the orientation of the substrate and the angular range of the incident electrons. The large peaks at the Fermi level are due to the high density of unoccupied $5d$ states. The orientation-dependent peaks are assigned to direct optical interband transitions between unoccupied states.