ELS and SES studies on clean and hydrogen-covered Cr(110) surfaces

The clean and hydrogen-covered Cr(110) surfaces have been investigated at 300 K by electron energy-loss spectroscopy (ELS) and secondary-electron emission spectroscopy (SES) (primary energy: Ep = 60−300 eV) with the in-situ combined supplementary techniques. The clean surface SES spectrum has peaks at 7.3, 9.2, 11.4, 13.2, 15.2, 17.6 and 20.6 eV above the Fermi level, which are thought to correspond to maxima in the unoccupied density of states. Only the 11.4 and 15.2 eV peak intensities are strongly reduced by irreversibe hydrogen adsorption. The clean surface ELS spectrum is characterized by peaks at 2, 3.5, 5.5, ∼ 10, 23, 35, 42, 48 and 55 eV. The ELS spectrum is interpreted by comparison with the optical data, the band calculation and the SES results. The 2 and 3.5 eV loss peaks are attributed to the interband transitions between d bands, and the 5.5 and ∼: 10 eV peaks to those associated with sp-like bands. By hydrogen adsorption, the damping and blurring of only the 5.5 and ∼: 10 eV peaks were observed, and a hydrogen-induced peak was found at ∼: 16 eV. These results are considered to indicate that the CrH bonding occurs mainly via sp bands; the role of d bands, however, cannot be neglected. Hydrogen-exposure dependence of the ELS spectrum is found to be practically independent of primary energy, in contrast to the Ni(100)H2 system, indicating that hydrogen is rapidly penetrated into the Cr selvedge lattice.