M. Erbudak

Segregation kinetics of Ag on a (100) surface of Al-3at%Ag

Abstract Surface segregation of Ag on a (100) surface of Al-3at%Ag at temperatures below the metastable miscibility gap of the bulk is determined as a function of time by means of Auger electron spectroscopy. An activation energy of 106 ± 13 kJ/mol is deduced from the data. This value agrees with results for bulk diffusion. This shows the capability of a surface tool in determining bulk properties of a metal.

Electron spin polarization in uranium sulfide

Abstract We present spin polarization and energy distribution curves of photo-electrons from US and compare them with a density of states calculation based on a cluster method. For photon energies hv ≤ 11 eV the photo-electron spin polarization is negative. Near threshold a structure is observed in the spectra, which is attributed to emission from the 5f-states.

Secondary-electron and energy-loss spectra of copper

Abstract The spectra of secondary electrons from copper show structure up to a kinetic energy of 300 eV, analogous to features observed in electron energy loss spectroscopy. We report EELS and SE data, up to 300 eV, obtained for a Cu(100) surface in order to show that they both are closely related to the unoccupied DOS. Features in SE spectra originate mostly from the emission channels out of the 3d and 3p levels, and those of EELS up to the threshold of 3p excitation energy stem from the transitions out of the 3d bands. This is well-reproduced by real-space multiple-scattering calculations of unoccupied density of states for different angular momentum components. The success of the interpretation confirms that the density of states dictates the observed features.

Imaging of surfaces by means of secondary electrons

Secondary electrons emitted from crystal surfaces show a strong enhancement of intensity along directions defined by atomic rows. The gross features of such patterns are formed by the projection of surface layers illuminated by an internal source of electrons. The patterns reveal crystallographic directions and planes at atomic resolution. While the strongly forward-peaked electron-atom scattering is responsible for the observed symmetry, these secondary electron diffraction (SED) patterns also contain features due to Bragg-like diffraction at interatomic planes.

Surface composition of Ni-10at%A1(111) in thermodynamic equilibrium

Abstract Ion-scattering spectroscopy using 1000 eV He ions was applied to determine the equilibrium concentration at the (111) surface of Ni-10at%Al. Special care was taken to eliminate the falsification of the results by sulfur segregation as well as by the effects of sputtering. A technique for rapid determination of the surface concentrations is presented. It was found that the surface has to be annealed at 800°C or higher to reach the equilibrium with 25 at% Al. The surface composition remains unchanged if the temperature is subsequently varied between 700°C and 1000°C.

Angular anisotropy in secondary-electron production and emission from Cu(001) and the reciprocity theorem

Abstract Angular-resolved inelastic electron scattering experiments at 2 keV are reported for a Cu(0 0 1) surface. In the observations, effects of incoming-beam and emitted-beam diffraction could unambiguously be separated. The results show quantitatively that the reciprocity theorem is valid for energy-loss processes.

Secondary-electron imaging of disordered submonolayers

Abstract Secondary-electron imaging (SEI), which allows real-time imaging of near-surface structures in real space, is applied to a (111) surface of an Al-3at%Ag alloy. In the fully segregated state, the Ag surface concentration is 0.3 monolayers. Although there is no long-range order, as evidenced by the absence of a low-energy electron-diffraction pattern, an analysis of the SEI image shows that a significant fraction of Ag atoms occupy three-fold symmetric hollow sites in stacking-fault positions. SEI is shown to be a useful new technique for structural studies of evolving surfaces even with submonolayer coverages, such as growing films with short-range order.

Core excitations and secondary electron spectra of Cu(100)

Abstract Electronic transitions near the 2s, 2p, 3s and 3p edges of Cu(100) are investigated with electron energy loss spectroscopy and compared with real-space multiple-scattering calculations that take into account the momentum transfer q in the electron scattering process. The interplay between q and the different angular momentum channels involved in the transitions show that while for the 2p-edge with a large energy loss (and with a large q ) dipole transitions dominate the spectrum, the non-dipole channels are very strong for the 3s-edge even with small q . The methods are extended to scattering states up to 300 eV above the Fermi level in order to identify structures in the secondary electron emission spectra. The strength of electron energy loss spectra in reflecting the electronic structure of solid surfaces is emphasized along with the necessity of a complete theoretical analysis before the dipole approximation may be applied.