Low-energy electron and positron diffraction measurements and analysis on Cu(100)

Abstract

The results of an experimental study and quantitative analysis of the intensity versus energy (I-V) curves are reported for low-energy electron diffraction and low-energy positron diffraction (LEPD) with a brightness-enhanced electrostatically focused positron beam. In a close comparative study, the incident electrons and positrons scattered at a large incident polar angle (theta\ensuremath{\ge}50\ifmmode^\circ\else\textdegree\fi{}) with respect to the surface normal off clean Cu(100) and the I-V spectra from six and seven diffraction beams were taken with electrons and positrons, respectively. The analysis of the experimental data from the electron studies indicates first- and second-layer relaxation that is consistent with earlier results. Use of the structure derived from the electron studies, analysis of the I-V curves from the LEPD studies suggests that the attenuation for positrons is greater than the value for electrons over the energy range 50--400 eV, possibly as a result of the enhanced electron-image cloud surrounding the positron. The real part of the inner potential is 0 eV for positrons compared with 11 eV for electrons, in rough agreement with predictions. Further, the best agreement between experiment and calculation for LEPD I-V curve analysis tends to favor the potential formed by changing of the sign of the Coulomb term (relative to electrons), eliminating the exchange, and retaining the correlation term.