Overlayer Test of Surface Photoemission Effect in Cu(100)

Angle-resolved photoemission from bulk valence bands of a single crystal yields direct-transition peaks that are often distorted due to interference with broadband indirect emission induced by the surface. The present study is a direct test of this surface effect by using an overlayer to modify the surface boundary condition. A Cu(100) single crystal exhibited a rather asymmetric $\mathrm{sp}$ direct-transition peak and a significant indirect emission intensity. Deposition of a thin Ag overlayer shielded the Cu surface from vacuum, and both the peak asymmetry and the indirect emission intensity were suppressed.