ANGLE-RESOLVED PHOTOEMISSION EXTENDED FINE-STRUCTURE OF THE NI 3P, CU3S, AND CU 3P CORE LEVELS OF THE RESPECTIVE CLEAN (111) SURFACES

We report a non-s initial-state angle-resolved photoemission extended fine-structure (ARPEFS) study of clean surfaces for the purpose of fur ther understanding the technique. The surface structure sensitivity of ARPEFS applied to clean surfaces and to arbitrary initial states is s tudied using normal photoemission data taken from the Ni 3p core level s of a Ni(111) single crystal and the Cu 3s and the Cu 3p core levels of a Cu(111) single crystal. The Fourier transforms of these clean sur face data are dominated by backscattering. Unlike the s initial-state data, the p initial-state data show a peak in the Fourier transform co rresponding to in-plane scattering from the six nearest neighbors to t he emitter. Evidence was seen for single-scattering events from the sa me plane as the emitters and double-scattering events. Using a recentl y developed, multiple-scattering calculation program, ARPEFS data from clean surfaces and from p initial states can be modeled to high preci sion. Although there are many layers of emitters when measuring photoe mission from a clean surface, test calculations show that the ARPEFS s ignal is dominated by photoemission from atoms in the first two crysta l layers. Thus ARPEFS applied to clean surfaces is sensitive to surfac e reconstruction The best-fit calculation for clean Ni(111) indicates an expansion of the first two layers.