Secondary electron emission from tungsten. Observation of the electronic structure of the semi-infinite crystal

Abstract

The fine structure in the angle-resolved secondary electron emission (SEE) spectra can be interpreted fully in terms of the electronic structure of the semi-infinite crystal. A large number of elements of structure can be related to the bulk band structure. In addition, extra features are unambiguously interpreted in terms of surface-specific electronic properties. The bulk contributions to the SEE structure can be interpreted by means of a band model by assuming conservation of momentum parallel to the surface during emission. Peaks in the SEE spectra of bulk origin relate, concerning their spectral position, to high density of states regions in K-space. All such elements of structure have been identified, and the locations in K space which contribute have been determined. The observation of bulk properties as structure in the SEE spectra is in fact a consequence of the quantum-mechanical matching at the surface. In a simple mode, neglecting this matching, the density-of-states contributions fold out of the expression for the emitted current. The matching conditions, which are discussed in a muffin-tin model, also imply that a number of surface-specific effects are observed. These are referred to as 'anomalies'. Four 'types' of 'anomalies' are discussed.