Abstract
Angle-resolved energy-distribution measurements of secondary-electron emission (SEE) from metals reveal spectral fine structure that relates directly to the density distribution of the one-electron states throughout space located above the vacuum level . The angular dependence of the SEE spectra from (100), (110), and (111) tungsten surfaces has been studied as a function of polar angle along azimuthal directions such that the energy- and angle-resolved SEE current effectively scans states throughout the irreducible body-centered-cubic zone. Calculations have been carried out in both "reduced" and "extended" space in order to assess the relative contribution of elastic umklapp scattering to the density distribution of contributing states profiles. The results indicate that the overall secondary-electron yield may be represented as the sum of basically two contributions . The bulk contribution represents emission due to Bloch waves propagating out of states in the semi-infinite crystal; the surface contribution represents that part of the current due to evanescent waves at the metal-vacuum interface. In addition, transmission-induced spectral features are observed (transmission resonances), which are not related to the density-of-states fine structure, but are due to a quantum-mechanical enhancement in the escape probability arising from wave-function matching at the emitter-vacuum interface. Bulk and surface band-structure effects are concurrently manifest in the SEE spectra via the wave-matching conditions imposed at the solid-vacuum interface. The results are discussed within the general conceptual framework provided by "the (time-reversed) incoming final-state wave-function" approach to electron emission phenomenology of metal surfaces, thereby establishing a relationship with recently developed low-energy electron diffraction, photoemission, and field-emission formalism.
- Received 1 August 1977
DOI:https://doi.org/10.1103/PhysRevB.18.5140
©1978 American Physical Society