Surface states and resonances in field emission from low-index facets of clean tungsten

摘要

The energies, widths, and shapes of features observed in the total energy distributions in field emission from W(l 0 0) and W(l 1 1) are compared with the results of a full-potential LAPW calculation of the surface density of states based on a supercell model of the crystal structure at the metal-vacuum interface. The Swanson hump on W(l 0 0) is attributed to two bands of surface states and surface resonances of d({sub}z{sup}2) symmetry that are highly localised at Γ{top}-, and a second peak observed at lower energy is attributed to a band of surface resonances, also of d({sub}z{sup}2) symmetry, centred at 0.11 A{top}o{sup}(-1) fromΓ{top}- alongΓ{top}-X(top)-. The energy scale of the calculated total energy distribution is compressed by about 20% relative to the experimental data. The present calculation yields strong evidence that the broad asymmetric peak observed on W(l 1 1) is due to emission from a band of surface resonances. Further calculations for W(l 1 1) are proposed both to test the accuracy of the band model and to take into account the velocity factor that enters in a calculation of the emission current.