Photofield emission study of metal surfaces

Theoretical calculations of photofield emission based on the relativistic electronic band structure of tungsten are carried out and the results are compared to experiment. Data from W(110) and W(111) for a number of different photon energies between 2.4 and 3.54 eV are reported. The measured yield is compared to the theoretical models of the photoexcitation process. Based on this comparison, it is concluded that the spatial variation of the vector potential A near the metal-vacuum interface is the dominant excitation mechanism in producing the photocurrent from a laser illuminated field emission tip. Photofield emission from surface electronic states is a unique probe to examine the radiation field near the vicinity of a metal surface since the surface states are localized within the first atomic layer of the surface. Studies of photofield emission from surface states on W9100), Mo(100) and Ir(111) are presented. Data analysis shows that photofield emission from localized surface states depends predominantly on the normal component of the vector potential A