PHOTOFIELD EMISSION-SPECTROSCOPY OF THE (111) AND (100) TANTALUM BAND-STRUCTURE AND SURFACE-DENSITY OF STATES

Optical transitions near the Fermi level in the (111) and (100) directions of tantalum were observed using the photofield emission method. The final and initial energies of the photoelectrons have been estimated based on the quantum energy and lowering of the top of the surface potential barrier at which shoulders in current-voltage characteristics appear. Electron energy values obtained for a few quantum energies are compared with the calculated band structure in which the total relativistic effect is taken into account. All excitations correspond to the band structure as direct transitions when the Fermi level indicated by theoretical calculation is shifted towards the high energy by about 0.4 eV. The experimental results confirm the existence of two bands close to each other near the Fermi level for the (111) direction. Besides, many peaks in the surface density of states lying below the Fermi level for the (111) and (100) planes of tantalum have been observed.