W Tungsten: Supplement Volume A4 Surface Properties. Electron Emission: W / A-B / A / 4 (W. Wolfram. Tungsten (System-Nr. 54)) - Tapa blanda

This voLume continues the description of the physicaL properties of tungsten metaL and covers specificaLLy surface properties, eLectron emission, and fieLd evaporation. Tungsten surfaces are probabLy the most extensiveLy studied metaL surfaces. RecentLy, experimentaLists and theorists have focused their interest on the atomic structure, Lattice dynamics, and eLectronic properties of the W(100) surface. WhiLe the structure of the recon­ structed Low-temperature surface is weLL estabLished, there are still unresoLved probLems concerning the structure at and above room temperature, the nature of the phase transition, and the driving force for the reconstruction. Other Low-index tungsten surfaces have been studied in much Less detail. There are numerous and partLy confLicting data on the surface energy, the seit-diffusion parameters, and the work function of singLe-crystaL and poLycrystaL tungsten surfaces. ELec­ tron emission, which is of fundamentaL importance for many appLications, comprises therm­ ionic, fieLd, photofieLd, and photoeLectric emission as weLL as emission induced by impinging eLectrons, atoms, or ions. Pioneering work in areas Like thermionic or fieLd emission is comprehensiveLy discussed. Very recent studies of vaLence-band and core-LeveL spectra moreover provide detaiLed information on intrinsic surface properties. FieLd evaporation phenomena are treated at the end of this voLume. Frankfurt am Main Woltgang HuisL November 1993 fable of Contents Page 1 Atomic Structure, LaHice Dynamies, and Electronic Structure of Tungsten Surfaces 1 1.1 W(100) . . . . . . . . . . . . . . . . . . . 1.1.1 Atomic Structure. Reconstruction and Relaxation Survey ................. .

The volume describes physical properties of tungsten metal and covers specifically surface properties, electron emission, and field evaporation. Tungsten surfaces are probably the most extensively studied metal surfaces. Recently, experimentalists and theorists have focussed their interest on the atomic structure, lattice dynamics, and electronic properties of the W(100) surface. While the structure of the reconstructed low-temperature surface is well established, there are still unresolved problems concerning the structure at and above room temperature, the nature of the phase transition, and the driving force for the reconstruction. There are numerous and partly conflicting data on the surface energy, the self-diffusion parameters, and the work function of single-crystal and polycrystal tungsten surfaces. Electron emission, which is of fundamental importance for many applications, comprises thermionic, field, photofield, and photoelectric emission as well as emission induced by impinging electrons, atoms, or ions. Pioneering work in areas like thermionic or field emission is comprehensively discussed. Very recent studies of valence-band and core-level spectra moreover provide detailed information on intrinsic surface properties.