Frank Stein

Wolfgang Kurtz

Gerhard Kirschstein

Gerhard Czack

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.

Supplement Volume A4 Surface Properties. Electron Emission

W Tungsten

Joachim Wagner

Ursula Trobisch

Hermann Jehn

Dietrich Schneider

In the first part of this volume the nitrogen-containing compounds of molybdenum are described. The Mo-N system shows that M0 N and MoN are the stable nitrides. MOlybdenum 2 metal dissolves nitrogen to some extent but only at high temperatures. To get better insight into the reactions between nitrogen and molybdenum, the solubility, diffusion, adsorption and desorption phenomena, and ion bombardment are included in the section of the Mo-N system. M0 N has a large range of homogeneity toward lower nitrogen concentrations. The black 2 hexagonal MoN has only a narrow range of homogeneity. In addition some molybdenum compounds containing nitrogen and oxygen are known. The second part contains a full description of the compounds of molybdenum with fluorine. The fluorides MoF n with n ~ 2 are metastable while those with n = 3 to 6 are stable and have been observed in the Mo-F system. Pure MoF can exist without traces of oxygen, in co nt rast 3 to earlier assumptions. MoF was unambigously prepared and characterized in 1957. Its crystal 4 structure is still unknown. MoF is often contaminated with the oxide fluoride MoOF and it is s 4 difficult to remove. Even sm all amounts affect the properties of MoF . MoF , which is liquid at s 6 room temperature and solidifies to a "plastic" crystal modification below ca. 17SC, is the most investigated of all the molybdenum fluorides.

Mo Molybdenum

Wolfgang Kurtz

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