[en] The improvements and optimal conditions for field-ion microscopy (FIM) of refractory metals and alloys are discussed. It is shown that at very low temperatures the imaging ions are not produced in the gas phase in front of the surface but by field-ion desorption of field-induced adsorbed atoms from the surface in apex positions. For the binary tungsten-molybdenum system, defects such as vacancies and grain boundaries and also rearrangements on lattice planes have been investigated. Gas-metal reactions between osmium and oxygen have been studied with the FIM by introducing oxygen dynamically in low concentration into the imaging helium gas. Field evaporation of tungsten-molybdenum alloys has been studied with atom-probe FIM to prove the abundances of different ionization states when field evaporation takes place from a pure metal or from an alloy. Whereas under moderate field strengths tungsten is mainly field-evaporated as W³⁺ and molybdenum as Mo³⁺ and Mo²⁺ in similar abundance from pure metals, the abundance of Mo³⁺ increases and that of Mo²⁺ decreases with increasing concentration of tungsten in the alloy. This is partly due to increasing field strengths and partly to the dominating influence of the electronic structure of tungsten over molybdenum by charge transfer. (author)

[en] In the binary system molybdenum-oxygen the electrical conductivity and the magnetoresistance is measured for the phases Mo₄O₁₁, Mo₁₇O₄₇, Mo₈O₂₃, Mo₉O₂₆, and Mo₁₈O₅₂ in the temperature range 4.2 K < T < 300 K at magnetic inductions up to 7 T. With increasing oxygen content of the compounds a transition from metallic conductivity to semiconductivity occurs at critical distances of the metal ions. The substitution of molybdenum by tungsten in the phase Mo₁₇O₄₇ causes a decrease of conductivity of the ternary compounds. (author)

No abstract available

[en] The effect of hydrogen on field ionization and field ion microscopic imaging of transition metals are discussed whereby two groups of metals are to be distinguished concerning the solubility of hydrogen in the metal in an endothermic or exothermic reaction. In the last case the atom probe proves enhanced field evaporation in the form of metalhydrides besides pure metal atom desorption. (author)

[en] Photoluminescence and photoconductivity measurements of densely sintered zinc silicates undoped and doped with Mn, As, Al and Ti have been extended to the uv region at temperatures between 20 K and 300 K where two emission bands exist for undoped zinc silicate with peaks at 285 nm and 382 nm with contrary temperature dependence. The photoconductivity of undoped zinc silicate can be enhanced by doping with Al and dimineshed by doping with Mn, As and Ti. The luminescence stimulation of Zn₂SiO₄:Mn, As after exitation can be achieved not only by infrared but also by suitable ultraviolet irradiation. (orig.)

[en] The importance of gases dissolved in the host material to the imaging is discussed. (G.Q.)

[en] Metals with high storage of hydrogen like those in the 4th and 5th column of the periodic table of the elements and their alloys allow field ion microscopic investigations at very low residual gas pressures below 10^-7 Pa with the hydrogen dissolved in the bulk as imaging ions when the temperature of the samples is sufficiently raised and hydrogen diffusion to the surface is enabled. (orig.)

[en] The initial stages of selected reactions of the refractory metals tungsten, niobium and tantalum with hydrogen, oxygen, nitrogen and methane have been studied with the field ion microscope in atomic resolution whereby the composition of single net planes converages and surface zones could absolutely be analyzed with the atom probe by using field desorption under defined conditions at low temperatures. 14 refs., 9 figs. (Author)

[en] Very pure osmium is investigated in the field of ion microscopy by using helium as imaging gas at 21 and 78 K in respect to bond order, crystal defects and influence of additional gases (Ne,H₂,O₂,N₂) in low concentrations. (orig.)

No abstract available