Liquid-like structure of vapour quenched SnAu- and SnCu-films

SnAu- and SnCu-alloys are vapour quenched at cryogenic temperatures. Resistivity and electron diffraction patterns were recorded in situ. The scattered intensities have been normalized to interference functions. The overall agreement with those of the corresponding liquid systems is quite well. The average interatomic distances obtained from the atomic distribution functions show a concentration dependence which corresponds closely to that found in liquid SnAu and SnCu respectively. This gives evidence to the statement that the nearest neighbour organisations of the films are very similar to those of the corresponding liquids. Furthermore it turned out that the local structures in the Sn-rich SnAu-system are substantial different from those in the Sn-rich SnCu-system, except in the vicinity of a minimum amount of noble metals (8–10 at.%), which is necessary to stabilize the amorphous state.     

Superconductivity of vapour quenched beryllium and beryllium-based alloys

The properties of Be films, quench-condensed upon a³He cooled substrate, have been investigated by resistance and tunneling measurements. The superconducting transition temperature,T _c , of Be films increased with thickness and a thick film limit of 9.95 K could be estimated. Alloying with Al or Pb decreasedT _c. The ratios between energy gaps andT _c 's indicated that Be is a weak coupling superconductor, and no phonon induced structure could be traced in tunneling curves neither in pure Be nor in the Be based alloys. Resistance change during annealing as well as superconducting data indicated that the vapour quenched Be films were amorphous as deposited.     

Superconducting transition temperatures of vapour quenched beryllium

T_c for vapour quenched Be is depressed in thin films. In the limit of infinite thickness we measure T_c = 9.95 ± 0.06 K.     

Structure of Be films quenched from the vapour

The crystallite boundary mismatch in crystalline films leads to tensile stresses which act on the substrate. Due to these stresses the substrate is bended. In the dense random packing of atoms in an amorphous film local tensile- and compressive stresses compensate and thus the films seem to be free of stresses with regard to the substrate. From this point of view the measurement of mechanical stresses produced by vapour quenched films can be used for structural analysis. Thus an apparatus is described which allows in situ measurements of mechanical stresses and electrical resistivity of vapour quenched films from 1.2 K to 400 K.An investigation of beryllium films revealed that stresses are produced even by films with a superconducting transition temperature of 9.6 K. From this fact it can be concluded that vapour quenched Be is not completely amorphous. Furthermore, it is shown that inhomogeneous films exist with a two phase double layer structure which is responsible for some peculiarities reported in the literature.     

Al表面的"类液"结构及其自扩散通道

应用分子动力学方法,采用嵌入势模型在熔点下和熔点上对Al(001),(110)和(111)表面的原子结构和自扩散现象进行研究.发现这些表面的第一层原子在低于熔点时,Al(110)面在700±10 K,Al(001)面在 860±10 K,Al(111)面在 930±10 K呈现明显自扩散且最终转变为"类液"结构,而其余各层仍保留有序状态.对这种"类液"结构进行均方位移、结构有序参数、径向分布函数和z向粒子密度分析,发现其结构和扩散行为与熔化的Al表面不同,并能在一定温度区间稳定存在.在"类液 关键词： 表面结构 分子动力学 自扩散     

Search for superconductivity in vapour quenched alkaline earth metals and lanthanides

Recent papers by Reale [1–3] report superconducting transitions in vapour quenched films of several alkali-, alkaline earth-, and rare earth metals which were not previously known to be superconducting. We report here a vain effort to verify that Mg, Ba, Ce, Pr, Nd or Yb are superconducting above 0.3 K.Supported by the Swedish National Science Research Council     

Mechanical stresses in vapour quenched films of Al and Al rich compounds

The measurement of mechanical stresses in vapour quenched metal films can give additional structural information. Especially the near absence of stresses yields a sufficient condition for the formation of amorphous structures, since stress contributions due to the crystallite boundary mismatch are present in every micro crystalline film. From this point of view we find that Al films containing more than 25 at.% Ag grow in an amorphous phase whereas films with less than 25 at.% Ag are micro crystalline. The influence of other impurities, especially oxygen, is also investigated. Further evidence is presented for the high superconducting transition temperatures of Al films evaporated from Al₂O₃ crucibles, which films are micro crystalline, to be due to the presence of Al₂O impurities in these films.     

Liquid-like Raman scattering by superionic materials

The Raman spectrum of a superionic conductor, α-AgI, is compared with the spectra of the melt of AgC$\text{l}$ and AgBr, in order to determine the responsible Raman processes. We conclude that because of the strong anharmonicity and high translational disorder in superionic conductors, spectra analyses based on the concept of harmonic lattice are unsuitable. A dynamical picture of ions similar to that of liquids appears to be more useful than the phonon concepts.     

On the structure of quenched condensed germanium-noble metal films

Electron diffraction patterns of quenched condensed pure Ge and Ge-noble metal films with concentrations of Cu of Au between 23 at-% and 60 at-% are taken directly after the condensation at 4.2 K and during annealing up to 330 K. The changes of the radii of the first and second diffraction rings, the annealing behaviour and the change in residual resistance point to the fact that a changed short range order more or less similar to that of liquid Ge is responsible for the metallic behaviour and superconductivity.     

Effect of annealing on the structure of quenched isotactic polypropylene

Smectic isotactic polypropylene films were annealed at different temperatures for different times. Density, wide-angle x-ray scattering (WAXS), differential scanning calorimetry, and the transport properties of methylene chloride vapor were used to follow the transformation of the smectic phase into the monoclinic phase. The results of WAXS diffractograms indicate different saturation levels of crystallization with the maximum order attained progressively more quickly at higher temperatures. Density measurements, however, show that, after a first saturation level, a further increase of this parameter occurs after long annealing times; and this second step is lower, the higher the temperature. Sorption and diffusion, analyzed to investigate the amorphous component, show that annealing the smectic phase at 50°C results in a decrease of amorphous fraction without transformation of the smectic phase. The transition from smectic to monoclinic phase occurs at temperatures higher than 60°C. During the annealing at 80°C there is first a decrease of amorphous fraction corresponding to the first saturation level of the density, and then a further decrease of amorphouse phase corresponding to the final increase of density after 24 hr of annealing.     

Free energy of quenched binary alloys and the time evolution of their structure function

An idea about the free energy of a binary alloy system under phase separation at low temperatures is discussed. Slow asymptotic decays in the structure functions for both a conserved and a non-conserved order parameter are studied.     

Long time behavior of structure function of alloy quenched to sufficiently low temperature

A slow asymptotic t^?a′ decay in the structure function of an unstable alloy quenched to a sufficiently low temperature is investigated. We find the exponent a′ = (d + 2)^?1, where d is the dimensionality, which is consistent with recent computer simulations.     

Effects of finite initial correlation length on scattering structure functions of quenched systems

We examined the effects of a large initial correlation length on the scattering structure function (SSF) when the order parameter is not conserved, using the approach developed by Ohta, Jasnow and Kawasaki. In particular, the SSF exhibits the usual scaling behaviour except that the scaling functions now contain an additional time-dependent parameter. The new scaling functions are computed for various values of the parameter in two and three dimensions.     

Fraunhofer selective diffraction produced by structure elements in sodium vapour

Observations are reported of selective diffraction produced by structure elements in sodium vapour separated from intermediary empty spaces by thin sheets of iron. The phenomena observed can be explained by the phase shifts in sodium vapour due to anomalous dispersion.     

Defect structure of quenched γ-BICOVOX by combined X-ray and neutron powder diffraction

A detailed investigation of the defect structure of the Co doped BIMEVOX solid electrolyte, Bi₂V_{1 − x}Co_xO_{5.5 − 3x/2} (x = 0.1 and x = 0.2), quenched from high temperature, has been carried out using X-ray and neutron powder diffraction data measured at room temperature. The structure is built up from alternating layers of [Bi₂O₂]_n²ⁿ⁺ and [V_{1 − x}Co_xO_{3.5 − 3x/2}]_n²ⁿ⁻ with disorder limited to the vanadate layer. The ideal V/Co co-ordination is octahedral with corner sharing of equatorial oxygens. The refinements show that the true structure is distorted, with disorder in both apical and equatorial oxygens and oxygen vacancies concentrated in the equatorial positions. Detailed analysis of the oxygen site occupancies reveals two main types of V/Co co-ordination viz. distorted octahedral and distorted tetrahedral. The majority of the sites in both compositions are tetrahedral.     

Investigating the topological structure of quenched lattice QCD with overlap fermions using a multi-probing approximation

The topological charge density and topological susceptibility are determined by a multi-probing approximation using overlap fermions in quenched SU(3) gauge theory. Then we investigate the topological structure of the quenched QCD vacuum, and compare it with results from the all-scale topological density. The results are consistent.Random permuted topological charge density is used to check whether these structures represent underlying ordered properties. The pseudoscalar glueball mass is extracted from the two-point correlation function of the topological charge density. We study 3 ensembles of different lattice spacing a with the same lattice volume 16~3×32. The results are compatible with the results of all-scale topological charge density, and the topological structures revealed by multi-probing are much closer to all-scale topological charge density than those from eigenmode expansion.