The influence of impurities on the electric and thermoelectric properties of CdSb single crystals

The influence of impurities on the electric and thermoelectric properties of CdSb single crystals prepared by the modified Czochralski method and the method of zone melting was studied. It was found which impurities are electrically active and which give rise to electron and hole conductivity and a schematic model of their substitutions in the CdSb lattice was proposed. The temperature dependence of the mobility was found for both electrons and holes and the density effective masses were determined.Reported by L. toura at the Conference on Thermoelectricity, 10–12. 7. 1961, Durham, England [26].     

Ground-state structures of atomic metallic hydrogen

Ab initio random structure searching using density functional theory is used to determine the ground-state structures of atomic metallic hydrogen from 500 GPa to 5 TPa. Including proton zero-point motion within the harmonic approximation, we estimate that molecular hydrogen dissociates into a monatomic body-centered tetragonal structure near 500 GPa (r(s)=1.23) that remains stable to 1 TPa (r(s)=1.11). At higher pressures, hydrogen stabilizes in an …ABCABC… planar structure that is similar to the ground state of lithium, but with a different stacking sequence. With increasing pressure, this structure compresses to the face-centered cubic lattice near 3.5 TPa (r(s)=0.92).     

Study of the atomic and electronic structures of liquid gold

The electronic and atomic structures of liquid gold has been studied theoretically and experimentally using X-ray photoelectron spectroscopy (XPS) and a combination of classical molecular dynamics and ab initio band calculations. The results obtained showed good agreement between the XPS data and the results of calculations of the total density of states. It is shown that the bonding of atoms in liquid gold clusters is covalent.     

Engineering electronic lifetimes in artificial atomic structures

By means of atomic manipulation, 51 Ag atoms have been precisely positioned to form a triangle with a base length of 245 A on a Ag(111) substrate. The scattering of the surface electrons at these adatoms results in a complex interference pattern. Spectroscopic data and dI/dV maps taken inside the triangle have been quantitatively evaluated by multiple scattering calculations of the wave pattern. Adjustment of the scattering parameters to the data yields the properties of the scatterers and the electron lifetimes. The experimental results for the electron lifetimes deviate from a (E-E(F))(-2) dependence and reflect the electronic band structure at the surface as well as the local influence of the triangle.     

Structural stabilities and electronic structures of Ti atomic chains

The present first principles density-functional calculations reveal that titanium can form one-dimensional chains in linear, dimer, zigzag and ladder structures. The most stable structure is a zigzag chain with a unit cell rather close to an equilateral triangular geometry with four nearest neighbors. Two intermediary chains between the linear and zigzag ones have the ladder and dimer structure, respectively. Titanium can also form a metastable zigzag structure with an obtuse bond angle. It is important and interesting to find that during the elongation of the zigzag chain, the bond angle will shift abruptly from a sharp angle to an obtuse one at a critical point, and the bonding character also transforms from mainly metallic to more covalent. This is the first time that such a structural transition is discussed in the atomic chain system. The electronic structures of these one-dimensional titanium chains are also discussed.     

The influence of the static lattice distortion on the localized modes of atomic impurities in alkali halides

We have studied the influence of static distortion on the localized modes of a Li⁺ impurity in KCl and KBr using the molecular model. For off-center equilibrium positions with the impurity on a symmetry axis of the cubic host lattice the concept of structure elements has been set up to derive the symmetry properties of the vibrating molecular region. In the frame-work of a rigid ion model with only central forces the 111-off-center position turns out to be the only possible stable off-center position. For the system KCl:Li⁺ the measured resonant modes in the region of 40 cm^–1 can only be interpreted in this model as cluster vibrations. In addition we have calculated defect induced Einstein-modes with frequencies near the upper band edge.     

The influence of cascade on the polarization of radiation produced in electronic or atomic collisions

A study is presented, in which we consider the influence of cascade effects on the polarization of light emission produced in electronic or atomic collisions. Cascade transitions are shown to cause a polarization transfer which may result in a total falsification and even in a sign reversal of the polarization. Closed expressions are derived for some special cases. A practical application is given in which the derived formulas are used to understand a serious discrepancy between theoretical predictions and experimental data in the case of the line polarization due to some 3p-3s transitions in neon induced by proton impact.     

Stereo-PEEM for three-dimensional atomic and electronic structures of microscopic materials

The principle and design of a new photoemission electron microscope (PEEM), which is called Stereo-PEEM, is described here. Stereo-PEEM can display not only the image of microscopic materials but also the angular distribution of high-energy photoelectrons up to about ±60°, which is about 100-fold the acceptance angle of usual PEEM. This wide angle acceptance for high-energy photoelectrons enables the three-dimensional (3D) display of atomic structure as well as the 3D electronic structure of individual micromaterials. The 3D atomic structure of a sample can be observed directly by taking stereophotographs using photons with angular momentum.     

The influence of hydrogen on the atomic distribution function and electrical resistance of amorphous chromium films

Electrical resistivity of amorphous chromium films (20–37 nm thick) deposited in a hydrogen atmosphere (P _{H 2}=8·10^–6–2·10^–4 hPa) onto a substrate cooled by liquid helium down to 2 K is measured, and electron-diffraction studies have been performed immediately after the quench condensation and after annealing to different temperatures up to 300 K. The preparation method employed permits a considerable hydrogen enrichment of the films to be reached. The maximum hydrogen concentration corresponds approximately to a stoichiometric composition of CrH. It is found that as the maximum concentration is approached the atomic distribution functionG(r) changes remarkably. The interatomic distances increase considerably (by 10%) and the atomic densities decrease. It is quite possible that amorphous chromium hydride is a final state with the maximum hydrogen concentration. For films with intermediate concentration,G(r) is found to vary substantially under annealing up to 90 K. The electron-diffraction and electronmicroscopic data, as well as the variations in resistivity due to annealing, suggest that with annealing up to 90 K, a hydrogen redistribution occurs in the amorphous films, initially homogenous in concentration. We observe also distinct indications of separation into phases with increased and reduced hydrogen contents.     

Infrared spectra of hydrogen impurities in BaTiO3 crystals

The IR spectra in the 2.8 μm region of the OH^? impurities in thick single domain crystals have been measured for different polarization geometries and various temperatures. Simple calculations of the Coulomb interactions between hydrogen and lattice ions show that these interactions are much more important than the hydrogen bonding ones for determining the positions of the hydrogen ions. The appearance of only one strong non-dichroic OH^? stretching line is due to an almost equal population of the proton axial sites. The side bands are interpreted as combinations of the stretching mode with a low-frequency translational mode. The large broadening of the main line just above T_c supports the model which attributes a considerable order—disorder character to the ferroelectric phase transition.     

Quasi-localized representation of electronic band structures in cubic crystals

Tabulated results and formulae are given for the parametrization of electronic band structures in simple cubic, body-centered cubic and face-centred cubic systems. This technique is based on the decoupling transformation and does not involve least squares fitting.A band labelling scheme is introduced which allows the decoupling transformation to be used to define the energy matrix of Wannier states in copper. This approach is used to re-examine the significance of the tight binding approximation for the d-states and to relate Fermi surface parameters directly to calculated band energies.     

The influence of atomic impurities on the orientational transitions in localized monolayer films of diatomic molecules adsorbed on crystalline surfaces

The orientational ordering in localized films consisting of a mixture of diatomic and mono-atomic particles and formed on the (100) face of a cubic crystal is considered. It is demonstrated that the presence of atomic impurities influence the formation of orientationally ordered states. In particular, it is shown that even a simple mean-field theory leads to a qualitatively correct picture of changes in orientational properties in the film when the molar ratio of spherically symmetric particles increases.     

First-principles study of atomic and electronic structures of kaolinite in soft rock

Kaolinite is a kind of clay mineral which often causes large deformations in soft-rock tunnel engineering and thus causes safety issues.To deal with these engineering safety issues,the physical/chemical properties of the kaolinite should be studied from basic viewpoints.By using the density-functional theory,in this paper,the atomic and the electronic structures of the kaolinite are studied within the local-density approximation(LDA).It is found that the kaolinite has a large indirect band gap with the conduction band minimum(CBM) and the valence band maximum(VBM) being at the Γ and the B points,respectively.The chemical bonding between the cation and the oxygen anion in kaolinite is mainly ionic,accompanied by a minor covalent component.It is pointed that the VBM and the CBM of kaolinite consist of oxygen 2p and cation s states,respectively.The bond lengths between different cations and anions,as well as of the different OH groups,are also compared.     

原子簇La8-xBaxCuO6的原子磁矩和自旋极化的电子结构研究

利用MS-Xα方法研究了化合物La2-yBayCuO4的原子磁矩和自旋极化的电子结构.理论计算得到母相氧化物La2CuO4的Cu原子磁矩为0.37μB,与实验值0.48±0.15μB基本一致. 研究结果显示, 由于Ba原子对部分La的替代,使构成化合物的基本原子簇La8-xBaxCuO6的点群对称性降低,分子轨道简并度解除,轨道杂化效应增强,减弱了氧化物的(准)二维特性,导致Cu-O层与其近邻原子层的耦合增强,因此影响了原子层间的电荷迁移方向,对Cu-O层中载流子的性质有重要影响. 由于Ba掺杂在化合物中产生的空穴,不仅进入O格点,也同时进入Cu格点,对Cu-O层上Cu和O原子价态、磁矩以及电子态密度分布有重要影响. 研究结果认为,由于掺杂产生的空穴对化合物超导电性的影响具有两面性:初期掺杂有利于产生超导电性;当掺杂较多时抑制超导电性. 这是导致La214体系的超导转变温度Tc随掺杂量y的变化(即Tc-y拱形曲线)的一个重要原因.     

Metastable structures and recombination pathways for atomic hydrogen on the graphite (0001) surface

We present scanning tunneling microscopy results which reveal the existence of two distinct hydrogen dimer states on graphite basal planes. Density functional theory calculations allow us to identify the atomic structure of these states and to determine their recombination and desorption pathways. Direct recombination is only possible from one of the two dimer states. This results in increased stability of one dimer species and explains the puzzling double peak structure observed in temperature programmed desorption spectra for hydrogen on graphite.     

Correlation of the chemical properties of carbon nanotubes with their atomic and electronic structures

The nature of chemical bonding in carbon nanoclusters is investigated by the PM3 semiempirical quantum-chemical method. The influence of the atomic structure on the electronic characteristics and chemical properties of nanoclusters is analyzed. A σ-π model is proposed for the chemical bonding in nanotubes. It is shown that, in the framework of the proposed model, nanotubes are objects characterized by a small contribution of π states to the valence band top.     

Study of the atomic and electronic structures of amorphous silicon nitride and defects in it

The structure of amorphous silicon nitride obtained by cooling from a melt has been simulated by Car-Parinello molecular dynamics. Several types of Si-Si defect coordination have been revealed. It has been found that, in addition to normal Si-Si bonds, numerous double Si-Si bonds (Si-Si-Si defects) are present in the amorphous structure.     

Low-temperature diffusion of gold in germanium under the influence of atomic hydrogen

An investigation is made of the diffusion of gold in germanium under the influence of the energy released by the recombination of hydrogen atoms to form molecules. Crystals of n-type germanium with gold films (d=1×10⁻⁷ m) are exposed to atomic hydrogen for various times (up to 10⁴ s) at temperatures close to room temperature. The diffusion of gold in the germanium is analyzed by laser mass spectrometry, and also by measuring the surface resistance, the minority carrier lifetime, and the infrared transmission spectra. Mechanisms are proposed for the stimulation of heterodiffusion and accompanying processes. Zh. Tekh. Fiz. 69, 73–76 (July 1999)