Vacancy behavior in Czochralski silicon growth

The vacancy defect behavior in silicon crystal growth has been investigated by kinetic Monte Carlo and continuum simulations. The vacancy concentration distributions in silicon crystal were obtained from continuum model simulations corresponding to experimental conditions and then the vacancy clusters distribution obtained from kinetic lattice Monte Carlo simulations. At the temperature above 1470 K, the diffusivity was almost constant because the clusters were not formed. In the clustering temperature region (1370–1270 K), the larger clusters were generated at the higher temperature, the smaller clusters were generated at the lower temperature. While the vacancy concentration led to increase in the number of clusters, the mean size of clusters was irrespective of the vacancy concentrations. Clustering phenomena were very susceptible to temperature and vacancy concentrations. The total number of vacancy clusters was linearly proportion to the crystal pull rate. The radial distribution of clusters obtained from multi-scale simulations was in good agreement with the distribution of voids in the experimental data.     

Co掺杂ZnO薄膜的湿化学法制备及其光致发光光谱

采用湿化学法在Si衬底上生长了纳米棒结构的Co掺杂ZnO薄膜,并研究了掺杂浓度对生成样品结构和性能的影响.研究表明这种湿化学法成本低廉、收益高、重复性良好.样品的XRD结果表明掺杂的ZnO没有出现杂相.SEM结果表明掺杂样品是由ZnO纳米棒团簇结构组成,且团簇的密度随着Co掺杂浓度的增大而增大.薄膜的光致发光光谱结果表明Co掺杂导致薄膜的带隙发生红移,同时也证明了Co原子有效地进入了ZnO晶格.     

Influence of Impurities and Testing Atmosphere on High-temperature Deformation of CsI Crystals

The influence of anion (bromine) and cation (cadmium and barium) impurities, as well as testing atmosphere (air, argon, vacuum) on high temperature deformation of CsI crystals is studied. This deformation in CsI has some peculiarities, which are the superplasticity signs and evidencing about instability of a lattice state. All the impurities studied caused the hardening, their effect in superplasticity depends on its solubility in the CsI lattice: the less the solubility, the stronger the effect. With testing in vacuum and argon, when the formation of point defect clusters occurs, enhanced the superplasticity evidence compared to that by testing in air, where clustering is prevented. These facts, as well as a quality resemblance of stress-strain curves of single- and polycrystalline specimens give the basis for the conclusion, that superplasticity is the manifestation of a plastic instability of the crystal, the instability centers may be precipitates and point defect clusters.     

Capture of adatoms by clusters in thin film deposition

The adatom diffusion and capture by clusters are considered as a random-walk problem. The method of solution is developed. Green's function for a square substrate lattice is obtained. This permits one to give a general solution for a steady-state adatom distribution around clusters and for Halpern's arrival probability. This solution is applicable for calculating capture numbers of some small capture centres. An interpolation formula for the capture number, as dependent on the perimeter length of the capture centre, is proposed for λ a. The adatoms fluxes to the 10 and 11 steps on the surface are calculated. The fluxes are anistropic but the anisotropy disappears with λ/a → ∞. The applicability of the steady-state approach is discussed. It is shown that this approximation is valid for low adatom density. The adatom fluxes to monatomic and diatomic immobile clusters are calculated under conditions when these clusters cannot be treated as capture centres. The conservation equations for these clusters are formulated whereby two different configurations of three-atomic clusters are taken into account.     

On the Binding Energy of Clusters with a Small Number of Lithium Atoms and Varying Scope of Interaction Between the Atoms. Hückel Molecular Orbital Approximation

The effect of the scope of interaction between the atoms in two-dimensional and threedimensional clusters containing 6, 7, 9, 10, 15 and 16 lithium atoms, upon the binding energy (BE) of the clusters has been investigated. BE of the clusters was calcuated by the HÜCKEL Molecular Orbital (HMO) method. It has been established that for clusters with the same number of atoms BE has its maximum value when the interaction of each atom of the cluster with the atoms of its first and second coordination spheres in the lithium lattice are taken into account. After the maximum BE decreases and tends to a constant value which is attained when the interaction of each atom of the cluster with the atoms of its six coordination spheres is taken into account. The reasons for the above result should be looked for in the limits of applicability of the calculation procedure based on the HMO method to the study of properties of various models of clusters containing a small number of metal (e.g. lithium) atoms.     

A quasi-lattice based on a cuboctahedron. 1. Projection method

A three-dimensional (3D) quasi-lattice (QL) based on a cuboctahedron is obtained by the projection from a seven-dimensional hypercubic base lattice space to a 3D tile-space. The projection is defined by a lattice matrix that consists of two projection matrices from the base lattice space to a tile-space and perp-space, respectively. In selecting points in the test window, the method of infinitesimal transfer of the test window is used and the boundary conditions of the test window are investigated. The QL obtained is composed of four kinds of prototiles, which are derived by choosing triplets out of seven basis vectors in the tile-space. The QL contains three kinds of dodecahedral clusters, which play an important role as packing units in the structure. A modification of the lattice matrix making the QL periodic in the z direction is also considered.     

X-ray diffraction study of the structure of detonation nanodiamonds

The spatial structure of aggregates formed by detonation nanodiamonds is investigated using the wide-angle and small-angle X-ray scattering techniques. The effective sizes of crystallites and the crystallite size distribution function are determined. The shape of scattering aggregates is restored from the small-angle X-ray scattering data. An analysis of the results obtained allowed the conclusion that the nanodiamond aggregates have an extended spatial structure composed of nine to ten clusters, each involving four to five crystallites with a crystal lattice of the diamond type.     

Effect of γ-irradiation on the lattice parameter and colour centre concentration in pure Ca2+, Sr2+ and Eu2+ doped KCI crystals

The changes of lattice parameter and colour centre concentration are examined in KCI crystals (both pure and Me²⁺-doped) irradiated by γ-rays at room temperature. For the pure crystals the relative volume change vs. F-centre concentration plot reveals the presence of two stages, one ascribed to the introduction of colour centre pairs (or F centres only) and other to the generation of the new dislocations (or new dislocations with trapped-hole centres). In Me²⁺ doped crystals the lattice expansion bears a complex character (in the initial irradiation stage a transient maximum appears). Additional anomaly appears in Eu²⁺ KCI in the high-dose range where in spite of a distinct F-centre concentration drop a marked raise of the lattice parameter is observed.     

Structural properties of liquid Fe-Si alloys

The atomic structure of liquid Fe-Si alloys within the whole concentration range (including pure components) was investigated at the temperature of 1550 °C by means of X-ray diffraction. Analysis of the reported data on physical properties of Fe-Si melts has been carried out. Interrelation between liquid-state structure and solid-state properties was considered. Fe-Si alloys in the liquid state are shown to be micro-inhomogeneous and they contain atomic micro-formations (clusters) that differ by atomic composition and packing. There are five types of clusters: two of them consist of atoms of one kind (Fe or Al); the composition of the other clusters depends on the stoichiometry of solid Fe₃Si, FeSi and Fe₂Si₅ phases. The entire concentration range of the Fe-Si system consists of four concentration intervals. Within each interval melts are constituted of the clusters of two kinds. The variation of the component concentrations in Fe-Si alloys results in changing of volume fraction of each type clusters, whereas the atomic composition and arrangement inside the clusters remains constant.     

The calculation of critical size of carbon clusters in ferrite

The formation of carbon clusters in ferrite is investigated by the simulation of random motion of carbon particles in a cubic primitive model lattice at different annealing temperatures. All computer runs are repeated to average the results. An interaction potential is assumed between the particles precipitated in the formed cluster and the particles in the matrix. Additionally a decay of the cluster is allowed. A cluster of critical size is formed if the probability of decay is lower than the precipitation rate. The critical size calculated depends on the annealing temperature as the results show unambigously.     

Effect of some Me2+ impurity ions on the lattice parameter of KCI crystals

The effect of concentration of substitutional Ca²⁺, Sr²⁺, Ba²⁺ and Pb²⁺ ions on the lattice parameter of KCI crystals is examined. The amount of lattice contraction induced by the alcaline earths ions qualitatively correlates with the pertinent ionic radii values (relative unit cell contraction induced by one impurity dipole amounts to −0.905, −0.110 and −0.020 for Ca²⁺, Sr²⁺ and Ba²⁺ ions, respectively). The initial drop of lattice parameter observed at low Me²⁺ concentration is tentatively ascribed to the drop of dislocation density. In Pb²⁺ doped crystals except for the above initial drop, at higher dopant concentration no effect upon the lattice parameter is found.     

Positron lifetime study of hafnium nitride films

Films of HfN can have expanded lattices which are restored by tempering, reflecting the presence of a high concentration of defects. The present study was made to get a qualitative understanding of the lattice relaxation on an atomic scale. The results support the proposal that the dominant mechanism is the migration of interstitial atoms into lattice vacancies.     

Effect of In and Sb Vacancies on Temperature Dependence of InSb Lattice Parameter at High Temperatures

The temperature dependence of the thermal expansion coefficient for InSb has been determined in the range 25–515 °C by precision measurements of the lattice parameter of InSb single crystals. It is shown that beginning from 460 °C the temperature dependence of the lattice parameter for InSb single crystals grown from melts of different compositions is essentially affected by vacancies in the indium and antimony sublattices. The vacancy concentration and possible deviation of InSb from the stoichiometric composition are estimated from a relative decrease in the lattice parameter.     

SAXS investigations of structure of formation in alcoholic ZrO2---SiO2 solutions

Small-angle X-ray scattering was used to examine in situ formation of ZrO₂---SiO₂ structures in alcoholic solution of tetraethoxysilan (TEOS) as a function of the ratio of ZrO₂ to SiO₂. For the moment of the first measurement (15 min after the preparation) primary particles with R_g ≈ 1.5 nm exist in all investigated mixed gels. These particles aggregated to secondary clusters. The resulting clusters can be described by means of fractal theory, where the determining mechanism of formation is cluster-cluster aggregation (diffusion or chemical limited). The time of gelation is a function of the ZrO₂ concentration. The higher the ZrO₂ concentration in the solution, the faster is the aggregation to secondary clusters. Gelation times were between 170 and 970 h.     

The effect of inter-cluster interactions on the structure of colloidal clusters

Colloidal systems present exciting opportunities to study clusters. Unlike atomic clusters, which are frequently produced at extremely low density, colloidal clusters may interact with one another. Here we consider the effect of such interactions on the intra-cluster structure in simulations of colloidal cluster fluids. A sufficient increase in density leads to a higher population of clusters in the ground state. In other words, inter-cluster interactions perturb the intra-cluster behaviour, such that each cluster may no longer be considered as an isolated system. Conversely, for dilute, weakly interacting cluster fluids little dependence on colloid concentration is observed, and we thus argue that it is reasonable to treat each cluster as an isolated system.     

Defect characterization of mixed SrCa tartrates

A few defect characteristics which are typical of gel-grown mixed single crystals of SrCa tartrates (Sr_1−XCa_xC₄H₄O₆ · 4H₂O) having different concentration, x, of the cations have been described. The temperature of decomposition has been found to be related, to some extent, to dislocation concentration. The magnitude of configurational entropy, which is a manifestation of lattice disorder, has been computed. The Vickers microhardness and dislocation density of crystals have been found to bear good correlation. An empirical formula has been suggested to explain the observed variation in microhardness with the concentration of ions in the mixed lattice.     

Solvothermal controlled growth of Zn-doped SnO2 branched nanorod clusters

Branched Zn-doped SnO₂ nanorod clusters with tunable size and aspect ratios were prepared by a facile solvothermal process. The introduction of a small quantity of Zn²⁺ proved to play an important role in directing the anisotropic growth of SnO₂ nanocrystals. The as-synthesized products exhibit tetragonal rutile structure and many lattice defects exist in the products. The possible growth mechanism has been proposed. These Zn-doped SnO₂ nanorods exhibited unique Raman spectrum in contrast with the undoped SnO₂ nanostructures. These Zn-doped SnO₂ nanorods showed good sensitivities to ethanol gas, acetone gas, and benzene gas.     

A model study of the growth of crystals consisting of a small number of metal atoms by the Hückel molecular orbital method (I). Addition of One atom to small crystals

The paper deals 1) with the regularities of the formation of (N + 1)-atomic clusters during the growth of N-atomic one-, two-, and three-dimensional crystals and 2) with the distribution with respect to stability of the (N + 1)-atomic clusters. The N-atomic crystals have the structure of a hypothetical metal with a simple cubic lattice and a small number of one-electron atoms. The binding energy (BE) of the clusters calculated by the Hückel molecular orbital method was assumed to be a measure of their stability. Interactions between nearest-neighbours only were taken into account. The most stable (N + 1)-atomic cluster formed from a one-dimensional crystal is that in which the N + 1-st atom is bonded to the end atom of the N-atomic one-dimensional crystal. For two-dimensional crystals, the N + 1st atom forms the strongest bond with an atom from the diagonal of the square. With three-dimensional crystals, the N + 1st atom is most strongly bonded to a corner atom of the small crystal. The inhomogeneity in the bond energy of the N + 1st atom to a surface atom of the small N-atomic crystal decreases with increasing N. According to earlier studies of ours, the BE per atom increases, whereas the mean energy of a nearest-neighbour bond decreases with increasing N.