高温下锂离子在低掺镁铌酸锂晶体中的扩散

研究了高温富锂气氛下锂离子在低掺镁铌酸锂晶体中的扩散.采用气相输运平衡法制备了掺杂1mol; MgO的不同锂含量的铌酸锂(Mg1LN)晶体,采用热分析仪测试了晶体的居里温度.制备了一系列不同锂含量的Mg1LN多晶料,拟合了晶体锂含量与居里温度的关系.采用Boltzmann-Matano法求解了扩散方程.结果表明,扩散温度为1100 ℃时,Mg1LN晶体中锂离子扩散系数为3.2×10-9~13.0×10-9 cm2/s,当扩散温度为1145 ℃时锂离子扩散系数约是1100 ℃时扩散系数的三倍.因此,适当提高扩散温度是提高气相输运平衡法制备近化学计量比低掺镁铌酸锂晶体效率的有效办法.     

Diffusion constant of Ga adatom on GaAs (001) surface: Molecular dynamics calculations

A valence force field to reproduce both the phonon dispersion curves of crystalline GaAs and first principle derived interaction energies of Ga adatom on GaAs (001) surface has been optimized. Calculations of diffusion constant of isolated Ga atoms on the GaAs surface have been performed by molecular dynamics classical trajectory simulations.     

Fast synthesis of Cu‐doped ZnO nanosheets at ambient condition

A new, fast and low cost method to produce Cu‐doped ZnO nanosheets is reported for the first time in this paper. Zinc foil specimens were immersed into CuSO₄ aqueous solutions with various concentrations for 3 seconds and then dried at ambient condition. The immersed specimens were characterized with a scanning electron microscope, an X‐ray diffractometer and a transmission electron microscope. The results show that Cu‐doped ZnO nanosheets with a multilayer structure on a cupper layer are formed. Cu‐doped ZnO nanosheets show hexagonal crystalline structure and comprises polycrystalline grains with diameters of 5∼10 nm. A physical modal is suggested to explain the prepared Cu‐doped ZnO nanosheet structure, based on the chemical reactions and a metallurgical cell.     

Colloidal silver formation at the surface of float glass

The formation of colloidal silver during the heating in air of silver films on float glass has been observed. The presence of colloidal silver gives to a yellow color and an absorption band centered at 400–420 nm. The results of this study indicate that the formation of colloidal silver is strongly dependent upon the concentration of stannous tin in the glass. The optical density of the absorption band induced in the glass is much greater for samples silvered on the tin-rich face of the glass and varies with the thermal history of the sample. Removal of the outer few micrometers of the glass surface results in a radical change in the amount of colloidal silver formed. Silver colloids are formed only if the sample is heated in an atmosphere containing oxygen, suggesting that the silver must be ionized before it will diffuse into the glass. The colloid formation process has an activation energy of approximately 30 kcal/mol, which is very near that reported for silver-sodium interdiffusion in similar glasses.     

Fluctuation of crystallization at center part of floating molten zone under reduced gravity condition

Fluctuation of crystallization was observed at floating molten zone under reduced gravity condition on airplane. The zone material was Ba(B_0.9Al_0.1)₂O₄. A pair of Pt tubes was used at the upper and the lower positions, and the molten zone was formed between two Pt tubes. Double peak temperature profile could be performed using two Pt tubes. Crystallization of the molten Ba(B_0.9Al_0.1)₂O₄ was started at center part of side surface of floating molten zone under reduced gravity condition. The formed crystal was melted again during the crystallization by the gravity fluctuation at the center part of the floating molten zone. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pattern transition of temperature distribution at Czochralski silicon melt surface

The melt surface temperature in Czochralski silicon growth was studied by CCD camera observation. The thermal radiation energy from the melt surface was converted into temperature by the blackbody calibration method and was recorded with a VCR as two-dimensional color images. The experimental results without a crystal revealed that the temperature distribution at the melt surface can change in four patterns depending on the crucible rotation rate: axisymmetric spoke pattern at low rotation rates, n-folded and island patterns at medium rotation rates, and cellular patterns at high rotation rates. To predict the fluid motion from the experimental observations, three-dimensional time-dependent numerical simulations of the silicon melt flow were executed. As a result, a qualitative transition model for the temperature distribution and the Czochralski silicon melt flow was derived.     

Computer simulations of the role of group V molecular reactions at steps during molecular beam epitaxial growth of III-V semiconductors

The Configuration Dependent Reactive Incorporation (CDRI) model is used to study the growth of III-V semiconductors by MBE. In particular, the role of the dissociative reaction of the group V molecular species from the physisorbed precursor state is studied. The model allows for the reaction to occur at pairs of vacant group V sites which are intra- or interplanar nearest neighbors on the group V sublattice. Within this model, it is shown that a relatively small number of depositions at steps can play an important role in determining the smoothness of the growth front and the effective migration length of the group III species. Conditions under which these depositions are likely to be less influential are also discussed.     

Luminescence properties of nonbridging oxygen hole centers at the silica surface

Two variants of the surface-nonbridging oxygen hole center, (Si–O)₃Si–O^? and (Si–O)₂(H–O)Si–O^?, stabilized in porous films of silica nano-particles were investigated by time resolved luminescence excited in the visible and UV spectral range by a tunable laser system. Both defects emit a photoluminescence around 2.0 eV with an excitation spectrum evidencing two maxima at 2.0 and 4.8 eV, this emission decreases by a factor ～2 on increasing the temperature from 8 up to 290 K. However, the different local structure influences the emission lineshape, the quantum yield and the decay lifetime. Such peculiarities are discussed on the basis of the symmetry properties of these defects.     

Diffusion of chromium in chrysoberyl

Cr³⁺ diffusion in chrysoberyl (BeAl₂O₄) irradiated by H⁺ ions and electrons has been studied and compared with diffusion in non-irradiated samples. Chrysoberyl crystals were irradiated with 6 MeV H⁺ ions to fluencies of 1×10¹⁶ cm^–2 for 25 min and with 10 MeV electrons to fluencies of 2×10¹⁷ cm^–2 for 1 h. Three different types of samples, which were doped with Cr³⁺, were annealed in horizontal alumina tube furnaces by 50 K intervals in the temperature range from 1773 to 1923 K for 200 h. Scanning electron microscope–energy dispersive X-ray spectrometer (SEM–EDX) was used to measure the diffusion. Arrhenius equations for the diffusion coefficient for Cr³⁺ in the temperature range 1773–1923 K were developed:     

Diffusion in amorphous NiZrAl alloys

Tracer diffusion coefficients for large and small sized impurities were measured in the bulk metallic glass Ni_xZr_yAl_z for several compositions. Molecular beam deposition was employed to grow thin films and secondary ion mass spectrometry was used to determine the concentration-depth profiles of several tracers. A dependence of the atomic mobility of the tracer on its size was found, as observed in the binary Ni_xZr_y amorphous alloy system. The presence of the Al reduces the diffusion coefficients in general, with a stronger decrease for the small sized tracer. The results support the existence of two different diffusion mechanisms proposed for amorphous metallic alloys.     

Diffusion of vanadium in GaAs

The diffusion of Vanadium has been studied in V-doped GaAs layers (GaAs:V) grown by Metal-Organic Chemical Vapour Deposition (MOCVD) using secondary ion mass spectroscopy (SIMS). The vanadium (V) concentration profiles of sandwiched structures made of alternatively undoped and V doped GaAs layers have shown a concentration independent diffusion coefficient (D_V) for varying V doping levels from 10¹⁸ to 10¹⁹ cm⁻³. Measurements of D_V at 550, 615 and 680 °C indicate that the temperature dependence of D_V can be represented by the Arrhenius equation:  cm² s⁻¹. It is suggested that V diffuses via interstitial sites.     

Investigations on nitride layer formation at the iron surface during gas nitriding

The morphology of the nitride layer forming at gas nitriding can decisively be influenced by the pretreatment of the surface. At a temperature of about 550 °C an activated surface very swiftly covers with iron nitrides. After passivating of the surface the nitride formation and the geometrical order of the nitride layer are determined by the heating rate. At high heating rates the formation of iron nitrides is localized to a few spots and the extension of the nitride layer proceeds by the growth of these spots. At low heating rates the surface is reactivated by the reducing gas before reaching the nitriding temperature. By further investigations is shown that nitriding of the surface starts with the formation of γ′-nitrides. ϵ-Nitrides occur in the further process of nitriding as a second layer on the γ′-phase.     

Diffusion of iodine in lead telluride

By using the non-stationary thermal-probe method, investigations were carrieed out on the distribution of the coefficient of thermal electromotive force along the depth of monocrystals of lead telluride, subjected to isothermal saturating annealing in vapours of alloying compositions. The alloying composition consisted of powdered lead telluride, synthesized by the iodide method, and contained elevated concentration of the metallic component and iodine. The PbTe monocrystals were obtained from the vapour phase and had a natural cut. The results of the investigations testify to considerable changes in the concentration of the electrically active proper defects within the entire volume of the crystals, this being obviously connected with diffusion of vacancies from the crystal volume.     

Dotierung von ZnSiP2 durch Diffusion

Diffusion experiments with gallium, indium, aluminium, tin, chromium, gold, lead and tellurium in the ternary semiconductor ZnSiP₂ were carried out. With elements of the third group of the periodic law it was obtained an unambiguous doping effect demonstrated by temperature dependence of the Hall coefficient and by investigations with the electron microprobe. Diffusion of gallium, aluminium and indium caused the formation of shallow donors in ZnSiP₂ with activation energies (at vanished impurity concentration) of 30 meV, 65 meV, 70 meV, respectively. From semi-insulating p-ZnSiP₂ often prepared by crystal growth low resistivity n-ZnSiP₂ was made by diffusion with gallium and indium.     

Behavior of a nematic liquid crystal in oscillatory flow at weak surface anchoring

The effect of the surface viscosity on the orientational dynamics of a nematic liquid crystal in an oscillatory flow has been studied. For the shear and the Poiseuille flows, the approximate analytical solutions of the nematodynamic equations are obtained at small flow amplitudes. The frequency range of the oscillatory flow is determined, in which the surface viscosity strongly affects the optical response of a nematic layer. The results obtained are compared with the data of direct numerical simulation of the nematodynamic equations and the method for the experimental determination of surface viscosity is proposed.     

Diffusion Control during Vapour Crystal Growth

The crystal growth rate under diffusion control is considered. Together with nutrient diffusion, the physi-sorption of an inert gas, which impedes the surface kinetics during vapour growth, is taken into consideration. In this way the size of the diffusion field surrounding vapour grown crystals was estimated. The relations obtained are checked with data for the growth of zinc single crystals in argon atmosphere. The appearance of shallow cavities on their basal faces is used as a morphological mark for growth under diffusion control. Besides, the microstructure of the inner edge of the macroscopically flat periphery, surrounding the shallow cavities is investigated experimentally, by means of SEM.     

On the Diffusion Anisotropy of Polycrystals

A model of diffusion anisotropy appearance in a textured polycrystalline aggregate under the grain boundary diffusion preponderance (the C type of kinetic) has been suggested. Although in the textured polycrystal there exists a distribution over 5 degrees of freedom describing the grain boundaries macroscopically, it is the misorientation distribution that has been shown to may give rise to the diffusion anisotropy. Presence of small-angle boundaries and a certain, sufficiently sharp texture is the key moment at this.