Steps and facets at the surface of soft crystals

We consider the shape of crystals which are soft in the sense that their elastic modulus μ is small compared to their surface tension γ, more precisely μa < γ where a is the lattice spacing. We show that their surface steps penetrate inside the crystal as edge dislocations. As a consequence, these steps are broad with a small energy which we calculate. We also calculate the elastic interaction between steps a distance d apart, which is a 1/d ² repulsion. We finally calculate the roughening temperatures of successive facets in order to compare with the remarkable shapes of lyotropic crystals recently observed by Pieranski et al. [#!Pieranski!#,#!EPJ!#]. Good agreement is found. Received 25 June 2001     

Identification of a TGBA liquid crystal phase via its defects

We have shown that cholesteryl nonanoate, a thermotropic compound which is well known to exhibit pretransitional effects at the smectic A (SmA) cholesteric (N*) transition (W.L. McMillan, Phys. Rev. A 4, 1238 (1971); 6, 936 (1972)), has in fact a TGBA phase in between. Our arguments rely on the observation of new TGBA defects, either in Robinson spherulites cooled from the N* phase or in free-standing films. The same new defects can be obtained in a well-documented TGBA phase of a tolane compound. We analyze qualitatively the TGBA defects in both geometries, in particular their relation to the disclination radius of the N* Robinson spherulites. Received 12 February 2001     

电感耦合等离子体原子发射光谱法高纯三甲基镓中的痕量杂质

对电感耦合等离子体原子发射光谱（ＩＣＰ－ＡＥＳ）法测定高纯三甲基镓（９９．９９９９Ｔ,相对于金属镓的含量）中Ｃu、Ｆe、Ｓi、Ｚn等３１种痕量杂质元素的含量进行了研究,考察了基体元素镓对杂质元素的光谱和非光谱干扰以及基体浓度对杂质元素谱线信噪比和检出限的影响在优化的实验条件下,获得了满意的结果。     

Determination of nucleation kinetics of potassium tetraborate tetrahydrate

In this study, the metastable zone width of potassium tetraborate tetrahydrate was determined for four different temperatures and cooling rates. The induction period of potassium tetraborate tetrahydrate in aqueous solution was examined according to polythermal method by using visual observation. The induction period, which changes inversely proportional to the nucleation rate has been used to determine the interfacial tension between the potassium tetraborate tetrahydrate and aqueous solution. By using interfacial tension, the nucleation parameters such as Gibbs free energy change for the formation of critical nucleus, ΔG*, free energy of formation, ΔG, radius of critical nucleus, r and number of molecules in the critical nucleus, i* has been calculated. The effect of Li⁺ and Ca²⁺ impurities on metastable zone width has been studied. The metastable zone width of aqueous solution of potassium tetraborate tetrahydrate decreases with increasing impurity concentrations. The equilibrium saturation concentration change is high in the presence of Ca²⁺ ions while it is low in the presence of Li⁺ ions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

电感耦合等离子体质谱法测定高纯氧化钽中28种痕量杂质元素

建立了用电感耦合等离子体质谱仪(ICP-MS)测定高纯氧化钽中28种痕量杂质元素的方法。讨论了质谱干扰及接口效应,采用标准加入法消除基体效应。各元素的方法检出限为0.001~0.1μg/g,回收率为90%~115%,方法适用于纯度为99.999%的高纯氧化钽中痕量杂质元素的测定。     

A comparative study of nonrelativistic and relativistic 5d atoms as impurities in silicon

A comparison is made between calculations performed nonrelativistically and relativistically for W, Re, Os, Ir, Pt, Au and Hg as substitutional impurities in silicon. The calculations were carried out using the relativistic extended Hückel method. The direct and indirect relativistic effects upon the 5d-like levels and band-gap levels are analysed.     

直流等离子体-中阶梯光栅光谱仪测定高纯氧化镧、氧化钇中稀土杂质

本文采用中阶梯光栅光谱仪,直流等离子体光谱法测定高纯(99.99%)氯化镧、氧化钇中稀土杂质元素,由于仪器具有很高的色散率,因而方法具有灵敏度高、干扰少的特点。     

Far-infrared absorption studies of Be acceptors in δ-doped GaAs/AlAs multiple quantum wells

We report a far-infrared absorption study of internal transitions of shallow Be acceptors in both bulk GaAs and a series of δ-doped GaAs/AlAs multiple quantum well samples with well thicknesses of 20, 15 and 10 nm. Low temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of Beacceptor states from the ground state to the first three odd-parity excited states, respectively. Using a variational principle, the 2p-1s transition energies of quantum confined Be acceptors are calculated as a function of the well width. It is found that the theoretical calculation of the 2p_z → 1s transitions is in good agreement with the D-like line experimental data.     

Hyperfine Fields of Light Interstitial Impurities in Ni

The magnetic hyperfine interaction of light interstitial impurities in Ni have been studied by means of the Korringa–Kohn–Rostoker (KKR) band structure method. This method allows to deal with the impurity problem by solving the corresponding Dyson equation for the Green’s function. It also allows to account for lattice relaxations. For this purpose a new technique was developed that allows to handle in principle arbitrary lattice distortions. Corresponding calculations have been performed for the magnetic hyperfine fields of the light interstitial impurities H to Ne in Ni. By minimising the force on the nearest neighbour host atoms their equilibrium position was determined. The resulting hyperfine fields for the equilibrium configuration are found to be in rather good agreement with available experimental data.     

Off-center substitutional ions in alkali-halide crystals

The potential wells of alkali and halogen ions as impurities in alkali halides are investigated by means of a deformation-dipole model with single-ion parameters. The calculations indicate that Li⁺ is off center in seven and F^? in six of the sixteen rocksalt-type crystals considered. In about half of the off-center systems the configuration has D_4h symmetry if the impurity is kept at its lattice position. The minimum-energy configuration of the off-center system KCl:Li⁺ is calculated in detail, and the influence of hydrostatic pressure is investigated. Our results are in qualitative agreement with experiment.