KNUDSEN measurements of the sublimation and the Heat of Formation of GeSe

KNUDSEN effusion studies of the sublimation of polycrystalline GeSe have been performed employing mass spectrometry in a temperature range of about 530–730°K and vacuum microbalance techniques in the temperature range 601–796°K and at pressures ranging from about 10^?6–10^?4 atm. The results are concordant and demonstrate that GeSe vaporizes congruently under present experimental conditions according to the reaction GeSe(s) = GeSe(g). The mean values for the third law heat and second law entropy of reaction based on direct mass-loss data are ΔH = 42.0 ± 1.5 kcal/mole and ΔS = 42.3 ± 1.6 eu. From these data the standard heat of formation and absolute entropy of GeSe(s) were calculated to be ?10.1 ± 2.0 kcal/mole and 16.9 ± 2.0 eu, respectively.     

The Thermal Expansion of GeS and GeTe

The thermal expansion of GeS has been studied above room temperature up to the melting point of 658 ± 5°C by X-ray diffraction techniques using a 190 mm diameter Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with distinct changes in the rate of expansion at about 250°C, 370°C and 510°C. No first-order structural transformation was observed for this system up to the melting point. The results of additional studies on GeTe are in general agreement with those of others and confirm trends in the thermal expansion behavior of the germanium monochalcogenide series.     

The Sublimation Kinetics of GeSe Single Crystals

The sublimation kinetics of (001) oriented GeSe single crystal platelets was studied by means of high temperature mass spectroscopy, quantitative vacuum microbalance techniques and hot stage optical microscopy. Solid GeSe sublimes under non-equilibrium conditions according to the reaction GeSe(s) → GeSe(g). The activational enthalpy and entropy for the mean experimental temperature 563°K are ΔH₅₆₃* = 32.3 kcal/mol and ΔS₅₆₃* = 19.1 eu. The vaporization coefficient α is less than unity for the temperature range studied and α decreases with increasing temperature. The combined experimental data are correlated by means of a multi-step surface adsorption mechanism.     

Transition metal complexes of γ-mercaptoalkylpiperidines

Summary Complexes with 1-methyl-3-(mercaptomethyl)piperidine (LH) and 1-methyl-2-(2-mercaptoethyl)piperidine (LH) Ligands in their thiolato (R), andN-protonated (HR) orN-methylated (MeR) zwitterionic form, of stoichiometry MR₂ (M=Ni, R=L or L; M=Cd, R=L), MR (M=Cu or Ag, R=L and L), [Ni(MeR)₂]I₂ · nH₂O (R=L, n=1; R=L, n=2), [Ni(HR)₂]X₂ (R=L or L, X=ClO₄; R=L, X=Br), and [Ag(HR)] ClO₄ (R=L) have been prepared and characterized. According to i.r. and electronic spectra, and magnetic measurements the nickel complexes exhibit polymeric frameworks built up from mercapto-bridged metal atoms in square-planar environments. Complexes with copper, silver, and cadmium exhibit similar polymeric arrangements through bridging sulphur atoms but with a different geometry at the metal centers, the first two being mainly linear, as anticipated, and the latter tetrahedral. In no case does coordinationvia nitrogen take place and therefore these ligands behave simply as mercaptides.     

The thermal expansion and high temperature transformation of GeSe

The thermal expansion of GeSe has been studied above room temperature up to the melting point of 670 ± 5°C by X-ray diffraction techniques using a 190 mm Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with a distinct change of the expansion coeffients for all axes above 400°C. The relative changes of the axes indicate a rearrangement of the structure towards cubic symmetry with increasing temperature. The transformation of GeSe from the orthorhombic to a normal NaCl-type structure is observed at 651 ± 5°C. The lattice parameter of the cubic form of GeSe is a₀ = 5.730 ± 0.003 Å at 656°C. The GeSe lattice remains cubic up to the melting point.     

High-performance liquid chromatographic,capillary electrophoretic and capillary electrophoretic-electrospray ionisation mass spectrometric analysis of selected alkaloid groups

Systems for efficient separation of selected alkaloid groups by high performance liquid chromatography (HPLC), capillary electrophoresis (CE) and capillary electrophoresis coupled with electrospray ionisation mass spectrometry (CE-ESI-MS) are described. The optimized HPLC system was applied for the separation of 23 standard indole alkaloids as well as for qualitative and quantitative analyses of crude alkaloid extracts of Rauvolfia serpentina X Rhazya stricta hybrid cell cultures. The developed conditions for CE analysis proved to be efficient for separation of mixtures of standard indole and beta-carboline alkaloids. The described buffer system is also applicable in the combination of CE with electrospray ionisation mass spectrometry. This analytical technique allowed the separation and identification of components of standard indole alkaloid mixture as well as crude extracts of R. serpentina roots, R. serpentina cell suspension cultures and cortex of Aspidosperma quebracho-blanco. The influence of buffer composition and analyte structures on separation is discussed.     

Micro-Raman imaging and micro-photoluminescence measurements of strain in ZnMgSe/ZnSe microdiscs

Semiconductor microdiscs are promising for applications in photonics and quantum-information processing, such as efficient solid-state-based single-photon emitters. Strain in the multilayer structure of those devices has an important influence on their optical properties. We present measurements of the strain distribution in ZnMgSe/ZnSe microdiscs by means of micro-photoluminescence and micro-Raman imaging. Photoluminescence measurements of microdiscs reveal substantially broadened emission lines with a shift to lower energy at the undercut part of microdiscs, indicating local relaxation in this area. The distribution of the strain in the microdiscs is obtained from an imaging micro-Raman analysis, revealing that the freestanding part of the microdiscs is free of defects.     

ALE-based 3D FE simulation of electromagnetic forming

Electromagnetic forming is a contact-free high-speed forming process. The deformation of the work piece is driven by the Lorentz force which results from the interaction of a pulsed magnetic field with eddy currents induced in the work piece by the field itself. The purpose of this work is to present a fully-coupled three-dimensional simulation of this process. For the mechanical structure, a thermoelastic, viscoplastic, electromagnetic material model is relevant, which is incorporated in a large-deformation dynamic formulation. The electromagnetic fields are governed by Maxwell's equations under quasistatic conditions. To consider their reduced regularity at material interfaces Nédélec elements are applied. Coupling takes the form of the Lorentz force, the electromotive intensity and the current geometry of the work piece. A staggered solution scheme based on a Lagrangian mesh for the work piece and an ALE formulation for the electromagnetic field is employed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Physical vapor transport and crystal growth of GeSexTe1−x solid solutions

Physical vapor transport studies of GeSe_xTe_1–x (x = 0.1, 0.2, 0.3, and 0.4) solid solutions demonstrated, that individual, large single crystals of these materials can be grown in closed ampoules. A compositional analysis of the grown crystals revealed, that the mass transport (crystal growth) process under steady-state conditions is pseudo-congruent and controlled by diffusion processes in the source material. From these experiments, the degree of nonstoichiometry (Ge-vacancy concentrations) of GeSe_xTe_1–x single crystals could be estimated. The effects of the cubic to rhombohedral phase transformation during cooling on the microstructure and morphology of the grown mixed crystals are observed. This work provides the basis for subsequent defect studies and electrical measurements on these crystals.