Präparation von Polykristallen der intermetallischen Verbindung MgZn2

The influence of mechanic vibration treatments on the solidification of the intermetallic compound MgZn₂ is investigated. A clear connection exists between velocity of vibrations and resulting grain refinement. A minification factor 50 could be proved as the extreme value for the given apparatus conditions. The grain sizes of the shaken probes follow a logarithmic normal distribution. A minification of already solidified primary crystallites, caused by a friction force between growth batch and front of solidification, is discussed as the decisive mechanism of the grain refinement.     

The simultaneous crystallization of ZnSnP2/ZnSiP2 — a heterocombination

In the solution growth of ternary semiconductors tin can be used as solvent. In this case the phase purity resp. the generation of a solid solution of the reaction products obtained is of interest. This problem was investigated using the growth of ZnSiP₂ from tin solutions. For characterizing the phases obtained by the growth X-ray diffraction. Mössbauer spectroscopy, electronoprobe analysis, luminescence spectroscopy, DTA-measurements and electrical measurements were used. The results of these measurements allow the following statements within the limits of measuring.

• 1 The growth of the pure ZnSiP₂ from tin melts is possible.
• 2 The phases ZnSnP₂ and ZnSiP₂ are generated side by side by a nonstoichiometric amount weighed of silicon.
• 3 The solubility of ZnSnP₂ in ZnSiP₂ or reverse could not be pointed out.
• 4 The precipitation of ZnSnP₂ on ZnSiP₂ takes place epitaxially.

     

Einsatz der Elektronenstrahl-Mikrosonde bei der Lösung metallurgischer Werkstoffprobleme

The electron-probe microonalysis provides a variety of informations on the condition of mettalic samples within the micro range, which in connection with an appropriate measuring technique enables numerous statements to be made on important metallographic problems. As examples from the operating practice of a high-quality steel plant the identification of structural constituents, determination of microsegregation, investigation of grain boundaries and material defects in steels are explained.     

Contribution to the Si doping of bridgeman GaAs

GaAs: Si with different doping level was grown by the gradient freeze method. The crystals were characterized by structural, electrical and optical methods concerning especially the dependence of the epd and the compensation degree on the carrier concentration.     

Herstellung und elektrische Eigenschaften von dotiertem ZnSiP2

The properties of ZnSiP₂ crystals prepared by adding of Ga and In to the melt differ essentially from that of undoped samples. Especially the activation energies determined from the temperature dependence of the Hall coefficient prove that in both cases a real doping with shallow impurities has taken place. Ga and In act as donors suggesting the conclusion that Ga and In atoms substitute Zn atoms. The existence of strong electrical inhomogenities in a part of the samples is discussed.     

Porous Salts Containing Cationic Al24-Hydroxide-Acetate Clusters from Scalable,Green and Aqueous Synthesis Routes

The solution chemistry of aluminum is highly complex and various polyoxocations are known. Here we report on the facile synthesis of a cationic Al₂₄ cluster that forms porous salts of composition [Al₂₄(OH)₅₆(CH₃COO)₁₂]X₄, denoted CAU-55-X, with X=Cl⁻, Br⁻, I⁻, HSO₄⁻. Three-dimensional electron diffraction was employed to determine the crystal structures. Various robust and mild synthesis routes for the chloride salt [Al₂₄(OH)₅₆(CH₃COO)₁₂]Cl₄ in water were established resulting in high yields (>95 %, 215 g per batch) within minutes. Specific surface areas and H₂O capacities with maximum values of up to 930 m² g⁻¹ and 430 mg g⁻¹ are observed. The particle size of CAU-55-X can be tuned between 140 nm and 1250 nm, permitting its synthesis as stable dispersions or as highly crystalline powders. The positive surface charge of the particles, allow fast and effective adsorption of anionic dye molecules and adsorption of poly- and perfluoroalkyl substances (PFAS).     

Herstellung und ausgewählte physikalische Eigenschaften von ZnSiP2

Undoped ZnSiP₂ crystals grown by different methods (vapour phase transport, solution growth) show in part considerable differences in their physical properties. The connections between growth, quality of the basic materials and the physical properties of ZnSiP₂ will be shown. Measurements of Hall effect, resistivity, luminescence and backscattering of protons yielded informations about the perfection and homogenity of the crystals and about the impurities and recombination centres characteristically for the various growth methods. The influence of doping by different elements on the properties of solution grown ZnSiP₂ crystals was investigated.     

Novel swelling/shrinking behaviors of glucose-binding hydrogels and their potential use in a microfluidic insulin delivery system

Hydrogels based on lightly crosslinked poly(methacrylamidophenylboronic acid-co-acylamide) swell monototically at pH 7.4 with exposure to increasing concentrations of glucose. At pH 10 these hydrogels first shrink and then reswell with increasing glucose concentration. A mechanism for these disctinct behaviors is proposed and preliminary results validating this mechanism are presented. A simple microfabricated glucose-sensitive valve based on this hydrogel is described.