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Vacuum Conditions (vacuum + condition)
Selected Abstracts1-D-Tin(II) Phenylchalcogenolato Complexes ,1[Sn(EPh)2] (E = S, Se, Te) , Synthesis, Structures, Quantum Chemical Studies and Thermal BehaviourEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2010Andreas Eichhöfer Abstract A series of three 1-D-tin(II) phenylchalcogenolato complexes ,1[Sn(EPh)2] (E = S, Se, Te) were synthesized in yields > 80,% by reaction of SnCl2 with two equivalents of PhESiMe3 in organic solvents. In the crystal the molecules form two different types of one-dimensional chains. In ,1[Sn(SPh)2] the tin atoms are distorted trigonal pyramidal coordinated by sulfur atoms (two bonds within a monomer and one longer bond between neighbored monomers), while in ,1[Sn(EPh)2] (E = Se, Te) the tin atoms show contacts to two neighbored monomers leading to a fourfold coordination of the tin atoms by either selenium or tellurium atoms. The bond situation is discussed on the basis of density functional calculations. Thermal treatment mostly leads to the formation of the corresponding phase pure tin(II) chalcogenides however sublimation plays an increasing role ongoing from the tellurolato to the thiolato complex especially for the use of vacuum conditions. The investigation of the volatile cleavage products reveals the occurence of more complex reactions in the gas phase than the formal stoichiometric cleavage of EPh2 (E = S, Se, Te) with formation of SnE. [source] Air-Stable n-Type Organic Field-Effect Transistors Based on Carbonyl-Bridged Bithiazole DerivativesADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Yutaka Ie Abstract An electronegative conjugated compound composed of a newly designed carbonyl-bridged bithiazole unit and trifluoroacetyl terminal groups is synthesized as a candidate for air-stable n-type organic field-effect transistor (OFET) materials. Cyclic voltammetry measurements reveal that carbonyl-bridging contributes both to lowering the lowest unoccupied molecular orbital energy level and to stabilizing the anionic species. X-ray crystallographic analysis of the compound shows a planar molecular geometry and a dense molecular packing, which is advantageous to electron transport. Through these appropriate electrochemical properties and structures for n-type semiconductor materials, OFET devices based on this compound show electron mobilities as high as 0.06,cm2 V,1 s,1 with on/off ratios of 106 and threshold voltages of 20,V under vacuum conditions. Furthermore, these devices show the same order of electron mobility under ambient conditions. [source] Electronic and Magnetic Properties of Ligand-Free FePt Nanoparticles,ADVANCED MATERIALS, Issue 5 2005H.-G. Boyen Ligand-free FePt nanoparticles are prepared in densely packed arrays (see Figure) under ultrahigh vacuum conditions, in which oxygen and hydrogen plasmas are used to remove the organic shells that are present after particle synthesis. The electronic structure and magnetic properties of the "bare", face-centered-cubic FePt particles are presented. Applications in high-density magnetic data recording are foreseen. [source] Synthesis of Diacylglycerols Containing CLA by Lipase-Catalyzed EsterificationJOURNAL OF FOOD SCIENCE, Issue 7 2006In-Hwan Kim ABSTRACT:, Diacylglycerols (DAG) were prepared by esterification of glycerol with conjugated linoleic acid (CLA) in the presence of an immobilized 1,3-regiospecific lipase from Rhizomucor miehei and vacuum conditions. The effects of several parameters, namely, temperature, enzyme loading, stirring speed, and vacuum, on the concentration and the purity of the DAG were studied. The reaction temperature influenced both the reaction rate and the concentration of the DAG. The rate of DAG synthesis increased as the enzyme loading increased. However, for high enzyme loadings, the concentration of triacylglycerols (TAG) increased significantly at long reaction times and, as a result, the purity of the DAG decreased. When the stirring speed increased from 150 to 450 rpm, the DAG concentration increased significantly. However, at stirring speeds above 450 rpm, no significant increases in DAG concentration were observed. When the pressure was decreased from 20 to 3 mmHg, the maximum concentration of DAG increased from 76.0% to 80.5%. No increase in the DAG concentration was observed when the pressure was decreased from 3 to 1 mm Hg, even though a slightly higher DAG purity was achieved at 1 mm Hg. For the range of absolute pressures tested, the concentrations of 1,2-DAG were less than 1%. [source] Optimization of Incorporation of Low-molecular-weight Cryoprotectants into Intact Fish MuscleJOURNAL OF FOOD SCIENCE, Issue 4 2004L. M. Goeller ABSTRACT: Chunks of freshwater trout muscle were immersed in sorbitol solutions (0% to 60%), under different vacuum conditions, for up to 30 min at 5 °C. Moisture loss, weight change, and sorbitol uptake were measured or calculated by mass balance, and cryoprotection during subsequent freezing and thawing was monitored as change in myosin Ca2+ ATPase activity. Vacuum treatment had no effect on measured parameters. Initial sorbitol uptake and weight loss were greater at higher sorbitol concentrations, but adequate cryoprotection was achieved by all treatments when diffusion time following immersion was extended sufficiently. Injection of 60% sorbitol was faster in achieving desired levels of sorbitol in fish meat and induced excellent cryoprotection. [source] Vacuum tribological behaviour of self-lubricating quasicrystalline composite coatingsLUBRICATION SCIENCE, Issue 2 2004F. J. Ía Garc de Blas Abstract High-temperature-resistant self-lubricating coatings are needed in space vehicles for components that operate at high temperatures and/or under vacuum. Thick composite lubricant coatings containing quasicrystalline alloys as the hard phase for wear resistance can be deposited by a thermal spray technique. The coatings also contain lubricating materials (silver and BaF2CaF2 eutectic) and NiCr as the tough component. This paper describes the vacuum tribological properties of TH103, a coating of this type, with a very good microstructural quality. The coating was deposited by high-velocity oxygen fuel spraying and tested under vacuum using a pin-on-disc tribometer. Different loads, linear speeds, and pin materials were studied. The pin scars and disc wear tracks were characterised using a combination of scanning electron microscopy and energy dispersive spectrometry. A minimum mean steady friction coefficient of 0.32 was obtained when employing an X750 Ni superalloy pin in vacuum conditions under 10 N load and 15 cm/s linear speed, showing moderate wear of the disc and low wear of the pin. [source] Influence of adsorbates on the piezoresponse of KNbO3PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2006F. Peter Abstract We report on the reduction of piezoresponse in KNbO3 originating from a surface layer. An analysis with surface sensitive measurements shows that this layer consists of chemisorbates and physisorbates. Heating the sample under ultra high vacuum conditions removes the surface layer on the perovskite to a large extend. This treatment has a drastic effect on the piezoresponse as the potential difference applied to the sample is no longer reduced by a voltage drop across the adsorbate layer, leading to a higher electric field compared to the case with an adsorbate layer. Experiments and simulations are presented confirming this postulation on KNbO3. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Second harmonic generation spectroscopy on Si surfaces and interfacesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2010Kjeld Pedersen Abstract Optical second harmonic generation (SHG) spectroscopy studies of Si(111) surfaces and interfaces are reviewed for two types of systems: (1) clean 7,×,7 and -Ag reconstructed surfaces prepared under ultra-high vacuum conditions where surface states are excited and (2) interfaces in silicon-on-insulator (SOI) structures and thin metal films on Si surfaces where several interfaces contribute to the SHG. In all the systems resonances are seen at interband transitions near the bulk critical points E1 and E2. On the clean surfaces a number of resonances appear below the onset of bulk-like interband transitions that can be referred to excitations of dangling bond surface states. Adsorption of oxygen leads to formation of a new surface resonance. Such resonances appearing in the region between the bulk critical points E1 and E2 are also shown to be important for Si/oxide interfaces in SOI structures. Finally, examples of spectroscopy on layers buried below thin Ag and Au films are given. [source] Isothermal close space sublimation of CdTe/ZnTe heterostructures in vacuum conditionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2010O. de Melo Abstract Thin films and structures of ZnTe and CdTe have been grown by isothermal close space sublimation using alternated exposure of single crystalline substrates to elemental Zn, Te and Cd sources. The results show that the use of vacuum conditions promotes the transport of vapors towards the surface and then efficient growth at lower temperatures. Films thickness ranged between 200 and 600 nm for 50 cycles samples. ZnTe and CdTe films were obtained even at temperatures as low as 310 °C. This is important because low temperatures worsen the inter- diffusion processes; as a consequence we have obtained relatively abrupt interfaces in the ZnTe/CdTe system. Its compositional, structural and optical properties are presented. These results offer new possibilities of this low cost technique for growing heterostructures. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Experiments on single levitated particles: a novel approach for investigations of electronic properties of structured II-VI-semiconductor nanoparticles in selected environmentsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2007C. Graf Abstract A novel approach for investigations of the electronic structure of II-VI semiconductor nanoparticles in selected environments is presented. CdSe/ZnS core shell nanoparticles are dispersed in a liquid non-volatile siloxane graft/block copolymer and injected in an electrodynamic trap, where a single liquid microdroplet is stably stored under ultra high vacuum conditions. In this way, it is possible to investigate quantum dots by soft X-ray spectroscopies in a liquid environment, which is not influenced by any outer surface. NEXAFS spectra of stored nanoparticles were recorded at the Zn 2p-, S 2p-, and Cd 3d-edge by measuring X-ray excited optical luminescence or the element-selective charging current of single, trapped microdroplets. The spectra are compared to those of similar CdSe/ZnS nanoparticles, which are dispersed in a controlled way in solid silica colloids as well as to those of matrix materials. An analysis of the data reveals that the electronic structure of the ZnS shell is significantly influenced by the outer functionalization and the dispersive media whereas the electronic structure of the core is shown to be independent from the surroundings. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structure and oxygen mobility in mayenite (Ca12Al14O33): a high-temperature neutron powder diffraction studyACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2007H. Boysen The structure of mayenite, Ca12Al14O33, was investigated by neutron powder diffraction up to 1323,K. It has been described previously as a calcium,aluminate framework, in which 32 of the 33 oxygen anions are tightly bound, containing large cages, 1/6 of them being filled randomly by the remaining `free' oxygen. At ambient temperature excess oxygen was found, corresponding to the composition Ca12Al14O33.5 which was attributed to the presence of hydroxide, peroxide and superoxide radicals in the cages. Above 973,K these are lost under vacuum conditions and the composition becomes stoichiometric. From the refined structural parameters it is concluded that the structure is more adequately described as a relatively stable aluminate framework consisting of eightfold rings of AlO4 tetrahedra with disordered Ca and `free' O distributed within. At high temperatures the density of the `free' oxygen is extremely spread out, with the expansion being related to the high ionic conductivity of this material. Since no continuous density distribution between adjacent cages was found and the `free' O forms bonds with part of the Ca, the diffusion proceeds via a jump-like process involving exchange of the `free' oxygen with framework oxygen. The results confirm the recent theoretical predictions of Sushko et al. [(2006), Phys. Rev. B, 73, 014101-1-10]. [source] Microscopic Evidence of the Metalation of a Free-Base Porphyrin Monolayer with IronCHEMPHYSCHEM, Issue 2 2007Florian Buchner Microscopic evidence of the in situ complexation of Fe-porphyrins is presented. The figure shows the sub-molecular resolved scanning tunneling microscopy images which document the metalation of 2H-TPP (central cavity; TPP: tetraphenylporphyrin) with evaporated iron (protrusions are identified as Fe-TPP). This promising technique enables future surface science investigations of clean iron porphyrin films under ultrahigh vacuum conditions. [source] | ||||||||||||||||