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61.
Jurgen Sleven Thomas Cardinaels Koen Binnemans Daniel Guillon Bertrand Donnio 《Liquid crystals》2013,40(11):1425-1433
This paper deals with the synthesis of vanadyl phthalocyanines substituted with eight alkoxy chains in the peripheral (2, 3, 9, 10, 16, 17, 23, 24) positions. The alkoxy chain length was varied, and octa-octyloxy (C8H17O), octa-dodecyloxy (C12H25O) and octa-hexadecyloxy (C16H33O) substituted vanadyl phthalocyanine complexes were prepared. Studies by polarizing optical microscopy and small angle X-ray diffraction (XRD) revealed that all the complexes are liquid crystalline and that these metallomesogens exhibit a columnar phase. The symmetry of the 2D lattice is rectangular, with a c 2 mm space group, as determined by the indexation of the XRD reflections; hence a rectangular columnar phase (Colr) was assigned. A double periodicity, although weak, along the axis of the columns was found, which indicates some degree of pairing or dimerization. A tentative explanation based on an antiferroelectric stacking is given. Transition enthalpies were determined by differential scanning calorimetry. The compounds start to decompose above 250°C before reaching the clearing temperatures. A significant bathochromic shift of the Q-band in the UV/Vis spectra of the vanadyl complexes compared with the metal-free ligands and other metallophthalocyanines (M=CoII, NiII, CuII, ZnII) was also observed. 相似文献
62.
Jurgen Sleven Thomas Cardinaels Koen Binnemans Daniël Nelis Jules Mullens Dirk Hinz-Hübner 《Liquid crystals》2013,40(2):143-148
Cobalt (II) phthalocyanines substituted with eight alkoxy chains in the peripheral (2, 3, 9, 10, 16, 17, 23, 24) positions were prepared. The alkoxy chain length was varied between n-butyloxy (C4H9O) and n-octadecyloxy (C18H37O). Studies by polarizing optical microscopy and high temperature X-ray diffraction revealed that all the complexes are liquid crystalline and that they exhibit a hexagonal columnar mesophase (Colh). Transition enthalpies were determined by differential scanning calorimetry. The clearing point could only be observed for compounds with a chain length longer than C13H27O. Both the melting and clearing points decrease with increasing chain length. The transition temperatures of these discotic metallomesogens are higher than those of the corresponding metal-free phthalocyanines, but are comparable with those of the corresponding copper (II) compounds. The thermal decomposition of the compounds was studied by thermogravimetry. 相似文献
63.
Wolf Jurgen Richter 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):395-400
Abstract Die Reaktion von Organodichlorphosphinen mit aliphatischen 1,2-Diolen in Abhängigkeit von der Basenkonzentration und den Substituenten wird untersucht; das Produktspektrum umfaßt neben 1,3,2-Dioxaphospholanen auch 2-Oxo-1,3,2-dioxaphospholane und Oxiphosphorane. Letztere lassen sich zum Hauptprodukt machen. The reaction of phosphorus dichlorides with aliphatic 1,2-diols is studied. The range of products varies strongly with the concentration of the base and the organic substituents. In addition to 1,3,2-dioxaphospholanes the corresponding 2-oxo-1,3,2-dioxaphospholanes and oxiphosphoranes are also formed. Using proper conditions the latter may become the dominant product. 相似文献
64.
The surface electronic structure of cleaved single crystals of the organic superconductor κ-(ET)2Cu(NCS)2 has been studied using photoemission microscopy. Two types of cleaved surfaces were observed, displaying different valence band photoemission spectra and different spectral behavior near the Fermi level, EF. In particular, spectra from one surface type display relatively broad spectral features in the valence band and finite spectral intensity at EF, while spectra from the other surface type show well-defined valence band emission features and zero photoemission intensity at EF. We propose that the spectral differences are due to a very short electron mean free path in this material, and our results are used to explain the differences between previously published photoemission spectra from this superconductor. We also report the results of an investigation of the electronic structure of defects in this material. 相似文献
65.
Numerical schemes are presented for a class of fourth order diffusion problems. These problems arise in lubrication theory for thin films of viscous fluids on surfaces. The equations being in general fourth order degenerate parabolic, additional singular terms of second order may occur to model effects of gravity, molecular interactions or thermocapillarity. Furthermore, we incorporate nonlinear surface tension terms. Finally, in the case of a thin film flow driven by a surface active agent (surfactant), the coupling of the thin film equation with an evolution equation for the surfactant density has to be considered. Discretizing the arising nonlinearities in a subtle way enables us to establish discrete counterparts of the essential integral estimates found in the continuous setting. As a consequence, the resulting algorithms are efficient, and results on convergence and nonnegativity or even strict positivity of discrete solutions follow in a natural way. The paper presents a finite element and a finite volume scheme and compares both approaches. Furthermore, an overview over qualitative properties of solutions is given, and various applications show the potential of the proposed approach. 相似文献
66.
§1. IntroductionIt is a classical topic to study, for quadratic number ?elds F = Q(√2p) with a prime p,the exact 2-power dividing the narrow class number h (F) and the norm of the fundamentalunit ε of F.The 2-primary subgroup of the narrow class group … 相似文献
67.
68.
Perry Skeath I. Lindau P. Pianetta P.W. Chye C.Y. Su W.E. Spicer 《Journal of Electron Spectroscopy and Related Phenomena》1979,17(4):259-265
A room-temperature reaction between Al adsorbate atoms and a GaAs (110) surface is observed by means of soft X-ray photoemission techniques. Evidence of two states of Al which are distinct from the bulk Al metal is seen at submonolayer coverages. The sequential appearance of these states suggest that both Al chemisorbed on the surface and Al replacing Ga in the surface lattice are present. The possible influence of surface lattice reconstruction and Al proximity effects on the replacement reaction is discussed. The replacement reaction is important in the context of metal contacts to GaAs (both ohmic and Schottky barriers) as well as for GaAs—AlGaAs heterojunctions. 相似文献
69.
C Binns C Norris I Lindau M.L Shek B Pate P.M Stefan W.E Spicer 《Solid State Communications》1982,43(11):853-855
A LEED, Auger photoemission study of ultra-thin overlayers of iron on palladium (111) is reported. At room temperature and below, the overlayer grows epitaxially in a simultaneous multi-layer mode. On annealing a sub-monolayer coverage to create flat two-dimensional platelets it was found that the density of the Fe 3d states at the Fermi level was reduced and the local iron magnetic moment could not be detected. 相似文献
70.
G. Rossi L. Caliari I. Abbati L. Braicovich I. Lindau W.E. Spicer 《Surface science》1982,116(2):L202-L206
We give the first photoemission results on the enhancement of Si reactivity to oxygen when a noble metal (Ag) is present. The tunability of synchrotron radiation (SR) has been used to get high surface sensitivity and to take advantage of cross section energy dependence. We show that when one monolayer of Ag is deposited onto Si(111), the exposure to oxygen (30 × 106L) originates the overgrowth of an oxide phase which is basically SiO2. This indicates that Ag breaks the sp3 configuration of Si atoms with a consequent dramatic increase in the Si reactivity. This behaviour rules out the model of Ag adsorbed on top of Si with an atomically abrupt interface. 相似文献