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排序方式: 共有94条查询结果,搜索用时 15 毫秒
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Wijkens P Jastrzebski JT van Der Schaaf PA Kolly R Hafner A van Koten G 《Organic letters》2000,2(11):1621-1624
A general method for the functionalization of Si-Cl terminated carbosilane dendritic molecules via organolithium or organomagnesium reagents is described. Quantitative exchange of the bromine atoms of 4-bromophenyl-functionalized dendrimers affords polylithiated species that are valuable starting materials for further functionalization, e.g., into pyridyl alcohols. The latter were successfully applied as catalyst precursors in a ruthenium-mediated ring-closure metathesis reaction. 相似文献
4.
Water adsorption and absorption on crystalline polyvinylidene fluoride with 30% trifluoroethylene, P(VDF-TrFE, 70:30), was examined by thermal desorption spectroscopy. Two distinctly different water adsorption sites are identified: one adsorbed species that resembles ice and another species that interacts more strongly with the polymer thin film. The existence of the latter species is consistent with X-ray diffraction studies of water absorbed into the bulk of copolymers of polyvinylidene fluoride with trifluoroethylene crystalline thin films. There are strong steric effects observed in the angle-resolved thermal desorption that may be a result of the large polymer thin film surface dipoles. 相似文献
5.
A series of overlayer structures, starting with a c(3 × 1) geometry are formed during the dissociative chemisorption of chlorine, bromine, and iodine on Fe(110). These adlayers provide an opportunity to systematically examine the corresponding changes in electronic band structure as a function of coverage and adsorbate. At coverage levels greater than
low-energy electron diffraction patterns obtained from the halogen-covered Fe(110) surface evolve continuously with coverage. The electronic band structure was examined as a function of coverage and adsorbate species via angle-resolved ultraviolet photoelectron spectroscopy. It is concluded that the electronic band structure measurements support an incommensurate structural model for halogen overlayer geometry on Fe(110) in which an overlayer lattice, that is in general incommensurate with the substrate, rotates and compresses with increases in coverage. An alternative interpretation of the diffraction results based on antiphase domain boundaries within the overlayer is not consistent with the photoemission data. The incommensurate model emphasizes adatom-adatom interactions over adatom-substrate interactions while the reverse is true for the antiphase boundary model. 相似文献
6.
Gordeev SN Zhukov AA de Groot PA Jansen AG Gagnon R Taillefer L 《Physical review letters》2000,85(21):4594-4597
We report on transport measurements of YBa 2Cu 3O (7-delta) single crystals with different oxygen contents in the geometry B, J ||ab (J perpendicularB). Our data show that the vortices become confined between the Cu-O planes below a well-defined temperature at which the effective size 2xi of the vortex core is approximately equal to the period of the Cu-O layers. This confinement strongly increases the vortex liquid freezing temperature. A new melting line is found separating a vortex liquid and a smectic phase, which shows an oscillatory field dependence reflecting differences between commensurate and incommensurate smectic states. 相似文献
7.
I. Ketsman Y.B. Losovyj A. Sokolov J. Tang Z. Wang K.D. Belashchenko P.A. Dowben 《Applied Physics A: Materials Science & Processing》2007,89(2):489-492
Gd-doped HfO2 films were deposited on p-type silicon substrates in a reducing atmosphere. Photoemission measurements indicate the n-type
character of Gd-doped HfO2 due to overcompensation with oxygen vacancies. The Gd 4f photoexcitation peak at 5.5 eV below the valence band maximum is
identified using both resonant photoemission and first-principles calculations of the f hole. The rectifying (diode-like)
properties of Gd-doped HfO2 to silicon heterojunctions are demonstrated.
PACS 79.60.-i; 68.55.Ln; 29.40.Wk; 81.05.Je 相似文献
8.
Jie XiaoN. Lozova Ya.B. Losovyj D. WootenI. Ketsman M.W. SwinneyJ. Petrosky J. McCloryYa.V. Burak V.T. AdamivA.T. Brant P.A. Dowben 《Applied Surface Science》2011,257(8):3399-3403
We have compared the photovoltaic charging of the (1 0 0) surface termination for Cu doped and undoped Li2B4O7. While the surface charging at the (1 0 0) surface of Li2B4O7 is significantly greater than observed at (1 1 0) surface, the Cu doping plays a role in reducing the surface photovoltage effects. With Cu doping of Li2B4O7, the surface photovoltaic charging is much diminished at the (1 0 0) surface. The density of states observed with combined photoemission and inverse photoemission remains similar to that observed for the undoped material, except in the vicinity of the conduction band edge. 相似文献
9.
Ming Xia LI Yan Ming WANG Ru Ru CHEN* Research Institute of Elemento-Organic Chemistry Nankai University Tianjin Pittsburgh University Medical Center Pittsburgh PA U. S. A 《中国化学快报》2001,(6)
The chiral diols ((,(,((,((-Tetraaryl-1,3-dioxolane-4,5-dimethanols) have been used for the formation of cyclic titanates and similar derivatives of Mg, Al and Zr. These complexes of oxophilic metal centers were employed in catalytic and stiochiometric enantioselective reactions such as enantioselective addition reactions of carbon-centered nucleophiles to aldehydes1, [2+2] cycloadditions2, and Diels-Alder reactions3. So far, the two hydrogen atoms of all this type of diols are in trans form… 相似文献
10.
We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material. 相似文献