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61.
n-type conducting layers have been formed in n- and p-type hexagonal SiC and n-type cubic SiC by implanting ions from column V of the periodic table; N, P, Sb, or Bi. The implantations were made at room temperature and with energies ranging from 5 to 300 keV. The implanted layers have been evaluated by van der Pauw-Hall effect and sheet resistivity measurements and by scanning electron microscopy for anneal temperatures ranging from 1100 to 1800°C. Type conversion of the implanted layers to n-type has been observed after a 750°C anneal. Considerable lattice reordering is suggested from the observed carrier mobility values after annealing at 1600°C. We have attempted to form p-type layers in n-type SiC by implanting Re, B, Al, Ga, and Tl. Application of anneal procedures identical to those used to form n-type layers have not resulted in measurable p-type layers. The p-n junctions formed by the donor-implanted layers have been evaluated as a function of anneal temperature. After annealing at 1200°C there is direct evidence of a thick semi-insulating region between the n-layer and the substrate which produces a p-i-n diode characteristic. The thickness of this i-layer can be substantially reduced with additional annealing, resulting in abrupt junction behavior for the diode. Well-annealed p-n junctions have been characterized as a function of operating temperature over the range of 23 to 400°C. The forward current-voltage behavior of these diodes is dominated by generation and recombination of the carriers in the depletion layer over most of the temperature range. There is some indication of diffusion currents at the highest temperatures. Avalanche breakdown behavior is observed for reverse bias. The capacitance-voltage behavior of these diodes as a function of frequency and temperature indicate the presence of a deep level which can be explained in terms of the bulk properties of the material. 相似文献
62.
63.
Brett I. Dunlap 《International journal of quantum chemistry》2001,81(6):373-383
Performing quantum chemical integral evaluation directly, without recursion and without direct coupling of angular momenta according to the rotation group is analyzed. The rotation group limits the structure of these closed‐form expressions. The result of all cross differentiation is a rotational invariant. Closed‐form expressions are obtained for the general three‐ and four‐center Gaussian integral. The solid harmonic addition formula can be used to express these integrals as sums of products of an exponent‐independent (angular) factor and a molecular‐orientation‐independent (exponential) factor in a variety of ways. The results are products of two such factors summed over the set of distinct, relevant polynomials of the exponents. The coefficients of these polynomials, angular factors, are complicated but common to all n‐center matrix elements and independent of any type of contraction. Derivatives must be obtained using the product rule. An implementation in the Solid Spherical Harmonic Gaussian (SSHG) computer code is outlined and preliminary comparison is made. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 373–383, 2001 相似文献
64.
The effect on energy loss intensities of the electrodynamic interactions with the substrate and neighboring adsorbed molecules is discussed. The experimentally observed large variations in the loss intensity from molecules adsorbed on various sites are considered. A simple dipole model of the molecule interacting with its image in the substrate and its neighbors on equivalent and inequivalent sites is used. Good agreement with experiment for a well characterized surface coverage of bridge and on-top bonded CO molecules on Ni(111) is found. 相似文献
65.
66.
S. Jha D. Suyanto Robert Hogg Glenn M. Julian R. A. Dunlap S -W. Cheong Z. Fisk J. D. Thompson 《Hyperfine Interactions》1990,61(1-4):1143-1146
Zeeman splitting of Mossbauer spectra of57Co doped into Eu2CuO4 and Gd2CuO4 indicates magnetic ordering of Cu moments for temperatures below about 150 K in Eu2CuO4 and below about 200 K in Gd2CuO4.
Supported by NASA Grant NAG 3-847 相似文献
67.
L. Asch B. D. Dunlap R. Marquardt W. Potzel F. J. Litterst G. D. Werner F. Weigel J. C. Spirlet G. M. Kalvius 《Hyperfine Interactions》1988,40(1-4):279-282
Mössbauer spectra of hexavalent neptunyls X2(NpO2)Cl4 and X4(NpO2)(CO3)3 with X=Na, K, Cs, (NH4) and [C2H5)4N] are discussed and compared to EPR data. In cases where reliable values of hyperfine parameters can be extracted, the Mössbauer spectra give fine details of bonding structure. It is found that the O–Np–O bond is not linear and that exchanging the cation results in small but definite changes.Work supported by the Bundesministerium für Forschung und Technologie and the U.S. Department of Energydeceased 相似文献
68.
LUDVÍK BENEŠ KLÁRA MELÁNOVÁ JAN SVOBODA VÍTĚZSLAV ZIMA 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(3-4):289-293
Intercalates of o-, m-, and p-toluidine into α-Zr(HPO4)2 · H2O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, toludine molecules are protonated in the interlayer space. Toluidine molecules are arranged in a bimolecular way in the intercalates containing more than 1.5 toluidine molecules per Zr atom. On the other hand, a monolayer of the toluidine molecules is supposed in the intercalates with less than one toluidine molecule per Zr atom. 相似文献
69.
Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems. The photoresolution of the enantiomers of helical-shaped, sterically overcrowded alkene 1 with circularly polarized light and the transduction of the stereochemical information by triggering the helical arrangement of a large collection of achiral molecules in a twisted nematic liquid crystalline phase (2) are examples of control and amplification of chirality. 相似文献
70.
We report in this article the use of thermosensitive water-dispersible polymer brush-grafted polymeric particles as carriers for Pd nanoparticles for the catalysis of hydrogenation of styrene in an aqueous/organic biphasic system. Thermoresponsive poly(methoxytri(ethylene glycol) methacrylate) brushes were grown from initiator-functionalized core-shell cross-linked poly( t-butyl acrylate) (P tBA) particles via surface-initiated atom-transfer radical polymerization. The t-butyl group of P tBA in the core was removed with trifluoroacetic acid, followed by loading of Pd2+ cations through ion exchange. Pd nanoparticles were prepared by reduction of Pd2+ ions with ethanol at 70 degrees C. Dynamic light scattering studies showed that the Pd nanoparticle-loaded thermosensitive hairy particles in water began to shrink when the temperature was above 30 degrees C. The supported Pd nanoparticles efficiently catalyzed hydrogenation of styrene in an aqueous/octane biphasic system and were reused five times with no changes in the yields in the first three cycles and slight decreases in the fourth and fifth cycles after the same period of time. Kinetics studies showed that the catalytic activity of Pd nanoparticles was modulated by the phase transition of the thermosensitive brush layer, resulting in a non-Arrhenius dependence of apparent initial rate constant, k app, on temperature. 相似文献