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981.
Roos M Künzel D Uhl B Huang HH Brandao Alves O Hoster HE Gross A Behm RJ 《Journal of the American Chemical Society》2011,133(24):9208-9211
The competition between intermolecular interactions and lateral variations in the molecule-substrate interactions has been studied by scanning tunneling microscopy (STM), comparing the phase formation of (sub)monolayers of the organic molecule 2,4'-BTP on buckled graphene/Ru(0001) and Ag(111) oriented thin films on Ru(0001). On the Ag films, the molecules form a densely packed 2D structure, while on graphene/Ru(0001), only the areas between the maxima are populated. The findings are rationalized by a high corrugation in the adsorption potential for 2,4'-BTP molecules on graphene/Ru(0001). These findings are supported by temperature programmed desorption (TPD) experiments and theoretical results. 相似文献
982.
We report on a computer simulation study of a Lennard-Jones liquid confined in a narrow slit pore with tunable attractive walls. In order to investigate how freezing in this system occurs, we perform an analysis using different order parameters. Although some of the parameters indicate that the system goes through a hexatic phase, other parameters do not. This shows that to be certain whether a system of a finite particle number has a hexatic phase, one needs to study not only a large system, but also several order parameters to check all necessary properties. We find that the Binder cumulant is the most reliable one to prove the existence of a hexatic phase. We observe an intermediate hexatic phase only in a monolayer of particles confined such that the fluctuations in the positions perpendicular to the walls are less than 0.15 particle diameters, i.e., if the system is practically perfectly 2D. 相似文献
983.
The synthesis of the monoclinic polymorph of {Cu[Hg(SCN)4]}n is reported. The compound, as determined by X-ray diffraction of a twinned crystal, consists of mercury and copper atoms linked by μ1,3-SCN bridges. The crystal packing shows a highly porous infinite 3D structure. Diagnostic resonances for the SCN- ligand and metal-ligand bonds in the IR, far-IR and Raman spectra are assigned and discussed. The electronic band structure along with density of states (DOS) calculated by the DFT method indicates that the compound is an indirect band gap semiconductor. The DFT calculations show that the observed luminescence of the compound arises mainly from an excited LLCT state with small MLCT contributions (from the copper to unoccupied π? orbital of the thiocyanate groups). The X-band EPR spectrum of the powdered sample at room temperature reveals an axial signal with anisotropic g factors consistent with the unpaired electron of Cu(II) ion in the dx2−y2 orbital. 相似文献
984.
Baragwanath AJ Freeman JR Gallant AJ Zeitler JA Beere HE Ritchie DA Chamberlain JM 《Optics letters》2011,36(13):2393-2395
The first demonstration, to our knowledge, of near-field imaging using subwavelength plasmonic apertures with a terahertz quantum cascade laser source is presented. "Bull's-eye" apertures, featuring subwavelength circular apertures flanked by periodic annular corrugations were created using a novel fabrication method. A fivefold increase in intensity was observed for plasmonic apertures over plain apertures of the same diameter. Detailed studies of the transmitted beam profiles were undertaken for apertures with both planarized and corrugated exit facets, with the former producing spatially uniform intensity profiles and subwavelength spatial resolution. Finally, a proof-of-concept imaging experiment is presented, where an inhomogeneous pharmaceutical drug coating is investigated. 相似文献
985.
Fenn A Wächtler M Breitzke H Buchholz A Lippold I Plass W Buntkowsky G 《Solid state nuclear magnetic resonance》2011,40(2):60-65
Five vanadium complexes as models for biological systems were investigated using 51V-MAS–NMR spectroscopy. All spectra show an uncommon line shape, which can be attributed to a shorter relaxation time of the satellite transition in contrast to the central one. A method for the reliable analysis of such kind of spectra is presented for the first time and the most important NMR parameters of the investigated complexes (quadrupolar coupling constant CQ, asymmetry of the EFG tensor ηQ, isotropic chemical shift δiso, chemical shift anisotropy δσ and asymmetry of the CSA tensor ησ) are presented. These results are of particular importance with respect to the analysis of the 51V-MAS–NMR spectra of vanadium moieties in biological matrices such as vanadium chloroperoxidase, which show hitherto unexplained low intensity of the satellite sideband pattern. 相似文献
986.
Rojas G Chen X Kunkel D Bode M Enders A 《Langmuir : the ACS journal of surfaces and colloids》2011,27(23):14267-14271
The nucleation and growth of 2D layers of tetraphenyl porphyrin molecules on Ag(111) are studied with variable-temperature scanning tunneling microscopy. The organic/metal heteroepitaxy occurs by strict analogy to established principles for metal heteroepitaxy. A hierarchy of energy barriers for diffusion on terraces and along edges and around corners of adislands is established. The temperature is key to activating these barriers selectively, thus determining the shape of the organic aggregates, from a fractal shape at lower temperatures to a compact shape at higher temperatures. The energy barriers for the terrace diffusion of porpyrins and the molecule-molecule binding energy were determined to be 30 meV < E(terrace) < 60 and 130 meV < E(diss) < 160 meV, respectively, from measurements of island sizes as a function of temperature. This study provides an experimental verification of the validity of current models of epitaxy for the heteroepitaxy of organics and is thus expected to help establish design principles for complex metal-organic hybrid structures. 相似文献
987.
Axel Stäbler 《代数通讯》2013,41(9):3934-3945
We explicitly compute étale covers of the smooth Fermat curves Y p+1 = Proj k[u, v, w]/(u p+1 + v p+1 ? w p+1) which trivialize the vector bundles Syz(u 2, v 2, w 2)(3), where k is a field of characteristic p ≥ 3. 相似文献
988.
A phase transition in high-dimensional random geometry is analyzed as it arises in a variety of problems. A prominent example is the feasibility of a minimax problem that represents the extremal case of a class of financial risk measures, among them the current regulatory market risk measure Expected Shortfall. Others include portfolio optimization with a ban on short-selling, the storage capacity of the perceptron, the solvability of a set of linear equations with random coefficients, and competition for resources in an ecological system. These examples shed light on various aspects of the underlying geometric phase transition, create links between problems belonging to seemingly distant fields, and offer the possibility for further ramifications. 相似文献
989.
990.
Groundwater discharge into an open pit lignite mining lake was investigated using radon-222 as a naturally occurring environmental tracer. The chosen study site was a meromictic lake, i.e., a water body that is divided horizontally into two separate layers – the upper mixolimnion (with seasonal mixing) and the lower monimolimnion (without seasonal mixing). For the estimation of groundwater discharge rates into the lake, a simple box model including all radon sinks and sources related to each layer was applied. Two field investigations were performed. During the October campaign, the total groundwater discharge into the lake was found to be 18.9 and 0.7 m3 d?1 for the mixolimnion and monimolimnion, respectively. During the December campaign, the groundwater discharge into the mixolimnion was 15.0 m3 d?1, whereas no discharge at all was observed into the monimolimnion. Based on the given water volumes, the residence time of lake water was 5.3 years for the monimolimnion and varies between 0.9 and 1.1 years for the mixolimnion. The investigation confirmed radon to be a useful environmental tracer for groundwater and surface water interactions in meromictic lake environments. 相似文献