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1.
A. Roberts M. L. von Bibra H-P. Gemünd E. Kreysa 《International Journal of Infrared and Millimeter Waves》1994,15(3):505-517
In this paper a comparison between a rigorous electromagnetic model for transmission through a hexagonal array of circular waveguides in a series of thick, metallic screens and experimental measurements in the far infrared is made. It is found that there is excellent agreement between theory and experiment when the frequency is below that where any diffracted orders propagate. The agreement is still very good above this frequency. Below a frequency approximately equal to the cut-off frequency of the circular waveguides little power is transmitted. As the thickness of the screen is increased, this decrease in transmission becomes more abrupt. Also, for thick screens, resonances appear in the transmission spectrum which are analogous to those which appear in the spectra of two grids separated by a distance comparable to the wavelength of the radiation being used. 相似文献
2.
Pascual JI Barth JV Ceballos G Trimarchi G De Vita A Kern K Rust HP 《The Journal of chemical physics》2004,120(24):11367-11370
We report scanning tunneling microscopy observations on the restructuring of a Ag(110) surface induced by the molecule 4-[trans-2-(pyrid-4-yl-vinyl)]benzoic acid (PVBA). Our data reveal that the surface undergoes a mesoscopic step faceting following exposure to submonolayer coverages and thermal activation. A sawtooth arrangement evolves implying long-range mass transport of substrate atoms and forming a regular arrangement of kink sites. Its formation is associated with the molecules' functional headgroups forming carboxylates with [100] Ag microfacets at step edges, and eventually operating to reshape the surface morphology. Interestingly, the resulting microfacets act as chiral templates for the growth of supramolecular PVBA structures. Theoretical modeling based on ab initio results indicates that chiral recognition processes discriminating between the two enantiomers of adsorbed PVBA molecules occur in this process. 相似文献
3.
We observe an efficient phase coherent photorefractive effect in ZnSe single quantum wells for ultrashort light pulses resonant to the excitonic transition. The effect is attributed to the formation of an electron grating in the quantum well induced by the interference of coherent excitons that preserve phase and polarization of the incident light fields. All characteristic features of the diffracted signal are explained and reproduced by numerical calculations that are based on the optical Bloch equations for a three-level system. 相似文献
4.
Line defects of a thin alumina film on NiAl(110) have been studied on the atomic level with scanning tunneling microscopy at 4 K. While boundaries between two reflection domains do not expose a characteristic structure, antiphase domain boundaries are well ordered. The latter boundaries result from the insertion of a row of O atoms, as atomically resolved images of the topmost oxygen layer show. The insertion occurs only in two of the three characteristic directions of the quasihexagonal O lattice. Depending on the direction, either straight or zigzagged boundaries form. An atomic characterization of line defects on the oxide surface is a first step to correlate their topographic structure and chemical activity. 相似文献
5.
6.
Olsen JC Fahrenbach AC Trabolsi A Friedman DC Dey SK Gothard CM Shveyd AK Gasa TB Spruell JM Olson MA Wang C Jacquot de Rouville HP Botros YY Stoddart JF 《Organic & biomolecular chemistry》2011,9(20):7126-7133
A limited range of redox-active, rotaxane-based, molecular switches exist, despite numerous potential applications for them as components of nanoscale devices. We have designed and synthesised a neutral, redox-active [2]rotaxane, which incorporates an electron-deficient pyromellitic diimide (PmI)-containing ring encircling two electron-rich recognition sites in the form of dioxynaphthalene (DNP) and tetrathiafulvalene (TTF) units positioned along the rod section of its dumbbell component. Molecular modeling using MacroModel guided the design of the mechanically interlocked molecular switch. The binding affinities in CH(2)Cl(2) at 298 K between the free ring and two electron-rich guests--one (K(a) = 5.8 × 10(2) M(-1)) containing a DNP unit and the other (K(a) = 6.3 × 10(3) M(-1)) containing a TTF unit--are strong: the one order of magnitude difference in their affinities favouring the TTF unit suggested to us the feasibility of integrating these three building blocks into a bistable [2]rotaxane switch. The [2]rotaxane was obtained in 34% yield by relying on neutral donor-acceptor templation and a double copper-catalysed azide-alkyne cycloaddition (CuAAC). Cyclic voltammetry (CV) and spectroelectrochemistry (SEC) were employed to stimulate and observe switching by this neutral bistable rotaxane in solution at 298 K, while (1)H NMR spectroscopy was enlisted to investigate switching upon chemical oxidation. The neutral [2]rotaxane is a chemically robust and functional switch with potential for applications in device settings. 相似文献
7.
Schmid M Shishkin M Kresse G Napetschnig E Varga P Kulawik M Nilius N Rust HP Freund HJ 《Physical review letters》2006,97(4):046101
A model for the straight antiphase domain boundary of the ultrathin aluminum oxide film on the NiAl(110) substrate is derived from scanning tunneling microscopy measurements and density-functional theory calculations. Although the local bonding environment of the perfect film is maintained, the structure is oxygen deficient and possesses a favorable adsorption site. The domain boundary exhibits a downwards band bending and three characteristic unoccupied electronic states, in excellent agreement with scanning tunneling spectroscopy measurements. 相似文献
8.
E. Träbert H.-P. Garnir P.-D. Dumont T. Bastin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):25-31
Peculiar properties of ion-atom collision systems, in particular deviations from statistical populations of singlet and triplet
levels, can be studied by optical spectroscopy. We have extended earlier studies by VUV spectroscopy of a number of collision
systems at various collision energies in the 0.01-MeV/nucleon to 1-MeV/nucleon range, involving H2
+, H+, He+, He2+, Ne+, Ar+, and N2
+ as projectiles and Ne, Ar, and N2 as target gases. Statistically significant deviations of the relative intensities of singlet and triplet lines from simple
ratios are observed in the displaced terms of the valence shell of Ne III, corroborating and extending earlier work. For Ar
III, the energy dependences of singlet-to-triplet excitation ratios are very different for different projectiles. For N II,
in contrast, all observed line ratios are practically independent of the projectile energy.
Received 17 November 2000 and Received in final form 31 January 2001 相似文献
9.
Steinrück HP Fuhrmann T Papp C Tränkenschuh B Denecke R 《The Journal of chemical physics》2006,125(20):204706
The vibrational fine structure of x-ray photoelectron (XP) spectra of a number of different small hydrocarbon molecules and reaction intermediates adsorbed on Pt(111) and Ni(111) has been investigated in detail. The data for methyl, methylidyne, acetylene, and ethylene can consistently be analyzed within the linear coupling model. The S factor, i.e., the intensity ratio of the first vibrationally excited to the adiabatic transition, is obtained to be 0.17+/-0.02 per C-H bond; for the deuterated species a value of 0.23+/-0.02 is obtained. Therefore, the vibrational fine structure can be used for fingerprinting in the analysis of XP spectra and for identifying unknown reaction intermediates. From the data, Deltar, the change of the minimum in the potential energy curve upon core ionization, is calculated within the linear coupling model using a first order correction. For all adsorbates, including the deuterated ones, a value of Deltar=0.060+/-0.004 A is obtained. Furthermore, from the binding energy of the adiabatic peak and from the energy of the vibrational excitation in the ionic final state some information on the adsorbate/substrate bond and the adsorption site can be derived. 相似文献
10.
Tränkenschuh B Fritsche N Fuhrmann T Papp C Zhu JF Denecke R Steinrück HP 《The Journal of chemical physics》2006,124(7):74712
Using time-dependent high-resolution x-ray photoelectron spectroscopy at BESSY II, the adsorption and desorption processes of CO on stepped Pt(355) = Pt[5(111) x (111)] were investigated. From a quantitative analysis of C 1s data, the distribution of CO on the various adsorption sites can be determined continuously during adsorption and desorption. These unique data show that the terrace sites are only occupied when the step sites are almost saturated, even at temperatures as low as 130 K. The coverage-dependent occupation of on-top and bridge adsorption sites on the (111) terraces of Pt(355) is found to differ from that on Pt(111), which is attributed to the finite width of the terraces and changes in adsorbate-adsorbate interactions. In particular, no long-range order of the adsorbate layer could be observed by low-energy electron diffraction. Further details are derived from sticking coefficient measurements using the method devised by King and Wells [Proc. R. Soc. London, Ser. A 339, 245 (1974)] and temperature-programmed desorption. The CO saturation coverage is found to be slightly smaller on the stepped surface as compared to that on Pt(111). The initial sticking coefficient has the same high value of 0.91 for both surfaces. 相似文献