Computing surface dipoles and potentials of self-assembled monolayers from first principles

We discuss methodological aspects of first principles calculations of surface dipoles and potentials in general, and surface-adsorbed self-assembled monolayers in particular, using density functional theory with a slab/super-cell approach. We show that calculations involving asymmetric slabs may yield highly erroneous results for the surface dipole and demonstrated the efficacy of a simple dipole correction scheme. We explain the importance of the electrostatic dipole distribution, show how to compute it, and establish conditions for the equivalence of calculations for the dipole distribution and the electrostatic potential distribution.     

Temperature dependence of the interband absorption edge of copper

The optical absorption spectra of bulk copper measured by Pells and Shiga have been fitted by means of a model calculation in the interband edge region. The optical gap and the dipole matrix element of the L₃-L'₂(E_F) transition have been determined as a function of the temperature and a comparison with similar results obtained for silver and gold is presented.     

Frequency and intensity measurements in the fundamental infrared band of HD

The fundamental band of HD has been studied at room temperature and 0.6 atm pressure with a 48-m absorption path and a resolution of 0.01 cm^?1. The frequencies of nine electric dipole and three electric quadrupole transitions were measured with an accuracy of 0.001 cm^?1, and their analysis gives improved molecular parameters for the v = 0 and 1 states of HD. The intensities of the dipole transitions were measured in order to determine the v = 1-0 electric dipole transition moment. These measurements extend earlier experiments to higher J values, thus refining the determination of the rotational dependence of the transition moment.     

Temperature,roughness and depth resolution in ion sputter profiles

The depth resolutions of evaporated silver layers on polished polycrystalline copper substrates are studied at various temperatures during argon ion sputtemg with AES. A detailed analysis of the profile shape at the interface reveals the nature of contributions to the terms governing interface resolution. The profiles are all accurately described by an error function leading edge followed by an exponential trailing edge. The characteristic of the trailing edge is governed by the development of roughness which depends on the depth, z, sputtered as z^0.875. The roughness is reduced at elevated temperatures by the action of surface diffusion such that the maximum reduction occurs at the highest temperature and the lowest sputtering rate. The characteristic of the leading edge is composed of three terms added in quadrature, (i) defect-enhanced diffusion of copper into the silver film, (ii) roughness as above, and (iii) a constant term due to film nucleation. In the present samples the increased interdiffusion at elevated temperatures and low sputtering rates largely offsets the improvements in topography so that, overall, the depth resolution appears to be a very weak function of temperature. However, in other systems where interdiffusion is small, the resolution could be greatly enhanced.     

Molecules with a permanent dipole moment in a periodic medium with quadratic nonlinearity

Nonlinear optical effects in a one-dimensional periodic medium containing spatially oriented molecules of J aggregates of a dye and silver nanoparticles are studied. It is shown that, in such composite medium, the presence of a permanent dipole moment of an exciton transition of molecules of J aggregates results in the appearance of new nonlinear optical properties.     

Electromagnetic processes in silver isotopes

Peculiarities of electromagnetic interactions in silver isotopes are considered. Excited states of Ag isotopes are studied as a function of the mass number A = 95–117. Low-lying excited states reveal clear features that are specific for rotational spectra for the energies E < 4–5 MeV. In the energy domain above the nucleon separation threshold of 5–10 MeV, single-particle excited states overlap and produce a continuous spectrum. For energies E = 10–35 MeV, excitation of giant dipole resonance plays the most important role in Ag isotopes. Experimental data on the cross sections of photonuclear reactions in Ag isotopes are analyzed.     

Tetrathia- and tetraselenafulvalene adsorbed on Ag(110): A theoretical study

We have studied the adsorption properties of the π-donor molecule TXF, where X stands for the chalcogens sulfur and selenium [TTF = tetrathiafulvalene, TSF = tetraselenafulvalene], respectively, on the (110) surface of silver by means of periodic plane-waves based DFT (Density Functional Theory) calculations using slab models. We have determined and characterized the stable adsorption sites and have evaluated the charge transfer from TXF molecules into the surface. The simulation of the vibrational spectra for TXF and the fully deuterated TXF species has permitted to identify the fingerprints of both molecules on this surface.     

Photoexcitation of dipole modes in 160,162,164Dy

High resolution photon scattering experiments on ^160,162,164Dy have revealed considerable fragmentation of dipole strength into two groups around 2.5 MeV and around 3 MeV. In assuming that the new J=1 states near 3 MeV correspond to magnetic excitations, the B(M1)↑ sums are effectively twice the sd-IBA-2 SU (3) value for g-factors obtained from magnetic moments. The new data also show a sudden drop in B(M1)↑ strength from Dy to Er.     

立体耦合光子晶体薄板微腔的高Q值特性研究

利用微腔之间的立体耦合,提出了基于无源材料硅的双层光子晶体薄板H1(DLPCS-H1)腔,薄板之间为空气层.使用三维时域有限差分方法和Padé近似方法分析了DLPCS-H1腔的偶极模的场分布和品质因子.通过对中间空气层高度的优化使DLPCS-H1腔的偶极模的品质因子得到了显著的提高,大约为单层光子晶体薄板H1腔的偶极模的品质因子的4倍.此外,还研究了三层光子晶体薄板H1腔,它的偶极模的品质因子约为单层光子晶体薄板H1腔的偶极模的品质因子的7倍.     

Photoproton spectrum from carbon with good energy resolution

The 90° photoproton spectrum from¹²C has been measured with good energy resolution using bremsstrahlung with maximum energyEγ=31 MeV. A fragmentation of the giant dipole resonance in fine structures with a typical width of 150 to 300 keV is observed.     

Laser Stark spectroscopy; a case study in the ν2 fundamental band of 14NH3

The ν₂ fundamental band of ¹⁴NH₃ is observed with a laser Stark spectrometer in Doppler-limited resolution. A set of 41 constants including the electric dipole moment and its rotational dependence are determined from 360 Stark resonances observed in the present work and 67 millimeter- and submillimeter-wave inversion and rotation-inversion lines reported in the literature. The rms residual of the fit is 3.1 × 10⁻⁴ cm⁻¹. Field-free transition frequencies of the band in the region 800–1160 cm⁻¹ are calculated from the constants and tabulated together with their estimated uncertainties and relative absorption intensities. Rotational dependence of the electric dipole matrix elements of a C_3v molecule is presented on the basis of the conventional theory of vibration-rotation.     

Experimental study of the enhanced Raman scattering in the Sarid-type 4-layered attenuated total reflection configurations

We experimentally explored the enhanced Raman scattering in pyridine (C₅H₅N) due to the excitation of long range surface plasmons (LRSP's) guided by a symmetrically bounded silver slab in the Sarid-type ATR (attenuated total reflection) configuration. We have observed that, with decreasing the metallic thickness, the absolute enhancement of the Raman cross section increases while the width of the polar angular distribution of the signal decreases. This observed dependence of the enhanced Raman intensity on the thickness of the thin Ag slab and the collecting solid angle is well explained by assuming that the Raman scattering is mediated by LRSP's. The observed maximum enhancement factor is 4 × 10⁶ for the 140 Å silver slab which agrees well with the theoretically predicted value of 6 × 10⁶.     

Measurements of N2-broadening and -shifting parameters of the water vapor spectral lines in the second hexad region

The water vapor line broadening and shifting in the ν₁+ν₂+ν₃ band induced by nitrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer at the spectral resolution of 0.01 cm⁻¹ for the line with upper states angular momentum up to 11. Line contour parameters are calculated using a semi-empirical approach extended by the use of empirical data to determine some fitting model parameters. We use the complete set of high accuracy vibration-rotation dipole transition moments calculated for all possible transitions using wavefunctions determined from variational nuclear motion calculations and an ab initio dipole moment surface. Calculated values of line contour parameters are in a good agreement with observed parameters.     

Synthesis,characterization and third-order nonlinear optical properties of polydiacetylene nanostructures,silver nanoparticles and polydiacetylene–silver nanocomposites

We have synthesized, characterized and studied the third-order nonlinear optical properties of two different nanostructures of polydiacetylene (PDA), PDA nanocrystals and PDA nanovesicles, along with silver nanoparticles-decorated PDA nanovesicles. The second molecular hyperpolarizability γ(?ω; ω, ?ω, ω) of the samples has been investigated by antiresonant ring interferometric nonlinear spectroscopic (ARINS) technique using femtosecond mode-locked Ti:sapphire laser in the spectral range of 720–820 nm. The observed spectral dispersion of γ has been explained in the framework of three-essential states model and a correlation between the electronic structure and optical nonlinearity of the samples has been established. The energy of two-photon state, transition dipole moments and linewidth of the transitions have been estimated. We have observed that the nonlinear optical properties of PDA nanocrystals and nanovesicles are different because of the influence of chain coupling effects facilitated by the chain packing geometry of the monomers. On the other hand, our investigation reveals that the spectral dispersion characteristic of γ for silver nanoparticles-coated PDA nanovesicles is qualitatively similar to that observed for the uncoated PDA nanovesicles but bears no resemblance to that observed in silver nanoparticles. The presence of silver nanoparticles increases the γ values of the coated nanovesicles slightly as compared to that of the uncoated nanovesicles, suggesting a definite but weak coupling between the free electrons of the metal nanoparticles and π electrons of the polymer in the composite system. Our comparative studies show that the arrangement of polymer chains in polydiacetylene nanocrystals is more favourable for higher nonlinearity.     

Pyrolysis of amines: Infrared spectrum of methyleneimine

Methyleneimine was detected in the gas phase by a moderately high resolution infrared spectrometer as one of the intermediate species produced by a pyrolysis of amines. Observed vibrational frequencies of some isotopic derivatives have been combined with the ab initio values to reach a most reliable force constants set. Some other spectroscopic parameters, involving geometrical parameters and dipole moment derivatives, have also been calculated ab initio and compared with the observation. Its half-life in our experimental apparatus was about 10 min, which is much longer than the previously reported values, 0.1 or 10 sec.     

A field emission study of silver on rhenium

Field emission measurements of the change in average work function ?f of rhenium with adsorbed silver indicate that a rhenium-silver dipole forms with silver positive, of moment μ₀=5.2±1.5 ×10^?30 C m and polarizability $\text{α=29±12}\text{A}\text{?}{}^3$. Measurement of the rate of thermal desorption yields a mean binding energy of 2.31 ± 0.04 eV for sub-monolayer silver and 2.69±0.04 eV for a 2.5 monolayer deposit. Changes in work function induced by adsorption of silver on low-index rhenium plane surfaces are characterised by the formation of well-defined states and in this, silver resembles gold. These states are thought to result from a relatively large difference between the binding energy of adatoms on the low-index planes and on the surrounding surfaces, and this differnce is maintained when the surfaces are covered with silver. At the lowest coverage, silver is believed to be absent from all four observed planes and the measured rise in work function is thought to be apparent and to result from a decrease in field strength on the plane due to extension of the plane area by surrounding adsorbed silver. The structures adopted by silver overlayers are not known, but it is argued that on (101?0) and (101?1?) the final state at high coverage has the Ag(111) surface structure. On (112?0) and (112?2?) the silver layer at high coverage is thought to have either Ag(110) or Ag(100) surface structure. The structures of intermediate states found on all four low-index planes remain unkown. Field emission spectroscopy shows that emission from clean (101?0) is free-electron like and confirms earlier observations that emission from (202?1) is not. Spectroscopy also reveals a feature in the spectrum from silver on (101?0) which may be identified with a known surface state on Ag(111), thus providing some support for the assignment of Ag(111) to the surface structure of thick silver layers (> 3 monolayers) on (101?0).     

A new spectral resonance of metallic nanorods

The extinction, integrated scattering, and absorption spectra of gold and silver nanorods with random and regular orientation are studied. The calculations are performed for spheroids, circular cylinders, circular cylinders with hemispherical ends (T-matrix method), and rectangular prisms (discrete dipole approximation). A new quadrupole resonance is discovered that arises between the usual plasmon dipole resonances excited by a field longitudinal or transverse with respect to the symmetry axis. The new resonance can be excited only by a TM incident wave and is the greatest for orientation of the symmetry axis of the particle at an angle of 54° with respect to the light beam.     

Inelastic electron scattering in nickel

Using a 200 keV electron spectrometer, with an energy resolution of ～0.25 eV and a momentum resolution of ～0.2 A^-1, we have measured the energy loss spectra for transmission of electrons through thin (～600 Å) Ni films. These results address the general question of the validity of momentum transfer estimates in electron loss scattering.Using low-energy electron backscattering, we have observed the dipole forbidden M₁ transition at 112 eV. For high-energy scattering, we have observed this transition only at high momentum transfer (q? 2 A^-1). These results indicates sizable contributions from high momentum transfer collisions in the low-energy experiments.     

Free energy of conformational changes in vapors from low resolution microwave spectroscopic intensities

An analysis of the factors controlling the relative intensities of low resolution microwave spectroscopic bands of conformers leads to a formula for ΔG, the free energy difference between two conformers, in terms of the relative intensities of two bands of the same rotational quantum number J. Estimates of the a dipole moment component, and the rotational constants A, B, C, for the two conformers also occur in the formula. A partial experimental test is discussed, which compares two isotopic forms rather than two conformers.     

Electrical properties, structure, and surface morphology of poly(p-xylylene)–silver nanocomposites synthesized by low-temperature vapor deposition polymerization

The crystalline structure, surface morphology, electrical, and optical properties of thin films of nanocomposites consisting of silver nanoparticles embedded in poly(p-xylylene) matrix prepared by low-temperature vapor deposition polymerization were studied. Depending on the filler content, the average size of silver nanoparticles varied from 2 to 5 nm for nanocomposites with 2 and 12 vol.% of silver, correspondingly. The optical adsorption in the visible region due to surface plasmon resonance also exhibited a clear correlation from silver content, revealing a red shift of the adsorption peak with the increase of the metal concentration. The temperature dependences of the dc resistance of pure p-xylylene condensate and p-xylylene–silver cocondensates during polymerization as well as temperature dependences of the formed poly(p-xylylene)–silver nanocomposites were examined. The observed variation of the temperature dependences of electrical resistance as a function of silver concentration are attributed to different conduction mechanisms and correlated with the structure of the composites. The wide-angle X-ray scattering and AFM measurements consistently show a strong effect of silver content on the nanocomposite structure. The evolution of the size of silver nanoparticles by thermal annealing was demonstrated.