Search results for "dipole"
showing 10 items of 982 documents
Effect of type, size and deformation on the polarizability of carbon nanotubes from atomic increments
2006
The interacting induced dipole polarization model is used for the calculation of the dipole–dipole polarizability α. The method is tested with single-wall carbon nanotubes (SWNTs) as a function of nanotube radius and elliptical deformation. The results are similar to ab initio reference calculations. For the zigzag tubes, the polarizability follows a remarkably simple law. The calculations effectively differentiate among SWNTs with increasing radial deformations. The polarizability and related properties can be modified continuously and reversibly by the external radial deformation. These results suggest a technology in which mechanical deformation can control chemical properties of the car…
Comparative study of polar perovskite surfaces
2004
A novel model of the ‘‘zig–zag’’ (1 1 0) polar surface termination of ABO3 perovskites is suggested and analyzed. Classical shell model calculations for BaTiO3, SrTiO3 and LaMnO3 show that such the (1 · 2) (1 1 0) surface reconstruction has the lowest energy, comparable to that for the (1 0 0) surfaces. The calculated surface energy reaches the saturation only when 6–8 atomic near-surface planes are allowed to relax. Surface relaxation leads to the formation of considerable dipole moment perpendicular to the surface. The predicted surface polarization of thin perovskite films, even in the cubic phase, could affect their dielectric properties. � 2004 Elsevier B.V. All rights reserved.
Ni61Mössbauer study of the hyperfine magnetic field near the Ni surface
1987
$^{61}\mathrm{Ni}$ M\"ossbauer measurements have been performed at 4.2 K on spherical Ni particles covered with a protective layer of SiO, with average diameter of 500 and 50 \AA{}. The hyperfine magnetic field at $^{61}\mathrm{Ni}$ nuclei for 500-\AA{} particles has been found to be 78.3(4) kOe, compared with the field for Ni foil of 75.0(2) kOe. The small difference is due to the demagnetization and dipolar fields in 500-\AA{} particles. The spectrum of 50-\AA{} particles has a surface component with the corresponding value of the hyperfine magnetic field of 40.3(5.4) kOe. This strongly indicates that, in accordance with recent theoretical studies, there is a decrease of the hyperfine mag…
Subwavelength mapping of surface photonic states
2003
We show that the spectral tailoring of optical local density of states (LDOS) may be achieved by lithographically designed nanostructures and that the subwavelength mapping of the spectral variation of the optical LDOS is feasible by varying the driving frequency of the effective dipole used in an illumination mode scanning near-field optical microscope.
The Single Molecule Probe: Nanoscale Vectorial Mapping of Photonic Mode Density in a Metal Nanocavity
2009
International audience; We use superresolution single-molecule polarization and lifetime imaging to probe the local density of states (LDOS) in a metal nanocavity. Determination of the orientation of the molecular transition dipole allows us to retrieve the different LDOS behavior for parallel and perpendicular orientations with respect to the metal interfaces. For the perpendicular orientation, a strong lifetime reduction is observed for distances up to 150 nm from the cavity edge due to coupling to surface plasmon polariton modes in the metal. Contrarily, for the parallel orientation we observe lifetime variations resulting from coupling to characteristic λ/2 cavity modes. Our results are…
Splitting of the surface phonon modes in wurtzite nanowires
2013
We analyze the surface optical modes of GaN nanowires (NW) and perform a comparative study with the characteristics expected for other polar NWs. The theoretical analysis of the modes is performed within the context of the effective medium theory that takes into account the dipolar interaction between neighboring NWs (Maxwell-Garnett approximation). It is shown that deviations of the exciting light from the NWs axis, which coincides with the wurtzite c-axis, result in the anticrossing of two distinct surface phonon branches, leading to their splitting in axial and planar components and the appearance of two peaks in the Raman spectra. Additional calculations are performed that determine th…
Near-field coupling of a point-like dipolar source with a thin metallic film: Implication for STM plasmon excitations
2012
International audience; Recent experiments have shown that it is possible to excite surface plasmons on metallic films by injecting tunnel electrons from a sharp metal tip located in the immediate proximity of the sample. When working close to a bare metal film, the excitation of surface plasmons gives rise to typical circular patterns that can be recorded in both image and Fourier planes. Important physical parameters of surface plasmon propagation such as their propagation length can be extracted from these images. In this Letter, we discuss theoretically the physics of the plasmonic excitations induced by a STM tip.
Laser and radiofrequency spectroscopy of the 5d 4 6s 6 D multiplet in Ta I
1993
The hyperfine structure (hfs) of181Ta has been investigated using laser radio-frequency double resonance and high resolution laser spectroscopy on collimated atomic beams. The magnetic dipole and electric quadrupole hyperfine structure coupling constants of the 5d46s 6D3/2, 5/2, 7/2, 9/2 metastable states have been determined using radio-frequency spectroscopy. In the 5d4 6s6D1/2 metastable state and the excited 5d3 6s 6p4D3/2,6D5/2, 9/2 as well as the unidentified 28 182.6 cm−1 and 30 021.2 cm−1 states, hfs constants have been obtained from high resolution laser spectroscopy. A radio-frequency converter has been developed in order to reach the frequency region 2.7–10 GHz.
Double-modulation sideband spectroscopy: μ0 and μ33 of silicon tetrafluoride
1992
Abstract The linear Stark effect in the ν 3 fundamental of 28 SiF 4 has been investigated with IR-IR double resonance employing CO 2 laser sidebands at microwave modulation frequencies. The frequencies needed for the double-resonance experiment were generated from one laser line by a novel double-modulation technique. As a result, the parameter of the vibration-induced dipole moment was determined to μ 33 = −0.10288(56) D. For the centrifugal distortion moment in the ν 3 excited state the value μ 0 = 6.06(36) × 10 −7 D was found. From the Stark splitting in the vibrational ground state, μ 0 = 6.81(10) × 10 −7 was determined.
A stable path to ferromagnetic hydrogenated graphene growth
2014
In this paper, we propose a practical way to stabilize half-hydrogenated graphene (graphone). We show that the dipole moments induced by an hexagonal-boron nitride (h-BN) substrate on graphene stabilize the hydrogen atoms on one sublattice of the graphene layer and suppress the migration of the absorbed hydrogen atoms. Based upon first principle spin polarized density of states (DOS) calculations, we show that the half hydrogenated graphene (graphone) obtained in different graphene-h-BN heterostructures exhibits a half metallic state. We propose to use this new exotic material for spin valve and other spintronics devices and applications.