共查询到20条相似文献,搜索用时 0 毫秒
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Coherent spin-dependent electron transport is investigated in three conditions: (1) a C60 molecule is connected to two ferromagnetic (FM) electrodes symmetrically, (2) a C59N molecule is connected to two FM electrodes symmetrically and (3) a C59N molecule is connected to two FM electrodes asymmetrically. This work is based on a single-band tight-binding model Hamiltonian and the Green’s function approach with the Landauer–Buttiker formalism. Electrodes used in this study are semi-infinite FM electrodes with finite cross-section. Obvious rectification effect is observed in the C59N molecule which is connected to the FMelectrodes asymmetrically. This effect is more in the P alignment of FM electrodes than in AP alignment of FM electrodes. This study indicates that the rectification behaviour is due to the asymmetry in molecule and junctions. Also in this investigation tunnel magnetoresistance (TMR) is calculated for these molecules. Asymmetry is observed in TMR of C59N which is coupled to the electrodes asymmetrically due to asymmetric junctions, but TMR of C60 is symmetric. 相似文献
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Using the extended Hubbard model and sum-over-state method, we have calculated the linear polarizability α and the third-order nonlinear polarizability γ for (C59N)2. We find that (C59N)2 has very big γ value (around esu), and its α and γ values are bigger than those of C59N. In particular, when 1.2 eV≤3ω, (C59N)2 as much larger γ values than C59N. 相似文献
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Rockenbauer A Csányi G Fülöp F Garaj S Korecz L Lukács R Simon F Forró L Pekker S Jánossy A 《Physical review letters》2005,94(6):066603
Electron spin resonance and ab initio electronic structure calculations show an intricate relation between molecular rotation and chemical bonding in the dilute solid solution. The unpaired electron of C59N is delocalized over several C60 molecules above 700 K, while at lower temperatures it remains localized within short range. The data suggest that below 350 K rigid C59N-C60 heterodimers are formed in thermodynamic equilibrium with dissociated rotating molecules. The structural fluctuations between heterodimers and dissociated molecules are accompanied by simultaneous electron spin transfer between C60 and C59N molecules. The calculation confirms that in the C59N-C60 heterodimer the spin density resides mostly on the C60 moiety, while it is almost entirely on C59N in the dissociated case. 相似文献
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Enrico?Da?Como Esther?Scheler Peter?Strohriegl John?M.?Lupton Jochen?Feldmann 《Applied Physics A: Materials Science & Processing》2009,95(1):61-66
Polyfluorene represents a unique model to study the influence of intramolecular conformation on the electronic properties
of chromophores with an extended π-conjugation. According to the degree of planarity between the adjacent repeat units the electronic and optical properties
can change substantially. This peculiar spectroscopic behavior has been described by identifying different phases, namely
the glassy, the γ- and the β-phase. Here, we present low-temperature single-molecule spectroscopy of a series of oligofluorenes differing in the number
of monomeric units, in order to gain information on the influence of chain length on the polymorphism. By monitoring the energy
of the 0-0 transition we have classified single molecules belonging to the different phases. We demonstrate that a large number
of molecules start to form the β-phase only when more than 9 repeat units constitute the molecular chain. The implications for the control of morphology in
polyfluorene thin films are discussed. 相似文献
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We consider the charge shuttle proposed by Gorelik et al. driven by a time-dependent voltage bias. In the case of asymmetric setup, the system behaves as a rectifier. For pure ac drive, the rectified current shows a rather rich frequency dependent response characterized by frequency locking at fractional values of the external frequency. Because of the nonlinear dynamics of the shuttle, rectification is present also for very low frequencies. These effects could be useful to unveil the internal dynamics of nanomechanical devices. 相似文献
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For solving the atomic structure of organic molecules such as small proteins which are difficult to crystallize, the use of a jet of doped liquid helium droplets traversing a continuous high energy electron beam is proposed as a means of obtaining electron diffraction patterns (serial crystallography). Organic molecules (such as small proteins) within the droplet (and within a vitreous ice jacket) may be aligned by use of a polarized laser beam. Iterative methods for solving the phase problem are indicated. Comparisons with a related plan for pulsed x-ray diffraction from single proteins in a molecular beam are provided. 相似文献
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《Comptes Rendus Physique》2002,3(4):501-508
Photon emission from a single molecule at room temperature exhibits nonclassical features. Continuous wave fluorescence excitation provides antibunching in the emitted photons sequence as a signature of the property to only emit one photon at a time. A short pulsed excitation can then produce single photons on demand, with an overall quantum efficiency up to 4.5% in our experimental setup. Direct measurement of the Mandel parameter Q(T) for an observation period of duration T follows a subpoissonian statistics on short time scale and superpoissonian statistics on longer time scale. The latter is attributed to blinking in the fluorescence due to the occurence of a metastable molecular triplet state. To cite this article: F. Treussart et al., C. R. Physique 3 (2002) 501–508. 相似文献
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We report our recent work on a hadronic molecule state of the KKN system with I =1/2 and jR = 1/2+. We assume that the A(1405) resonance and the scalar mesons, f0(980), ao(980), are reproduced as quasi-bound states of KN and KK, respectively. Performing non-relativistic three-body calculations with a variational method for this system, we find a quasibound state of the KIlN system around 1910 MeV below the three-body breakup threshold. This state corresponds to a new baryon resonance of N* with JP : 1/2+. We find also that this resonance has the cluster structure of the two-body bound states keeping their properties as in the isolated two-particle systems. We also briefly discuss another hadronic molecular state composed by two K and one N, which corresponds to a resonance. 相似文献
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Tunnelling electrons may scatter inelastically with an adsorbate, releasing part of their energy
through the excitation of molecular vibrations. The resolution of inelastic processes with a low
temperature scanning tunnelling microscope (STM) provides a valuable tool to chemically
characterize single adsorbates and their adsorption mechanisms. Here, we present a molecular scale
picture of single molecule vibrational chemistry, as resolved by STM. To understand the way a
reaction proceed it is needed knowledge about both the excitation and damping of a molecular
vibration. The excitation is mediated by the specific coupling between electronic molecular
resonances present at the Fermi level and vibrational states of the adsorbate. Thus, the
two-dimensional mapping of the inelastic signal with an STM provides the spatial distribution of
the adsorbate electronic states (near the Fermi level) which are predominantly coupled to the
particular vibrational mode observed. The damping of the vibration follows a competition between
different mechanisms, mediated via the creation of electron-hole pairs or via anharmonic coupling
between vibrational states. This latter case give rise to effective energy transfer mechanisms
which eventually may focus vibrational energy in a specific reaction coordinate. In this
single-molecule work-bench, STM provides alternative tools to understand reactivity in the limit of
low excitation rate, which demonstrate the existence of state-specific excitation strategies which
may lead to selectivity in the product of a reaction. 相似文献
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By applying non-equilibrium Green's function formalism combined with density functional theory, we have investigated the electronic transport properties of nitrogen doped fullerene absorbed on the self-assembled alkanethiol monolayer. The molecular dipole moment, which in microscopy leads to the molecule-electrode coupling changing asymmetrically is responsible for the observed molecular rectification. 相似文献
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J. Biemond 《Physica A》1977,88(2):385-394
The dielectric alignment of a dilute non-polar component in a polar solvent may be determined by NMR spectroscopy. In this paper a series expansion of the alignment up to second order terms in the dipolar interaction is presented for a non-polar molecule replacing a single polar molecule in a rigid lattice of molecular dipoles. Assuming isotropic polarizabilities for all molecules Van Vleck earlier applied the lattice model in a theory of the dielectric constant of a dilute solution.In the present calculation the polarizabilities of the non-polar molecule and the dipoles are assumed to be anisotropic and isotropic, respectively. The anisotropy of the non-polar molecule is relevant, since the value of the alignment is zero for the isotropic case. Different results are obtained for cubic lattices and for a lattice points are uniformly distributed.In absence of a rigid dipole moment of the solvent molecules the latter formula may be compared with that implicity deduced by Buckingham for the Kerr effect. In the limit of strong dipoles the orientation imposed by the rigid dipole moments appears to be the major contribution to the alignment of the non-polar molecule. 相似文献
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Néel N Kröger J Limot L Frederiksen T Brandbyge M Berndt R 《Physical review letters》2007,98(6):065502
The tip of a low-temperature scanning tunneling microscope is approached towards a C60 molecule adsorbed at a pentagon-hexagon bond on Cu(100) to form a tip-molecule contact. The conductance rapidly increases to approximately 0.25 conductance quanta in the transition region from tunneling to contact. Ab-initio calculations within density functional theory and nonequilibrium Green's function techniques explain the experimental data in terms of the conductance of an essentially undeformed C60. The conductance in the transition region is affected by structural fluctuations which modulate the tip-molecule distance. 相似文献
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We report a method in which temperature dependent single-molecule fluorescence measurements are used to study the kinetics and thermodynamics of the acid-base interaction in films of photoresist polymer. We use the two distinct fluorescent prototropic forms of Coumarin 6 (C6-->C6+) to indicate the state of the acid-base system. Data are analyzed using a statistical model of the intensity probability distributions, yielding temperature dependent proton exchange rates, which is confirmed through agreement with a simple two-state Monte Carlo model. The temperature dependent rates are used to calculate the activation enthalpy for proton exchange. 相似文献
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The lifetimes of long-lived negative molecular ions SF6−-, C6H5NO2−, and C6F6− are measured with a static mass spectrometer. A great spread in published data for the lifetimes of these ions is explained
using a concept of multiexponential decay of molecular ions. The influence of the Boltzmann distribution of neutral target
molecules over vibrational states on the lifetime of negative molecular ions is studied in terms of the Illenberger-Smirnov-Kompaneits
simple statistical model. It is shown that this distribution has a profound effect on the multiexponential decay of molecular
anions and, as a consequence, on the lifetime of negative molecular ions measured on different mass spectrometers. 相似文献
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富勒烯自由基通常是在空气中短暂存在或不稳定的短寿命物种,超分子屏蔽是近年来被发展用于稳定富勒烯自由基稳定的一种有效策略.本文将共价桥联碳质π电子共轭双嵌N分子碗作为客体C59N·富勒烯自由基的理想宿主体,通过密度泛函理论计算研究了二者之间的主客体相互作用、热力学、自旋电子密度等性质.结果发现C59N·富勒烯自由基嵌螯在该钳形双分子碗的凹穴内而被屏蔽,从而有效避免单电子结构的暴露和C59N·自由基之间的化学二聚,即显著增强其动力学稳定性和寿命,这种策略对富勒烯自由基在自旋电子学、超分子电子器件或光电转换器件等领域的应用具有潜在指导价值.此外,本研究还发现通过超分子屏蔽策略,理论上可以实现对(C59N)2二聚体分子中键连两个碳笼的C-C进行重构,这也为富勒烯相关体系中C-C键构建的提供了一种新的思路与途径. 相似文献