Molecular transport junctions: asymmetry in inelastic tunneling processes

Inelastic electron tunneling spectroscopy (IETS) measurements are usually carried out in the low-voltage ("Ohmic", i.e., linear) regime where the elastic conduction/voltage characteristic is symmetric to voltage inversion. Inelastic features, normally observed in the second derivative d(2)I/dV(2) are also symmetric (in fact antisymmetric) in many cases, but asymmetry is sometimes observed. We show that such asymmetry can occur because of different energy dependences of the two contact self-energies. This may be attributed to differences in contact density of states (different contact material) or different energy dependence of the coupling (STM-like geometry or asymmetric positioning of molecular vibrational modes in the junction). The asymmetry scales with the difference between the energy dependence of these self-energies and disappears when this dependence is the same for the two contacts. Our nonequilibrium Green function approach goes beyond proposed WKB scattering theory in properly accounting for Pauli exclusion, as well as providing a path to generalizations, including consideration of phonon dynamics and higher-order perturbation theory.     

Inelastic electron tunneling spectroscopy in molecular junctions: peaks and dips

We study inelastic electron tunneling through a molecular junction using the nonequilibrium Green's function formalism. The effect of the mutual influence between the phonon and the electron subsystems on the electron tunneling process is considered within a general self-consistent scheme. Results of this calculation are compared to those obtained from the simpler Born approximation and the simplest perturbation theory approaches, and some shortcomings of the latter are pointed out. The self-consistent calculation allows also for evaluating other related quantities such as the power loss during electron conduction. Regarding the inelastic spectrum, two types of inelastic contributions are discussed. Features associated with real and virtual energy transfer to phonons are usually observed in the second derivative of the current I with respect to the voltage Phi when plotted against Phi. Signatures of resonant tunneling driven by an intermediate molecular ion appear as peaks in the first derivative dI/dPhi and may show phonon sidebands. The dependence of the observed vibrationally induced lineshapes on the junction characteristics, and the linewidth associated with these features are also discussed.     

Influence of organic additives on structure formation of Pt/Alumina catalysts

The activity of Pt/alumina catalysts prepared via -Al₂O₃ impregnation with an aqueous solution of H₂PtCl₆ in the presence of organic additives, after calcination is abnormally high, which can be due to the formation of electron deficient platinum.

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, -Al₂O₃ H₂PtCl₆ , , .

     

On the norms of singular integral operators along certain curves with intersections

It is well known [K] that the norm and essential norm of singular integral operator for contours composed by two rays depend on the angle between the rays. The goal of the paper is both to show that for the contour that is an intersection oftwo straight lines the norm and essential norm of singular integral operatordo not depend on the angle between the lines, andto calculate these norms. Some generalizations for the case when is an intersection of several simple contours are also considered.     

A concept of the mass center of a system of material points in the constant curvature spaces

This article demonstrates that in the Lobatchevsky space and on a sphere of arbitrary dimensions, the concept of the mass center of a system of mass points can be correctly defined. Presented are: a uniform geometric construction for defining the mass center; hyperbolic and spheric lever rules; the theorem of uniqueness for determining the mass center in these spaces. Among the compact manifolds, only the sphere possesses this property.     

The Dynamics of Pendulums on Surfaces of Constant Curvature

We define the notion of a pendulum on a surface of constant curvature and study the motion of a mass at a fixed distance from a pivot. We consider some special cases: first a pivot that moves with constant speed along a geodesic, and then a pivot that undergoes acceleration along a fixed geodesic.      

Duality of Nonscalarized Multiobjective Linear Programs: Dual Balance,Level Sets,and Dual Clusters of Optimal Vectors

A new concept of duality is proposed for multiobjective linear programs. It is based on a set expansion process for the computation of optimal solutions without scalarization. The duality gap qualifications are investigated; the primal–dual balance set and level set equations are derived. It is demonstrated that the nonscalarized dual problem presents a cluster of optimal dual vectors that corresponds to a unique optimal primal vector. Comparisons are made with linear utility, minmax and minmin scalarizations. Connections to Pareto optimality are studied and relations to sensitivity and parametric programming are discussed. The ideas are illustrated by examples.     

Universal spectrum of two-dimensional turbulence on a rotating sphere and some basic features of atmospheric circulation on giant planets

The Kolmogorov-Batchelor-Kraichnan (KBK) theory of two-dimensional turbulence is generalized for turbulence on the surface of a rotating sphere. The energy spectrum develops considerable anisotropy; a steep -5 slope emerges in the zonal direction, while in all others the classical KBK scaling prevails. This flow regime in robust steady state is reproduced in simulations with linear drag. The conditions favorable for this regime may be common for giant planets' atmospheric circulations; the same steep spectra are found in their observed zonal velocity profiles and utilized to explain their basic characteristics.     

Models of environment and T1 relaxation in Josephson charge qubits

A theoretical interpretation of the recent experiments of Astafiev et al. on the T1-relaxation rate in Josephson charge qubits is proposed. The experimentally observed reproducible nonmonotonic dependence of T1 on the splitting E(J) of the qubit levels suggests further specification of the previously proposed models of the background charge noise. From our point of view the most promising is the "Andreev fluctuator" model of the noise. In this model the fluctuator is a Cooper pair that tunnels from a superconductor and occupies a pair of localized electronic states. Within this model one can naturally explain both the average linear T1(E(J)) dependence and the irregular fluctuations.     

Current-induced light emission and light-induced current in molecular-tunneling junctions

The interaction of metal-molecule-metal junctions with light is considered within a simple generic model. We show, for the first time, that light-induced current in unbiased junctions can take place when the bridging molecule is characterized by a strong charge-transfer transition. The same model shows current-induced light emission under potential bias that exceeds the molecular excitation energy. Results based on realistic estimates of molecule-lead coupling and molecule-radiation field interaction suggest that both effects should be observable.