Mortko Kozhushner

Rectification mechanism in diblock oligomer molecular diodes.

We investigated a mechanism of rectification in diblock oligomer diode molecules that have recently been synthesized and showed a pronounced asymmetry in the measured I-V spectrum. The observed rectification effect is due to the resonant nature of electron transfer in the system and the localization properties of bound state wave functions of resonant states of the tunneling electron interacting with an asymmetric molecule in an electric field. The asymmetry of the tunneling wave function is enhanced or weakened depending on the polarity of the applied bias. The conceptually new theoretical approach, the Greens function theory of sub-barrier scattering, is able to provide a physically transparent explanation of this rectification effect based on the concept of the bound state spectrum of a tunneling electron. The theory predicts the characteristic features of the I-V spectrum in qualitative agreement with experiment.

Temperature dependence of cryochemical H-tunneling reactions

The temperature dependence of tunneling transition of the atomic particle in solids is studied near absolute zero. The different mechanisms of the temperature dependence are considered. They are the medium reorganization, the potential barrier parameters modulation, and the under-barrier friction The nonadiabatic effects are also considered. The rate constant K is described by formula ln K=ln K0+C4T4+C5T5+C6T6+C8T8 at low temperatures. It was conducted through the comparison of theory with the experimental data from the article of Kumada et al. [Chem. Phys. Lett. 261, 463 (1996)]. It turned out that good agreement takes place if one takes into account the quantum properties of the hydrogen crystal with the assumption of the dominated role of medium reorganization.

Multicenter scattering theory of mediator effect in electron tunneling transitions

The theory of the “bridge” effect, i.e., electron tunneling with the participation of intermediate particles, is developed. It is shown and proved that the general incorrectness of the approach that operates with the restricted basis of the bound states on the bridge particles to obtain a subbarrier electron Green’s function. This approach is adequate only in the energy region near the bound energy of the bridge centers at the large center-to-center distances. Our theory is based on the concept of multiple subbarrier scattering of tunneling electron on the intermediate particles. The regular method of the calculation of the energies of the collectivized bound states as the poles of the total scattering amplitude is developed. It is shown that the probability of the tunneling transition depends on the value and sign of the amplitude of electron subbarrier scattering on one particle, and this amplitude can be calculated by the variation-asymptotic method developed by the authors earlier. The bridge induced ...

Complex Dielectric Permittivity of Metal-Containing Nanocomposites: Non-phenomenological Description

Addition of metal nanoparticles radically alters the complex dielectric permittivity of a matrix-insulator. A non-phenomenological theory describing these changes is developed by assuming that a large concentration of electron traps with the critical binding energy in the amorphous matrix exists. Such traps in the vicinity of the nanoparticles can be partially occupied by the electrons. The trapped electron with its neighbor nanoparticle then represents an appreciable dipole moment. Reorientations of this moment in the external electric field occurs due to electron jumps between the traps over a sphere surrounding a nanoparticle. The calculation of the interaction of the dipole moment with an external field is carried out taking into account the dielectric permittivity of the matrix. By deriving and solving the equation for the dipole relaxation function, the real and imaginary parts of the permittivity may be evaluated. The calculated dependences of the dielectric permittivity on frequency and temperature agree qualitatively with experiment.

Temperature dependence of the rate constants of cryochemical reactions

The temperature dependence of the reaction rate constant for tunneling transfer of an atomic particle in solid near absolute zero was studied. Different mechanisms describing the temperature dependence were considered: reorganization of the medium, modulation of parameters of the potential barrier, and under-barrier friction. It was established that for the rate constant (K) at low temperatures the equation InK=InK0+C4T4+C5T5+C6T6+C8T8 is valid. Experimental data were compared with the theory. A good agreement is achieved when the quantum nature of the hydrogen crystal is applied under the assumption of a predominant role of reorganization of the medium.

Modeling of the diffusion-kinetics-controlled adsorption of cations on a sorbent surface

A mathematical model for describing the sorption of two kinds of cations from dilute immobile liquid solutions on a flat sorbent surface was proposed. A criterion of the transition from the kinetics-controlled sorption mode, in which the selectivity of the sorbent is governed by the ratio between the rate constants of the reactions of the different cations from the solution and adsorption sites on the sorbent surface, to the diffusion-controlled mode, in which the selectivity is determined by the difference between the diffusion coefficient for the migration of the cations to the sorbent surface, was proposed. Formulas were obtained for calculating the surface concentration of adsorbed cations as a function of the time. The calculation results are in a reasonable agreement with the experimental data.

Multiple Subbarrier Scattering: A Theory for the Bridge Effect

The electron tunneling via an extrinsic bridge atom by a superexchange mechanism is considered. It is shown that the bridge effect must be described by a transition amplitude gain, whose exponential rise with the bridge length is caused by subbarrier scattering on the bridge particles. A total operator of scattering on a linear bridge is expressed through operators of scattering on individual particles of the bridge.

Theory of temperature dependence of hydrogen tunneling reactions

Abstract The different possible mechanisms of the temperature dependence of the tunnelling transition of an atomic particle in solids near absolute zero and the non-adiabatic effects are determined and considered. The general expression for the rate constant is obtained, taking into account the quantum properties of hydrogenous crystal. Comparison of the theoretical formula with experimental data [3] has permitted the leading mechanism, i.e. medium reorganization, of temperature dependence to be established. Good agreement has been achieved between theory and the discussed experimental data at reasonable values of the system parameters.