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Mesoscopic Systems (mesoscopic + system)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Phonon-electric effect in nano-scale transistors

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2005
D. W. Horsell
Abstract A novel dc current is shown to exist in a nano-scale transistor structure. This current is accounted for by a non-equilibrium distribution of electrons generated by hot electrons from the gate. It is shown that by this mechanism the gate leakage current can be substantially magnified. It is this, along with the asymmetry inherent to the mesoscopic system, that can maintain a dc current flow across the channel. We realize this current experimentally and show that it may dominate other currents present in the system. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

From quantum chemistry and the classical theory of polar liquids to continuum approximations in molecular mechanics calculations,

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005
Sergio A. Hassan
Abstract Biological macromolecules and other polymers belong to the class of mesoscopic systems, with characteristic length scale of the order of a nanometer. Although microscopic models would be the preferred choice in theoretical calculations, their use in computer simulations becomes prohibitive for large systems or long simulation times. On the other hand, the use of purely macroscopic models in the mesoscopic domain may introduce artifacts, with effects that are difficult to assess and that may compromise the reliability of the calculations. Here is proposed an approach with the aim of minimizing the empirical nature of continuum approximations of solvent effects within the scope of molecular mechanics (MM) approximations in mesoscopic systems. Using quantum chemical methods, the potential generated by the molecular electron density is first decomposed in a multicenter-multipole expansion around predetermined centers. The monopole and dipole terms of the expansion at each site create electric fields that polarize the surrounding aqueous medium whose dielectric properties can be described by the classical theory of polar liquids. Debye's theory allows a derivation of the dielectric profiles created around isolated point charges and dipoles that can incorporate Onsager reaction field corrections. A superposition of screened Coulomb potentials obtained from this theory makes possible a simple derivation of a formal expression for the total electrostatic energy and the polar component of the solvation energy of the system. A discussion is presented on the physical meaning of the model parameters, their transferability, and their convergence to calculable quantities in the limit of simple systems. The performance of this continuum approximation in computer calculations of amino acids in the context of an atomistic force field is discussed. Applications of a continuum model based on screened Coulomb potentials in multinanosecond simulations of peptides and proteins are briefly reviewed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source]

Density functional theory for chemical engineering: From capillarity to soft materials

AICHE JOURNAL, Issue 3 2006
Jianzhong Wu
Abstract Understanding the microscopic structure and macroscopic properties of condensed matter from a molecular perspective is important for both traditional and modern chemical engineering. A cornerstone of such understanding is provided by statistical mechanics, which bridges the gap between molecular events and the structural and physiochemical properties of macro- and mesoscopic systems. With ever-increasing computer power, molecular simulations and ab initio quantum mechanics are promising to provide a nearly exact route to accomplishing the full potential of statistical mechanics. However, in light of their versatility for solving problems involving multiple length and timescales that are yet unreachable by direct simulations, phenomenological and semiempirical methods remain relevant for chemical engineering applications in the foreseeable future. Classical density functional theory offers a compromise: on the one hand, it is able to retain the theoretical rigor of statistical mechanics and, on the other hand, similar to a phenomenological method, it demands only modest computational cost for modeling the properties of uniform and inhomogeneous systems. Recent advances are summarized of classical density functional theory with emphasis on applications to quantitative modeling of the phase and interfacial behavior of condensed fluids and soft materials, including colloids, polymer solutions, nanocomposites, liquid crystals, and biological systems. Attention is also given to some potential applications of density functional theory to material fabrications and biomolecular engineering. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source]

Full counting statistics for electron number in quantum dots

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008
Yasuhiro Utsumi
Abstract Measurements of the average current and its fluctuations (noise) have been powerful tools to study the quantumtransport in mesoscopic systems. Recently it became possible to measure the probability distribution of current, ,full counting statistics' (FCS), by using quantum point-contact charge-detectors. Motivated by recent experiments, we developed the FCS theory for the joint probability distribution of the current and the electron number inside quantum dots (QDs). We show that a non-Gaussian exponential distribution appears when there is no dot state close to the lead chemical potentials. We show that the measurement of the joint probability distribution of current and electron number would reveal nontrivial correlations, which reflect the asymmetry of tunnel barriers. We also show that for increasing strength of tunneling, the quantum fluctuations of charge qualitatively change the probability distribution of the electron number. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]