G. P. Triberis

Thermoelectric properties of a weakly coupled quantum dot: enhanced thermoelectric efficiency

We study the thermoelectric coefficients of a multi-level quantum dot (QD) weakly coupled to two electron reservoirs in the Coulomb blockade regime. Detailed calculations and analytical expressions of the power factor and the figure of merit are presented. We restrict our interest to the limit where the energy separation between successive energy levels is much larger than the thermal energy (i.e., the quantum limit) and we report a giant enhancement of the figure of merit due to the violation of the Wiedemann-Franz law when phonons are frozen. We point out the similarity of the electronic and the phonon contribution to the thermal conductance for zero-dimensional electrons and phonons. Both contributions show an activated behavior. Our findings suggest that the control of the electron and phonon confinement effects can lead to nanostructures with improved thermoelectric properties.

Percolation-theoretic considerations for the thermoelectric power and the conductivity due to small polaron motion in disordered systems

Abstract Percolation-theoretic considerations have been used by various workers to evaluate the dc hopping conductivity and the thermoelectric power in disordered systems. We apply percolation theory to the small polaron hopping regime. Expressions for the thermoelectric power at low and high temperatures are obtained for a situation in which we have a symmetrical band of localized states with the Fermi level in the middle, and for an asymmetrical case in which we have a band of localized states above the Fermi level, and the conductivity for the low temperature case is evaluated. The correlation between bonds due to the energy of the common site is included in the present treatment.

DNA in the material world: electrical properties and nano-applications.

Contradictory experimental findings and theoretical interpretations have spurred intense debate over the electrical properties of the DNA double helix. In the present review article the various factors responsible for these divergences are discussed. The enlightenment of this issue could improve long range chemistry of oxidative DNA damage and repair processes, monitoring protein-DNA interactions and possible applications in nano-electronic circuit technology. The update experimental situation concerning measurements of the electrical conductivity is given. The character of the carriers responsible for the electrical conductivity measured in DNA is investigated. A theoretical model for the temperature dependence of the electrical conductivity of DNA is presented, based on microscopic models and percolation theoretical arguments. The theoretical results, excluding or including correlation effects, are applied to recent experimental findings for DNA, considering it as a one dimensional molecular wire. The results indicate that correlation effects are probably responsible for large hopping distances in DNA samples. Other theoretical conductivity models proposed for the interpretation of the responsible transport mechanism are also reviewed. Some of the most known and pioneering works on DNAs nano-applications, future developments and perspectives along with current technological limitations and patents are presented and discussed.

Near-Field Optical Properties of Quantum Dots, Applications and Perspectives

Recent years have witnessed tremendous research in quantum dots as excellent models of quantum physics at the nanoscale and as excellent candidates for various applications based on their optoelectronic properties. This review intends to present theoretical and experimental investigations of the near-field optical properties of these structures, and their multimodal applications such as biosensors, biological labels, optical fibers, switches and sensors, visual displays, photovoltaic devices and related patents.

Small polaron hopping and transport properties of As-Te based glasses

The behavior of the DC conductivity and thermopower of a variety of compositions in As-Te-I. As-Te-Ge and As-Te chalcogenide series has been analysed using In σ versus T −2.5 and S versus T 2.5 plots as suggested in the multiphonon assisted small polaron hopping model of Triberis and Friedman. Using this model and experimental data for σ and S , obtained by other workers, the densities of states of these glasses are evaluated. The agreement of the experimental data with this model is very satisfactory giving a meaningful interpretation of the transport properties of these As-Te based glasses.

The effect of correlations on the study of thermopower for the small polaron hopping regime in disordered systems

Abstract We investigate the importance of correlations, due to the energy of the common site, in a percolation cluster, studying the thermopower for the small poralon hopping regime in a disordered system. For this purpose, a percolation treatment for the thermopower is presented, ignoring correlations, and comparison is made with the method in which correlations are included. The drastic way in which correlations affect the temperature dependence of thermopower becomes apparent.

Theory of spontaneous emission of quantum dots in the linear regime

We develop a fully quantum-mechanical theory for the interaction of light and electron-hole excitations in semiconductor quantum dots. Our theoretical analysis results in an expression for the photoluminescence intensity of quantum dots in the linear regime. Taking into account the single-particle Hamiltonian, the free-photon Hamiltonian, the electron-hole interaction Hamiltonian, and the interaction of carriers with light, and applying the Heisenberg equation of motion to the photon number expectation values, to the carrier distribution functions and to the correlation term between the photon generation (destruction) and electron-hole pair, we obtain a set of luminescence equations. Under quasi-equilibrium conditions, these equations become a closed-set of equations. We solve them analytically, in the linear regime, and we find an approximate solution of the incoherent photoluminescence intensity. The validity of the theoretical analysis is tested by investigating the emission spectra in the high-temperature regime, interpreting the experimental findings for the emission spectra of a lens-shaped In(0.5)Ga(0.5)As self-assembled quantum dot. Our theoretical predictions for the interlevel spacing as well as for the dephasing time caused by electron-longitudinal optical phonon interactions are in good agreement with the experimental results.

A conductivity study on V2O5 layers deposited from gels

Abstract Triberis and Friedman applied percolation theory to the small polaron hopping regime and they evaluated the DC conductivity in disordered systems. Correlation due to the energy of the common site in a percolation cluster were included. We analyse the behavior of the DC conductivity of V2O5 thin layers deposited from gels using ln σ versus T − 1 4 plots, as suggested by their model, using experimental data for σ obtained by other workers. The agreement of the experimental data with this model is very satisfactory giving a meaningful interpretation of the transport properties of these materials. The density of states of these V2O5 layers deposited from gels of various V4+ content C is evaluated.

Density of states and extent of wave function: two crucial factors for small polaron hopping conductivity in 1D

Abstract We introduce a theoretical model to scrutinize the conductivity of small polarons in 1D disordered systems, focusing on two crucial – as will be demonstrated – factors: the density of states and the spatial extent of the electronic wave function. The investigation is performed for any temperature up to 300 K and under electric field of arbitrary strength up to the polaron dissociation limit. To accomplish this task, we combine analytical work with numerical calculations.

Thermal conductance of a weakly coupled quantum dot

We calculate the heat current through a quantum dot, weakly coupled to two electron reservoirs, when small temperature and voltage differences are applied between the reservoirs. The electronic contribution to the thermal conductance, κe, is then readily obtained. We restrict our interest in the regime where Δe >> kBT, where Δe is the level spacing, and we show that for a dot with equidistant energy levels κe exhibits periodical resonance peaks as a function of the Fermi energy in the reservoirs. The periodicity of these peaks is the same as the Coulomb blockade peaks in the conductance. The resonance values of κe tend rapidly to zero as exp(−Δe/kBT)(Δe/kBT)2. This finding underlies a clear violation of the Wiedemann‐Franz law. We point out the consequence of this violation in achieving large values of the figure of merit ZT.