Thermoelectric effect in molecular electronics

Abstract

We provide a theoretical estimate of the thermoelectric current and voltage over a Phenyldithiol molecule. We also show that the thermoelectric voltage is (1) easy to analyze, (2) insensitive to the detailed coupling to the contacts, (3) large enough to be measured and (4) give valuable information, which is not readily accessible through other experiments, on the location of the Fermi energy relative to the molecular levels. The location of the Fermi-energy is poorly understood and controversial even though it is a central factor in determining the nature of conduction (n-or p-type). We also note that the thermoelectric voltage measured over Guanine molecules with an STM by Poler et al., indicate conduction through the HOMO level, i.e., p-type conduction.

Thermoelectric Effects in Nanoscale Junctions

“…We show that the thermopower is a highly non-linear function of the thermal gradient and it is very sensitive to the junction geometry, even in the simplest case of non-interacting electrons. This precludes an easy interpretation of its sign in terms of electrons or holes as it has been argued in some literature [3,[8][9][10][11].In addition, we calculate the global and local electron distribution functions, which exhibit NE characteristics.The theory also allows us to define the local electron temperature by means of a temperature floating probe that is locally coupled to the system, and whose temperature is adjusted so that the system dynamics is minimally perturbed. This temperature, which can be measured experimentally, shows important features such as hot spots in the cold lead at small coupling between the nanowire and the bulk electrodes, and temperature oscillations in the wire at intermediate coupling.…”

“…The ratio S = − ∆V ∆T is called thermopower [2], and has been measured in a variety of nano-scale systems such as quantum point contacts [3], atomic-size metallic wires [4], quantum dots [5], Si nanowires [6] and recently in molecular junctions [7]. In a bulk material, when S < 0 the transient current is carried by electrons; when S > 0 it is carried by holes.In nanoscale systems this NE problem has recently received a lot of attention [3,[8][9][10][11][12][13]. In these theories the single-particle scattering formalism [14] is used to relate the thermopower to single-particle transmission probabilities.…”

“…In nanoscale systems this NE problem has recently received a lot of attention [3,[8][9][10][11][12][13]. In these theories the single-particle scattering formalism [14] is used to relate the thermopower to single-particle transmission probabilities.…”

Single-Molecule Analysis Methods Using Nanogap Electrodes and Their Application to DNA Sequencing Technologies

“…The Seebeck coefficient is the voltage generated when a temperature gradient exists between two nanoelectrodes (Figure 14a). The Seebeck coefficient of SMJs is given by the following equation: 83,84 …”

Scattering theory of thermocurrent in quantum dots and molecules

“…Recent advances in heat measurements in nanoscale systems allow to study thermoelectric properties of molecular junctions and similar systems. These studies bring a deeper understanding of transport mechanisms [1][2][3][4] and additional information concerning electronic and vibrational excitation spectra of molecules [5,6]. Also, in the recent years a new field of molecular thermoelectronics have emerged [7].…”