The design of thermoelectric materials for the efficient conversion of waste heat into electricity requires simultaneous tuning of their electrical and thermal conductance. A comparative theoretical ...study of electron and phonon transport in thiophene and ethylenedioxythiophene (EDOT) based molecular wires is performed. It is shown that modifying thiophene by substituting ethylenedioxy enhances the thermoelectric figure of merit ZT for molecules of the same length. Furthermore, it is demonstrated that the electrical conductance of EDOT‐based wires decays more slowly with length than that of thiophene‐based wires and that their thermal conductance is lower. The room‐temperature ZT of undoped EDOT is found to be rather low. However, doping of EDOT by the electron acceptor tolunenesulfunate increases the Seebeck coefficient and electrical conductance, while decreasing the thermal conductance, leading to a thermoelectric figure of merit as high as ZT = 2.4.
The thermoelectric performance of thiophene molecular wires can be enhanced by ethylenedioxy substitution, to yield ethylenedioxythiophene molecular wires, whose electrical conductance decays slowly with length and whose thermal conductance is reduced.
We studied the single‐molecule conductance through an acid oxidant triggered phenothiazine (PTZ‐) based radical junction using the mechanically controllable break junction technique. The electrical ...conductance of the radical state was enhanced by up to 200 times compared to the neutral state, with high stability lasting for at least two months and high junction formation probability at room‐temperature. Theoretical studies revealed that the conductance increase is due to a significant decrease of the HOMO–LUMO gap and also the enhanced transmission close to the HOMO orbital when the radical forms. The large conductance enhancement induced by the formation of the stable PTZ radical molecule will lead to promising applications in single‐molecule electronics and spintronics.
Single‐molecule conductances of phenothiazine radicals have been measured using the mechanically controllable break junction technique. Triggered by an acid oxidant, the radical cation of phenothiazine enhances the charge‐transport property by up to 200 times with high stability and high junction formation probability at room temperature, which leads to promising applications in single‐molecule electronics and spintronics.
We studied charge transport through core‐substituted naphthalenediimide (NDI) single‐molecule junctions using the electrochemical STM‐based break‐junction technique in combination with DFT ...calculations. Conductance switching among three well‐defined states was demonstrated by electrochemically controlling the redox state of the pendent diimide unit of the molecule in an ionic liquid. The electrical conductances of the dianion and neutral states differ by more than one order of magnitude. The potential‐dependence of the charge‐transport characteristics of the NDI molecules was confirmed by DFT calculations, which account for electrochemical double‐layer effects on the conductance of the NDI junctions. This study suggests that integration of a pendant redox unit with strong coupling to a molecular backbone enables the tuning of charge transport through single‐molecule devices by controlling their redox states.
Charge‐transport phenomena through core‐substituted naphthalenediimide (NDI) single‐molecule junctions have been studied using the electrochemical scanning‐tunneling microscopy based break‐junction technique in combination with DFT calculations. Three well‐distinguished conductance states of the NDI molecule could be accessed, which can be reversibly switched by adjusting the potential.
Since the synthesis of graphene-boron nitride heterostructures, their interesting electronic properties have attracted huge attention for real-world nanodevice applications. In this work, we combined ...density functional theory (DFT) with a Green's function approach to examine the potential of graphene-boron nitride-graphene heteronanosheets (h-NSHs) for discriminating single molecule sensing. Our result demonstrates that the graphene-boron nitride-graphene (h-NSHs) can be used for discriminate sensing of the 2,4-dinitrotoluene (DNT), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), pentaerythritol tetranitrate (PENT), and 2,4,6-trinitrotoluene (TNT) molecules. We demonstrate that as the length of the BN region increases, the sensitivity of the heteronanosheets to the presence of these explosive substances increases.
Graphene-boron nitride-graphene (h-NSHs) heterostructures can be used for discriminate sensing of 2,4-dinitrotoluene (DNT), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), pentaerythritol tetranitrate (PENT), and 2,4,6-trinitrotoluene (TNT) molecules.
Using quantum theory (QT) combined with Tight-binding Approximation (TBA), we studied the electronic properties for single-orbital one dimensional, two-dimensional and diatomic crystalline chain to ...get simply qualitative understanding of electronic structure calculation in the periodic systems. Density of states (DOS) is one of the electrical properties that we try to understand within the band structures that lead to be able to know the mechanism of transport in the materials. The band structure and density of state (DOS) for both cases were calculated by using FORTRAN code. The calculation of DOS for ordered and disordered systems were performed via a numerical decimation method.
We have investigated a large set of symmetric and asymmetric molecules to demonstrate a general rule for molecular-scale quantum transport, which provides a new route to materials design and ...discovery. The rule states “the conductance GXBY of an asymmetric molecule is the geometric mean of the conductance of the two symmetric molecules derived from it and the thermopower SXBY of the asymmetric molecule is the algebraic mean of their thermopowers”. The studied molecules have a structure X–B–Y, where B is the backbone of the molecule, while X and Y are anchor groups, which bind the molecule to metallic electrodes. When applied to experimentally measured histograms of conductance and thermopower, the rules apply to the statistically most probable values. We investigated molecules with anchors chosen from the following family: cyano, pyridl, dihydrobenzothiol, amine and thiol. For the backbones B, we tested 14 different structures. We found that the formulas (G XBY)2 = G XBX*G YBY and S XBY = (S XBX + S YBY)/2 were satisfied in the large majority of the cases, provided the Fermi energy is located within the HOMO–LUMO gap of the molecules. The circuit rules imply that if measurements are performed on molecules with n A different anchors and n B different backbones, then properties of n A(n A + 1)n B/2 molecules can be predicted. So for example, in the case of 20 backbones and 10 anchors, 30 measurements (or reliable calculations) can provide a near quantitative estimate for 1070 measurements of other molecules, at no extra cost.
We provide a brief overview of recent measurements and predictions of thermoelectric properties of single-molecules and porous nanoribbons and discuss some principles underpinning strategies for ...enhancing their thermoelectric performance. The latter include (a) taking advantage of steep slopes in the electron transmission coefficient T(E), (b) creating structures with delta-function-like transmission coefficients and (c) utilising step-like features in T(E). To achieve high performance, we suggest that the latter may be the most fruitful, since it is less susceptible to inhomogeneous broadening. For the purpose of extrapolating thermoelectric properties of single or few molecules to monolayer molecular films, we also discuss the relevance of the conductance-weighted average Seebeck coefficient.
Nous procédons à un bref survol des mesures et prédictions récentes concernant les propriétés thermoélectriques de molécules individuelles ou de nanorubans poreux, puis nous discutons quelques-uns des principes sous-jacents aux stratégies visant à augmenter leurs performances thermoélectriques. On relèvera parmi ces dernières (a) l'utilisation de pentes élevées du coefficient de transmission électronique T(E), (b) la création de structures avec des pics de transmission et (c) l'exploitation de ces derniers. Pour atteindre de hautes performances, nous suggérons que cette dernière approche puisse être la plus fructueuse, puisqu'elle est moins susceptible de présenter des élargissements inhomogénes. Afin d'extrapoler les propriétés thermoélectriques d'une ou de quelques molécules à des films moléculaires monocouche, nous discutons aussi la pertinence de l'utilisation d'une moyenne du coefficient Seebeck pondérée par la conductance.
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