Efficiency of Thermoelectric Energy Conversion in Biphenyl-dithil Junctions




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PHYSICAL REVIEW B 83 195415 2011 Efficiency of thermoelectric energy conversion in biphenyl dithiol junctions Effect of electron phonon interactions Nikolai Sergueev 1 2 Seungha Shin 2 Massoud Kaviany 2 and Barry Dunietz1 1 Department of Chemistry University of Michigan Ann Arbor Michigan 48109 USA Department of Mechanical Engineering University of Michigan Ann Arbor Michigan 48109 USA Received 3 November 2010 revised manuscript received 1 February 2011 published 9 May 2011 2 The electron phonon interaction is the dominant mechanism of inelastic scattering in molecular junctions Here we report on its effect on the thermoelectric properties of single molecule devices Using density functional theory and the nonequilibrium Green s function formalism we calculate the thermoelectric figure of merit for a biphenyl dithiol molecule between two Al electrodes under an applied gate voltage We find that the effect of electron phonon coupling on the thermoelectric characteristics strongly varies with the molecular geometry Two molecular configurations characterized by the torsion angles between the two phenyl rings of 30 and 90 exhibit significantly different responses to the inelastic scattering We also use molecular dynamics calculations to investigate the torsional stability of the biphenyl dithiol molecule and the phonon thermal transport in the junction DOI 10 1103 PhysRevB 83 195415 PACS number s 81 07 Nb 68 37 Ef 72 10 d 73 63 b I INTRODUCTION Charge and energy transport at the nanoscale is of current interest with implications in electronic structural and transport properties of electronic devices 1 12 These also include applications based on the thermoelectric TE effect where thermal energy is converted into electrical energy However the TE effect has been mainly observed in bulk materials Recent experiments13 16 on atomic and molecular junctions have demonstrated that nanoscale devices can also exhibit a TE behavior These experiments have inspired theoretical interest






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