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In contrast to the static operations of conventional semiconductor devices, the dynamic conformational freedom in molecular devices opens up the possibility of using individual molecules as new types of devices such as a molecular conformational switch or for molecular data storage. Bistable molecules—such as those having two stable cis and trans isomeric configurations—could provide, once clamped between two electrodes, a switching phenomenon in the non-equilibrium current response. Here, we model molecular switch junctions formed at silicon contacts and demonstrate the potential of such tunable molecular switches in electrode/molecule/electrode configurations. Using the non-equilibrium Green function (NEGF) approach implemented with the density-functional-based tight-binding (DFTB) theory, a series of properties such as electron transmissions, currentvoltage characteristics in the different isomer conformations, and potential energy surfaces (PESs) as a function of the reaction coordinates along the trans to cis transition were calculated for two azobenzene-based model compounds. Furthermore, in order to investigate the stability of molecular switches under ambient conditions, molecular dynamics (MD) simulations at room temperature were performed and time-dependent fluctuations of the conductance along the MD pathways were calculated. Our numerical results show that the transmission spectra of the cis isomers are more conductive than trans counterparts inside the bias window for both model compounds. The currentvoltage characteristics consequently show the same trends. Additionally, calculations of the time-dependent transmission fluctuations along the MD pathways have shown that the transmission in the cis isomers is always significantly larger than that in their trans counterparts, showing that molecular switches can be expected to work as robust molecular switching components.


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Silicon-Based Molecular Switch Junctions

Show Author's information Daijiro NozakiGianaurelio Cuniberti( )
Institute for Material Science and Max Bergmann Center of BiomaterialsDresden University of TechnologyDresdenD-01062Germany

Abstract

In contrast to the static operations of conventional semiconductor devices, the dynamic conformational freedom in molecular devices opens up the possibility of using individual molecules as new types of devices such as a molecular conformational switch or for molecular data storage. Bistable molecules—such as those having two stable cis and trans isomeric configurations—could provide, once clamped between two electrodes, a switching phenomenon in the non-equilibrium current response. Here, we model molecular switch junctions formed at silicon contacts and demonstrate the potential of such tunable molecular switches in electrode/molecule/electrode configurations. Using the non-equilibrium Green function (NEGF) approach implemented with the density-functional-based tight-binding (DFTB) theory, a series of properties such as electron transmissions, currentvoltage characteristics in the different isomer conformations, and potential energy surfaces (PESs) as a function of the reaction coordinates along the trans to cis transition were calculated for two azobenzene-based model compounds. Furthermore, in order to investigate the stability of molecular switches under ambient conditions, molecular dynamics (MD) simulations at room temperature were performed and time-dependent fluctuations of the conductance along the MD pathways were calculated. Our numerical results show that the transmission spectra of the cis isomers are more conductive than trans counterparts inside the bias window for both model compounds. The currentvoltage characteristics consequently show the same trends. Additionally, calculations of the time-dependent transmission fluctuations along the MD pathways have shown that the transmission in the cis isomers is always significantly larger than that in their trans counterparts, showing that molecular switches can be expected to work as robust molecular switching components.

Keywords: charge transport, Molecular electronics, molecular switches, silicon–molecule interface

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Received: 04 May 2009
Revised: 03 June 2009
Accepted: 03 June 2009
Published: 01 August 2009
Issue date: August 2009

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© Tsinghua University Press and Springer-Verlag 2009

Acknowledgements

Acknowledgements

This work has been partially funded by the Volkswagen Foundation by the Deutsche Forshuhgsgemeinschaft (DFG) under Contracts No. CU 44/5-2, CU 44/8-1, and CU 44/3-3, and by the WCU (World Class University) program through the Korea Science and Engineering Foundation funded by the Ministry of Education, Science and Technology (Project No. R31-2008-000-10100-0). We acknowledge the Center for Information Services and High Performance Computing (ZIH) at the Dresden University of Technology for computational resources. We thank Rafael Gutiérrez, Haldun Sevinçli, Florian Pump and Cormac Toher for fruitful discussions.

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