Charge Transport in Strongly Coupled Molecular Junctions: 鈥淚n-Phase鈥?and 鈥淥ut-of-Phase鈥?Contribution to Electron Tunneling

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• 作者：Partha Pratim Pal ; Ranjit Pati
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：September 8, 2011
• 年：2011
• 卷：115
• 期：35
• 页码：17564-17573
• 全文大小：1036K
• 年卷期：v.115,no.35(September 8, 2011)
• ISSN：1932-7455

文摘

We report a first-principles study on the evolution of nonequilibrium charge transport in a two-terminal molecular-scale device with the increase in the length of the molecular wire built out of cubane oligomers. In particular, for wires of three different lengths, we look into the relative contribution of the 鈥渋n-phase鈥?and the 鈥渙ut-of-phase鈥?components of the total electronic current under the influence of an external bias. In the low-bias regime, the 鈥渙ut-of-phase鈥?contribution to the total current is minimal and the 鈥渋n-phase鈥?elastic tunneling of the electrons is responsible for the net electronic current. This is true, irrespective of the length of the molecular spacer. In this regime, the current鈥搗oltage characteristics follow Ohm鈥檚 law and the conductance of the wires is found to decrease exponentially with the increase in length, which is in agreement with experimental results. However, after a certain 鈥渙ffset鈥?voltage, the current increases nonlinearly with bias and the 鈥渙ut-of-phase鈥?tunneling of electrons reduces the current substantially. This behavior is attributed to the reduction in constructive interference due to phase randomization at the resonant tunneling regime, and thus, the height of the transmission peak is reduced. We subsequently studied the interaction of conduction electrons with the vibrational modes as a function of external bias in the three different oligomers since they are one of the main sources of phase-breaking scattering. The number of vibrational modes that couple strongly with the electronic levels is found to increase with the length of the spacer, which is consistent with the existence of the lowest 鈥渙ffset鈥?voltage for the longest wire under study.