Switching of Conductance in a Molecular Wire: Role of Junction Geometry, Interfacial Distance, and Conformational Change
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- 作者：Kamal B. Dhungana ; Subhasish Mandal ; Ranjit Pati
- 刊名：The Journal of Physical Chemistry C
- 出版年：2012
- 出版时间：August 16, 2012
- 年：2012
- 卷：116
- 期：32
- 页码：17268-17273
- 全文大小：403K
- 年卷期：v.116,no.32(August 16, 2012)
- ISSN：1932-7455
文摘
Achieving atomic level control at the metal鈥搈olecule interface in a single molecule conductance measurement is a daunting challenge. An equally important issue is the lack of atomic level structural information of the interface, which makes the theoretical interpretation of observed conductance much harder; conductance sensitively depends upon the junction geometry. In this article, we report a junction dependent conductance study in a ruthenium鈥揵is(terpyridine) molecular device, which has been fabricated and characterized ( J. Am. Chem. Soc. 2008, 130, 2553) using a scanning tunneling microscope. An ensemble of device structures is created by varying metal鈥搈olecule binding sites, the orientation of the molecule at the interface, interfacial distances, and conformational change within the molecule to study junction dependent effects. An orbital dependent density functional theory in conjunction with a parameter free, single particle Green鈥檚 function approach is used to study the current鈥搗oltage (I鈥?i>V) characteristics. For the ONTOP junction geometry, our results show a sharp increase in current at a threshold voltage (Vth). The current is found to be relatively small (OFF state) for bias range below the threshold value. As we approach the weakly coupled regime, a drop in Vth is found; following a sharp increase in current at Vth, a current plateau (ON state) is observed with the increase of bias beyond Vth. A similar nonlinear I鈥?i>V curve with a current switching feature is reported by the experiment. An analysis of bias dependent transmission and orbital characters of participating eigen-channels is presented to understand the origin of distinct I鈥?i>V features observed in strongly and weakly coupled junctions.