Impact of Anchoring Groups on Ballistic Transport: Single Molecule vs Monolayer Junctions

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• 作者：Veronika Obersteiner ; David A. Egger ; Egbert Zojer
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：September 10, 2015
• 年：2015
• 卷：119
• 期：36
• 页码：21198-21208
• 全文大小：716K
• ISSN：1932-7455

文摘

Tuning the transport properties of molecular junctions by chemically modifying the molecular structure is one of the key challenges for advancing the field of molecular electronics. In the present contribution, we investigate current鈥搗oltage characteristics of differently linked metal鈥搈olecule鈥搈etal systems that comprise either a single molecule or a molecular assembly. This is achieved by employing density functional theory in conjunction with a Green鈥檚 function approach. We show that the conductance of a molecular system with a specific anchoring group is fundamentally different depending on whether a single molecule or a continuous monolayer forms the junction. This is a consequence of collective electrostatic effects that arise from dipolar elements contained in the monolayer and from interfacial charge rearrangements. As a consequence of these collective effects, the 鈥渋deal鈥?choice for an anchoring group is clearly different for monolayer and single molecule devices. A particularly striking effect is observed for pyridine-docked systems. These are subject to Fermi-level pinning at high molecular packing densities, causing an abrupt increase of the junction current already at small voltages.