Regensburg 2016 – scientific programme

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DS: Fachverband Dünne Schichten

DS 9: Organic Thin Films II

DS 9.6: Talk

Monday, March 7, 2016, 16:15–16:30, H11

Tip-induced gating of carbene-based molecular circuits — Giuseppe Foti and •Hector Vazquez — Inst. of Physics, Academy of Sciences of the Czech Rep., CZ

In this talk I will discuss N-heterocyclic carbene-based (NHC) molecules on gold [1] and explore their adsorption, mechanical and transmission properties by means of first-principles simulations based on DFT and NEGF.

First, I will examine the adsorption properties of NHCs on Au(111). NHCs bind selectively to the Au atop sites through a strong Au-C bond. I will then address the mechanical properties of NHCs through simulations where the metal-molecule junction is stretched. Upon elongation, the strong Au-C bond induces rearrangements of the Au surface and ultimately a Au-Au bond, and not the Au-C bond, breaks. Finally, I will discuss the conducting properties of NHC-based molecular junctions. We consider several tip structures and find a strong dependence of the position of the NHC molecular levels with the atomistic structure of the tip [2]. The LUMO position changes by almost 0.8 eV with tip shape. This is understood in terms of the net charge transfer, electron redistribution and work function for each tip structure. The differences in the LUMO position effectively gate the molecular levels and result in large conductance variations. These findings open the way to modulating the conductance of NHC-based molecular circuits through the controlled design of the tip atomistic structure.

[1] C.M. Crudden et al., Nature Chemistry 6 409 (2014).

[2] G. Foti and H. Vazquez (under review).