Tunneling junctions transport

Nijhuis CA, Reus WF, Barber JR, Dickey MD, Whitesides GM (2010) Charge transport and rectification in arrays of SAM-based tunneling junctions. Nano Lett 10 3611-3619... 

The details of the transport process occurring in atomically resolved STM are significantly different from the tunneling process associated with classical metal-insulator-metal (M-I-M) tunnel junctions. In the latter case the thickness of the insulator between the conducting electrodes is typically 20-30 A, whereas the ability to resolve the electronic density of individual atoms using STM requires a lateral resolution of 2 A. To obtain such... 

In addition to the physical interactions described above, the tip may also be used to alter the local chemical conditions within the tunnel junction. For example, catalytic rehydrogenation of carbonaceous fragments on Pt(lll) by tip-directed production of atomized hydrogen in vacuum at the Pt-Ir tip has been described [524]. Similar modification schemes may also be envisioned based on limiting the transport of reactants and products into or away from the partly occluded tunnel junction. As noted earlier, such effects may be important in the study of electrodeposition and etching process [126-131]. Nonetheless, much remains to be understood about the detailed physics and chemistry of the immersed tunnel junction. 

In principle a STM should be adequate to measure the electrical resistance of a single molecule since it suffices to measure I-V curves of the metal (tip)-molecule-metal (substrate) system. However, published results in the literature concerning this subject have to be considered cautiously because of the generally unknown nature of the molecule-metal contacts. An illustrative experiment demonstrates the relevance of the interface (Kushmerick et al, 2002). This experimental work studies charge transport using the cross-wire tunnel junction technique, where two... 

The rest of this Chapter is organized as follows. In Sec. 1, we discuss the NEGF-DFT formalism in detail. In Sec. 2, the transport properties of an Au-Cgo-Au tunnel junction is investigated. Section 3 is reserved for a short summary, and some technical details are given in Appendix. 

As an example of the NEGF-DFT formalism discussed in the last section, we now report an analysis on the transport properties of an Au-Ceo-Au molecular tunnel junction whose device structure is shown in the lower panel of Fig. 1. So far a considerable amount of effort has been devoted to investigate transport properties of Ceo and other fullerene molecules both experimentally [54-59] and theoretically [25,60-62]. However, to obtain a complete picture of the transport properties of such junctions, many details have yet to be clarified, including how conductance and I-V curves depend on the lead material and geometry, and on the position and orientation of the Cgo molecule. Ceo tunnel junctions with Au leads have not been studied before. 

As an example, some details of transport features of Au-Cgo-Au molecular tunnel junctions were discussed. The physical mechanism of resonance transmission through the molecule was responsible for most of the transport properties. The resonance is mediated by the LUMO-derived states, and charge transfer plays a very important role. The I-V curves show metallic... 

Seideman, T. and Guo, H. (2003) Quantum transport and current-triggered dynamics in molecular tunnel junctions. J. Theor. Comput. Chem., 2, 439-458. 

Kuznetsov and Ulstrup initialized recently a discussion on the importance of conformational dynamics and electrical double layer effects on charge transport characteristics in single metal/redox-molecule/metal tunneling junctions [237,253]. Tao et al. explored the stabihty and break down of Au-thiol contacts, and addressed quantitatively local ionic and electron heating in single junctions composed of redox-inactive molecules [254]. 

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