Crossed-wire junctions

Fig. 8 IETS obtained from an Au-Cl lthiol-Au crossed wire junction. (Reprinted with permission from [77], pp 20-25 )...

The crossed-wire junction method was used to measure charge transport through OPE 95 and OPV 110. The order of conductance was again found to follow the series OPV > OPE > dodecanedithiol [41], despite disruption of conjugation in 110 by the two CH2 units. Oriented SAMs of molecule 112 displayed a slight rectification of the tunnel current when measured in a crossed-wire geometry [42], thus reflecting the asymmetry of the molecule. 

The abihty to measure and to control charge transport across nanometer-scale metal-molecule-metal junctions represents a key step toward the realization of molecular-based electronics [190-192]. Various experimental approaches have been employed to study molecular junctions in two- and three-terminal configurations. These include scanning probe microscopies (STM, STS, CP-AFM) [193-208], crossed-wire junctions [209], mechanical [210-215] and electromigration [216,217] break junctions, nanopores [218] and mercury drop electrodes [219]. Approaches in condensed media, and in par-... 

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... 

FIGURE 3.8. (a) Schematic representation of the crossed-wire tunnel junction (not to scale), (b) Plots of I(V) (current in logarithmic scale) for junctions formed from three molecular compounds. (Reprinted with permission from Ref.50 Kushmetrick etai, J.Am. Chem. Soc. 124,10654—10655 (2002). Copyright 2002 American Chemical Society.)... 

Kushmerick and coworkers [40-42, 70] developed an elegant way to sandwich around 1000 molecules in a molecular junction. An Au wire with a diameter of 10 [tm was modified with a SAM of the molecules of interest. The SAM-covered wire was brought into the vicinity of a second 10 im diameter wire in a crossed-wire geometry (Fig. 10.9). A molecular junction was formed by applying a small d.c. current across the first wire in a magnetic field, which caused the wire to deflect. Upon touching the other wire, the I(V) characteristics of the molecular junction could be measured. 

FIGURE 47.11 Arrows indicate impinging forced-convection flows from oven blowers. The inadvertent thermocouple junction (crossed wires) will record oven local air temperature rather than the intended measurement target the solder-joint area. 

Figure 16.1 The thermoelectric effect is a cross effect between thermodynamic forces and flows, (a) In the Seebeek effect, two dissimilar metal wires are joined and the junctions are maintained at different temperatures. As a result an EMF is generated. The EMF generated is generally of the order of 10 V per Kelvin of temperature difference and it may vary from sample to sample, (b) In the Peltier effect, the two junctions are maintained at the same temperature and a current is passed through the system. The current flow drives a heat flow Jq from one junction to the other. The Peltier heat current is generally of the order of 10 J s per amp. [1]...

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