Alkanedithiol/Au junctions

Gharge Transport in Single Au Alkanedithiol Au Junctions Coordination Geometries and Conformational Degrees of Freedom. Journal of the American Chemical Society, 130, 318-326. 

Au-a,co-alkanedithiol-Au junctions represent one of the simplest molecular junctions which have been studied since 1971 [241]. These alkanedithiol-based junctions were developed as a model system and test bed for various experimental approaches, as well as for theoretical studies for exploring fundamental concepts of charge transport in molecular junctions. 

The discrepancies in the reported conductance data of Au-alkanedithiol-Au junctions attracted our attention, and we decided to carry out an in-depth experimental study of the charge transport properties of Au-a,oo-alkanedithiol-Au molecule junctions in a non-conducting solvent. The combination with quantum chemistry ab initio simulations yielded a detailed view of this archetype of molecular junctions, and helped to resolve the puzzle on the role of microscopic geometries at the contacts and in the molecular conformation. 

Fig. 14 Experimental (a) and calculated (b) conductance values of Au-n-alkanedithiol-Au junctions vs number n of methylene units in a semilogarithmic representation. The three sets of conductance values - high (H), medium (M), and low (L) - are shown as squares, circles, and triangles. The straight lines were obtained from a linear regression analysis with decay constants (3n defined per methylene (CH2) unit. The conductances of many different, nonequivalent gauche isomers cover the window below the medium values in (b) [64]...

Comparison of the experimental data with the trends predicted from quantum chemistry ab initio simulations demonstrated that the multiple conductance values of Au-alkanedithiol-Au junctions could be attributed to different Au-sulfur coordination geometries and to different conformations of the alkyl chain. In particular, the medium conductance corresponds to an all-trans conformation of the alkyl chain, with each sulfur atom coordinated in atop position to a single... 

Charge Transport in Single Au/Alkanedithiol/Au Junctions-An STM Approach... 

Charge transport in Au alkanedithiol Au junctions was measured with a variety of techniques. These include mechanically controlled break junctions (MCBJ [213], STM [205,208,270-275] and conducting AFM break... 

Table 1 Summary of the conductance values of Au-a.oo-alkanedithiols-Au molecular junctions recorded in 1,3,5-trimethylbenzene [64] ...

The invariance of IETS in an M-A-M junction vs an M-I-A-M device is exceptionally well demonstrated by the work of Reed [30], Figure 7 shows the Au-alkanedithiol-Au structure he used to create a single barrier tunnel diode. The IET spectra obtained from this device were stable and repeatable upon successive bias sweeps. The spectrum at 4.2 K is characterized by three pronounced peaks in the 0-200 mV region at 33,133, and 158 mV. From comparison with previously reported IR, Raman, and high-resolution electron energy-loss (HREEL) spectra of... 

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