Molecular break junctions

Fig. 1 Sketches of break junction-type test beds for molecular transport. On the far left is a tunneling electron microscopy (TEM) image of the actual metallic structure in (mechanical) break junctions from the nanoelectronics group at University of Basel. The sketches in the middle (Reprinted by permission from Macmillan Publishers Ltd Nature Nanotechnology 4, 230-234 (2009), copyright 2009) and right (reproduced from Molecular Devices, A.M. Moore, D.L. Allara, and P.S. Weiss, in NNIN Nanotechnology Open Textbook (2007) with permission from the authors) show possible geometries for molecules between two gold electrodes, and (on the upper right) a molecule that has only one end attached across the junction...

Chen IWP, Fu M-D, Tseng W-H, Chen C-h, Chou C-M, Luh T-Y (2007) The effect of molecular conformation on single molecule conductance measurements of 7i-conjugated oligoaryls by STM break junction. Chem Commun 29 3074—3076... 

Keywords Break junction Charge transport Electrolyte gate Metal nanocluster Molecular junction Scanning tunneling microscopy Scanning tunneling spectroscopy... 

In the following we will focus on three molecular electronics test beds as developed and employed for applications at electrified solid/liquid interfaces (1) STM and STS, (2) assemblies based on horizontal nanogap electrodes, and (3) mechanically-controlled break junction experiments. For a more detailed description of the methods we refer to several excellent reviews published recently [16-22]. We will also address specific aspects of electrolyte gating and of data analysis. 

Figure 20. A representation of the technique used in the mechanically controllable break junction for recording the current through a single molecule, (a) The gold wire was coated with a SAM of the molecular wires (b) and then broken, under solution (c), via extension of the piezo element under the silicon surface (see Figure 19). Evaporation of the volatile components and slow movement of the piezo downward (see Figure 19) permits one molecule to bridge the gap (d) that is shown, in expanded view, in the insert. The insert shows a benzene-1,4-dithiolate molecule between proximal gold electrodes. The thiolate is normally FI-terminated after deposition end groups denoted as X can be either FI or Au, the Au potentially arising from a previous contact/retraction event.

Controllable Break Junctions at Room Temperature , in Molecular Electronics, Jortner J., Ratner, M., Eds., Black-well Science Oxford, 1997, pp. 191-213. 

Fig. 17.11 The current (right axis) and conductance (left axis) of a molecular junction plotted against the applied voltage. Each plot shows several sweeps of the potential. The different plots correspond to different junctions prepared by the mechanically controlled break junction technique using gold contacts with the molecule shown, (from H. B. Weber, J. Reichert, F. Weigend, R. Ochs, D. Beckmann, M. Mayor, R. Ahlrichs, and H.v. Lohneysen, Chem. Phys. 281, 113 (2002).)...

One of the most promising applications of fullerene molecules is nanoelectronics. Recently, several groups have reported the results of ab initio calculations of current-volt characteristics of the fullerene molecule [94,95]. These investigations were stimulated by scanning tunneling microscopy (STM) experiments in which the C o molecules were adsorbed on metallic surfaces [96, 97] as well as the break-junction experiments [98] and the demonstration of a prototype of a molecular transistor on the basis of carbon nanotube [99]. 

Infrared absorption spectroscopy Isophthalic acid Low energy electron diffraction Lowest imoccupied molecular orbital Mechanically controlled break-junction Mercury-sulfate electrode Potential of zero charge q = 0 Quasireference electrode Real hydrogen electrode Reference electrode Alkanedithiols HS(CH2)nSH Self-assembled monolayer(s)... 

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-... 

The work by Kruger et al. was initiated by an investigation into the influence of mechanical force on the thiolate - gold interaction which was relevant to mechanical break junctions. In this review we focus on the aspects of this work which relate to mechanochemistry, and not to the mechanical strength of gold nanowires. Their research applied first principles molecular dynamics simulations to investigate the abstraction of an ethylthiolate molecule from an Au(211) substrate, thus investigating the response of the substrate - molecule interaction to an external force applied to the surface normal (Fig. 7). 

Electrochemical STM Break-Junction for Surface Nanostructuring and Nanoelectronics and Molecular Electronics... 

One successful application of STM beyond imaging has been the STM break junction (STM-BJ) technique [56] and modification thereof [13, 57, 58], which are becoming very popular experimental platforms for nanoelectronics and molecular electronics [59-61]. In this technique. Figure 9.5a, a tip (usually Au) is brought into mechanical contact to a defined depth (crash-to-contact) with a single-crystalline surface of the same material. The tip is then withdrawn at a suitable rate such that a metal nanoconstruction is formed, elongated, and eventually broken (break-of-contact). During tip withdrawal, the conductance is recorded as a function of piezo displacement. The procedure can be repeated many thousands of... 

Zhou, X.S., Liang, J.H., Chen, Z.B. and Mao, B.W. (2011) An electrochemical jump-to-contact STM-break junction approach to construct single molecular junctions with different metallic electrodes. Electrochemistry Communications, 13, 407-410. 

Modification of head group (R) allows control of monolaya- surface properties and monolayer thickness, (b) gold break junction spanning molecule acting as a molecular diode. 

Using a parameterized electronic-structure method, Hasmy et studied theoretically the formation of such linear chains in break-junction experiments through molecular-dynamics simulations. They compared the three coinage elements, Cu, Ag, and Au, and found that in particular for Au longer linear chains could be formed before the breaking of the junction, whereas only shorter chains were found for the other elements. They ascribed this effect to sd orbital hybridization. 

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