Nano-switches

A number of research-groups passed electricity through single molecules such as DNA or organic molecules often less than one nanometer long. Measurements of the DNA conductivity were recently obtained by several groups [11,12]. 

First step towards synthesizing reversible molecular switches, and integrating these switches into an electronic circuits, had been done pioneered by Rotaxane-based-technology developed by HP. Any digital microelectronic device is based on memory elements and switches, set up as capacitors, diodes and transistors. Complex elements, such as bi-stable flip-flops, are created from these simple elements combining e.g. two transistor to set up a Schmitt trigger. 

In a recent development novel nano-cluster based devices enabled to switch the conductivity of a non-junction by changing the oxidation state of a bridging molecule. Some redox-active molecules contain a molecular center where reduction or oxidation can be achieved more or less reversibly supporting quite large currents. A fundamental prerequisite is the overlapping of the electron energy bands of the molecule with those of 

A cluster-switch-array might work with fewer than 30 electrons. In e.g. the reduced state, the cluster-switch exhibits high conductivity at a low voltage drop. At a certain threshold voltage the tunneling current decreases markedly. The threshold voltage is chosen to change the redox state of the molecule used as a switch. 

A direct biomolecular trigger would operate too slowly to be applied as an electronic circuit but is a very promising technology to construct novel (bio)analytical devices with ultra-high sensitivity actually at single molecule level. Further on, we could demonstrate that individual gold nanoclusters can be controlled by adding protons to molecules bound at the cluster surface. 

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Conductivity differences were seen in a bistable [3]catenane closed-loop molecule, with a naphthalene group as one station, and tetrathiafulvalene as the second station, decorated by a tetracationic catenane salt that could travel on the catenane, like a train between two stations, making a nano-switch [141]. 

Stoddarts nano-switch design, in which a catenate molecule is able to move between two positions of equcd energy controlled by oxidizing or reducing conations. Such bifunctional switches can serve as parts of nanomachines or nancKomputers. 

Schiffrin and coworkers [948] obtained a nano-switch based on a layer of Au nanoparticles on a viologen moiety anchored to a gold substrate. The I-V characteristics of the Au nanoparticles obtained by in situ scanning tunneling spectroscopy (STS) revealed a dependence on the redox state of the viologen... 

Barnett, R.N., Hakkinen, H., Scherbakov, A.G. and Landman, U. (2004) Hydrogen Welding and Hydrogen Switches in a Monatomic Gold Nanowire. Nano Letters, 4, 1845-1852. 

Surface switching coupled with geometric and potential asymmetry was used to cause directional motion of a droplet. Sophisticated design and active control of surface properties are important technology for motion control on the micro/nano-scales. 

Figure 8.47. SRSAXS raw data (open symbols) and model fit (solid line) for a nano structured material using a finite lattice model. The model components are demonstrated absorption factor Asr, density fluctuation background Ipu smooth phase transition/. The solid monotonous line demonstrates the shape of the Porod law in the raw data. At sq the absorption is switching from fully illuminated sample to partial illumination of the sample...

Quek SY, Kamenetska M, Steigerwald ML, Choi HJ, Louie SG, Hybertsen MS, Neaton JB, Venkataraman L (2009) Mechanically controlled binary conductance switching of a singlemolecule junction. Nat Nano 4(4) 230-234... 

Stewart DR, Ohlberg DAA, Beck PA, Chen Y, Williams RS, Jeppesen JO, Nielsen KA, Stoddart JF (2004) Molecule-independent electrical switching in Pt/organic monolayer/Ti devices. Nano Lett 4 133-136... 

Chen F, He J, Nuckolls C, Roberts T, Klare JE, Lindsay S (2005) A molecular switch based on potential-induced changes of oxidation state. Nano Lett 5 503-506... 

Klinke, C. Chen, J. Afzali, A. Avouris, P. 2005. Charge transfer induced polarity switching in carbon nanotube transistors. Nano Lett. 5 555-558. 

Using nano LC-MS at submicroliter per minute flow rates requires special attention to plumbing, system dead volume, valve switching, large volume sample injection, precolumn methodology, automation, online sample clean-up, and multichannel parallel operation of a single MS. The techniques discussed below are particularly useful for nano LC-MS-MS applications. 

In general, optically, electrically or chemically triggered switches would seem to be preferable to mechanically activated ones, as are photo-, electro- and chemo devices with respect to mechano devices and electronic or photonic computing with respect to mechanical computing. The ultimate in (nano)mechanical manipulation of a molecular device is represented by the realization of a bistable switch based on the motion of a single atom by means of the scanning tunnelling microscope [8.295] (see also Section 9.9). 

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