Molecular nanopore junctions

FIGURE 3.6. (a) Cross-sectional schematics of a silicon wafer with a nanopore etched through a suspended silicon nitride membrance. SAM is formed between sandwiched Au eletrodes in the pore area (circled), (b) I(V) characteristics of a Au-2 -amino-4-ethynylphenyl-4-ethynylphenyl-5 -nitro-1 -benzenethiolate-Au (chemical structure shown below) molecular junction device at 60 K. The peak current density is 50 A/cm2, the NDR is 2400 pQ. cm2, the peak-to-valley ratio is 1030 1. [Adapted from Ref.30 Chen el al., Science 286, 1550-1552 (1999).]... 

A method to form metal-SAM-metal nanowires with a diameter < 40 nm was developed by Mallouk and coworkers [51, 76]. The nanowires were produced by electrodeposition of Au or Pd into the nanopores of a polycarbonate membrane. A SAM was formed at the end of the wire and a second metal contact (Au, Ag or Pd) was deposited on top of this. The polycarbonate was subsequently dissolved in dichloromethane, which released a large quantity (1011 cm-2) of nanowires that could be aligned individually between pairs of lithographically fabricated metal electrodes. A schematic illustration of the nanowire molecular junctions is shown in Fig. 10.14. 

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-... 

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