Square-tip junctions

Scientists at Bell Laboratories [46, 73] used shadow angle evaporation to deposit metallic electrodes on different faces of a square quartz tip, with a diameter of 20-30 nm, as illustrated in Fig. 10.11. The square shape of the tip is thought to reduce the risk of shorts produced by the evaporation process. The fabrication method was divided into several steps. First, an A1 gate was evaporated onto one 

Thiol end-capped oligothiophenes 105a-c were used to form the SAMs between the electrodes. A series of distinct periodic steps in the conductance was observed for all samples at low temperature ( 100 K). These features were suggested to originate from vibrational modes in the molecules. A (weakly coupled) gate potential could be applied to the molecular junction, which shifted the step position in the I(V) curves but not the step widths. This observation was taken as an indication that only a single molecule was electrically active in the molecular junction. 

---