Electron transport through single phenylene-ethynylene molecular junctions at low temperature

We present low-temperature electron transport measurements of individual phenylene-ethynylene molecular wires, connected to nanometer-spaced gold electrodes. Low-bias current-voltage (I-V) characteristics measured at 4.2 K are stable and show irregular steps. After application of a large voltage, the low-bias I-V curves switch between different stable configurations, some of which show negative differential resistance (NDR). Similar behavior, including the NDR, has been observed in molecules irrespective of whether they contain a NO2 side group or not. We suggest that different I-V curves measured, including the NDR, could be due either to conformational changes in the molecules or a change in coupling of the molecular junction. (C) 2004 American Institute of Physics.