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 4.2K 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.