Molecular break-junctions: interaction with light and conductance switching

In this work, we analyzed electronic transport across metal-molecule-metal bridges using gold mechanically-controlled break-junctions. In particular, we studied the influence of illumination on these contacts as well as stochastic conductance fluctuations which can be detected on molecular junctions. When visible light is applied to tunnel junctions, i.e. bare break-junctions, the conductance increases. This can be explained by thermal expansion of the electrodes of the break-junction. Molecular contacts also exhibit an increase of the conductance where the mechanism is not yet clear. Without illumination, we measured the conductance of molecular junctions for extended periods of time, this can be performed for several days. We observed stochastic fluctuations of the conductance where one specific value of fluctuation is preferred. This preferred value is independent of the conductance value of the junction. Such fluctuations were observed on several samples comprising different molecules and might be identified with single molecules breaking and re-establishing chemical contact.