Mapping the details of contact effect of modulated Au-octanedithiol-Au break junction by force-conductance cross-correlation.

We have measured the force and conductance of Au-octanedithiol-Au junctions using a modified conducting atomic force microscopy break junction technique with sawtooth modulations. Force-conductance two-dimensional cross-correlation histogram (FC-2DCCH) analysis for the single-molecule plateaus is demonstrated. Interestingly, four strong correlated regions appear in FC-2DCCHs consistently when modulations with different amplitudes are applied, in sharp contrast to the results under no modulation. These regions reflect the conductance and force changes during the transition of two molecule/electrode contact configurations. As the modulation amplitude increases, intermediate transition states of the contact configurations are discerned and further confirmed by comparing individual traces. This study unravels the relation between force and conductance hidden in the data of a modulated single-molecule break junction system and provides a fresh understanding of electron transport properties at molecule/electrode interfaces.