Noise characterization of metal-single molecule contacts

Abstract

Noise spectra of molecule-free and molecule-containing mechanically controllable break junctions were investigated. The molecule-free junctions revealed typical $1/f$ noise characteristics. We studied three molecules as they bridged the electrodes: 11-mercaptoundecanoicacid, 1,8-octanedithiol, and 1,4-benzenedithiol, which possess different bonding strengths. For all of them, an additional Lorentzian-shape 1/f² noise component was registered with a characteristic frequency when the electrodes were bridged by an individual molecule. Measurements of time-dependent voltage fluctuations for the molecule-containing junctions bring out two-current state fluctuations, which in the frequency domain correspond to the 1/f² noise. Moreover, it is revealed that characteristic frequencies of these noise components are independent of molecule bonding strengths at the interface, but correlate with the molecule weights and current amplitudes in the lock-in state, in which the electrode gap is bridged by a single molecule. We attribute the noise monitored during charge transport through a molecular junction to the current induced molecular reconfigurations and suggest that the noise analysis can be used for characterization of metal-molecule coupling.