Hysteretic contact potential changes in nanometallic tunnel junctions in air

We have used a hybrid scanning tunneling -- atomic force microscope to measure current and forces generated between nanotunnel junction (NTJ) electrodes. Cyclic bias voltage scans performed in air reveal hysteretic increases in force above a {~}1 V threshold. Current measurements exhibit simultaneous increases in magnitude and noise. Our results are consistent with hysteretic changes in contact potentials and indicate that, in addition to tunneling and electrochemistry, molecules can mediate widespread occurrences of ion trapping and sudden detrapping in NTJ's.