Bias-induced local heating effects on multi-walled carbon nanotube-Au contacts

Exploiting a mechanically controllable break junction (MCBJ) technique, we prepared multi-walled carbon nanotubes (MWNTs) bridging over Au electrodes and investigated their conductance-bias voltage (G-V) characteristics in a high-bias regime. Above a threshold bias voltage, we observed a rapid and irreversible increase in conductance, which appears only with increasing bias. This phenomenon can be attributed to irreversible contact annealing due to contact heating. Observation of two-level fluctuations in the MWNT conductance at high biases also implies defect annealing inside Au electrodes. The conductance increment is occasionally observed at one bias polarity but not at a reverse polarity. The asymmetry in the heating effect with respect to the bias polarity suggests that the electron transport in MWNTs is ballistic, and the energy dissipation takes place only at the anode contact.