Non-linear current-voltages character of Au quantum point contact

In this study, we simultaneously observed the configuration and the non-linear current-voltages character (I-V) of gold quantum point contacts (Au-QPC). UHV Transmission Electron Microscope (UHV-TEM) which combined with Scanning Tunneling Microscope (STM) enabled us to observe the configuration of QPC. TEM images were synchronized with the measured I-V. The bias voltage to Au-QPC swept from 0V to 0.3V at room temperature in UHV($\sim $1$\times $10$^{?|7}$[Pa]). The Au-QPC with short length($<\sim $1nm) showed the non-linear I-V which were fitted to a cubic function ( I=aV+cV$^{3 })$. The value of c/a in our results ($\sim $20[1/V$^{2}$]) was lager than that of previous reports (0.3$\sim $2[1/V$^{2}$]). Simultaneous TEM images revealed a changed of the width of Au-QPC. The width was found to increase from 1.1nm (0.02V) to 1.9 nm (0.27V). On the other hand, the Au-QPC with long length (nanowire $>\sim $1nm) showed the linear I-V, and the width was kept constant. We suggested that the changing of the width caused the non-linear I-V. The mechanism of increasing the width should be solved by further investigation.