In-situ control of quantum point contacts using scanning probe microscopy scratch lithography

Quantum point contacts (QPCs) are formed by mechanically scratching Au channels with a scanning probe microscope (SPM) in ambient condition. A variation of electrical properties of the Au channels was caused by a direct modification of the channels using SPM scratching and was in-situ controlled by monitoring the conductance across the scratched region. Such in-situ measurements provide a more accurate method of controlling device properties than by controlling geometric dimensions alone. Scratch experiments were carried out using a diamond-coated tip in ambient air. The conductance of the Au channels was slowly decreased with the increase of process time as the channel was constricted by the scratching. The conductance changed in quantized steps of the conductance quantum, G₀= 2e²/h, at the moment of breaking of the Au channels. Furthermore, the control time to adjust the conductance from 12 G₀ to 0 G₀ was successfully increased from 4 to 32 sec when the scan speed of the SPM tip was decreased from 100 to 20 pm/s. It is suggested that atomic-size contact is successfully formed by SPM scratching. These results imply that SPM scratch nanolithography is promising for the fabrication of nanoscale devices consisting of QPCs.