Electrical characterization and Auger depth profiling of nanogap electrodes fabricated by I2-assisted focused ion beam

Iodine (I2)-assisted, 30keV Ga+ focused ion beam (FIB) has been employed to fabricate nanogap Au electrodes and has been compared to conventional FIB milling. Electrical characterization shows that I2 assistance improves insulation resistance from 300–400GΩto20–50TΩ. Auger depth profiling reveals that the Ga concentration profile in FIB-milled samples has a peak value of 25at.% at 7nm and extends, with a decreasing Gaussian tail, down to 40nm, whereas in I2-processed samples Ga concentration is reduced below 5at.%. I2 assistance is found to increase minimum gap size from 8to16nm and to markedly roughen Au surface morphology.