Fabrication of sub-10 nm planar nanotips for transport experiments of biomolecules

Electron beam lithography (EBL) and lift-off process have been used to fabricate two- and three-terminal nano-devices consisting of metallic (Cr/Au, Ti/Au or Ti/Pt) arrow-shaped electrodes on Si/SiO2, with tip separation between 100 and less than 10 nm. Standard EBL process allowed us to obtain nanotips with separation around 40 nm. In order to reduce the tip separation down to about 20 nm, before the EBL process, we used the defocused e-beam to brush the PMMA resist for a precise time (10÷40 s). A further reduction of the tip gap (less than 10 nm) is obtained by Au electroplating deposition. The nanotips were electrically characterized by current-voltage (I-V) measurements in the range ± 2 V. In a typical I-V measurement in air of an "open-circuit" nanodevice, no significant current is observed (current range -10÷ +10 pA, "open circuit" resistance ≈ 1 TΩ) confirming the success of the technological process.