Cross beam lithography (FIB+EBL) and dip pen nanolithography for nanoparticle conductivity measurements

Focused ion beam lithography is a very powerful technique for directly writing patterns on many substrates, it is a maskless and resistless technique that allows a very wide range of applications, providing a resolution down to 10 nm. Using a system composed by a 30 keV gallium ion beam column plus a 30 keV electron beam, nanogaps for electrical measurements of nanoparticle were fabricated with a resolution down to the nanometer scale, by exploiting FIB milling (FIBM) and electron beam lithography (EBL). Starting from prepatterned samples a square pattern reduces the width of the gold wire and a narrow line pattern opens a gap of less than 7 nm. Electrical measurements and AFM tapping mode imaging were performed on the gaps. We patterned the ends of the gold leads with dip pen nanolithography using mercapto-undecanol (MUD) to form a bond between the nanoparticle and the alcohol group attached to the gold surface. After this assembly, devices showed an increase in conductivity (10-100-fold increase). Measuring the device again one week later, we saw almost no change in conductivity, showing that we deposit a multiparticle cluster and measure its conductivity.