Coulomb blockade systems fabricated by atomic force microscopy

We demonstrate a method for controlled fabrication of single electron devices using atomic force microscopy (AFM). The technique employs both AFM-operated nanocarving (i.e. scraping or plowing prepatterned metallic structures) as well as AFM-assisted nanomanipulation (i.e. controlled positioning of nanoparticles). Tunneling barriers are formed by dynamic plowing of ∼20 nm wide trenches through thin Au wires realized by optical and electron beam lithography. During this AFM machining, in situ resistance-measurements are performed until electrical isolation is obtained. Single electron systems including one or more isolated islands are subsequently fabricated by shifting single nanoparticles (PbS or Au with respective diameters of 20 nm and 10 nm) into the tunneling barrier. The particle position is controlled in situ by both AFM imaging and conductivity measurements. The electrical properties of such Coulomb blockade systems are investigated for both the Au and PbS particles by transport measurements at liquid He (4.2 K) temperature. The measured I-V curves give evidence for the presence of Coulomb blockade effects with a step-like behavior that becomes more pronounced with decreasing temperature.