Formation scheme of quantum point contacts based on nanogaps using field-emission-induced electromigration

We propose a new fabrication scheme of quantum point contacts (QPCs) composed of nanogaps at room temperature. This scheme is based on electromigration induced by a field emission current, which is so-called "activation." By applying the activation to ferromagnetic Ni nanogaps with sub-10 nm separation, QPCs can be easily obtained at room temperature. The conductance changed in quantized steps of 0.5G0 (G0 = 2e2/h) at the final stage of activation with a preset current Is of 0.5 mA. Then, the conductance during the activation was varied from 2G0 to 9.5G0 by increasing the preset current Is from 0.5 mA to 1.5 mA. Furthermore, after performing the activation with the preset current Is of 1.5 mA, the QPC device formed by the activation exhibited magnetoresistance (MR) ratio of approximately 1.5%. These results indicate that few-atom Ni contacts are achieved using Ni nanogaps controlled by the activation with precisely tuned preset current.