Gap separation-controlled nanogap electrodes by molecular ruler electroless gold plating
A simultaneous fabrication process of multiple nanogap electrodes at desired gap separations by the technique of molecular ruler electroless gold plating (MoREP) is reported. Initial gold nanogap electrodes with a gap separation of 22 nm were immersed into MoREP solutions consisting of chloroauric acid, surfactant molecules of alkyltrimethylammonium bromide (CnTAB, n = 12–18) and ascorbic acid as a reducing agent. The electroless plating locally self-terminates between the gap when the surfactant molecules physisorbed to the surface of one electrode interdigitate with the ones of the opposite electrode. The mean nanogap separation correlated with the alkyl chain length, and can be controlled between 2.5 ± 0.6 and 3.3 ± 0.8 nm by choosing the alkyl chain length of the surfactant molecules (C12–C18). A double-gate single-electron transistor (SET) was chemically assembled by introducing chemically a synthesized gold nanoparticle into the MoREP nanogap electrodes, and showed stable Coulomb diamonds under application of both gate voltages.