Self-assembly of gold nanoclusters on micro- and nanoelectronic substrates

Layer-by-layer self-assembly of hexanethiol stabilized gold nanoclusters by a series of alkanedithiol coupling agents [HS(CH2)(n)SH, n = 6, 8, 9, 12] onto SiO2/Si substrates with micron- and nanometre-scale Au electrodes is investigated by electron transport and XPS measurements. The self-assembly process for each layer consists of a two-step cycle of alkanedithiol treatment and gold cluster deposition. For maximized electron transport, critical features to optimize are the alkanedithiol chain length and the extent of dithiol coupling agent displacement of the hexanethiol ligand. Substitution of a phenethyl for the hexyl structure in the cluster ligand shell significantly enhances conductivity while substitution of a phenylene structure in the dithiol coupling agent has little effect on electron transport. Current-voltage characteristics for self-assembled depositions on the micron- scale electrode are found to be ohmic whereas I-V characteristics for analogous self-assemblies on the nanometre-scale electrode are initially nonlinear but become increasingly ohmic after about 3 cycles of deposition. The nonlinear features observed at the nanoscale are believed to be associated with Coulomb blockade.