Colloidal Au/Linker Molecule Multilayer Films:  Low-Temperature Thermal Coalescence and Resistance Changes

A decrease in the resistance of colloidal Au multilayer films, fabricated by the layer-by-layer assembly process on flexible polymer substrates, was observed upon heating. This decrease occurs because of the oxidation and desorption of the linker molecules from the film, leading to a coalescence of the Au particles, thus forming more conducting pathways. Three linker molecules: 2-mercaptoethanol (ME), 1,6-hexanedithiol (HD), and 1,10-decanedithiol (DD), having different lengths, were chosen for the fabrication of the films. The initial resistance of the films was considerably different for the three linker molecules, 50 Ω, 1 MΩ, and >100 MΩ, respectively. The films were heated at three different temperatures: 120, 160, and 180 °C. The resistance of the films was found to be a strong function of the time and temperature of heating. After heating for sufficiently long times or at higher temperatures, the resistance of the ME film decreased to 5 Ω and to about 50 Ω for the HD and DD films. The lowest resistivity obtained, 6 × 10 -5 Ω·cm, was about 25 times that of bulk gold. The films were characterized by UV−vis spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy.