Au/SiO₂nanocomposite film substrates with a high number density of Au nanoparticles for molecular conductance measurement

Abstract

Au/SiO2 nanocomposite films consisting of an extremely high number density of Au nanoparticles dispersed in a SiO2 matrix a few nanometres thick were deposited by a co-sputtering method, and employed for molecular conductance measurement by immobilizing and bridging conjugated biphenyl molecules on dispersed Au nanoparticles. The number density of Au nanoparticles in the insulating SiO2 matrix was approximately 14 000 µm−2, and the average interparticle distance from their neighbours was about 8 nm. The current increased considerably up to the range of nanoamperes after the immobilization of the conjugated biphenyl molecules, 105 times larger than without molecules before immobilization. Although the Au nanoparticles can be connected to only 30% of all combinations of neighbouring Au nanoparticles by biphenyl molecules 2.4 nm long from the topological analysis, the biphenyl molecules can bridge most of the Au nanoparticles, and their bridging continuity is over 100 nm in length. Thus the measured current is suggested to come from the continuously bridged molecules between the Au nanoparticles. Furthermore the I–V data of the whole Au/SiO2 nanocomposite film immobilized with conjugated molecules are confirmed to be in a reasonable range in comparison with the scanning tunnelling spectroscopy data of similar conjugated molecules.