Assessment of a nanoparticle bridge platform for molecular electronics measurements

Abstract

A combination of electron beam lithography, photolithography and focused ionbeam milling was used to create a nanogap platform, which was bridged by goldnanoparticles in order to make electrical measurements and assess the platformunder ambient conditions. Non-functionalized electrodes were tested to determinethe intrinsic response of the platform and it was found that creating devices inambient conditions requires careful cleaning and awareness of the contributionscontaminants may make to measurements. The platform was then used to makemeasurements on octanethiol (OT) and biphenyldithiol (BPDT) molecules byfunctionalizing the nanoelectrodes with the molecules prior to bridging the nanogap withnanoparticles. Measurements on OT show that it is possible to make measurements onrelatively small numbers of molecules, but that a large variation in response canbe expected when one of the metal–molecule junctions is physisorbed, whichwas partially explained by attachment of OT molecules to different sites on thesurface of the Au electrode using a density functional theory calculation. Onthe other hand, when dealing with BPDT, high yields for device creation arevery difficult to achieve under ambient conditions. Significant hysteresis in theI–V curves of BPDT was also observed, which was attributed primarily to voltage inducedchanges at the interface between the molecule and the metal.