Junction symmetry effects in resonant tunneling through InAs nanocrystal quantum dots

Tunneling spectra of InAs nanocrystals anchored to gold via linker molecules or deposited onto graphite were measured using scanning tunneling microscopy, in a double-barrier tunnel-junction configuration. The effects of the junction symmetry on the tunneling spectra, due to both the voltage division and the tunneling rates, are studied experimentally and modeled theoretically. We observe resonant tunneling through nanocrystal states without charging when the tip is retracted from nanocrystals deposited on graphite. Charging is regained upon reducing the tip-nanocrystal distance, making the junctions more symmetric. In contrast, charging-free resonant tunneling was not achieved for the nanocrystal/linker-molecule/Au system.