Resonant electron tunneling through semiconducting nanocrystals in a symmetrical and an asymmetrical junction

We studied resonant electron tunneling through individual CdSe and CdS nanocrystals in two types of configuration. With nanocrystals electrodeposited on bare gold, the spectra show resonant tunneling via discrete unoccupied (CB region) and occupied levels (VB region) at positive and negative bias, respectively. In this asymmetrical configuration, the bias is only distributed across the tip/dot barrier; this allows one, in principle, to derive the electronic structure of nanocrystals from tunneling spectra. With colloidal nanocrystals covalently anchored to a gold substrate via hexane dithiol, tip-to-gold and gold,to-tip tunneling occurs via the same set of unoccupied levels.