Imaging and tunneling spectroscopy of gold nanocrystals and nanocrystal arrays

Scanning tunneling microscopy (STM) and spectroscopy (STS) have been used t o determine the structural and electronic properties of thiol-passivated 29 000 amu gold nanocrystals, both individually and in spontaneously formed qu asi-two-dimensional arrays. Experiments were performed at temperatures of 3 00 K, 77 K, and 8 K. Even at room temperature, tunneling through these 1.7 nm nanocrystals is shown to give rise to a Coulomb blockade. At cryogenic t emperatures, the spectroscopy of the nanocrystals in arrays and in isolatio n shows an incremental charging effect (the Coulomb staircase) and evidence is found for quantization of the electronic states.