Making electrical nanocontacts to nanocrystal assemblies: Mapping of room-temperature Coulomb-Blockade thresholds in arrays of 28-kDa gold nanocrystals

The local mapping of the electronic properties of arrays of 28-kDa gold nanocrystals via combined conducting-probe atomic force microscopy (CP-AFM) and displacement-voltage (z-V) spectroscopy, was illustrated. A key advantage of z-V spectroscopy over conventional current-voltage spectroscopy for the measurement of threshold voltages is that the feedback loop remains active during the bias-voltage sweep. A small increase in the current can result in a large relative displacement which allows accurate determination of Coulomb-blockade threshold voltages. The results show that use of CP-AFM allows complementary topography and phase data to be acquired before and after spectroscopy measurements which enables the comparison of local array morphology.