Shape Control in Electrodeposited, Epitaxial CdSe Nanocrystals on (111) Gold

Semiconductor nanocrystals can be epitaxially electrodeposited onto single-crystal substrates. The lateral size of the nanocrystals was previously shown to be controlled mainly by the lattice mismatch between the substrate and semiconductor. Here we show that, although the lateral dimensions of the nanocrystals are only slightly dependent on the current density and temperature of deposition, the vertical dimension is strongly dependent on these parameters. This allows control of the shape and aspect ratio of the nanocrystals, from spherical at high deposition current to taller crystals with a shape between columnar and square pyramidal with rounded tops at low currents. The shape of the taller crystals is explained by considering the reduced role of kinetic factors at low current density. Cross-sectional TEM is used to image the nanoparticle shape, while photoelectrochemical spectral measurements allow approximate band gap values to be estimated for the various nanocrystals.