  Transport properties of artificial solids composed of colloidal CdSe
nanocrystals (NCs) are studied from 6 K to 250 K, before and after annealing.
Annealing results in greatly enhanced dark and photocurrent in NC solids, while
transmission electron microscopy (TEM) micrographs show that the inter-dot
separation decreases. The increased current can be attributed to the
enhancement of inter-dot tunneling caused by the decreased separation between
NCs and by chemical changes in their organic cap. In addition, the absorption
spectra of annealed solids are slightly red-shifted and broadened. These
red-shifts may result from the change of the dielectric environment around the
NCs. Our measurements also indicate that Coulomb interactions between charges
on neighboring NCs play an important role in the tunneling current.
