| We examine electronic transport through two-dimensional arrays of gold nanocrystals. Recently developed techniques of particle synthesis and array self-assembly provide ordered (and disordered) monolayers of six-nanometer diameter gold nanocrystals on substrates with in-plane electrodes. These well-characterized superlattices allow investigation of basic questions about electronic conduction in metal quantum dot assemblies, answers to which have previously remained elusive.; We first address the relation between current and voltage. Central to transport is the Coulomb blockade, the energetic cost of adding a single electron to a nanocrystal. Theoretical studies suggest power-law scaling of current beyond a threshold voltage in Coulomb blockade dominated systems. In ordered arrays, our data follow a power-law form, but with a scaling exponent significantly higher than the theoretical prediction. In disordered arrays, power-law scaling is violated; we explain that disorder disturbs the branching of current-carrying paths responsible for power-law conduction.; Second, we examine the effect of temperature on transport. We find a large low-temperature regime (up to about 100 K) in which thermal energy acts only to linearly suppress the threshold voltage, leaving the current scale unaffected. We provide a simple, analytic model of thermally assisted tunneling which quantitatively describes the data.; Third, we develop a simple and novel technique to tune the interparticle electronic couplings of the arrays—deposition of small amounts of germanium on the monolayers. The germanium dopant lowers the voltage threshold, and also increases conductivity. It also increases the temperature dependence of transport, suggesting the introduction of trapped states between the gold nanocrystal cores. |
