Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

elieve that by observing identical experimental histories for each sample, weare able to extract useful information from conductivity data at various temperatures[33].Figure 18 shows an Arrhenius plot of ln(r) versus 1/T for a sample of2.7-nm-diameter CdSe nanocrystals and a sample of 4.5-nm-diameter CdSenanocrystals. Although the temperature range is limited, a linear region of thedark conductivity, r(T), is evident in the Arrhenius plot at high temperatures(f300–180 K), which is typical of a simple activated hopping process [Eq.(19)]. Some form of hopping transport has been assumed from the fielddependence of the current in similar structures of CdS nanocrystals [116] andseems natural given the film morphology in which the nanocrystals are separatedby f12–14 A˚ of insulating organic surfactant [18]. At lower temperatures(f180–60 K), a second region with a nearly linear dependence of ln(r)versus 1/T is also observed. In this intermediate range, the temperaturedependence is much smaller than at high temperatures, suggesting that asecond, smaller activation energy dominates the transport in this temperatureregion. The current typically reaches a constant value below f60 K at currentscomparable to those observed in reverse bias at room temperature. Wetherefore believe that leakage currents may dominate the low-temperature(