Architectonic Quantum Dot Solids

Summary Following the above experiments, we now outline ourconcept of the changes in electronic properties of the QDsuperlattices as interparticle separation distance, a ,isreduced. For a > 1 nm, electronic states are localized onthe individual QDs, although the QDs are strongly dipole-coupled to one another. Localization arises from thepresence of the Coulomb gap, and from disorder in thesuperlattice. At 300 K and large D /2 r , the conductivity isdominated by thermally activated hopping. Throughoutthis weak-coupling regime the reflectivity of the filmincreases, and o sp red shifts with decreasing D /2 r . Theexponential increase in l (2) occurs as a is decreased from1 to 0.6 nm. Throughout this regime, charge tunneling andexchange interactions are important. The characteristic(tunneling) time constant of the film decreases throughoutthis region.The increase in tunneling coupling continues withcompression until D /2 r is near 1.1, at which pointexchange interactions overcome the Coulomb gap. Chargecarriers can then be generated with no cost in energy, andaccording to the Mott criterion for a metal-insulatortransition,