Kevin Whitham

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Confined-but-connected quantum dot solids (QDS) combine the advantages of tunable, quantum-confined energy levels with efficient charge transport through enhanced electronic interdot coupling. We report the fabrication of QDS by treating self-assembled films of colloidal PbSe quantum dots with polar nonsolvents. Treatment with dimethylformamide balances the(More)
Epitaxial attachment of quantum dots into ordered superlattices enables the synthesis of quasi-two-dimensional materials that theoretically exhibit features such as Dirac cones and topological states, and have major potential for unprecedented optoelectronic devices. Initial studies found that disorder in these structures causes localization of electrons(More)
We create and optimize a structurally well-defined electron donor-acceptor planar heterojunction interface in which electric-field and/or photon-induced charge transfer occurs. Electric-field-induced charge transfer in the dark and exciton dissociation at a pentacene/PCBM interface were probed by in situ thickness-dependent threshold voltage shift(More)
As nanocrystal (NC) synthesis techniques and device architectures advance, it becomes increasingly apparent that new ways of connecting NCs with each other and their external environment are required to realize their considerable potential. Enhancing inter-NC coupling by thermal annealing has been a long-standing challenge. Conventional thermal annealing(More)
We used a bilayer field effect transistor (FET) consisting of a thin PbS nanocrystals (NCs) film interfaced with vacuum-deposited pentacene to probe trap states in NCs. We interpret the observed threshold voltage shift in context of charge carrier trapping by PbS NCs and relate the magnitude of the threshold voltage shift to the number of trapped carriers.(More)
The formation of epitaxially connected quantum dot solids involves a complex interplay of interfacial assembly, surface chemistry, and irreversible-directed attachment. We describe the basic mechanism in the context of a coherent phase transition with distinct nucleation and propagation steps. The proposed mechanism explains how defects in the preassembled(More)
Epitaxially connected superlattices of self-assembled colloidal quantum dots present a promising route toward exquisite control of electronic structure through precise hierarchical structuring across multiple length scales. Here, we uncover propagation of disorder as an essential feature in these systems, which intimately connects order at the atomic,(More)
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