Successive Ionic Layer Absorption and Reaction for Postassembly Control over Inorganic Interdot Bonds in Long-Range Ordered Nanocrystal Films

Epitaxially connected assemblies of nanocrystals (NCs) present an interesting new class of nanomaterial in which confinement of charge carriers is intermediate between that of a quantum dot and a quantum well. Despite impressive advances in the formation of high-fidelity assemblies, predicted collective properties have not yet emerged. A critical knowledge gap toward realizing these properties is the current lack of understanding of and control over the formation of epitaxial interdot bonds connecting the NCs within the assemblies. In this work we demonstrate successive ionic layer absorption and reaction (SILAR) to enhance the interdot bonding within the NC assembly. SILAR treatment improved the fraction of interdot bonds from 82% to 91% and increased their width from 3.1 to 4.0 nm. Absorption spectra and charge transport measurements indicate that the effect of postassembly growth on quantum confinement in this system depends on the composition of the SILAR shell material. Increased NC film conductance following SILAR processing indicates that building and strengthening interdot bonds lead to increased electronic coupling and doping in the assemblies. The postassembly film growth detailed here presents an opportunity to repair structural defects and to tailor the balance of quantum confinement and interdot coupling in epitaxially connected NC assemblies.