The goal of this work is to identify favored pathways for preparation of defect resilient attached wurtzite CdX (X = S, Se, Te) nanocrystals. We seek guidelines for oriented attachment of faceted nanocrystals that are most likely to yield pairs of nanocrystals with either few or no electronic defects, or electronic defects that are in and of themselves desirable and stable. Using a combination of in-situ high resolution transmission electron microscopy (HRTEM) and electronic structure calculations, we evaluate the relative merits of atomic attachment of wurtzite CdSe nanocrystals on the {11 � 00} or {112 � 0} family of facets. Pairwise attachment on either facet can lead to perfect interfaces, provided the nanocrystal facets are perfectly flat and the angles between the nanocrystals can adjust during the assembly. Considering defective attachment, we observe for {11 � 00} facet attachment that only one type of edge dislocation forms, creating deep hole traps. For {112 � 0} facet attachment, we observe that four distinct types of dislocations form, some of which lead to deep hole traps while others only to shallow hole traps. HRTEM movies of the dislocation dynamics show that dislocations at {11 � 00} interfaces can be removed, albeit slowly. Whereas only some extended dislocations at {112 � 0} interfaces could be removed, others were trapped at the interface. Based on these insights, we identify the most resilient pathways to atomic attachment of pairs of wurtzite CdX nanocrystals and consider how these insights can translate to creation of electronically useful materials from quantum dots with other crystal structures.

By combining colloidal nanocrystal synthesis, self assembly, and solution phase epitaxial growth techniques, we developed a general method for preparing single dot thick atomically attached quantum dot (QD) superlattices with high quality translational and crystallographic orientational order along with state-of-the-art uniformity 1 in the attachment thickness. The procedure begins with colloidal synthesis of hexagonal prism shaped core/shell QDs (e.g. CdSe/CdS), followed by liquid subphase selfassembly and immobilization of superlattices on a substrate. Solution phase epitaxial growth of additional semiconductor material fills in the voids between the particles resulting in a QD-in-matrix structure. The photoluminescence emission spectra of the QD-in-matrix structure retains characteristic 0D electronic confinement. Importantly, annealing of the resulting structures removes inhomogeneities in the QD-QD inorganic bridges, which our atomistic electronic structure calculations demonstrate would otherwise lead to Anderson-type localization. The piece-wise nature of this procedure allows one to independently tune the size and material of the QD core, shell, QD-QD distance, and the matrix material. These four choices can be tuned to control many properties (e.g. degree of quantum confinement, quantum coupling, band alignments, etc.) depending on the specific applications. Finally, cation exchange reactions can be performed on the final QD-in-matrix, as demonstrated herein with a CdSe/CdS to HgSe/HgS conversion.