In contrast to molecular systems, which are defined with atomic precision, nanomaterials generally show some heterogeneity in size, shape, and composition. The sample inhomogeneity translates into a distribution of energy levels, band gaps, work functions, and other characteristics. The lack of atomistic control during nanomaterial synthesis also limits our ability to perform “total-synthesis” of sophisticated nano-heterostructures with precisely arranged multiple components and fine-tuned properties. We discuss a general synthetic strategy which largely circumvents these limitations of traditional colloidal synthesis. Colloidal Atomic Layer Deposition (c-ALD) allows a significant reduction of inhomogeneity for nanomaterials without compromising their structural perfection. We report a novel realization of c-ALD step sequence which significantly improves synthetic control and quality of synthesized nanomaterials. In traditional gas-phase ALD, the substrate and gaseous reactants act as the stationary and mobile phases, respectively. Such distinction facilitates removal of unreacted precursors by pulsing inert gas after each half-reaction. For c-ALD, we inverted the stationary and mobile phases – reactants form the stationary phase while the substrate is moved in and out of the reactor as the mobile phase. This approach brings c-ALD closer to traditional ALD and is expected to make it a similarly powerful and versatile technique. Our improved c-ALD enables synthesis of epitaxial nano-heterostructures of unprecedented complexity, ultimately enabling bandgap and strain engineering in colloidal nanomaterials synthesized with close-to-atomistic accuracy. Improved synthetic control elucidates the effects of quantum confinement and strain on the properties of semiconductor nanostructures.

Colloidal atomic layer deposition

2019 Spring National Meeting

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