Unveiling the Nanocluster Conversion Pathway for Highly Monodisperse InAs Colloidal Quantum Dots.

Colloidal quantum dots (CQDs) have garnered significant attention in nanoscience and technology, with a particular emphasis on achieving high monodispersity in their synthesis. Recent advances in understanding the chemistry of reaction intermediates such as magic-sized nanoclusters (MSC) have paved the way for innovative synthetic strategies. Notably, monodisperse CQDs of various compositions, including indium phosphide, indium arsenide, and cadmium chalcogenide, have been successfully prepared using nanocluster intermediates as single-source precursors. Still, the early stage conversion chemistry of these nanoclusters preceding CQD formation has not been fully unveiled yet. Herein, we report the first-order conversion of amorphous nanoclusters (AMCs) to InAs MSCs prior to the formation of CQDs. We find that MSC, isolated via gel-permeation chromatography, is more stable than purified AMCs, as demonstrated in various chemical and thermolytic reactions. While the surface of InAs AMCs and MSC is similarly bound with carboxylate ligands, detailed structural analyses employing synchrotron X-ray scattering and X-ray absorption spectroscopy unveil subtle distinctions arising from the distinct surface properties and structural disorder characteristics of InAs nanoclusters. We propose that InAs AMCs undergo a surface reduction and structural ordering process, resulting in the formation of an InAs MSC in a thermodynamically local minimum state. Furthermore, we demonstrate that both types of nanoclusters serve as viable precursors, providing a similar monomer supply rate at elevated temperatures of around 300 °C. This study offers invaluable insights into the interplay of structure and chemical stability in binary nanoclusters, enhancing our ability to design these nanoclusters as precursors for highly monodisperse CQDs.

P- and N-type InAs nanocrystals with innately controlled semiconductor polarity.

InAs semiconductor nanocrystals (NCs) exhibit intriguing electrical/optoelectronic properties suitable for next-generation electronic devices. Although there is a need for both n- and p-type semiconductors in such devices, InAs NCs typically exhibit only n-type characteristics. Here, we report InAs NCs with controlled semiconductor polarity. Both p- and n-type InAs NCs can be achieved from the same indium chloride and aminoarsine precursors but by using two different reducing agents, diethylzinc for p-type and diisobutylaluminum hydride for n-type NCs, respectively. This is the first instance of semiconductor polarity control achieved at the synthesis level for InAs NCs and the entire semiconductor nanocrystal systems. Comparable field-effective mobilities for holes (3.3 × 10-3 cm2/V·s) and electrons (3.9 × 10-3 cm2/V·s) are achieved from the respective NC films. The mobility values allow the successful fabrication of complementary logic circuits, including NOT, NOR, and NAND comprising photopatterned p- and n-channels based on InAs NCs.

Semiconductor Nanocrystals: Unveiling the Chemistry behind Different Facets.

ConspectusDeveloping next-generation colloidal semiconductor nanocrystals with high-quality optoelectronic properties and precise processability relies on achieving complete mastery over the surface characteristics of nanocrystals (NCs). This requires precise engineering of the ligand-NC surface interactions, which poses a challenge due to the complex reactivity of the multiple binding sites across the entire surface. Accordingly, recent progress has been made by strategically combining well-defined surface models with quantitative surface reactions to advance our understanding and manipulation of NC surface chemistry. Our lab has contributed to this progress by developing a size-dependent shape model of IV-VI NCs, gaining insights into their unique facet-specific chemistry, and developing a systematic ligand modification strategy for target applications. Furthermore, we have created well-defined facets in III-V NCs via a co-passivation strategy, addressing the previously lacking specific shapes.This Account is divided into three parts. First, we discuss the complexities involved in comprehensively understanding the nanocrystal surface structure at the atomistic level. We explain why we focused on well-defined NCs with a large exciton Bohr radius to explore facets, an essential aspect of surface heterogeneity across the entire NC. Second, we present our work on one of the most studied nanocrystals, IV-VI materials, and how facet-specific surface chemistry has led to a meaningful understanding and control of the NC's surface. We discovered a size-dependent facet distribution in IV-VI NCs and suggested facet-specific surface chemistry to improve the photophysical properties of NCs. We further modulate the electronic properties of NC assemblies for efficient optoelectronic applications. Third, we describe our recent success in achieving well-defined facets and their facet-specific chemistry in III-V NCs, which have yet to be explored as much as classical II-VI or IV-VI materials. We explain how controlling the surfaces in III-V NCs has been challenging. We present a precise growth platform for the geometric modulation of NCs, which can be further explored for shape-dependent exciton behavior and surface reactivities.Taken together, we present a compelling case for utilizing facet-specific chemistry as a platform for mechanistic investigation and morphology exploration, which can pave the way for developing high-quality and precisely designed NCs for optoelectronic technologies, unlocking new multidisciplinary applications.