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Surface energy is a fundamental property of materials and is particularly important in describing nanomaterials where atoms or molecules at the surface constitute a large fraction of the material. Traditionally, surface energy is considered to be a positive quantity, where atoms or molecules at the surface are less thermodynamically stable than their counterparts in the interior of the material because they have fewer bonds or interactions at the surface. Using calorimetric methods, we show that the surface energy is negative in some prototypical colloidal semiconductor nanocrystals, or quantum dots with organic ligand coatings. This implies that the surface atoms are more thermodynamically stable than those on the interior due to the strong bonds between these atoms and surfactant molecules, or ligands, that coat their surface. In addition, we extend this work to core/shell indium phosphide/zinc sulfide nanocrystals and show that the interfacial energy between these materials is highly thermodynamically favorable in spite of their large lattice mismatch. This work challenges many of the assumptions that have guided thinking about colloidal nanomaterial thermodynamics, investigates the fundamental stability of many technologically relevant colloidal nanomaterials, and paves the way for future experimental and theoretical work on nanocrystal thermodynamics.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionAddition to "Essentially Trap-Free CsPbBr3 Colloidal Nanocrystals by Postsynthetic Thiocyanate Surface Treatment"Brent A. Koscher, Joseph K. Swabeck, Noah D. Bronstein, and A. Paul Alivisatos*Cite this: J. Am. Chem. Soc. 2018, 140, 1, 527Publication Date (Web):December 22, 2017Publication History Published online22 December 2017Published inissue 10 January 2018https://pubs.acs.org/doi/10.1021/jacs.7b13027https://doi.org/10.1021/jacs.7b13027correctionACS PublicationsCopyright © 2017 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views3250Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (230 KB) Get e-Alertsclose Get e-Alerts

Abstract The interplay between crystallization and chirality has fascinated chemists for over 170 years now. Many questions deal with the transfer of chirality from molecular level building blocks and crystal capping ligands to the macroscopic morphologies of crystals. Also the interest in nanoscale chiral crystallization and the relationship between chiral ligands and inorganic nanocrystals has recently arose. In this review we highlight several different topics related to studies of the interplay between chirality and crystallization that involve inorganic nanocrystals. Specifically, we differentiate between the effects of chiral molecules on inorganic nanocrystals with chiral or achiral crystal structures. In the first case, chirality may appear both at the atomic‐scale and the particle shape, and in the second case chirality may be induced only at the particle shape level. We also discuss recent progress on the relationship between the atomic scale chirality and crystal morphology.

The development of a colloidal synthesis procedure to produce nanomaterials with high shape and size purity is often a time-consuming, iterative process. This is often due to quantitative uncertainties in the required reaction conditions and the time, resources, and expertise intensive characterization methods required for quantitative determination of nanomaterial size and shape. Absorption spectroscopy is often the easiest method for colloidal nanomaterial characterization. However, due to the lack of a reliable method to extract nanoparticle shapes from absorption spectroscopy, it is generally treated as a more qualitative measure for metal nanoparticles. This work demonstrates a gold nanorod (AuNR) spectral morphology analysis tool, called AuNR-SMA, which is a fast and accurate method to extract quantitative structural information from colloidal AuNR absorption spectra. To demonstrate the practical utility of this model, we apply it to three distinct applications. First, we demonstrate this model's utility as an automated analysis tool in a high-throughput AuNR synthesis procedure by generating quantitative size information from optical spectra. Second, we use the predictions generated by this model to train a machine learning model to predict the resulting AuNR size distributions under specified reaction conditions. Third, we apply this model to spectra extracted from the literature where no size distributions are reported and impute unreported quantitative information on AuNR synthesis. This approach can potentially be extended to any other nanocrystal system where absorption spectra are size dependent, and accurate numerical simulation of absorption spectra is possible. In addition, this pipeline could be integrated into automated synthesis apparatuses to provide interpretable data from simple measurements, help explore the synthesis science of nanoparticles in a rational manner, or facilitate closed-loop workflows.

We report the results of charge transport studies on single CdTe nanocrystals contacted via evaporated Pd electrodes. Device charging energy, E c, monitored as a function of electrode separation drops suddenly at separations below approximately 55 nm. This drop can be explained by chemical changes induced by the metal electrodes. This explanation is corroborated by ensemble X-ray photoelectron spectroscopy studies of CdTe films as well as single particle measurements by transmission electron microscopy and energy dispersive X-rays. Similar to robust optical behavior obtained when nanocrystals are coated with a protective shell, we find that a protective SiO 2 layer deposited between the nanocrystal and the electrode prevents interface reactions and an associated drop in E c,max. This observation of interface reactivity and its effect on electrical properties has important implications for the integration of nanocrystals into conventional fabrication techniques and may enable novel nanomaterials.

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 in the attachment thickness. The procedure begins with colloidal synthesis of hexagonal prism shaped core/shell QDs (<i>e</i>.<i>g</i>., CdSe/CdS), followed by liquid subphase self-assembly 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 piecewise 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 (degree of quantum confinement, quantum coupling, band alignments, <i>etc.</i>) 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.

What makes things twist? Crystallization and chirality have been entangled since Pasteur's observations on chiral tartaric acid crystals, yet there is still limited understanding of how chiral compounds form chiral crystal morphologies. For example, although a chiral seed crystal can promote a particular handedness, it is not clear why such seeds do not do so with 100% efficiency. Ben-Moshe et al. examined chiral nanocrystals of tellurium grown from solution using various electron microscopy and diffraction techniques (see the Perspective by Popov). They found that screw dislocation- mediated growth is responsible for chiral polyhedral shape formation, and chiral crystals can thus form even in the presence of achiral ligands. Science , this issue p. 729 ; see also p. 688

The self-assembly of nanocrystals enables new classes of materials whose properties are controlled by the periodicities of the assembly, as well as by the size, shape, and composition of the nanocrystals. While self-assembly of spherical nanoparticles has advanced significantly in the past decade, assembly of rod-shaped nanocrystals has seen limited progress due to the requirement of orientational order. Here, the parameters relevant to self-assembly are systematically quantified using a combination of diffraction and theoretical modeling; these highlight the importance of kinetics on orientational order. Through drying-mediated self-assembly, we achieve unprecedented control over orientational order (up to 96% vertically oriented rods on 1 cm&lt;sup&gt;2&lt;/sup&gt; areas) on a wide range of substrates (ITO, PEDOT:PSS, Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;). This opens new avenues for nanocrystal-based devices competitive with thin film devices, as problems of granularity can be tackled through crystallographic orientational control over macroscopic areas.

We demonstrate that performing a replacement reaction on single crystalline Ag nanospheres of approximately 10 nm in diameter in an organic solvent produces hollow Au nanocrystals with an octahedral shape. Different from those Au shells made by starting with Ag particles about 1 order of magnitude larger, which largely reproduce that of the sacrificial Ag counterparts, the hollow nanocrystals obtained in this work show significant changes in the external morphology from the spherical Ag precursors. This evolution of a faceted external morphology during chemical transformation is made possible by the enhanced role of surface effects in our smaller nanocrystals. The competition between the Au atom deposition and Ag atom dissolution on various nanocrystal surfaces is believed to determine the final octahedral shape of the hollow Au nanocrystals. Simultaneous achievement of surface-mediated shape control and a hollow morphology in a one-pot, single-step synthetic procedure in this study promises an avenue to finer tuning of particle morphology, and thus physical properties such as surface plasmon resonance.

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTVirtual Issue Celebrating the Life and Career of Millie DresselhausThe Queen of Carbon ScienceGeorge C. Schatz, Greg D. Scholes, Peter J. Stang, Cindy J. Burrows, Francoise M. Winnick, A. Paul Alivisatos, Charles M. Lieber, Paul S. Weiss, and Jillian M. BuriakCite this: Chem. Mater. 2017, 29, 12, 5017–5018Publication Date (Web):June 27, 2017Publication History Published online27 June 2017Published inissue 27 June 2017https://doi.org/10.1021/acs.chemmater.7b02398Copyright © 2017 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views2301Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-AlertsSUBJECTS:Carbon nanotubes,Chemical vapor deposition,Raman spectroscopy,Thin films,Two dimensional materials Get e-Alerts

We demonstrate a simple and versatile approach to produce hierarchical assemblies of nanoparticles by combining block copolymers and small molecules. Directed nanoparticle assemblies can be achieved with a variety of nanoparticles and small molecules without modification of the nanoparticle ligands. This novel approach opens up new routes toward the fabrication of nanoparticle-based functional devices using a "Bottom-Up" approach.