Shape-Programmed Nanofabrication: Understanding the Reactivity of Dichalcogenide Precursors

TitleShape-Programmed Nanofabrication: Understanding the Reactivity of Dichalcogenide Precursors
Publication TypeJournal Article
Year of Publication2013
AuthorsGuo YJ, Alvarado SR, Barclay JD, Vela J
Journal TitleACS Nano
Volume7
Pages3616-3626
Date Published04
Type of ArticleArticle
ISBN Number1936-0851
Accession NumberWOS:000318143300078
Keywordsanisotropic, basis-set, bond dissociation energies, bond-dissociation enthalpies, CDSE NANOCRYSTALS, cuinse2 nanocrystals, dichalcogenide precursors, gaussian-type basis, molecular-orbital methods, morphology control, optical-properties, seeded growth, selective growth, selenide nanocrystals, solution-phase, structures, synthesis
Abstract

Dialkyl and diaryl dichalcogenides are highly versatile and modular precursors for the synthesis of colloidal chalcogenide nanocrystals. We have used a series of commercially available dichalcogenide precursors to unveil the molecular basis for the outcome of nanocrystal preparations, more specifically, how precursor molecular structure and reactivity affect the final shape and size of II-VI semiconductor nanocrystals. Dichalcogenide precursors used were diallyl, dibenzyl, di-tert-butyl, diisopropyl, diethyl, dimethyl, and diphenyl disulfides and diethyl, dimethyl, and diphenyl diselenides. We find that the presence of two distinctively reactive C-E and E-E bonds makes the chemistry of these precursors much richer and interesting than that of other conventional precursors such as the more common phosphine chalcogenides. Computational studies (DFT) reveal that the dissociation energy of carbon-chalcogen (C-E) bonds in dichalcogenide precursors (R-E-E-R, E = S or Se) increases in the order (R): diallyl < dibenzyl < di-tert-butyl < diisopropyl < diethyl < dimethyl < diphenyl. The dissociation energy of chalcogen-chalcogen (E-E) bonds remains relatively constant across the series. The only exceptions are diphenyl dichalcogenides, which have a much lower E-E bond dissociation energy. An increase in C-E bond dissociation energy results in a decrease in R-E-E-R precursor reactivity, leading to progressively slower nucleation and higher selectivity for anisotropic growth, all the way from dots to pods to tetrapods. Under identical experimental conditions, we obtain CdS and CdSe nanocrystals with spherical, elongated, or tetrapodal morphology by simply varying the identity and reactivity of the dichalcogenide precursor. Interestingly, we find that precursors with strong C-E and weak E-E bond dissociation energies such as Ph-S-S-Ph serve as a ready source of thiol radicals that appear to stabilize small CdE nuclei, facilitating anisotropic growth. These CdS and CdSe nanocrystals have been characterized using structural and spectroscopic methods. An intimate understanding of how molecular structure affects the chemical reactivity of molecular precursors enables highly predictable and reproducible synthesis of colloidal nanocrystals with specific sizes, shapes, and optoelectronic properties for customized applications.

URL<Go to ISI>://WOS:000318143300078
DOI10.1021/nn400596e