Anisotropic Noble Metal Nanocrystal Growth: The Role of Halides*

The Nature and Implications of Uniformity in the Hierarchical Organization of Nanomaterials*

“…Reagent mixtures are typically purchased from distributors without full disclosure of the constituent chemicals and those mixtures can further undergo a multitude of reactions to generate new species. Without knowledge of what chemical species are present, researchers cannot understand the mechanistic underpinnings of these systems or control their uniformity (15,19,20,(34)(35)(36). For semiconductor metal chalcogenides, many key advances have been made with the solvent tri-N-octylphosphine oxide (TOPO).…”

“…Subsequent research instead showed that phosphonates and phosphonic acids present in or produced at high temperatures coordinate stronger than TOPO and dictate the reaction pathway (21,34). Similarly, halide impurities in ubiquitously used surfactants for noble metal nanoparticle syntheses [e.g., cetyltrimethylammonium bromide (CTAB)] went unidentified for almost a decade of research (17,19,35,36). Only after extensive efforts to identify, purify, and systematically dope in halides were researchers able to reproducibly synthesize nanostructures with controlled shape (17-19, 35, 36).…”

A “Tips and Tricks” Practical Guide to the Synthesis of Gold Nanorods*

“…The mechanism behind the formation of Au nanorods is still a matter of much interest, since a general mechanistic model would allow us to identify specific guidelines for the design of a synthetic pathway for each nanostructure. [11][12][13][14] Xia's group recently published a highly informative perspective article dealing with the distinction between thermodynamic and kinetic control during crystal growth. 15 An entire section of this paper is dedicated to the symmetry breaking event, a necessary step in the development of anisotropic structures, such as nanorods.…”

The Many “Facets” of Halide Ions in the Chemistry of Colloidal Inorganic Nanocrystals

“…Recent review articles, such as that by Juarez and Lohse, have attempted at giving an outlook on the influence of halide ions on the synthesis of semiconductor and metal NCs, respectively. 12 , 13 However, we aim to go beyond the conventional wisdom to paint a unifying picture that can be put to good use by a practicing nanochemist in designing more focused NC synthesis and functionalization strategies. The seemingly unconnected reports in the literature give rise to chemical trends having underlying principles common to all classes of nanomaterials, and we aim to demonstrate the same to the reader by furnishing an updated account of research in this area and by finally providing a thorough outlook.…”