739 publications from this institution
We show that metastable rocksalt CdSe nanocrystals can persist at ambient pressure depending on the physical size of the particle. The size-dependence of the hysteresis loop was measured for the solid−solid transition in CdSe nanocrystals, between four- and six-coordinate structures. A systematic shift of the entire hysteresis loop to lower pressure results in a threshold size of ∼11 nm for ambient metastability of the six-coordinate rocksalt structure. Smaller nanocrystals transform back to the four-coordinate structure as occurs in the CdSe bulk solid. Surface energy contributions are used to explain the shift. The results have important implications for the optimum synthesis of metastable nanocrystal solids under ambient conditions.
Methods are described for attaching semiconductor nanocrystals to solid inorganic surfaces, using self-assembled bifunctional organic monolayers as bridge compounds. Two different techniques are presented. One relies on the formation of self-assembled monolayers on these surfaces. When exposed to solutions of nanocrystals, these bridge compounds bind the crystals and anchor them to the surface. The second technique attaches nanocrystals already coated with bridge compounds to the surfaces. Analyses indicate the presence of quantum confined clusters on the surfaces at the nanolayer level. These materials allow electron spectroscopies to be completed on condensed phase clusters, and represent a first step towards synthesis of an organized assembly of clusters. These new products are also disclosed.
We propose the goal of recording every spike from every neuron in a neural circuit, and use that information to infer its connectivity diagram. The ultimate goal is to record simultaneously all the activity from every neuron in the brain.
Cadmium selenide nanocrystals are reproducibly synthesized at high-temperature in continuous flow, chip-based microfluidic reactors and exhibit size distributions comparable to those for conventional macroscale syntheses. Nanocrystal size, probed by fluorescence, is precisely controlled by independently varying the temperature, flow rate, and concentration of precursor solution flowing through heated microchannels. These experiments demonstrate the ability to fine-tune physical properties and test wide ranges of conditions precisely and rapidly inside chip-based microreactors, enabling rational, cost-effective, and environmentally friendly development and production of novel nanostructures.
The concept of self-assembled dendrimers is explored for the creation of discrete nanoparticle assemblies. Hybridization of branched DNA trimers and nanoparticle-DNA conjugates results in the synthesis of nanoparticle trimer and tetramer complexes. Multiple tetramer architectures are investigated, utilizing Au-DNA conjugates with varying secondary structural motifs. Hybridization products are analyzed by gel electrophoresis, and discrete bands are observed corresponding to structures with increasing numbers of hybridization events. Samples extracted from each band are analyzed by transmission electron microscopy, and statistics compiled from micrographs are used to compare assembly characteristics for each architecture. Asymmetric structures are also produced in which both 5 and 10 nm Au particles are assembled on branched scaffolds.
