Fabrication of bismuth nanowires with a silver nanocrystal shadowmask

We fabricated bismuth (Bi) nanowires with low energy electron beam lithography using silver (Ag) nanocrystal shadowmasks and a subsequent chlorine reactive ion etching. Submicron-size metal contacts on the single Bi nanowire were successfully prepared by in situ focused ion beam metal deposition for transport measurements. The temperature dependent resistance measurements on the 50 nm wide Bi nanowires showed that the resistance increased with decreasing temperature, which is characteristic of semiconductors and insulators

Enhancement of Coherent X ray Diffraction from Nanocrystals by Introduction of X ray Optics

Coherent X-ray Diffraction is applied to investigate the structure of individual nanocrystalline silver particles in the 100nm size range. In order to enhance the available signal, Kirkpatrick-Baez focusing optics have been introduced in the 34-ID-C beamline at APS. Concerns about the preservation of coherence under these circumstances are addressed through experiment and by calculations

Quantifying Electrophoretic Deposition of Nanocrystal Superlattices Using Quartz Crystal Microbalance

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Biosynthesis of Silver Nanoparticles from Desmodium triflorum: A Novel Approach Towards Weed Utilization

A single-step environmental friendly approach is employed to synthesize silver nanoparticles. The biomolecules found in plants induce the reduction of Ag+ ions from silver nitrate to silver nanoparticles (AgNPs). UV-visible spectrum of the aqueous medium containing silver ions demonstrated a peak at 425 nm corresponding to the plasmon absorbance of silver nanoparticles. Transmission electron microscopy (TEM) showed the formation of well-dispersed silver nanoparticles in the range of 5–20 nm. X-ray diffraction (XRD) spectrum of the AgNPs exhibited 2θ values corresponding to the silver nanocrystal. The process of reduction is extracellular and fast which may lead to the development of easy biosynthesis of silver nanoparticles. Plants during glycolysis produce a large amount of H+ ions along with NAD which acts as a strong redoxing agent; this seems to be responsible for the formation of AgNPs. Water-soluble antioxidative agents like ascorbic acids further seem to be responsible for the reduction of AgNPs. These AgNPs produced show good antimicrobial activity against common pathogens

Plasmonic colloidal nanoparticles with open eccentric cavities via acid-induced chemical transformation

Surface-enhanced Raman spectroscopy (SERS) has been considered a promising technique for the detection of trace molecules in biomedicine and environmental monitoring. The ideal metal nanoparticles for SERS must not only fulfill important requirements such as high near-field enhancement and a tunable far-field response but also overcome the diffusion limitation at extremely lower concentrations of a target material. Here, we introduce a novel method to produce gold nanoparticles with open eccentric cavities by selectively adapting the structure of non-plasmonic nanoparticles via acid-mediated surface replacement. Copper oxide nanoparticles with open eccentric cavities are first prepared using a microwave-irradiation-assisted surfactant-free hydrothermal reaction and are then transformed into gold nanoparticles by an acidic gold precursor while maintaining their original structure. Because of the strong near-field enhancement occurring at the mouth of the open cavities and the very rough surfaces resulting from the uniformly covered hyperbranched sharp multi-tips and the free access of SERS molecules inside of the nanoparticles without diffusion limitation, adenine, one of the four bases in DNA, in an extremely diluted aqueous solution (1.0 pM) was successfully detected with excellent reproducibility upon laser excitation with a 785-nm wavelength. The gold nanoparticles with open eccentric cavities provide a powerful platform for the detection of ultra-trace analytes in an aqueous solution within near-infrared wavelengths, which is essential for highly sensitive, reliable and direct in vivo analysis.None1132sciescopu

Surface functionalization and self-assembly of ligand-stabilized silicon nanocrystals

textSilicon nanocrystals or quantum dots combine the abundance and nontoxicity of silicon with size-tunable energy band structure of quantum dots to form a new type of functional material that has applications in biomedical fluorescence imaging, photodynamic therapy, light-emitting devices, and solar cells. The surface is the major concern for using silicon nanocrystals in bio-related applications. Room temperature hydrosilylation is introduced to functionalize silicon nanocrystals in the dark to minimize temperature/photon-induced side reactions that can potentially damage the nanocrystal surface and capping ligands. As a proof of concept, silicon nanocrystals are passivated with styrene at room temperature, without showing styrene polymerization. Silicon nanocrystals are also conjugated to iron oxide nanocrystals through room temperature hydrosilylation to generate fluorescent/magnetic cell labeling probes. Thermally-induced thiolation is used to generate silicon nanocrystals passivated with silicon-sulfur bond that is metastable and can turn to silicon-carbon bond through a ligand exchange. The band gap and emission color of silicon nanocrystals depend on size. Monodisperse silicon nanocrystals and their self-assembly are of great importance for the applications in light-emitting devices and solar cells. Silicon nanocrystals are size-selected through a modified size-selective precipitation. Face-centered cubic superlattices are formed with monodisperse silicon nanocrystals, and characterized by using grazing incidence small angle X-ray scattering. The structure of silicon nanocrystal superlattice is stable at temperatures up to 375oC, due to the covalent Si-C bond on the nanocrystal surface. Silicon and gold nanocrystals are assembled to a simple hexagonal AlB2 binary superlattice that shows interesting thermal behavior. Finally, superlattices made with alkane thiol-capped sub-2 nm gold nanocrystals are used as model systems to study the superlattice phase transitions. Halide ions are found to be critical for order-to-order structural rearrangements in dodecanethiol-capped 1.9 nm gold nanocrystals superlattices at 190oC. Reversible amorphous-to-crystalline transition upon heating is discovered for octadecanethiol capped 1.66 nm gold nanocrystal superlattices, which is attributed to the ligand melting transition.Chemical Engineerin