Langmuir-Blodgett Transfer of Nanocrystal Monolayers: Layer Compaction, Layer Compression, and Lattice Stretching of the Transferred Layer.

Grazing incidence small angle X-ray scattering (GISAXS) was used to study the structure and interparticle spacing of monolayers of organic ligand-stabilized iron oxide nanocrystals floating at the air-water interface on a Langmuir trough, and after transfer to a solid support via the Langmuir-Blodgett technique. GISAXS measurements of the nanocrystal arrangement at the air-water interface showed that lateral compression decreased the interparticle spacing of continuous films. GISAXS also revealed that Langmuir-Blodgett transfer of the nanocrystal layers to a silicon substrate led to a stretching of the film, with a significant increase in interparticle spacing.

Mechanisms of Energy Transfer and Enhanced Stability of Carbidonitride Phosphors for Solid-State Lighting.

Phosphor-converted light emitting diodes (pcLEDs) produce white light through the use of phosphors that convert blue light emitted from the LED chip into green and red wavelengths. Understanding the mechanisms of degradation of the emission spectra and quantum yields of the phosphors used in pcLEDs is of critical importance to fully realize the potential of solid-state lighting as an energy efficient technology. Toward this end, time-resolved photoluminescence spectroscopy was used to identify the mechanistic origins of enhanced stability and luminescence efficiency that can be obtained from a series of carbidonitride red phosphors with varying degrees of substitutional carbon.

Stacking of hexagonal nanocrystal layers during Langmuir-Blodgett deposition.

Hexagonally ordered close-packed monolayers of sterically stabilized FePt nanocrystals were deposited on substrates using the Langmuir-Blodgett technique. Monolayers of nanocrystals were also stacked by sequential Langmuir-Blodgett transfer. The structures of the nanocrystal monolayers and multilayer stacks were examined with scanning electron microscopy (SEM) and grazing-incidence small-angle scattering (GISAXS).

Printed magnetic FePt nanocrystal films.

Patterned monolayers and multilayers of FePt nanocrystals were printed onto substrates by first assembling nanocrystals on a Langmuir-Blodgett (LB) trough and then lifting them onto prepatterned polydimethylsiloxane (PDMS) stamps, followed by transfer printing onto the substrate. Patterned features, including micrometer-size circles, lines, and squares, could be printed using this approach. The magnetic properties of the printed nanocrystal films were also measured using magnetic force microscopy (MFM).

Gold seed removal from the tips of silicon nanorods.

A chemical method was developed to remove the gold (Au) seed particles from the tips of solution-liquid-solid (SLS) grown silicon (Si) nanorods. The nanorods are capped with hydrophobic ligands during the synthesis, which made it necessary to perform the Au etching in an aqua regia and chloroform emulsion. Preliminary etching experiments revealed that a thin Si shell coated the Au seeds and prevented Au removal.

Colloidal silicon nanorod synthesis.

The colloidal synthesis of crystalline silicon (Si) nanorods with diameters of 5 to 10 nm and lengths of 15 to 75 nm is demonstrated. Trisilane was decomposed in a hot solvent in the presence of dodecylamine and gold (Au) nanocrystals. Nanorods form by Au-seeded solution-liquid-solid growth with dodecylamine serving as capping ligands that stabilize the nanorod dispersion.

Multifunctional Particles: Magnetic Nanocrystals and Gold Nanorods Coated with Fluorescent Dye-Doped Silica Shells.

Multifunctional colloidal core-shell nanoparticles of magnetic nanocrystals (of iron oxide or FePt) or gold nanorods encapsulated in silica shells doped with the fluorescent dye, Tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy) were synthesized. The as-prepared magnetic nanocrystals are initially hydrophobic and were coated with silica using a microemulsion approach, while the as-prepared gold nanorods are hydrophilic and were coated with silica using a Stöber-type of process. Each approach yielded monodisperse nanoparticles with uniform fluorescent dye-doped silica shells.

Solution-liquid-solid (SLS) growth of silicon nanowires.

Here we report the solution-liquid-solid (SLS) synthesis of silicon (Si) nanowires. Nanowires are grown by trisilane (Si3H8) decomposition in a high boiling solvent, octacosane (C28H58) or squalane (C30H62), in the presence of either Au or Bi nanocrystals. To our knowledge, this is the first report of a colloidal synthetic route carried out in a solvent at atmospheric pressure that provides crystalline Si nanowires in large quantities.