The morphology and evolution of bipyramidal gold nanoparticles.

We examine the growth and evolution with time of bipyramidal gold nanoparticles grown by a seed-mediated process. The nanoparticles are characterized both by their physical dimensions determined by transmission electron microscopy and by the wavelength position of their localized surface plasmon resonance. Each growth's physical dimensions correspond to particular initial conditions, and we observe two distinct modes of temporal evolution during growth. The effects of varying silver nitrate concentration and growth time are also explored. We observe a linear relationship between the tip radius of curvature and the wavelength of the longitudinal localized surface plasmon resonance (LSPR) peak. Critical parameters for synthesizing bipyramidal nanoparticles with sharp tips and correct length to width ratio are determined.

Novel growth and properties of GaAs nanowires on Si substrates.

Straight, vertically aligned GaAs nanowires were grown on Si(111) substrates coated with thin GaAs buffer layers. We find that the V/III precursor ratio and growth temperature are crucial factors influencing the morphology and quality of buffer layers. A double layer structure, consisting of a thin initial layer grown at low V/III ratio and low temperature followed by a layer grown at high V/III ratio and high temperature, is crucial for achieving straight, vertically aligned GaAs nanowires on Si(111) substrates. An in situ annealing step at high temperature after buffer layer growth improves the surface and structural properties of the buffer layer, which further improves the morphology of the GaAs nanowire growth. Through such optimizations we show that vertically aligned GaAs nanowires can be fabricated on Si(111) substrates and achieve the same structural and optical properties as GaAs nanowires grown directly on GaAs(111)B substrates.

The effect of V/III ratio and catalyst particle size on the crystal structure and optical properties of InP nanowires.

InP nanowires were grown on 111B InP substrates by metal-organic chemical vapour deposition in the presence of colloidal gold particles as catalysts. Transmission electron microscopy and photoluminescence measurements were carried out to investigate the effects of V/III ratio and nanowire diameter on structural and optical properties. Results show that InP nanowires grow preferably in the wurtzite crystal structure than the zinc blende crystal structure with increasing V/III ratio or decreasing diameter. Additionally, time-resolved photoluminescence (TRPL) studies have revealed that wurtzite nanowires show longer recombination lifetimes of approximately 2500 ps with notably higher quantum efficiencies.

Tuning spin properties of excitons in single CdTe quantum dots by annealing.

Using polarization-resolved photoluminescence imaging in external magnetic fields we measure statistically significant distributions of exchange splitting, diamagnetic shift and effective g-factor of excitons in tens of single CdTe quantum dots. Comparison between the as-grown and annealed structures shows strong suppression of ensemble inhomogeneities, with the average exchange splitting reduced by half and significant narrowing of the g-factor distribution. Remarkably, the average value of the excitonic g-factor remains unchanged. This unique ability to yield highly uniform quantum dot ensembles without hampering the exciton Zeeman splitting makes annealing a highly attractive means for tuning the spin properties of quantum dot excitons.

Longitudinal-transverse separations of deep-inelastic structure functions at low Q2 for hydrogen and deuterium.

We report on a study of the longitudinal to transverse cross section ratio, R=sigmaL/sigmaT, at low values of x and Q2, as determined from inclusive inelastic electron-hydrogen and electron-deuterium scattering data from Jefferson Laboratory Hall C spanning the four-momentum transfer range 0.06

Optical waveguides fabricated by ion implantation of Si(+) and N(+) in SiO(2): a Raman investigation.

We report an investigation of optical waveguides that are fabricated by successive ion implantations at different energies of Si(+) or N(+) ions into SiO(2) thermally grown on (100) Si substrates. Implantations of both the species result in optical waveguides that sustain propagation over the 5-cm length of the sample. Loss coefficients for the waveguides are measured by using Raman spectroscopy and are compared with the values obtained in the usual manner by collecting elastically scattered light. A typical loss determined by the Raman technique was 3.2 dB/cm for the Si-implanted waveguide. Raman data that are obtained in the waveguided configuration show a contribution to loss from luminescence. The luminescence signal is found to be modulated by an interference between the directly scattered radiation from the waveguide region and that reflected from the Si-SiO(2) interface. Rapid thermal annealing is found to reduce the intensity of the luminescence and thus lower the value of the loss coefficient. The lowest loss obtained for the Si-implanted samples is 2.7 dB/cm and 3 dB/cm for the N(+)-implanted sample.

Primary human alveolar epithelial cells can elicit the transendothelial migration of CD14+ monocytes and CD3+ lymphocytes.

The ability of freshly isolated primary human alveolar epithelial cells (type II pneumocytes) to induce leucocyte migration across an endothelial monolayer was investigated. Three-way factorial analysis of variance (ANOVA) demonstrated that resting alveolar endothelial cells (AEC) could produce detectable quantities of monocyte chemoattractant protein 1 (MCP-1), which was upregulated in response to tumour necrosis factor-alpha (TNF-alpha) in a dose- and time-dependent fashion. Interferon-gamma (IFN-gamma) had no significant effect on this process. TNF-alpha and IFN-gamma both induced AEC to provoke migration of CD14+ monocytes and CD3+ lymphocytes across endothelium. IFN-gamma and TNF-alpha synergized in their ability to induce production of T lymphocyte, but not monocyte, chemoattractants from AEC. Leucocyte transendothelial migration was inhibited by anti-MCP-1 neutralizing antibody and by heparin, a polyanionic glycosaminoglycan (GAG). These data suggest that human AEC play a role in the multiple mechanisms that facilitate monocyte and T lymphocyte migration into the alveolar compartment of the lung under homeostasis and inflammatory conditions. One of these mechanisms is mediated via constitutive MCP-1 production by alveolar epithelial cells, which is upregulated by TNF-alpha.

Use of a rapid thermal annealing system to initiate indiffusion for fabrication of Ti:LiNbO(3) optical channel waveguides.

A rapid thermal annealing (RTA) system has been used to initiate indiffusion of Ti into LiNbO(3) for fabrication of optical channel waveguides. Four separate processes are investigated, each with different RTA temperature vs time variations followed by furnace heating. The sample processed with a fast initial ramp of temperature vs time to 875 degrees C yielded the lowest waveguide propagation loss of 1 dB/cm at a wavelength of 632.8 nm, compared with samples processed with other RTA variations and with a sample undergoing only furnace processing. Use of a dry O(2) ambient during RTA resulted in a smoother waveguide surface with no outdiffusion, when compared with use of a wet O(2) ambient.

Measurement of the high energy two-body deuteron photodisintegration differential cross section.

The first measurements of the d(gamma,p)n differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The results indicate evidence of an angular dependent scaling threshold. Results at straight theta(cm) = 37 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 4 GeV, while those at 70 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 1.5 GeV.

Longitudinal electroproduction of charged pions from (1)H, (2)H, and (3)He.

Separated longitudinal and transverse cross sections for charged pion electroproduction from (1)H, (2)H, and (3)He were measured at Q(2) = 0.4 (GeV/c)(2) for two values of the invariant mass, W = 1.15 GeV and W = 1.60 GeV, in a search for a mass dependence which would signal the effect of nuclear pions. This is the first such study that includes recoil momenta significantly above the Fermi surface. The longitudinal cross section, if dominated by the pion-pole process, should be sensitive to nuclear pion currents. Comparisons of the longitudinal cross section target ratios to a quasifree calculation reveal a significant suppression in (3)He at W = 1.60 GeV. The W = 1.15 GeV results are consistent with simple estimates of the effect of nuclear pion currents, but are also consistent with pure quasifree production.