Borosilicate nanoparticles prepared by exothermic phase separation

Nanoparticles play an important role in chemical and biological sciences due to their ability to bind and concentrate many molecules on their surface. Polymers and silica are widely used to make nanoparticles, but efforts to make nanoparticles from borosilicate glass--which exhibits high tolerance to chemicals and solvents, combined with excellent mechanical and thermal stability--have proved unsuccessful. Here we show that borosilicate nanoparticles (100-500 nm in size) can be synthesized by simply mixing a silicon-boron binary oxide solution, prepared using non-aqueous organic solvents, with water. This induces a vigorous exothermic phase separation in which borosilicate nanoparticles burst out of a silica phase. In addition to potential applications in the life sciences, monodisperse borosilicate particles could also have applications in the production of photonic bandgap devices with high optical contrast, contrast agents for ultrasonic microscopy or chemical filtration membranes.     

<Emphasis Type="Italic">In situ</Emphasis> etching for total control over axial and radial nanowire growth

We report a method using in situ etching to decouple the axial from the radial nanowire growth pathway, independent of other growth parameters. Thereby a wide range of growth parameters can be explored to improve the nanowire properties without concern of tapering or excess structural defects formed during radial growth. We demonstrate the method using etching by HCl during InP nanowire growth. The improved crystal quality of etched nanowires is indicated by strongly enhanced photoluminescence as compared to reference nanowires obtained without etching.      

Solid‐state lasers for projection

Abstract— The unique advantage of projection displays is the ability to produce large images from small devices. The use of lasers as the projection light source will mean a further step in terms of compactness as well as efficiency for projection systems. However, the advent of laser projection is currently still limited by the availability of low‐cost green lasers. Blue‐diode‐pumped solid‐state lasers are one promising way to realize green as well as red lasers that are specifically suited for projection applications. An efficient solid‐state laser that is based on Pr³⁺:YLF as the laser material, pumped by a blue‐laser diode and emitting at 523 nm, is presented here. The laser reaches power‐conversion efficiencies of more than 7% and output powers of up to 378 mW at green wavelengths. By making only minor modifications to the laser resonator, a red laser emitting at 640 nm can be realized within the same setup. An output power of 166 mW at a power‐conversion efficiency of 6.9% is demonstrated in the red. By combining a red‐ and a green‐emitting blue‐diode‐pumped solid‐state laser with another blue diode, an integrated RGB projection light source can be realized that is based on a single‐diode technology.     

Suzuki–Miyaura Reactions of Aryl Chloride Derivatives with Arylboronic Acids using Mesoporous Silica‐Supported Aryldicyclohexylphosphine

The Suzuki–Miyaura reactions using mesoporous‐supported aryldicyclohexylphosphine as ligand have been investigated. The catalysts were based on SBA‐15 type mesoporous silica which was transformed in a four‐step synthesis leading to a phosphine‐containing hybrid material The most productive catalytic system studied was generated in situ from this material and the homogeneous palladium complex, Pd(OAc)₂. Other catalytic systems were studied for comparison [homogeneous cataysts, a “preformed” catalyst obtained by reaction of PdCl₂(PhCN)₂ and the phosphine‐containing material]. Variations involving the solvent system, the substrate aryl chloride and the arylboronic acid reactant were also studied. For both in situ and preformed catalyst systems, high conversions and yields are obtained for activated aryl chlorides. Success of the reaction for unactivated aryl chlorides was limited to the catalyst formed in situ. The catalyst formed in situ was also shown to be reactive under aqueous reaction conditions in the cross‐coupling of 1‐(4‐chlorophenyl)ethanone with phenylboronic acid.     

Error studies of the Coupling Darcy-Stokes System with velocity-pressure formulation

In this paper we study the Coupling Darcy-Stokes Systems. We establish a coupled variational formulation with the velocity and the pressure. The velocity is approximated with curl conforming finite elements and the pressure with standard continuous elements. We establish optimal a priori and a posteriori error estimates. We conclude our paper with some numerical simulations.     

Electrical properties of self-assembled branched InAs nanowire junctions

We investigate electrical properties of self-assembled branched InAs nanowires. The branched nanowires are catalytically grown using chemical beam epitaxy, and three-terminal nanoelectronic devices are fabricated from the branched nanowires using electron-beam lithography. We demonstrate that, in difference from conventional macroscopic junctions, the fabricated self-assembled nanowire junction devices exhibit tunable nonlinear electrical characteristics and a signature of ballistic electron transport. As an example of applications, we demonstrate that the self-assembled three-terminal nanowire junctions can be used to implement the functions of frequency mixing, multiplication, and phase-difference detection of input electrical signals at room temperature. Our results suggest a wide range of potential applications of branched semiconductor nanostructures in nanoelectronics.     

Control of GaP and GaAs nanowire morphology through particle and substrate chemical modification

We demonstrate two very different morphologies for GaP and GaAs nanowires grown by Au-assisted MOVPE on Si(111) substrates: rodlike wires and tapered wires with sharp tips. We show that the morphology is related to the stability of the particles at the wire tips during growth, and we propose that the mechanism of this effect is diffusion of Au away from the tip. Diffusion occurs, leading to tapered wires, only if there is a clean Si surface to act as a reservoir for the Au. Furthermore, the presence of indium in the particles, even at background levels from previous growth runs, inhibits the migration of Au. These results demonstrate a dramatic example of the sensitivity of wire morphology to substrate and particle chemistry, which could provide an important tool to tune nanowire morphology through particle alloying or surface treatment.