High pressure and low temperature conducting properties of organic semiconducting metal-anthraquinones

High pressure and low temperature conducting properties of 1,4-diamino anthraquinone, with metals such as cobalt, nickel, copper, and silver, and reported. The complexes formed are oxidatively and thermally stable and are insoluble in common organic solvents. They possess interesting conducting properties. All are semiconductors, showing conductivity in the range 1.98 × 10^?1 to 1.36 × 10^?6 S/cm, depending upon the metal atom present in the complex. Low temperature (300 K to 30 K) and high pressure (up to 6 GPa) conductivity properties of these materials are reported. Copper complexes have been studied in detail, as they show interesting conducting properties. © 1993 John Wiley & Sons, Inc.     

Surface-enhanced Raman scattering of rhodamine 6G on nanowire arrays decorated with gold nanoparticles

We investigate the surface-enhanced Raman scattering (SERS) of rhodamine 6G (R6G) adsorbed on Au nanoparticles attached to InP nanowires. We find that nanowire arrays act as frameworks for effective SERS substrates with a significantly higher Raman signal sensitivity than a planar framework of Au nanoparticles adsorbed two-dimensionally on a flat surface. The SERS signal displays a clear polarization-dependent effect when the nanowires are arranged in a row. We also find that the SERS signal increases with time during continuous laser illumination. The plasmon-enhanced optical forces between Au nanoparticles may either move pairs of nanoparticles closer together or attract adsorbed molecules by moving them to the junctions of Au nanoparticle aggregates. Such effects by plasmon optical forces may cause the observed increase of the SERS signal with continuous laser illumination.     

Axonal guidance on patterned free-standing nanowire surfaces

We demonstrate high-fidelity guidance of axons using rows of nanowires. The axons are prevented from crossing the rows, making it possible to guide and sort a large number of axons as opposed to when chemical patterns are used. Focal adhesion forms at the nanowires establishing a possible site of information transfer between the surface and the cells. Rows of gallium phosphide (GaP) nanowires were epitaxially grown on GaP(111) substrates in patterns defined by electron beam lithography.     

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.     

Direct atomic scale imaging of III-V nanowire surfaces

We have succeeded in direct atomic scale imaging of the exterior surfaces of III-V nanowires by scanning tunneling microscopy (STM). By using atomic hydrogen, we expose the crystalline surfaces of InAs nanowires with regular InP segments in vacuum while retaining the wire morphology. We show images with atomic resolution of the two major types of InAs wurtzite nanowire surface facets and scanning tunneling spectroscopy (STS) data. Ab initio calculations of the lowest energy surface structures and simulated STM images, agree very well with experiments.     

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.     

Growth and optical properties of strained GaAs-GaxIn 1-x P core-shell nanowires

We have synthesized GaAs-Ga(x)In(1-x)P (0.34 < x < 0.69) core-shell nanowires by metal-organic vapor phase epitaxy. The nanowire core was grown Au-catalyzed at a low temperature (450 degrees C) where only little growth takes place on the side facets. The shell was added by growth at a higher temperature (600 degrees C), where the kinetic hindrance of the side facet growth is overcome. Photoluminescence measurements on individual nanowires at 5 K showed that the emission efficiency increased by 2 to 3 orders of magnitude compared to uncapped samples. Strain effects on the band gap of lattice mismatched core-shell nanowires were studied and confirmed by calculations based on deformation potential theory.     

Failure of the vapor-liquid-solid mechanism in Au-assisted MOVPE growth of InAs nanowires

We report the temperature dependence of the Au-assisted growth of InAs nanowires in MOVPE. Extensive studies of the growth of such nanowires have attributed growth to the so-called vapor-liquid-solid (VLS) mechanism, with a liquid Au-In alloy particle. We assert here that growth is instead assisted by a solid particle and does not occur at all when the particle is a liquid. Thus the temperature range of InAs nanowire growth is limited by the melting of the Au-In alloy. Comparison with growth of InAs nanowires in the same system assisted by a layer of SiO(x) is used to support this conclusion.     

Treatment of wood pulp with nitrogen dioxide before oxygen bleaching

Summary Pretreatment of kraft pulp with nitrogen dioxide and oxygen before conventional oxygen bleaching with magnesium sulfate as protector leads to markedly decreased lignin contents after a given duration of the oxygen bleaching. An increased temperature during the pretreatment favours the delignification. The most striking effect of the pretreatment is that it leads to a suppressed rate of depolymerization of the cellulose during the oxygen bleaching.