Synthesis and characterization of ZnO nanorods and nanoflowers grown on GaN-based LED epiwafer using a solution deposition method

We report the growth of hexagonal ZnO nanorods and nanoflowers on GaN-based LED epiwafer using a solution deposition method. We also discuss the mechanisms of epitaxial nucleation and of the growth of ZnO nanorods and nanoflowers. A GaN-based LED epiwafer was first deposited on a sapphire substrate by MOCVD with no electrode being fabricated on it. Vertically aligned ZnO nanorods with an average height of similar to 2.4 mu m were then grown on the LED epiwafer, and nanoflowers were synthesized on the nanorods. The growth orientation of the nanorods was perpendicular to the surface, and the synthesized nanoflowers were composed of nanorods. The micro-Raman spectra of the ZnO nanorods and nanoflowers are similar and both exhibit the E-2 (high) mode and the second-order multiple-phonon mode. The photoluminescence spectrum of ZnO nanostructures exhibits ultraviolet emission centred at about 380 nm and a broad and enhanced green emission centred at about 526 nm. The green emission of the ZnO nanostructures combined with the emission of InGaN quantum wells provides a valuable method to improve the colour rendering index (CRI) of LEDs.

Photoluminescence properties of Eu3+-doped ZnS nanocrystals prepared in a water/methanol solution

Monodispersed ZnS and Eu3+-doped ZnS nanocrystals have been prepared through the co-precipitation reaction of inorganic precursors ZnCl2, EuCl3, and Na2S in a water/methanol binary solution. The mean particle sizes are about 3-5 nm. The structures of the as-prepared ZnS nanoparticles are cubic (zinc blende) as demonstrated by an x-ray powder diffraction. Photoluminescence studies showed a stable room temperature emission in the visible spectrum region for all the samples, with a broadening in the emission band and, in particular, a partially overlapped twin peak in the Eu3+-doped ZnS nanocrystals. The experimental results also indicated that Eu3+-doped ZnS nanocrystals, prepared by controlling synthetic conditions, were stable. (C) 2002 American Institute of Physics.

Characterization of CdSe and CdSe/CdS core/shell nanoclusters synthesized in aqueous solution

CdSe nanoclusters overcoated with CdS shell were prepared with macapoacetic acid as stabilizer. The optical properties of CdSe nanoclusters and the influence of CdS shell on the electronic structures of CdSe cores were studied by optical absorption, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. Based on PL and PLE results and the theoretical calculation on fine structure of bandedge exciton, a model of formation of excimer within the small clusters was proposed to explain the large Stokes shift of luminescence from absorption edge observed in PL results. (C) 2000 Elsevier Science B.V. All rights reserved.

Stretchable Graphene: A Close Look at Fundamental Parameters through Biaxial Straining

Tunable biaxial stresses, both tensile and compressive, are applied to a single layer graphene by utilizing piezoelectric actuators. The Gruneisen parameters for the phonons responsible for the D, G, 2D and 2D' peaks are studied. The results show that the D peak is composed of two peaks, unambiguously revealing that the 2D peak frequency (omega(2D)) is not exactly twice that of the D peak (omega(D)). This finding is confirmed by varying the biaxial strain of the graphene, from which we observe that the shift of omega(2D)/2 and omega(D) are different. The employed technique allows a detailed study of the interplay between the graphene geometrical structures and its electronic properties.

The Category-Theoretic Solution of Recursive Domain Equations

Recursive specifications of domains plays a crucial role in denotational semantics as developed by Scott and Strachey and their followers. The purpose of the present paper is to set up a categorical framework in which the known techniques for solving these equations find a natural place. The idea is to follow the well-known analogy between partial orders and categories, generalizing from least fixed-points of continuous functions over cpos to initial ones of continuous functors over $\omega $-categories. To apply these general ideas we introduce Wand's ${\bf O}$-categories where the morphism-sets have a partial order structure and which include almost all the categories occurring in semantics. The idea is to find solutions in a derived category of embeddings and we give order-theoretic conditions which are easy to verify and which imply the needed categorical ones. The main tool is a very general form of the limit-colimit coincidence remarked by Scott. In the concluding section we outline how compatibility considerations are to be included in the framework. A future paper will show how Scott's universal domain method can be included too.

An Integrated Solution for Software Process Improvement

Since 1990s, the software industry in China has been developed very rapidly and the total revenue in recent three years of 2005, 2006 and 2007 were 390.0, 480.0, and 583.4 billions RMB respectively, increased by 28.3% annually on an average basis [1]. By the end of 2007, there were about 18,000 software enterprises in China, and the population of software professionals was 1.48 millions roughly. In the global software market, China, with annual revenue about 82.2 billions USD (8.74% of the total: 940 billions USD), currently ranks on the fourth after USA, EU and Japan. However, the software industry in China is still comparatively weak. Most software enterprises have only tens of employees and millions RBM of revenue. And the software development productivity in China varies highly across the software industry in terms of organization, development type, business area, region, language, project size and team size [2]. Co-operative efforts from the government, the industry and the academy are needed [3]. Continuous software process improvement is an effective way to change the challenging situation of the software industry in China.

Molecular Dynamics Simulation on Characteristics of Decomposition of Methane Hydrate in the Presence of Hydrogen Peroxide Solution

In this work, the characteristics of the decomposition of methane hydrate Structure I (SI) in the presence of hydrogen peroxide solution is investigated using the molecular dynamics simulation. The mechanism of the transformation process from the solid hydrate to the liquid is analyzed with the effect of hydrogen peroxide (HP) solution. In addition, the effect of ethylene glycol (EG) with the same molar concentration with HP on the methane hydrate dissociation is also studied. The results illustrate that both HP and EG promote well the hydrate dissociation. The work provides the important reference value for the experimental investigation into the promotion effect of HP on the hydrate dissociation.

Corrosion inhibition of carbon steel in tetra-n-butylammonium bromide aqueous solution by benzotriazole and Na3PO4

The corrosion inhibition behavior of benzotriazole, Na3PO4 and their mixture on carbon steel in 20 wt.% (0.628 mol l(-1)) tetra-n-butylammonium bromide aerated aqueous solution was investigated by weight-loss test, potentiodynamic polarization measurement, electrochemical impedance spectroscopy and scanning electron microscope/energy dispersive X-ray techniques. The inhibition action of BTA or SP or inhibitors mixture on the corrosion of carbon steel is mainly due to the inhibition of anodic process of corrosion. The results revealed that inhibitors mixtures have shown synergistic effects at lower concentration of inhibitors. At 2 g l(-1) BTA and 2 g l(-1) SP showed optimum enhanced inhibition compared with their individual effects.

Experimental Investigation on Propane Hydrate Dissociation by High Concentration Methanol and Ethylene Glycol Solution Injection

The dissociation behaviors of propane hydrate by high concentration alcohols inhibitors injection were investigated. Methanol (30.0, 60.1, 80.2, and 99.5 wt %) and ethylene glycol (30.0, 60.1, 69.8, 80.2, and 99.5 wt %) solution were injected, respectively, as alcohols inhibitors in 3.5 L transparent reactor. It is shown that the average dissociation rates of propane hydrate injecting methanol and ethylene glycol solution are 0.02059-0.04535 and 0.0302-0.0606 mol.min(-1).L-1, respectively. The average dissociation rates increase with the mass concentration increase of alcohols solution, and it is the biggest when 99.5 wt % ethylene glycol solution was injected. The presence of alcohols accelerates gas hydrate dissociation and reduces the total need of external energy to dissociate the hydrates. Density differences act as driving force, causing the acceleration effects of ethylene glycol on dissociation behaviors of propane hydrate are better than that of methanol with the same injecting flux and mass concentration.

A three-dimensional analytical solution of the microheater temperature before bubble nucleation

A three-dimensional analytical solution of the microheater temperature based on heat diffusion equation is developed and compared with experimental results. Dimensionless parameters are introduced to analyze the temperature rise time and the distribution under steady state. To study the microheater temperatures before bubble nucleation, a set of working fluids and microheaters are considered. It is shown that the dimensionless time xi(-)(0) required for the temperature rise from room to 95% of the steady state temperature is about 75, not dependent on working fluids and microheaters. Heat transfer to the surrounding liquid is mainly caused by conduction, not by convection and radiation mechanisms. The microheater length affects the surface temperature uniformity, while its width influences the steady temperatures significantly, yielding the transition from heterogeneous to homogeneous nucleation mechanism from square microheaters to narrow line microheaters.