InN nanoflowers grown by metal organic chemical vapor deposition

Hexangular indium nitride nanoflower pattern is observed from scanning electron microscopy and atomic force microscopy. The sample is grown on c-plane (0001) sapphire by metal organic chemical vapor deposition with intentional introduction of hydrogen gas. With the aid of hydrogen, a stable existence of metallic indium is achieved. This will induce the growth of InN nanoflowers via self-catalysis vapor-liquid-solid (VLS) process. It is found that the VLS process is modulated by the interface kinetics and thermodynamics among the sapphire substrate, indium, and InN, which leads to the special morphology of the authors' InN nanoflower pattern. (c) 2006 American Institute of Physics.

A surface kinetics model for the growth of Si1-xGex by UHV/CVD using SiH4/CeH4

The surface reaction mechanism of Si1-xGex/Si growth using SiH4 and GeH4 in UHV/CVD system was studied. The saturated adsorption and desorption of SiH4 from Si(1 0 0) surface was investigated with the help of TPD and RHEED, and it was found that all the 4 hydrogen atoms of one SiH4 molecule were adsorbed to the Si surface, which meant that the dissociated adsorption ratio was proportional to 4 power of surface vacancies. The analysis of the reaction of GeH4 was also done. A new surface reaction kinetic model on Si1-xGex/Si epitaxial growth under UHV conditions by SiH4/GeH4 was proposed based on these studies. The predictions of the model were verified by the experimental results. (C) 2000 Elsevier Science B.V. All rights reserved.

The dependence of GexSi1-x epitaxial growth on GeH4 flow using chemical vapour deposition

GexSi1-x epilayers were grown at 700-900 degrees C by atmospheric pressure chemical vapour deposition. GexSi1-x, Si and Ge growth rates as functions of GeH4 flow are considered separately to investigate how the growth of the epilayers is enhanced. Arrhenius plots of Si and Ge incorporation in the GexSi1-x growth show the activation energies associated with the growth rates are about 1.2 eV for silicon and 0.4 eV for germanium, indicating that Si growth is limited by surface kinetics and Ge growth is limited by mass transport. A model based on this idea is proposed and used to simulate the growth of GexSi1-x. The calculation and experiment are in good agreement. Growth rate and film composition increase monotonically with growth pressure; both observations are explained by the model.

Study on the kinetics of hydrate formation in a bubble column

Gas hydrate formation experiments were performed using methane in the presence of tetrahydrofuran (THF) in aqueous solution in a transparent bubble column in which a single pipe or a sintered plate was used to produce bubbles. The mole fraction of THF in aqueous solution was fixed at 6%. The hydrate formation kinetic behaviors on the surface of the rising bubble, the mechanical stability of hydrate shell formed on the surface of the bubble, the interactions among the bubbles with hydrate shell were observed and investigated morphologically. The rise velocities of individual bubbles with hydrate shells of different thickness and the consumption rates of methane gas were measured. A kinetic model was developed to correlate the experimentally measured gas consumption rate data. It was found that the hydrate formation rate on the surface of the moving bubble was high, but the formed hydrate shell was not very easy to be broken up. The bubbles with hydrate shells tended to agglomerate rather than merge into bigger bubble. This kind of characteristic of hydrate shell hindered the further formation of hydrate and led to the lower consumption rate of methane. The consumption rate of methane was found to increase with the decrease of temperature or increase of pressure. The increase of gas flux led to a linear increase in consumption rate of methane. It was demonstrated that the developed kinetic model could be used to correlate the consumption rate satisfyingly.

Effects of pH on the Interactions and Conformation of Bovine Serum Albumin: Comparison between Chemical Force Microscopy and Small-Angle Neutron Scattering

The conformation of bovine serum albumin (BSA), as well as its interactions with negatively charged mica surfaces in saline solutions of different pH values, have been studied by small-angle neutron scattering (SANS) and chemical force microscopy (CFM), respectively. A new approach to extract the contribution of elementary interactions from the statistically averaged force-extension curves through self-consistent fitting was proposed and used to understand the effects of pH on the interactions and conformation of BSA in saline solutions. When pH increases, the SANS results reveal that the sizes of BSA molecules increase slightly, while the statistical analysis of the CFM results shows that the averaged pull-off force for the elongation monotonously decreases. The decrease of pull-off force with the increase of pH results from the decrease in the strength of hydrogen bonding and the number of interaction pairs, as well as the slight increase of the strength of van der Waals interaction. When pH approaches the isoelectric point (pI) of BSA, results from both SANS and CFM suggest a loss of long-range interactions in BSA molecules. Our results also suggest that the force-extension curve is mainly contributed by the van der Waals interaction. The combination of SANS and CFM provides new insight to understand the interactions and conformation of BSA molecules

On the chemical synthesis and drug delivery response of folate receptor-activated, polyethylene glycol-functionalized magnetite nanoparticles

We describe here the chemical synthesis and in vitro drug delivery response of polyethylene glycol (PEG)-functionalized magnetite (Fe3O4) nanoparticles, which were activated with a stable ligand, folic acid, and conjugated with an anticancer drug, doxorubicin. The functionalization and conjugation steps in the chemical synthesis were confirmed using Fourier transform infrared spectroscopy. The drug-release behavior of PEG-functionalized and folic acid-doxorubicin-conjugated magnetic nanoparticles was characterized by two stages involving an initial rapid release, followed by a controlled release. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Mass transfer kinetics of neodymium(III) extraction by calix[4]arene carboxylic acid using a constant interfacial area cell with laminar flow

BACKGROUND: Thermodynamics and kinetics data are both important to explain the extraction property. In order to develop a novel separation technology superior to current extraction systems, many promising extractants have been developed including calixarene carboxylic acids. The extraction thermodynamics behavior of calix[4]arene carboxylic acids has been reported extensively. In this study, the mass transfer kinetics of neodymium(III) and the interfacial behavior of calix[4]arene carboxylic acid were investigated.

Extraction kinetics of cerium(IV) from sulfuric acid medium by the primary amine N1923 using a constant interfacial area cell with laminar flow

BACKGROUND: Thermodynamic studies on Ce(IV) extraction with primary amine N1923 demonstrate that primary amine N1923 is an excellent extractant for separation of Ce(IV) from Re(III). In order to clarify the mechanism of extraction and to optimize the parameters in practical extraction systems used in the rare earth industry, the extraction kinetics was investigated using a constant interfacial area cell with laminar flow in the present work.RESULTS: The data indicate that the rate constant (k(ao).) becomes constant when stirring speed exceeds 250 rpm. The apparent forward extraction rate is calculated to be 10(-1.70). The activation energy (E.) was calculated to be 20.5 kJ/mol from the slope of log kao against 1000/T. The minimum bulk concentration of the extractant necessary to saturate the interface (C-min) is lower than 10(-5) mol L-1.CONCLUSION: Studies of interfacial tension and the effects of stirring rate and specific interfacial area on the extraction rate show that the extraction rate is kinetically controlled, and a mass transfer model has been proposed. The rate equation has been obtained as: -d[Ce(IV)]/dt = 10(-1.70)[Ce(IV)] [(RNH3)(2)SO4](1.376). The rate-controlling step has been evaluated from analysis of the experimental results.

Chain propagation kinetics on melt grafting reaction

Graft copolymerization in the molten state is of fundamental importance as a probe of chemical modification and reactive compatibilization. However, few grafting kinetic studies on reactive extrusion have been carried out because of the inherent difficulties, as expected. In this work, we have studied chain propagation kinetics on melt grafting using pre-irradiated linear low density polyethylene (LLDPE) and three monomers, acrylic acid (AA), methacrylic acid (MAA), and methyl methacrylate (MMA), as the model system. We measured the apparent chain propagation rate coefficients of grafting (k(p,g)) and homopolymerization (k(p,h)) at an initial stage for the melt grafting by FT-IR spectroscopy and electron spin resonance spectroscopy. It was observed that the convective mixing affected the rate coefficients. The magnitude of k(p,h) and k(p,g) were in the same order, but k(p,h) was slightly larger than k(p,g) The k(p,g) of the three grafting systems increased in the order: LLDPE/MMA < LLDPE/MAA < LLDPE/AA. These results are explained in terms of phase separation, solubility, and inherent reactivity of the monomer.

Extraction kinetics of Sc(III), Y(III), La(III) and Gd(III) from chloride medium by Cyanex 302 in heptane using the constant interfacial cell with laminar flow

The extraction kinetics of Sc, Y, La and Gd(III) from the hydrochloric acid medium using Cyanex 302 (hereafter HL) in heptane solution have been measured by the constant interfacial cell with laminar flow. Reaction regions are explored at liquid-liquid interface. Extraction regimes are deduced to be diffusion-controlled for Sc(Ill) and mixed controlled for Y, La and Gd(Ill). Extraction mechanisms are discussed according to the dimeric model of Cyanex 302 in non-polar solution. From the temperature dependence of rate measurement, the values of E-a, Delta H-+/-, Delta S-+/- and Delta G(300)(+/-) are calculated and it is found that the absolute values of these parameters keep crescent trend for Sc, Y, La and Gd(III). At the same time, it is found that it can easily achieve the mutual separation among the Sc, Y and La(III) with kinetics extraction methods.

Isothermal crystallization kinetics of iPP during self-nucleation process

In this paper, the isothermal crystallization kinetics of polypropylene (iPP) during self-nucleation was studied by means of differential scanning calorimetry(DSC). The iPP was melted at 438 K and then isothermally crystallized in the range of temperature between 421 and 425 K. The mechanism of nucleation and growth of iPP was discussed. The Avrami equation was applied to analyzing the process of isothermal crystallization of iPP from the melt. The average value of Avrami exponent is n=3.01, suggesting that the primary crystallization maybe corresponds to three-dimensional spherulitic growth. The K-g value obtained from Lauritzen-Hoffman equation is 1.128 X 10(5) K-2, which suggests that crystallization species should be regime I. The decrease of crystallization active energy and chain folding work indicates that the self-nucleation can greatly promote the overall crystallization of iPP.

Design of silicone rubber according to requirements based on the multi-objective optimization of chemical reactions

The explicit expression between composition and mechanical properties of silicone rubber was derived from the physics of polymer elasticity, the implicit expression among material composition, reaction conditions and reaction efficiency was obtained from chemical thermodynamics and kinetics, and then an implicit multi-objective optimization model was constructed. Genetic algorithm was applied to optimize material composition and reaction conditions, and the finite element method of cross-linking reaction processes was used to solve multi-objective functions, on the basis of which a new optimization methodology of crosslinking reaction processes was established. Using this methodology, rubber materials can be designed according to pre-specified requirements.

Kinetics of extraction and stripping of y(III) by Cyanex 272 as an acidic extractant using a constant interfacial cell with laminar flow

The extraction and stripping kinetics of yttrium(III) with bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272, HA) dissolved in heptane as an acid extractant have been investigated by constant interfacial cell with laminar flow. The experimental hydrodynamic conditions have been chosen so that the contribution of diffusion to the measured rate of reaction is minimized. The plot of interfacial area on the rate has shown a linear relationship, which makes the interface the most probable local for the chemical reactions. At the same time, the extraction thermodynamic and kinetic methods are compared to determine the equilibrium extraction constant. A rate equation and the rate-determining step of the extraction and stripping of yttrium(III) have also been obtained, respectively.

Kinetics of atomic force microscope-based scanned probe oxidation on an octadecylated silicon(111) surface

Atomic force microscope (AFM)-based scanned probe oxidation (SPO) nanolithography has been carried out on an octadecyl-terminated Si(111) surface to create dot-array patterns under ambient conditions in contact mode. The kinetics investigations indicate that this SPO process involves three stages. Within the steadily growing stage, the height of oxide dots increases logarithmically with pulse duration and linearly with pulse voltage. The lateral size of oxide dots tends to vary in a similar way. Our experiments show that a direct-log kinetic model is more applicable than a power-of-time law model for the SPO process on an alkylated silicon in demonstrating the dependence of oxide thickness on voltage exposure time within a relatively wide range. In contrast with the SPO on the octodecysilated SiO2/silicon surface, this process can be realized by a lower voltage with a shorter exposure time, which will be of great benefit to the fabrication of integrated nanometer-sized electronic devices on silicon-based substrates. This study demonstrates that the alkylated silicon is a new promising substrate material for silicon-based nanolithography.