Optical study of lateral carrier transfer in (In,Ga)As/GaAs quantum-dot chains

We have studied the lateral carrier transfer in a specially designed quantum dot chain structure by means of time-resolved photoluminescence (PL) and polarization PL. The PL decay time increases with temperature, following the T-1/2 law for the typical one-dimensional quantum system. The decay time depends strongly on the emission energy: it decreases as the photon energy increases. Moreover, a strong polarization anisotropy is observed. These results are attributed to the efficient lateral transfer of carriers along the chain direction. (c) 2008 American Institute of Physics.

Studies of electron-transfer and charge-transfer coupling processes at a liquid/liquid interface by double-barrel micropipet technique

Investigation of a heterogeneous electron-transfer (ET) reaction at the water/1,2-dichloroethane interface employing a double-barrel micropipet technique is reported. The chosen system was the reaction between Fe(CN)(6)(3-) in the aqueous phase (W) and ferrocene in 1,2-dichloroethane (DCE). According to the generation and the collection currents as well as collection efficiency, the ET-ion-transfer (IT) coupling process at such an interface and competing reactions with the organic supporting electrolyte in the organic phase can be studied. In addition, this technique has been found to be an efficient method to distinguish and measure the charge-transfer coupling reaction between two ions (IT-IT) processes occurring simultaneously at a liquid/liquid interface. On this basis, the formal Gibbs energies of transfer of some ions across the W/DCE interface, such as NO3-, NO2-, Cl-, COO-, TBA(+), IPAs+, Cs+, Rb+, K+, Na+, and Li+, for which their direct transfers are usually difficult to obtain because of the IT-IT coupling processes, were quantitatively evaluated.

Mechanisms of sodium and potassium ions transfer facilitated by dibenzo-15-crown-5 across the water /1,2-dichloroethane interface using micropipettes

The transfer of sodium and potassium ions facilitated by dibenzo-15-crown-5 (DB15C5) has been studied at the micro-water/1,2-dichloroethane (water/DCE) interface supported at the tip of a micropipette. Cyclic volt-ammetric measurements were performed in two limiting conditions: the bulk concentration of Na+ or K+ in the aqueous phase is much higher than that of DB15C5 in the organic phase (DB15C5 diffusion controlled process) and the reverse condition (metal ion diffusion controlled process). The mechanisms of the facilitated Na+ transfer by DB15C5 are both transfer by interfacial complexation (TIC) with 1 : 1 stoichiometry under these two conditions, and the corresponding association constants were determined at log beta(1) = 8.97 +/- 0.05 or log beta(1) = 8.63 +/- 0.03. However, the transfers of K+ facilitated by DB15C5 show different behavior. In the former case it is a TIC process and its stoichiometry is 1 : 2, whereas in the latter case two peaks during the forward scan were observed, the first of which was confirmed as the formation of K (DB15C5)(2) at the interface by a TIC mechanism, while the second one may be another TIC process with 1 : 1 stoichiometry in the more positive potential. The relevant association constants calculated for the complexed ion, K+(DB15C5)(2), in the organic phase in two cases, logbeta(2), are 13.64 +/- 0.03 and 11.34 +/- 0.24, respectively.

Investigation of ion transfer across the micro-water/nitrobenzene interface facilitated by a fullerene derivative

A functionalized fullerene derivative containing a monoaza-18-crown-6 moiety was investigated by facilitated ion (such as Li+, Na+, K+, NH4+, Mg2+, and Ca2+) transfer across the micro-water/nitrobenzene interface supported at the tip of a micropipet. The current responses were detected by cyclic voltammetry and Osteryoung square wave voltammetry, which demonstrated that the facilitated ion transfer does occur by an interfacial complexation-dissociation process. The diffusion coefficient of this compound in nitrobenzene was approximately (5.90 +/- 0.04) x 10(-7) cm(2) s(-1), which is 1 order of magnitude less than other common ionophores due to the large size of the molecule. The selectivity of this molecule toward the metal ions followed the sequence Na+ > Li+ > K+ > NH4+ > Ca2+ similar to Mg2+. In addition, this compound was also easy to form film at the water/nitrobenzene interface to inhibit the simple ion transfer of tetramethylammonium ion. However, the adsorption of this ionophore has less influence on the facilitated metal ion transfer.

Voltammetric study of the sodium ion transfer across micro-water/1,2-dichloroethane interface facilitated by terminal-vinyl liquid crystal crown ether

Sodium ion transfer across micro-water/1,2-dichloroethane (DCE) interface facilitated by a novel ionophore, terminal-vinyl liquid crystal crown ether (LCCE) was studied by cyclic voltammetry. LCCEs have potential applications because of their physicochemical properties and the utilization of crown ethers as selective ionophoric units in other functionalized compounds are interesting. Host-guest-type behavior for such compounds in the liquid-crystalline state is studied. The experimental results suggest that the transfer of the sodium ion facilitated by LCCE was controlled by diffusion of LCCE from bulk solution of DCE to the interface. The diffusion coefficient of LCCE in DCE was calculated to be equal to (3.62 +/- 0.20) x 10(-6) cm(2)/s. Steady-state voltammograms are due to sodium ion transfer facilitated by the formation of 1: 1 metal (M)-LCCE complex at the interface and the mechanism tends to be transfer by interfacial complexation or dissociation (TIC or TID). The stability constant of the complex formed was determined to be log beta(o) = 5.5 in DCE phase. The influence of parameters such as concentration of sodium ion and concentration of LCCE on the sodium ion transfer was investigated.

Fabrication of agar-gel microelectrodes and their application in the study of ion transfer across the agar-water 1,2-dichloroethane interface

In this paper, we describe a simple procedure to make agar-gel microelectrodes by filling micropipettes. These microelectrodes were used to study K+ transfer across the agar-water \ 1,2-dichloroethane interface facilitated by dibenzo-18-crown-6 (DB18C6), and the transfer of tetraethylammonium (TEA(+)). The results observed were similar to those obtained at micro-liquid \ liquid interfaces. The effect of various amounts of agar in the aqueous phase was optimized and 3% agar was chosen based on the potential window and solidification time. The different shapes of micro-agar-gel electrodes were prepared in a similar way. The fabricated agar-gel microelectrodes obey the classical micro-disk steady-state current equation, which is different from the behavior of a normal micropipette filled with aqueous solution without silanization. (C) 2001 Elsevier Science B.V. All rights reserved.

Studies on the electron transfer centers of amino oxidase immobilized on self-assembly monolayer using electrochemical methods

The direct electron transfer of amino oxidase on electrode surface based on self-assembly technique occurs at 505 mW(vs. Ag/AgCl), indicating that copper atoms are the electron transfer centers and catalytic centers of amino oxidase.

PROMOTER EFFECT OF POLY(4-VINYLPYRIDINE) ON THE DIRECT ELECTRON-TRANSFER BETWEEN CYTOCHROME-C AND GOLD ELECTRODE

The electrochemistry of cytochrome c was studied at the PVP-modified gold electrode. It was found that the promoter effect is related to the amount of PVP at the gold electrode. From our results, it can be seen that the nitrogen element in the polymer is important for accelerating the electron transfer of cytochrome c.

ELECTROCHEMICAL STUDY OF ISOPOLY AND HETEROPOLY ANION TRANSFER ACROSS THE WATER NITROBENZENE INTERFACE .2. VANADIUM-CONTAINING HETEROPOLYTUNGSTATE ANIONS

The electrochemical transfer behaviour of vanadium-containing heteropolytungstate anions [PW12-xVxO40]((3+r)-) (x = 1-4) across the water \nitrobenzene interface has been investigated by cyclic voltammetry and chronopotentiometry with cyclic linear current scanning. The transfer of PW11V1O404-, HPW10V2O404-, H2PW10V2O403-, H3PW9V3O403- and H4PW8V4O(40)(3-) across the water \nitrobenzene interface can be observed within the potential window. The effects were observed of pH in the water phase on the transfer behaviour and the formation of vanadium-containing heteropolytungstate anions in solution. Heteropolytungstate anions become more stable due to their involving the vanadium atom. The degree of protonation and the dissociation constant of the trivalent vanadium-containing heteropolytungstate anion of protonation increase with increasing vanadium content. The transfer processes are diffusion-controlled The standard transfer potential, the standard Gibbs energy and the dissociation constant for vanadium-containing heteropolytungstate anions have been obtained and the transfer mechanisms are discussed.

ELECTROCHEMICAL STUDY OF CHOLINE DERIVATIVES TRANSFER ACROSS THE LIQUID LIQUID INTERFACE

Transfer behaviors across the water/nitrobenzene interface were studied for five choline derivatives by chronopotentiometry with linear current scanning, cyclic voltammetry and differential pulse voltammetry. The irreversible hydrolysis reactions coupled to the phase transfer of ions across the water/nitrobenzene interface were observed. The Gibbs energies of the transfer of choline derivatives show the effects of an additive constitution on hydrophobic property of the medicine.

KINETICS OF ION TRANSFER ACROSS LIQUID LIQUID INTERFACE BY CHRONOPOTENTIOMETRY WITH LINEAR CURRENT SCANNING

The equation of the potential-current curve for the ion transfer across the liquid/liquid interface during the linear current scanning has been derived theoretically. A method to calculate the kinetics parameters for the ion transfer by the way of linear current scanning is presented. The transfer of TPAs~+ ions, which is a typical basic electrolyte ion usually used in liquld/liquid interface electrochemistry, was practically investigated at the water/nitrobenzene interface.

Gene transfer into conchospores of Porphyra haitanensis (Bangiales, Rhodophyta) by glass bead agitation

Genetic transformation by electroporation of protoplasts is a standard procedure for many plants. However, for the genus Porphyra, the method is not effective because of low viability of protoplasts and is a time-consuming and expensive procedure. Based on the life history of Porphyra, a spore-targeted strategy of genetic transformation was developed, that is, using fresh conchospores of Porphyra haitanensis Chang & Zheng transformed by agitation with glass beads. A SV40 promoter-driven lacZ reporter gene was expressed in conchospores 48 h after the agitation. More transformants were obtained by increasing the agitation time from 10 to 25 s. The maximum number of transformants was more than six out of 1 million agitated conchospores. Transfer of a SV40 promoter-driven egfp gene into conchospores resulted in significant green GFP fluorescence. The expression of lacZ and egfp revealed that this strategy of spore-targeted transformation using glass bead agitation is feasible in P. haitanensis and that the SV40 promoter is effective for monitoring expression of foreign genes in this red algal species.

Temperature Dependence of the Tribological Properties of Laser Re-Melted Al-Cu-Fe Quasicrystalline Plasma Sprayed Coatings

The aim of this study was to investigate the effect of temperature on tribological properties of plasma-sprayed Al-Cu-Fe quasicrystal (QC) coating after laser re-melting treatment. The laser treatment resulted in a more uniform, denser and harder microstructure than that of the as-sprayed coatings. Tribological experiments on the coatings were conducted under reciprocating motion at high frequency in the temperature range from 25 to 650 degreesC. Remarkable influence of temperature on the friction behavior of the coating was recorded and analyzed. Microstructural analysis indicated that the wear mechanisms of the re-melted QC coatings changed from abrasive wear at room temperature, to adhesive wear at 400 degreesC and severe adhesive wear at 650 degreesC owing to the material transfer of the counterpart ball. It was also observed that the ratio of the icosahedral (i)-phase to beta-Al-50(Fe,CU)(50) phase in the coating was higher after test at 400 'C than that at 650 'C. The variation of the ratio UP of coating and of the property of the counterpart ball and coating with the temperature are the two main factors influencing the wear mechanisms and value of the friction coefficient.

Mechanical and thermal structure of a cylindrical plume in the earth's mantle

A mantle plume is understood as a hot, narrow, upwelling flow in the earth's mantle and accompanied by an efficient transfer of mass and energy from deep to upper layer of the earth. The cylindrical plume in earth's mantle plays an important role in explaining the origin of the surface hot spots and linear island chains. From the basic hydrodynamical equations, the detailed mechanical and thermal structure of a cylindrical plume of Newtouian fluids with temperature and pressure-dependent viscosity are given in the present paper. For two sets of rheological parameters the radial profiles of upward velocity, temperature and viscosity in the plume and radiuses of the plume at various depths have been calculated.

Transport Phenomena in Ammonothermal Growth of Gallium Nitride

GaN can be used to fabricate blue/green/UV LEDs and high temperature, high power electronic devices. Ideal substrates are needed for high quality III-nitride epitaxy, which is an essential step for the manufacture of LEDs. GaN substrates are ideal to be lattice matched and isomorphic to nitride-based films. Bulk single crystals of GaN can be grown from supercritical fluids using the ammonothermal method, which utilizes ammonia as fluid rather than water as in the hydrothermal process. In this process, a mineralizer such as amide, imide or azide is used to attack a bulk nitride feedstock at temperatures from 200 - 500癈 and pressures from 1 - 4 kbar. Baffle design is essential for successful growth of GaN crystals. Baffle is used to separate the dissolving zone from the growth zone, and to maintain a temperature difference between the two zones. For solubility curve with a positive coefficient with respect to temperature, the growth zone is maintained at a lower temperature than that in the dissolving zone, thus the nutrient becomes supersaturated in the growth zone. The baffle opening is used to control the mixing of nutrients in the two zones, thus the transfer of nutrient from the lower part to the upper part. Ammonothermal systems have been modeled here using fluid dynamics, thermodynamics and heat transfer models. The nutrient is considered as a porous media bed and the flow is simulated using the Darcy-Brinkman-Forchheimer model. The resulting governing equations are solved using the finite volume method. We investigated the effects of baffle opening and position on the transport phenomena of nutrient from dissolving zone to the growth zone. Simulation data have been compared qualitatively with experimental data.