Pressure-assisted field-amplified sample injection with reverse migrating micelles for analyzing trace steroids in MEKC

This paper describes a novel method that applies pressure-assisted field-amplified sample injection with reverse migrating micelles (PA-FASI-RMM) for the online concentration of neutral analytes in MEKC with a low-pH BGE. After injection of a plug of water into the separation capillary, negative voltage and positive pressure were simultaneously applied to initialize PA-FASI-RMM injection. The hydrodynamic flow generated by the positive pressure compensated the reverse EOF in the water plug and allowed the water plug to remain in the capillary during FASI with reverse migrating micelles (FASI-RMM) to obtain a much longer injection time than usual, which improved stacking efficiency greatly. Equations describing this injection mode were introduced and were supported by experimental results. For a 450-s online PA-FASI-RMM injection, three orders of magnitude sample enhancement in terms of peak area could be observed for the steroids and an achievement of detection limits was between 1 and 10 ng/mL.

Preliminary study on the photoproduction of hydroxyl radicals in aqueous solution with Aldrich humic acid, algae and Fe(III) under high-pressure mercury lamp irradiation

Under a high-pressure mercury lamp (HPML) and using an exposure time of 4 h, the photoproduction of hydroxyl radicals ((OH)-O-.) could be induced in an aqueous solution containing humic acid (HA). Hydroxyl radicals were determined by high-performance liquid chromatography using benzene as a probe. The results showed that (OH)-O-. photoproduction increased from 1.80 to 2.74 muM by increasing the HA concentration from 10 to 40 mg L-1 at an exposure time of 4 h (pH 6.5). Hydroxyl radical photoproduction in aqueous solutions of HA containing algae was greater than that in the aqueous solutions of HA without algae. The photoproduction of (OH)-O-. in the HA solution with Fe(111) was greater than that of the solution without Fe(III) at pH ranging from 4.0 to 8.0. The photoproduction of (OH)-O-. in HA solution with algae with or without Fe(111) under a 250 W HPML was greater than that under a 125 W HPML. The photoproduction of (OH)-O-. in irradiated samples was influenced by the pH. The results showed that HPML exposure for 4 h in the 4-8 pH range led to the highest (OH)-O-. photoproduction at pH 4.0.

Oxygen pressure dependences of structure and properties of ZnO films deposited on amorphous glass substrates by pulsed laser deposition

ZnO films are prepared on glass substrates by pulsed laser deposition (PLD) at different oxygen pressures, and the effects of oxygen pressure on the structure and optoelectrical properties of as-grown ZnO films are investigated. The results show that the crystallite size and surface roughness of the films increase, but the carrier concentration and optical energy gap E-g decrease with increasing oxygen pressure. Only UV emission is found in the photoluminescence (PL) spectra of all the samples, and its intensity increases with oxygen pressure. Furthermore, there are marked differences in structure and properties between the films grown at low oxygen pressures (0.003 and 0.2 Pa) and the films grown at high oxygen pressures (24 and 150 Pa), which is confirmed by the fact that the crystallite size and UV emission intensity markedly increase, but the carrier concentration markedly decreases as oxygen pressure increases from 0.2 to 24 Pa. These results show that the crystal quality, including the microstructural quality and stoichiometry proportion, of the prepared ZnO films improves as oxygen pressure increases, particularly from 0.2 to 24 Pa.

10 GHz optical short pulse generation using tandem electroabsorption modulators monolithically integrated with distributed feedback laser by ultra-low-pressure selective area growth

In this work, a novel light source of tandem InGaAsP/InGaAsP multiple quantum well electroabsoption modulator( EAM ) monolithically integrated with distributed feedback laser is fabricated by ultra-low-pressure ( 22 x 10(2) Pa ) selective area growth metal-organic chemical vapor diposition technique. Superior device performances have been obtained, such as low threshold current of 19 mA, output light power of 4.5 mW, and over 20 dB extinction ratio at 5 V applied voltage when coupled into a single mode fiber. Over 10 GHz 3dB bandwidth in EAM part is developed with a driving voltage of 2 V. Using this sinusoidal voltage driven integrated device, 10 GHz repetition rate pulse with an actual width of 13.7 ps without any compression elements is obtained due to the gate operation effect of tandem EAMs.

ECR plasma in growth of cubic GaN by low pressure MOCVD

To heteroepitaxally grow the crystalline cubic-GaN (c-GaN) film on the substrates with large lattice mismatch is basically important for fabricating the blue or ultraviolet laser diodes based on cubic group III nitride materials. We have obtained the crystalline c-GaN film and the heteroepitaxial interface between c-Gan and GaAs (001) substrate by the ECR Plasma-Assisted Metal Organic Chemical Vapor Deposition (PA-MOCVD) under low-pressure and low-temperature (similar to600degreesC) on a homemade ECR-plasma Semiconductor Processing Device (ESPD). In order to decrease the growth temperature, the ECR plasma source was adopted as the activated nitrogen source, therefore the working pressure of MOCVD was decreased down to the region less than 1 Pa. To eliminate the damages from energetic ions of current plasma source, a Multi-cusp cavity,coupling ECR Plasma source (MEP) was selected to use in our experiment. To decrease the strain and dislocations induced from the large lattice mismatch between c-GaN and GaAs substrate, the plasma pretreatment procedure i.e., the initial growth technique was investigated The experiment arrangements, the characteristics of plasma and the growth procedure, the characteristics on-GaN film and interface between c-GaN and GaAs(001), and the roles of ECR plasma are described in this contribution.

Hetero-epitaxial growth of ZnO films on silicon by low-pressure metal organic chemical vapor deposition

Quality ZnO films were successfully grown on Si(100) substrate by low-pressure metal organic chemical vapor deposition method in temperature range of 300-500 degrees C using DEZn and N2O as precursor and oxygen source respectively. The crystal structure, optical properties and surface morphology of ZnO films were characterized by X-ray diffraction, optical refection and atomic force microscopy technologies. It was demonstrated that the crystalline structure and surface morphology of ZnO films strongly depend on the growth temperature.

Optimization of VI/II pressure ratio in ZnTe growth on GaAs(001) by molecular beam epitaxy

ZnTe epilayers were grown on GaAs(0 0 1) substrates by molecular beam epitaxy (MBE) at different VI/II beam equivalent pressure (BEP) ratios (R-VI/II) in a wide range of 0.96-11 with constant Zn flux. Based on in situ reflection high-energy electron diffraction (RHEED) observation, two-dimensional (2D) growth mode can be formed by increasing the R-VI/II to 2.8. The Te/Zn pressure ratios lower than 4.0 correspond to Zn-rich growth state, while the ratios over 6.4 correspond to Te-rich one. The Zn sticking coefficient at various VI/II ratios are derived by the growth rate measurement. The ZnTe epilayer grown at a R-VI/II of 6.4 displays the narrowest full-width at half-maximum (FWHM) of double-crystal X-ray rocking curve (DCXRC) for (0 0 4) reflection. Atomic force microscopy (AFM) characterization shows that the grain size enlarges drastically with the R-VI/II. The surface root-mean-square (RMS) roughness decreases firstly, attains a minimum of 1.14 nm at a R-VI/II of 4.0 and then increases at higher ratios. It is suggested that the most suitable R-VI/II be controlled between 4.0 and 6.4 in order to grow high-quality ZnTe epitaxial thin films.

Uniform mems chip temperatures in the nucleate boiling heat transfer region by selecting suitable, medium boiling number range

The not only lower but also uniform MEMS chip temperatures can he reached by selecting suitable boiling number range that ensures the nucleate boiling heat transfer. In this article, boiling heat transfer experiments in 10 silicon triangular microchannels with the hydraulic diameter of 55.4 mu m were performed using acetone as the working fluid, having the inlet liquid temperatures of 24-40 degrees C, mass fluxes of 96-360 kg/m(2)s, heat fluxes of 140-420 kW/m(2), and exit vapor mass qualities of 0.28-0.70. The above data range correspond to the boiling number from 1.574 x 10(-3) to 3.219 x 10(-3) and ensure the perfect nucleate boiling heat transfer region, providing a very uniform chip temperature distribution in both streamline and transverse directions. The boiling heat transfer coefficients determined by the infrared radiator image system were found to he dependent on the heat Axes only, not dependent on the mass Axes and the vapor mass qualities covering the above data range. The high-speed flow visualization shows that the periodic flow patterns take place inside the microchannel in the time scale of milliseconds, consisting of liquid refilling stage, bubble nucleation, growth and coalescence stage, and transient liquid film evaporation stage in a full cycle. The paired or triplet bubble nucleation sites can occur in the microchannel corners anywhere along the flow direction, accounting for the nucleate boiling heat transfer mode. The periodic boiling process is similar to a series of bubble nucleation, growth, and departure followed by the liquid refilling in a single cavity for the pool boiling situation. The chip temperature difference across the whole two-phase area is found to he small in a couple of degrees, providing a better thermal management scheme for the high heat flux electronic components. Chen's [11 widely accepted correlation for macrochannels and Bao et al.'s [21 correlation obtained in a copper capillary tube with the inside diameter of 1.95 mm using R11 and HCFC123 as working fluids can predict the present experimental data with accepted accuracy. Other correlations fail to predict the correct heat transfer coefficient trends. New heat transfer correlations are also recommended.

A DUAL ION-BEAM EPITAXY SYSTEM

The design and characteristics of a dual ion beam epitaxy system (DIBE) are discussed. This system is composed of two beam lines, each providing a mass-separated ion beam converging finally with the other into the target chamber. The ions are decelerated and deposited on a substrate which can be heated to a temperature of 800-degrees-C. Currents of a few hundred microamperes are available for both beams and the deposit energies are in the range from tens to 1000 eV. The pressure of the target chamber during processing is about 7 x 10(-6) Pa. Preliminary experiments have proved that compound semiconductor materials such as GaN can be synthesized using the DIBE system.

CONSTRUCTION AND APPLICATIONS OF A DUAL MASS-SELECTED LOW-ENERGY ION-BEAM SYSTEM

A direct ion beam deposition system designed for heteroepitaxy at a low substrate temperature and for the growth of metastable compounds has been constructed and tested. The system consists of two mass-resolved low-energy ion beams which merge at the target with an incident energy range 50-25 000 eV. Each ion beam uses a Freeman ion source for ion production and a magnetic sector for mass filtering. While a magnetic quadrupole lens is used in one beam for ion optics, an electrostatic quadrupole lens focuses the other beam. Both focusing approaches provide a current density more than 100-mu-A/cm2, although the magnetic quadrupole gives a better performance for ion energies below 200 eV. The typical current of each beam reaches more than 0.3 mA at 100 eV, with a ribbon beam of about 0.3-0.5 x 2 cm2. The target is housed in an ultrahigh vacuum chamber with a base pressure of 1 x 10(-7) Pa and a typical pressure of 5 x 10(-6) Pa when a noncondensable beam like argon is brought into the chamber. During deposition, the target can be heated to 800-degrees-C and scanned mechanically with an electronic scanning control unit. The dual beam system has been used to grow GaN using a Ga+ and a N+ beam, and to study the oxygen and hydrogen ion beam bombardment effects during carbon ion beam deposition. The results showed that the simultaneous arrival of two beams at the target is particularly useful in compound formation and in elucidation of growth mechanisms.

A fixed arc length direct current plasma torch for reduced pressure deposition of thin films

Because of its high energy density direct current(dc)thermal plasmas are widely accepted as a processing medium which facilitates high processing rates high fluxes of radical species the potential for smaller jnstallations a wide choice of reactants and high quench rates[1].A broad range of industrial processing methods have been developed based on dc plasma technology. However,nonstationary features limited new applications of dc plasma in advanced processing, where reliability£¬reproducibility and precise controllability are required£. These challenges call for better understanding of the arc and jet behavior over a wide range of generating parameters and a comprehensive control of every aspect of lhe plasma processing.

Temperature and pressure dependence of phase separation of trans-decahydronaphthalene/polystyrene solution

The cloud-point temperatures (T-c1's) of ti-ans-decahydronaphthalene (TD)/polystyrene (PS, M-w = 270 kg/mol) solutions were determined by fight scattering measurements over a range of temperatures (1-16 degreesC), pressures (100-900 bar), and compositions (4.2-21.6 vol% polymer). The system phase separates upon cooling and the T-c1 was found to increase with the rising pressure for the constant composition. In the absence of special effects this finding indicates positive excess volumes. The special attention was paid to the demixing temperatures as a function of the pressure for the different polymer solutions and the plots in the T-volume fraction plane and P-volume fraction plane. The cloud-point curves of polymer solutions under changing pressures were observed for different compositions, demonstrates that the TD/PS system exhibits UCST (phase separation upon cooling) behavior. With this data the phase diagrams under pressure were calculated applying the Sanchez-Lacombe (SL) lattice fluid theory. Furthermore, the cause of phase separation, i.e., the influence of Flory-Huggins (FH) interaction parameter under pressure was investigated.

Pressure effects on the thermodynamics of trans-decahydronaphthalene/polystyrene polymer solutions: Application of the Sanchez-Lacombe lattice fluid theory

The cloud-point temperatures (T-cl's) of trans-decahydronaphthalene(TD)/polystyrene (PS, (M) over bar (w) = 270 000) solutions were determined by light scattering measurements over a range of temperatures (1-16degreesC), pressures (100-900 bar), and compositions (4.2-21.6 vol.-% polymer). The system phase separates upon cooling and T-cl was found to increase with rising pressure for constant composition. In the absence of special effects, this finding indicates positive excess volume for the mixing. Special attention was paid to the demixing temperatures as a function of pressure for different polymer solutions and the plots in the T-phi plane (where phi signifies volume fractions). The cloud-point curves of polymer solutions under different pressures were observed for different compositions, which demonstrated that pressure has a greater effect on the TD/PS solutions when far from the critical point as opposed to near the critical point. The Sanchez-Lacombe lattice fluid theory (SLLFT) was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of mixing, and the volume changes of mixing. The calculated results show that modified PS scaling parameters can describe the thermodynamics of the TD/PS system well. Moreover the SLLFT describes the experimental results well.

Thermodynamics of phase behavior in PEO/P(EO-b-DMS) homopolymer and block co-oligomer mixtures under pressure

The cloud-point temperatures (T-cl's) of poly(ethylene oxide) (PEO) and poly(ethylene oxide)-block-polydimethylsiloxane (P(EO-b-DMS)) homopolymer and block-oligomer mixtures were determined by turbidity measurements over a range of temperatures (105 to 130degrees), pressures (1 to 800 bar), and compositions (10-40 wt.-% PEO). The system phase separates upon cooling and T-cl was found to decrease with an increase in pressure for a constant composition. In the absence of special effects, this finding indicates negative excess volumes. Special attention was paid to the demixing temperatures as a function of the pressure for the different polymer mixtures and the plots in the T-phi plane (where phi signifies volume fractions). The cloud-point curves of the polymer mixture under pressures were observed for different compositions. The Sanchez-Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalphy of mixing, and the volume changes of mixing. The calculated results show that modified P(EO-b-DMS) scaling parameters with the new combining rules can describe the thermodynamics of the PEO/P(EO-b-DMS) system well with the SL theory.