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We report on the growth, structural, and optical properties of GaAs/GaAsPBi coreâ€"shell nanowires (NWs) synthesized by molecular beam epitaxy (MBE). The structure presents advantageous optical properties, in particular, for near- and mid-infrared optical applications. Scanning electron microscopy shows that although the stems of GaAs/GaAsP and GaAs/GaAsBi coreâ€"shell NWs preserve the hexagonal prism shape, the GaAs/GaAsPBi coreâ€"shell NWs develop a quasi-three-fold orientational symmetry affected by the hexagonal prismatic core. Detailed structural analyses of a GaAs/GaAsPBi coreâ€"shell stem show that it crystallized with zincblende structure with a nominal shell composition of GaAs0.617P0.362Bi0.021. Photoluminescence of GaAs/GaAsPBi coreâ€"shell NWs shows the luminescent peak at 1.02 eV with high internal quantum efficiency at room temperature (IQERT ∼ 6%) superior to those of MBE-grown GaAs core NWs and GaAsPBi multiple quantum wells earlier reported. Energy-dispersive x-ray spectroscopy performed on the GaAs/GaAsPBi coreâ€"shell NWs yields an estimated bandgap different from the optically measured value. We attribute this discrepancy to the NW compositional fluctuations that also may explain the high IQERT. [ABSTRACT FROM AUTHOR]

Quaternary alloy GaAsPBi is a novel III–V compound with attractive optical properties and can in principle be grown lattice-matched to GaAs. However, the practical realization of the alloy by metal-organic vapor phase epitaxy and molecular beam epitaxy (MBE)—the two main growth technologies—is fraught with difficulties. Here, using standard solid-source MBE, GaAsPBi films, and GaAsPBi/GaAs multiple quantum wells (MQW) have been grown lattice-matched to (001) GaAs. The structural integrity of the films/MQW is investigated and confirmed by various in- and ex-situ diffraction and spectroscopic techniques. All GaAsPBi structures—films and MQWs—are luminescent at room temperature. Photoluminescence shows that all the samples exhibit an S-shape temperature dependency, indicating strong localizations. Of most significance to practical applications is the observation that the emission from GaAsPBi MQWs is more efficient than their non-quantum well (QW) counterparts (up to 30× at room temperature). These results confirm the long-known benefits of carrier confinements by QWs, demonstrated here for the first time in the GaAsPBi-based system despite the challenge of the crystal growths. [ABSTRACT FROM AUTHOR]

Lead-based relaxor ferroelectric materials surged a favorable interest owing to their remarkable dielectric properties. Ferroelectric materials are sensitive to temperature changes. Dielectric properties are known to decrease when the temperature is higher than the temperature of the maximum dielectric constant. The objective of this research is to study the phase transition which was investigated by XRD, microstructure by SEM, the chemical bonds of samples identified by FTIR and the temperature dependent dielectric constants and loss tangents investigated as functions of temperature and frequency of (1 - x)Pb(Zr0.52Ti0.48)O3-xPb(Fe1/2 Nb1/2)O3 when x = 0, 10, and 30 mol%. A phase transition from morphotropic phase boundary (MPB) to tetragonal phase was observed. Grain size increased with increasing PFN was in the range of 0.99 to 3.61 µm. The shoulder of 0.7PZT52/48-0.3 PFN tend to disappear, the maximum absorbance around 419 cm-1 in FTIR according to the harmonic oscillator. The dielectric dispersion increased slightly as well as the dielectric maximum temperature decreased while dielectric constant at room temperature increased when added-PFN into PZT52/48 indicating ferroelectric nature. Meanwhile, the d33 and kp initially increase for x = 0 to 0.1 then decrease with the increase of the PFN contents for x = 0.3 due to amount of exceeded Fe3+/Nb5+ ion. [ABSTRACT FROM AUTHOR]

Relaxor and ferroelectric materials are outstanding for electronic application, indicating kind of ferroelectric material is still ambiguously due to different behavior of stoichiometric ratio of precursors. The samples of 0.94Pb(Fe1/2Nb1/2)O3-0.06PbTiO3 (PFNT94/6) and 0.9Pb(Fe1/2Nb1/2)O3-0.1PbTiO3 (PFNT90/10) were mixed with ZnO at 0, 1, 2, and 3 wt.%, and were synthesized using mixed oxide. Phase transition and microstructure were analyzed by using X-ray diffractometer (XRD) and SEM technique, respectively. The results showed that PFNT94/6-xZnO and PFNT90/10-xZnO shifted to tetragonal phase and suppressed pyrochlore phase when increasing ZnO content. Grain size decreased with increasing ZnO contents in range of 0.89-2.18 µm of PFNT94/6 due to coarsening processes dominate, the production of a highly porous is easily be found and decreased the average grain size, conversely, grain size increased with increasing ZnO contents in range of 3.15-11.52 µm of PFNT90/10. The PFNT94/6 exhibits broaden peak of dielectric constant, meanwhile, the dielectric constant maximum temperature at 144°C of PFNT90/10. The dispersion of dielectric constant decreases with increasing ZnO contents. The relaxor ferroelectric of PFNT90/10 ceramic shifted to normal ferroelectric with increasing ZnO contents. Ferroelectric properties were investigated on polarization electric field, polarization of PFNT94/6 exhibited relaxor ferroelectric at low field, PFNT90/10 showed normal ferroelectric as well as endurable breakdown. The relaxor ferroelectric material can be modified to ferroelectric material by adding ZnO. [ABSTRACT FROM AUTHOR]

We synthesized polycrystalline sodium cobalt oxide (NaCoO2) by using solid state reaction (SSR) method in a magnetic field. The powder of Na2CO3and Co3O4were mixed by ball milling and compacted in a magnetic field. The characterization of microstructure of powder size and crystal structure were analyzed through XRD. Thermoelectric properties and the lattice parameter of NaCoO2showed little change in magnetic field. The lattice parameters of NaCoO2 are a = 2.8443 Å, b = 2.8443 Å, and c = 10.8091 Å in the hexagonal structure (a = b ≠ c). [ABSTRACT FROM AUTHOR]

Abstract: The research proposed the design and implementation USB data acquisition system (DAQ) for measurement Seebeck coefficient. This system consists of microcontroller PIC18F4550 and high- resolution analog to digital converter (A/D) MCP3553, voltage reference LM4140 and the “Microchip USB Device Firmware Framework”. The PC software develops in Delphi visual programming. The system was used to measure bulk Ca3Co4O9 thermoelectric material and the performance was satisfied. [Copyright &y& Elsevier]

The article investigates the measurable parameters of thermoelectric power and cooling modules including hot and cold side temperatures, voltage, and current. Experiments were undertaken between the hot and cold sides of thermoelectric module and load resistance with various temperature differences. It states that information on the power output with varying temperature is essential when designing a thermoelectric power generation system.

Graft copolymers containing poly(phenylene xylyene) (PPX) backbone and polystyrene fullerene (PSFu) grafting chains (PPX-g-PSFu) were prepared by using a purposed synthetic route comprising a combination of reaction mechanisms namely the modified Wessling route, an iniferter polymerization, and an atom transfer radical addition (ATRA). The monomer was first prepared by reacting dichloroxylene with tetrahydrothiophene. After that the monomer was polymerized in a sodium hydroxide solution to provide a polymer precursor. Subsequently, the polymer precursor was modified by reacting it with a dithiocarbamate (DTC) compound. The macroiniferter was obtained and then copolymerized with styrene and chloromethylstyrene via an iniferter polymerization. Finally, the graft copolymer was reacted with fullerene through an ATRA technique to attach the C60 groups onto the graft copolymer molecule. The products obtained from each of the steps were characterized by using various techniques including Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, gel permeation chromatography, differential scanning calorimetry, UV-visible spectroscopy, and thermal gravimetric analysis. The aforementioned results suggest that the graft copolymers were prepared. The grafting yield and grafting efficiency were found to increase with the monomers concentration and the amount of DTC used. Some homopolymer contaminants also occurred but those could be minimized and subsequently removed by extraction with selective solvents. These graft copolymer products might be used for the development of a bulk heterojunction polymer solar cell. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [ABSTRACT FROM AUTHOR]

Fluorine-doped tin dioxide (FTO) films were deposited on silicon wafers by inverted pyrosol technique using solutions with different doping concentration (F/Sn=0.00, 0.12, 0.75 and 2.50). The physical and electrical properties of the deposited films were analyzed by SEM, XRF, resistivity measurement by four-point-probe method and Hall coefficient measurement by van der Pauw method. The electrical properties showed that the FTO film deposited using the solution with F/Sn=0.75 gave a lowest resistivity of 3.2·10–4 ohm cm. The FTO films were analyzed by temperature programmed desorption (TPD). Evolved gases from the heated specimens were detected using a quadruple mass analyzer for mass fragments m/z, 1(H+), 2(H2 +), 12(C+), 14(N+), 15(CH3 +), 16(O+), 17(OH+ or NH3 +), 18(H2O+ or NH4 +), 19(F+), 20(HF+), 28(CO+ or N2 +), 32(O2 +), 37(NH4F+), 44(CO2 +), 120(Sn+), 136(SnO+) and 152(SnO2 +). The majority of evolved gases from all FTO films were water vapor, carbon monoxide and carbon dioxide. Fluorine ( m/z 19) was detected only in doped films and its intensity was very strong for highly-doped films at temperature above 400°C. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) is a useful material for gas-sensing applications because of its high surface to volume ratio structure. In this work, multi-wall CNTs are incorporated into tin oxide thin film by means of powder mixing and electron beam evaporation and the enhancement of gas-sensing properties is presented. The CNTs were combined with SnO2powder with varying concentration in the range of 0.25–5% by weight and electron beam evaporated onto glass substrates. From AFM and TEM characterization, CNT inclusion in SnO2thin film results in the production of circular cone protrusions of CNT clusters or single tube coated with SnO2layer. Experimental results indicate that the sensitivity to ethanol of SnO2thin film increases by the factors of 3 to 7, and the response time and recovery time were reduced by the factors of 2 or more with CNT inclusion. However, if the CNT concentration is too high, the sensitivity is decreased. Moreover, the CNT doped film can operate with good sensitivity and stability at a relatively low temperature of 250–300∘C. The improved gas-sensing properties should be attributed to the increasing of surface adsorption area of metal oxide produced by CNT protrusion. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The Au NPs were successfully decorated on TiO 2 NRs surface by the DP method. • The hybrid nanostructure would allow high SERS sensitivity and recyclability. • The hybrid nanostructure SERS substrates were promising detection of TNT. Abstract High-performance recyclable SERS substrates with well-ordered hybrid nanostructure gold nanoparticles (Au NPs) decorated on titanium dioxide nanorods (TiO 2 NRs) were successfully prepared by combining two methods. The TiO 2 NRs were fabricated by electron-beam evaporation with glancing-angle deposition (GLAD) technique, then the Au NPs were decorated onto the TiO 2 NRs surfaces by deposition-precipitation (DP). The physical structures of the obtained hybrid nanostructures were characterized by field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscope (TEM), and grazing incident angle X-ray diffraction (GIXRD). The results indicated that size and density of Au NPs on TiO 2 NRs were controlled by HAuCl 4 concentration for optimization of the SERS performance whose the detection of MB molecules was achieved at an enhancement factor of 6.5 × 107 with 9.76%-RSD at 1626 cm−1. More significantly, the optimized hybrid nanostructure SERS substrates exhibit excellent recyclability. These hybrid nanostructure SERS substrates were therefore promising towards detection of TNT for homeland security applications, as well as an on-site SERS platform. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effects of magnesium oxide-coated titanium dioxide (MgO–TiO2) thin film on the performance of ITO/TiO2/MEH–PPV/Au solar cells were investigated. The ITO/MgO–TiO2/MEH–PPV/Au solar cells were fabricated using nano-porous MgO–TiO2 layer infiltrated with poly (2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene) (MEH–PPV) to form an active layer on the solar cells. The TiO2 films were prepared by a sol-gel dip-coating technique onto indium tin oxide (ITO) coated glass substrates. To vary the MgO loading content, the TiO2 films were dip-coated in 1 × 10−1, 1 × 10−2, 1 × 10−3, 1 × 10−4 and 1 × 10−5 M solutions of magnesium acetate. After sintering at 450 °C, thin insulating MgO layers were formed on the nano-porous TiO2 films. The ITO coated glass and gold (Au) were used as cathode and anode, respectively. The results revealed that the MgO–TiO2 modification increased open circuit voltage, fill factor, and power conversion efficiency of the ITO/TiO2/MEH–PPV/Au solar cells. These improvements resulted from negative shifts of flat-band potentials of the nano-porous TiO2 films once coated with a thin insulating MgO layer. Moreover, the MgO coating was found to improve the life time of the solar cells. [Copyright &y& Elsevier]

Abstract: Thin TiO2 films have been deposited on glass substrates by a radio-frequency (rf) magnetron sputtering technique. The films were coated under argon atmosphere at three different rf-powers: 80, 100 and 120W, and three working pressures: 1.0×10−2, 2.5×10−3 and 1.0×10−3 mbar. Film structures were analyzed with XRD. At 100 and 120W, films coated under low working pressure have developed the rutile phase with the preferred (110) orientation. However, at 80W, the films have been observed only in an amorphous phase for all working pressures. This effect could be understood as sputtered TiO2 molecules were more energetic at high rf-powers and encountered fewer collisions at low pressure before deposited onto the substrates. The films have also been annealed at 773 or 873K. The post-deposition annealing has significantly improved crystallization of the TiO2 films. In this contribution, results on optical and wetting properties of these films are also reported. [Copyright &y& Elsevier]

Abstract: TiO2 films deposited by various coating techniques were investigated for self-cleaning applications. The optical coating layers of TiO2 films prepared from a sol–gel precursor were deposited on glass substrates using spin coating, dip coating and screen printing techniques. Effects of film deposition techniques on crystal structure, microstructure, thickness, photocatalytic activity, hydrophilicity and optical properties of the films were investigated using XRD, AFM, SEM, surface profilometer, UV–vis spectrophotometer and contact angle measurement. Dip coating the TiO2 optical film two and three times resulted in superhydrophilic surfaces. Increasing number of dipping times was found to increase the photocatalytic activity. [Copyright &y& Elsevier]