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TiO{sub 2}/PANI And MWNT/PANI Composites Thin Films For Hydrogen Gas Sensing
The MWNT and TiO{sub 2} doped Polyaniline (PANI) composites were synthesized by In-situ chemical oxidative polymerization method at low temperature. The MWNT/PANI and TiO{sub 2}/PANI composite thin films were prepared using spin coating method onto finger type interdigited electrodes to develop the chemiresistor type gas sensor for hydrogen gas sensing application. It was observed that the MWNT and TiO{sub 2} doped PANI composite thin films show a higher response in comparision to neat PANI. The structural and morphological properties of these composite films were characterized by X-Ray differaction (XRD) pattern and sccaning electrone microscopy (SEM) respectively.
The electrochemical performance of ordered mesoporous carbon/nickel compounds composite material for supercapacitor
A series of high performance ordered mesoporous carbon/nickel compounds composites have been synthesized by a combination of incipient wetness impregnation and hydrothermal method for the first time. X-ray diffraction (XRD), N{sub 2} adsorption/desorption isotherms and transmission electron microscopy (TEM) are used to characterize the composites derived at the hydrothermal temperature of 125, 150, 175, 200, 250, 275 and 300 {sup o}C. The formation of nanosized nickel compounds, fully inside the mesopore system, was confirmed with XRD and TEM. An N{sub 2} adsorption/desorption isotherms measurements still revealed mesoporosity for the host/guest compounds. It is noteworthy that an OMC/nickel nitrate hydroxide hydrate composite (OMCN-150) exhibits more excellent performance. Based on the various hydrothermal temperatures of the composite, the capacitance of an OMCN-150 delivering the best electrochemical performance is about 2.4 (5 mV s{sup -1}) and 1.5 (50 mV s{sup -1}) times of the pristine OMC. The capacitance retention of an OMCN-150 is 96.1%, which indicates that the electrochemical performance of the supercapacitor is improved greatly, and represents novel research and significant advances in the field of electrode composite materials for supercapacitor. -- Graphical abstract: A series of high performance nickel compound/ordered mesoporous carbon composites were synthesized by a combination of incipient wetness impregnation and hydrothermal method for the first time. Display Omitted
Twins and their boundaries during homoepitaxy on Ir(111)
The growth and annealing behavior of strongly twinned homoepitaxial films on Ir(111) have been investigated by scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction. In situ surface x-ray diffraction during and after film growth turned out to be an efficient tool for the determination of twin fractions in multilayer films and to unravel the nature of lateral twin crystallite boundaries. The annealing of the twin structures is shown to take place in a two-step process; first, the length of the lateral twin crystallite boundaries is reduced, without affecting the amount of twinned material, and then, at much higher temperatures, the twins themselves anneal. Within moderately annealed films lateral twin crystallite boundaries are visible at the film surface as fractional steps from which strain fields extend. The nature of these boundaries is discussed.
One-Step Growth of Ge doped ZnO Tubes by Thermal Evaporation
In this paper we report a simple thermal evaporation technique (horizontal tube furnace) to grow the bulk-quantity of germanium (Ge) doped zinc oxide (ZnO) tubes on the Si substrate by using one-step thermal evaporation of a mixed powder of Ge and ZnO. The microstructure and optical properties of the Ge doped ZnO tubes have been investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, photoluminescence (PL) spectrometer and Raman spectrometer. The investigation of structural properties indicated that the structures consist of bulk quantities of cylindrical rod and tube with diameter around 1micron. EDX reveals that the tube structures have Ge, Zn and O{sub 2} compositions and XRD analysis indicated the product is mainly composed of Ge, zinc germanium oxide (Zn{sub 2}GeO{sub 4}) and small proportion of ZnO. Room temperature photoluminescence (PL) spectrum shows broad emission peaks around 400 nm, opening up a route to potential applications in future optoelectronic devices. Raman measurement also measured at room temperature for these tubes.
An approach to preparing porous and hollow metal phosphides with higher hydrodesulfurization activity
This paper describes an effective method for the synthesis of metal phosphides. Bulk and supported Ni{sub 2}P, Cu{sub 3}P, and CoP were prepared by thermal treatment of metal and the amorphous red phosphorus mixtures. Porous and hollow Ni{sub 2}P particles were also synthesized successfully using this method. The structural properties of these products are investigated using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), inductively coupled plasma (ICP-AES) and X-ray photoemission spectroscopy (XPS). A rational mechanism was proposed for the selective formation of Ni{sub 2}P particles. In experimental conditions, the Ni{sub 2}P/SiO{sub 2} catalyst exhibits excellent hydrodesulfurization (HDS) activity for dibenzothiophene (DBT). - Graphical abstract: Bulk and supported Ni{sub 2}P, Cu{sub 3}P, and CoP were prepared by thermal treatment of their metal and amorphous red phosphorus mixtures. Porous and hollow Ni{sub 2}P particles were successfully synthesized by this method also. In the experimental condition, a Ni{sub 2}P/SiO{sub 2} catalyst exhibits excellent hydrodesulfurization activity for dibenzothiophene. Highlights: > A new synthetic route by heat treating mixtures of metal and red phosphorus in flowing N{sub 2} to prepare corresponding metal phosphides. > Porous and hollow Ni{sub 2}P particles may successfully be obtained using the route. > It is very easy to synthesize other bulk and supported metal phosphides using the mixing of bulk and supported metal and red phosphorus by the method. > The Ni{sub 2}P/SiO{sub 2} catalyst synthesized by the route shows a good HDS of dibenzothiophene. > Its operation is simple (only heat treating pure metal and red phosphorus), and the reaction time is short (only 0.5 h).
Preparation and thermoelectric properties of ternary superionic conductor CuCrS{sub 2}
Transition metal chalcogenide CuCrS{sub 2} powder was synthesized by mechanical alloying (MA) and then consolidated by spark plasma sintering (SPS) technique at 673-1073 K. The phase structure, microstructure and thermoelectric properties of samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Seebeck coefficient/electrical conductivity measuring system, respectively. All the bulks indicated a single phase CuCrS{sub 2}, while the high relative density over 90% were attained for the samples sintered at 873-1073 K. The electrical conductivity of bulk samples displayed a typical characteristic of semiconductor. With increasing measuring temperature, the conductive behaviour of bulk samples sintered over 973 K showed a semiconductor transformation from n-type to p-type due to the changes of main carrier type. The sample obtained by applying SPS at 873 K got the highest power factor 83.2 {mu}W m{sup -1} K{sup -2}, and the largest ZT value 0.11 at 673 K. - Graphical abstract: The samples sintered above 873 K, both of the Seebeck coefficient and electrical conductivity exhibit an increase tendency with increasing temperature, which is due to the mechanism of mix-conduction for CuCrS{sub 2}. Highlights: Black-Right-Pointing-Pointer Single phase CuCrS{sub 2} powder was synthesized by ball-milling at 425 rpm for 40 h. Black-Right-Pointing-Pointer Dense CuCrS{sub 2} bulks were fabricated using SPS techniques at sintering temperature 873-1073 K. Black-Right-Pointing-Pointer Seebeck coefficient of CuCrS{sub 2} samples sintered over 973 K change the signs. Black-Right-Pointing-Pointer Highest power factor reached 83.2 {mu}W m{sup -1} K{sup -2} at 673 K for the sample sintered at 873 K. Black-Right-Pointing-Pointer ZT value was 0.11 at 673 K for the sample sintered at 873 K.
Absence of vapor-liquid-solid growth during molecular beam epitaxy of self-induced InAs nanowires on Si
The growth mechanism of self-induced InAs nanowires (NWs) grown on Si (111) by molecular beam epitaxy was investigated by in situ reflection high energy electron diffraction and ex situ scanning and transmission electron microscopy. Abrupt morphology transition and in-plane strain relaxation revealed that InAs NWs nucleate without any significant delay and under the absence of indium (In) droplets. These findings are independent of the As/In-flux ratio, revealing entirely linear vertical growth rate and nontapered NWs. No evidence of In droplets nor associated change in the NW apex morphology was observed for various growth termination procedures. These results highlight the absence of vapor-liquid-solid growth, providing substantial benefits for realization of atomically abrupt doping and composition profiles in future axial InAs-based NW heterostructures on Si.
Ce-doped EuO: Magnetic properties and the indirect band gap
We have prepared and investigated thin films of EuO doped with the rare-earth element cerium. X-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy were used to determine the quality of these films prepared by pulsed laser deposition. Ce doping leads to an enhanced Curie temperature near 150 K, close to that seen for oxygen-deficient EuO{sub 1-x}. However, the magnetization of Ce-doped EuO exhibits differences from that observed for Gd-doped and oxygen-deficient samples. The high-resolution angular-resolved photoemission from Ce-doped EuO reveals filling of conduction-band states near the X point. This indicates that the band gap in EuO is indirect, and that at 2% doping Ce-doped EuO{sub 1-x} is at least semimetallic.
Electronic properties and bonding characteristics of AlN:Ag thin film nanocomposites
We present theoretical and experimental results on the bonding and structural characteristics of AlN:Ag thin film nanocomposites obtained by means of density functional theory (DFT) computations, high resolution transmission electron microscopy (HRTEM) observations, Auger electron spectroscopy (AES), and x-ray diffraction (XRD) measurements. From the theoretical calculations it was determined that the presence of the Ag substitutional of N or Al atoms affects the electronic density of states (EDOS) of the resulting systems. In particular, occupied energy states are introduced (between others) that lie within the energy gap of the AlN matrix due to Ag-d, Al-p (accompanied with a charge transfer from Al to Ag), Ag-p, and N-p hybridizations, respectively. The effect is predicted to be even more pronounced in the case of Ag nanoparticle inclusions affecting the EDOS of the composite system. These predictions were verified by the HRTEM images that gave unequivocal evidence for the presence and stability of Ag nanoparticles in the AlN matrix. In addition, the AES data suggested a metal-metal (Ag-Al) bonding preference, while the XRD patterns revealed that the atomic Ag dispersions in the AlN thin films results in a small elongation of the Wurtzite lattice, which is in agreement with the DFT predictions. These results may useful in tailoring the electronic response of AlN-based systems and the design of devices for various opto-electronic applications.
Facile synthesis of Cu{sub 2}O nanocube/polycarbazole composites and their high visible-light photocatalytic properties
Cu{sub 2}O nanocube/polycarbazole composites have been prepared by an one-pot solvothermal process using carbazole as a reductant. The polycarbazole layer not only protected and stabilized Cu{sub 2}O particles, but also prohibited the recombination of photogenerated electrons-holes pair and facilitated interfacial charge transfer between polycarbazole and Cu{sub 2}O. The composition, structure and morphology of the obtained products was systematically studied by X-ray powder diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM), High-resolution transmission electron microscopy (HRTEM), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and UV-visible spectrophotometer. Furthermore, the visible-light photocatalytic behavior of the Cu{sub 2}O nanocube/polycarbazole composites on the methyl orange was investigated. - Graphical abstract: The uniform and monodisperse Cu{sub 2}O nanocube/polycarbazole composites were prepared by an one-pot solvothermal process. As covered by polycarbazole, the photocatalytic activities of Cu{sub 2}O nanocubes were improved. The polycarbazole not only protected and stabilized Cu{sub 2}O cubes, but also prohibited the recombination of photogenerated electrons-holes pair and facilitated interfacial charge transfer between polycarbazole and Cu{sub 2}O. Highlights: > The Cu{sub 2}O/polycarbazole nanocube composite has a better photocatalytic activity. > We obtained the composite by an one-pot solvothermal process. > Carbazole monomers as reductants.
Layered double hydroxide/polyethylene terephthalate nanocomposites. Influence of the intercalated LDH anion and the type of polymerization heating method
Conventional and microwave heating routes have been used to prepare PET-LDH (polyethylene terephthalate-layered double hydroxide) composites with 1-10 wt% LDH by in situ polymerization. To enhance the compatibility between PET and the LDH, terephthalate or dodecyl sulphate had been previously intercalated in the LDH. PXRD and TEM were used to detect the degree of dispersion of the filler and the type of the polymeric composites obtained, and FTIR spectroscopy confirmed that the polymerization process had taken place. The thermal stability of these composites, as studied by thermogravimetric analysis, was enhanced when the microwave heating method was applied. Dodecyl sulphate was more effective than terephthalate to exfoliate the samples, which only occurred for the terephthalate ones under microwave irradiation. - Graphical abstract: Conventional and microwave heating routes were used to prepare PET-LDH (polyethylene terephthalate-layered double hydroxide) composites with 1-10 wt% LDH by in situ polymerization. To enhance the compatibility between PET and the LDH, terephthalate or dodecyl sulphate was previously intercalated into the LDH. The microwave process improves the dispersion and the thermal stability of nanocomposites due to the interaction of the microwave radiation and the dipolar properties of EG and the homogeneous heating. Highlights: > LDH-PET compatibility is enhanced by preintercalation of organic anions. > Dodecylsulphate performance is much better than that of terephthalate. > Microwave heating improves the thermal stability of the composites. > Microwave heating improves as well the dispersion of the inorganic phase.
Enhancement of oxygen vacancies and solar photocatalytic activity of zinc oxide by incorporation of nonmetal
B-doped ZnO and N-doped ZnO powders have been synthesized by mechanochemical method and characterized by TG-DTA, XRD, SEM-EDX, XPS, UV-visible and photoluminescence (PL) spectra. X-ray diffraction data suggests the hexagonal wurtzite structure for modified ZnO crystallites and the incorporation of nonmetal expands the lattice constants of ZnO. The room temperature PL spectra suggest more number of oxygen vacancies exist in nonmetal-doped ZnO than that of undoped zinc oxide. XPS analysis shows the substitution of some of the O atoms of ZnO by nonmetal atoms. Solar photocatalytic activity of B-doped ZnO, N-doped ZnO and undoped ZnO was compared by means of oxidative photocatalytic degradation (PCD) of Bisphenol A (BPA). B-doped ZnO showed better solar PCD efficiency as compare to N-doped ZnO and undoped ZnO. The PCD of BPA follows first order reaction kinetics. The detail mechanism of PCD of Bisphenol A was proposed with the identification of intermediates such as hydroquinone, benzene-1,2,4-triol and 4-(2-hydroxypropan-2-yl) phenol. - Graphical Abstract: B-doped ZnO and N-doped ZnO synthesized by mechanochemical method were characterized by various techniques. Solar photocatalytic degradation of Bisphenol-A is in the order of B-ZnO>N-ZnO>ZnO. Highlights: Black-Right-Pointing-Pointer B-doped ZnO and N-doped ZnO powders have been synthesized by mechanochemical method. Black-Right-Pointing-Pointer PL spectra suggest oxygen vacancies are in order of B-doped ZnO>N-doped ZnO>ZnO. Black-Right-Pointing-Pointer Solar PCD efficiency is in order of B-doped ZnO>N-doped ZnO>ZnO for Bisphenol A.
Increase in the Tb{sup 3+} green emission in SiO{sub 2}-LaF{sub 3} nano-glass-ceramics by codoping with Dy{sup 3+} ions
95SiO{sub 2}-5LaF{sub 3} sol-gel derived nano-glass-ceramics single doped with 0.1Dy{sup 3+} or 0.1Tb{sup 3+} mol % and codoped with 0.1Dy{sup 3+} and xTb{sup 3+} (x=0.1,0.3) mol % were successfully obtained. XRD and HRTEM measurements confirm the precipitation of LaF{sub 3} nanocrystals during the ceramming process, with mean size ranging from 10 to 20 nm and increasing with the thermal treatment temperature. About 75% of lanthanide ions are partitioned into LaF{sub 3} nanocrystals, as calculated from luminescence decays. The effect of increasing the Tb{sup 3+} concentration and also of codoping with Dy{sup 3+} in the Tb{sup 3+} green emission from the {sup 5}D{sub 4} level have been studied. The energy transfer mechanisms between Tb{sup 3+} ions and also between Tb{sup 3+}-Dy{sup 3+} ions, which favor the green emission, have been analyzed.
Thermoluminescence Characteristics of Nanocrystalline LiF Phosphors Synthesized at Different pH Values
Nanocrystalline lithium fluoride (LiF) phosphors have been prepared by the chemical co-precipitation method at different pH values (7.0, 8.0, 9.0). The formation of nanocrystalline structure has been confirmed by X-ray diffraction and transmission electron microscope. The thermolumniscence (TL) properties of LiF phosphors irradiated with gamma rays at different doses have been studied. The analysis of TL glow curve has revealed the existence of two well resolved glow peaks, one low temperature peak at around 145 deg. C and other one at higher temperature around 375 deg. C. The LiF nano-crystallites synthesized at 8.00 pH have been found to show maximum TL intensity at studied gamma doses (0.1 Gy-15 Gy).
Mechanism of Charge Transport in Cobalt and Iron Phthalocyanine Thin Films Grown by Molecular Beam Epitaxy
Cobalt phthalocyanine (CoPc), iron phthalocyanine (FePc) and their composite (CoPc-FePc) films have been grown by molecular beam epitaxy (MBE). Grazing incidence X-ray diffraction (GIXRD) and scanning electron microscope (SEM) studies showed that composite films has better structural ordering compared to individual CoPc and FePc films. The temperature dependence of resistivity (in the temperature range 25 K- 100 K) showed that composite films are metallic, while individual CoPc and FePc films are in the critical regime of metal-to-insulator (M-I) transition The composite films show very high mobility of 110 cm{sup 2} V{sup -1} s{sup -1} at room temperature i.e. nearly two order of magnitude higher compared to pure CoPc and FePc films.
Growth of M- and A-plane GaN on LiGaO{sub 2} by plasma-assisted MBE
We have performed non-polar M- and A-plane GaN growth on LiGaO{sub 2}(LGO) by plasma-assisted molecular beam expitaxy (MBE). We demonstrate that non-polar GaN growth on LGO yields high phase purity and flat surfaces. We find that annealing of the substrates prior to growth is a suitable method for avoiding a peeling off of the film from the substrate after growth.
Coherent femtosecond low-energy single-electron pulses for time-resolved diffraction and imaging: A numerical study
We numerically investigate the properties of coherent femtosecond single electron wave packets photoemitted from nanotips in view of their application in ultrafast electron diffraction and non-destructive imaging with low-energy electrons. For two different geometries, we analyze the temporal and spatial broadening during propagation from the needle emitter to an anode, identifying the experimental parameters and challenges for realizing femtosecond time resolution. The simple tip-anode geometry is most versatile and allows for electron pulses of several ten of femtosecond duration using a very compact experimental design, however, providing very limited control over the electron beam collimation. A more sophisticated geometry comprising a suppressor-extractor electrostatic unit and a lens, similar to typical field emission electron microscope optics, is also investigated, allowing full control over the beam parameters. Using such a design, we find {approx}230 fs pulses feasible in a focused electron beam. The main limitation to achieve sub-hundred femtosecond time resolution is the typical size of such a device, and we suggest the implementation of more compact electron optics for optimal performance.