Investigation on Structural,Morphological, Optical and Ammonia Sensing Properties Indium Doped Nano Crystalline ZnO Thin Films Synthesized by Spray Pyrolysis Technique

In the present work, nanostructured In doped ZnO thin films were synthesized using spray pyrolysis technique with different molarity concentrations (0.001–0.004). X-ray diffraction patterns confirms the polycrystalline nature of the films with hexagonal structure. The crystallite size is going to be increases with increase in dopant concentration. The field-emission scanning electron micrograph of undoped ZnO exhibits spherical shaped particles with intergrain pores and the intergrain pores decreases with increases in indium concentration. The transmittance and band gap is going to be decreases with increase in indium concentration. The ammonia (NH₃) sensing properties of the undoped ZnO and In doped ZnO thin films were carried out at room temperature and the sensing responses of the samples towards NH₃ concentrations were reported.     

Influence of Mg doping on the morphology and optical properties of ZnO films for enhanced H2 sensing

Highly oriented ZnO and Mg doped ZnO thin films were fabricated on Al₂O₃ substrate by sputtering at room temperature. The effect of Mg doping on the structural, optical, and morphological properties of ZnO film was investigated. The intensity of (002) peak in X‐ray diffraction measurements revealed the influence of Mg doping on the crystallinity and orientation of ZnO film. Photoluminescence (PL) results show that the Ultraviolet (UV) emission peak was shifted to lower wavelength side for Mg:ZnO film indicating the possibility for quantum confinement. UV–vis–NIR optical absorption revealed an improvement in optical transmittance from 70 to 85%, and corresponding optical band gap from 3.25 to 3.54 eV. Atomic force microscope (AFM) images revealed the nano‐size particulate microstructure of the films. The surface topography of Mg doped ZnO film confirmed decreased grain size with large surface roughness and increased surface area, favorable for sensing. Pure ZnO and Mg doped ZnO film were used as active layer and tested for its sensing performance to hydrogen. Compared to undoped ZnO, 22 at.% Mg doped ZnO film showed much higher sensor response to H₂ at a concentration as low as 200 ppm and at a lower operating temperature of 180°C. A linear sensor response was observed for H₂ concentration in the range of 100–500 ppm. Microsc. Res. Tech. 76:1118–1124, 2013. © 2013 Wiley Periodicals, Inc.     

Multifractal analysis of Mg-doped ZnO thin films deposited by sol–gel spin coating method

A multifractal analysis has been performed on the 3D (three-dimensional) surface microtexture of magnesium-doped zinc oxide (ZnO:Mg) thin films with doping concentration of 0, 2, 4, and 5%. Thin films were deposited onto the glass substrates via the sol–gel spin coating method. The effect of magnesium doping, on the crystal structure, morphology, and band gap for ZnO:Mg thin films has been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–Vis spectroscopy. It has been observed that the surface of ZnO thin films is multifractal in nature. However, multifractality and complexity observed to decrease with increasing content of Mg in ZnO thin films due to formation of islands on the surface in accordance with Volmer–Weber growth mechanism. The investigations revealed that crystallinity, microtexture, morphology, and optical properties of the thin films can be tuned by controlling the Mg content within the ZnO lattice. In particular, their optical band gap energies were 3.27, 3.31, 3.34, and 3.33 eV at 0, 2, 4, and 5%, respectively. The prepared thin films of ZnO:Mg with tuned characteristics would have promising applications in optoelectronic devices.     

Novel method for fabrication of room temperature polypyrrole–ZnO nanocomposite NO2 sensor

Nanocomposites of polypyrrole (PPy) and zinc oxide (ZnO) nanoparticles (NPs) were prepared by spin coating method. These nanocomposites were characterized by Fourier transform infrared (FTIR), Field emission scanning electron microscope (SEM), Atomic force microscopy (AFM), Transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–vis techniques, which proved the polymerization of pyrrole monomer and the strong interaction between polypyrrole and ZnO NPs. The nanocomposites were used for gas sensing to CH₃OH, C₂H₅OH, NH₃, H₂S and NO₂ at room temperature. It was revealed that PPy–ZnO nanocomposites with different ZnO weight ratios (10%, 20%, 30%, 40% and 50%) could detect NO₂ at low concentration with very higher selectivity and sensitivity at room temperature than the reported PPy. The PPy–ZnO nanocomposites responded to NO₂ at concentration as low as 10 ppm. PPy–ZnO nanocomposite containing ZnO (50%) showed the maximum sensitivity 38% with 92.10% stability to 100 ppm NO₂ gas at room temperature. The sensing mechanism of PPy–ZnO nanocomposites to NO₂ was presumed to be the effects of p–n junction between PPy and ZnO.     

Nanoparticle shape and configuration analysis by transmission electron tomography

Tomographic reconstruction by transmission electron microscopy is used to reveal three‐dimensional nanoparticle shapes and the stacking configurations of nanoparticle ensembles. Reconstructions are generated from bright‐field image tilt series, with a sample tilt range up to ± 70°, using single or dual tilt axes. We demonstrate the feasibility of this technique for the analysis of nanomaterials, using appropriate acquisition conditions. Tomography reveals both cubic and hexagonal close‐packing configurations in multi‐layered arrays of size‐selected In nanospheres. By tomography and phase‐contrast lattice imaging, we relate the three‐dimensional shape of PbSe octahedral nanoparticles to the underlying crystal structure. We also confirm simple‐cubic packing in multi‐layers of PbSe nanocubes and see evidence that the particle shapes have cubic symmetry. The shapes of TiO₂ nanorod bundles are shown by tomographic reconstruction to resemble flattened ellipsoids.     

Microstructure and mechanical properties of laser-MIG hybrid welding of 1420 Al-Li alloy

This paper investigates the microstructure and mechanical properties of 1420 aluminum–lithium (Al-Li) alloy joints before and after heat treatment by CO₂ laser-metal inter gas (MIG) hybrid welding. The 5-mm-thick 1420 Al-Li alloy plates were welded by CO₂ laser-MIG hybrid welding. Full penetration joints without any defects were produced. Optic and scanning electron microscopy were used to study the microstructure and fractograph characteristics. The results show that the microstructures of the heat-affected zone (HAZ) and fusion zone exist as a predominantly discontinuous equiaxed dendritic structure and as a fine cellular dendritic structure, respectively. After heat treatment, the microstructures change from dendritic structure to a spheroidal crystal; the grain size of fusion zone is obviously larger than that of the base metal and the HAZ. Furthermore, the hardness recovers substantially to a level similar to that of the parent material. The tensile strengths of the joints in the as-welded condition and after heat treatment are 223 and 267 MPa, reaching up to 57 and 68 % of the parent materials’ strength, respectively. The fractographs show that the joint as-welded condition exhibits the characteristics of dominated dimples and a small amount tear ridges, which are associated with the mixed ductile and brittle facture mechanisms. The fracture mode transforms from a transgranular to an intergranular after heat treatment; cleavage cracking coupled with an intergranular microvoid coalescence fracture mechanism occurs.     

用湿化学法在石英玻璃衬底上制备ZnO纳米线阵列

运用湿化学法在石英玻璃衬底上制备了ZnO纳米线阵列,用SEM、XRD和分光光度计对其形貌、晶体结构和发光性能进行了表征。结果表明:所制备的ZnO纳米线为六角纤锌矿结构,其直径为60～200nm,长度为0.1～3μm;ZnO纳米线的光致发光(PL)峰值为380nm,在波段为340～380nm时有很强的吸收峰,具有优越的紫外光响应特性;ZnO纳米线阵列具有高度取向性。     

Al、Sn掺杂对于ZnO薄膜微结构及光学特性的影响

采用真空电子束蒸发金属薄膜及后续热氧化技术在石英衬底上分别制备出了ZnO、Al∶ZnO以及Sn∶ZnO薄膜。通过X射线衍射仪(XRD),紫外-可见分光光度计和原子力显微镜(AFM)等分析仪器对比研究了Al、Sn掺杂对ZnO薄膜结晶质量、光学性质及表面形貌的影响。测试结果表明,Al、Sn掺杂可以使薄膜结晶质量得到提高,薄膜应力部分释放,薄膜表面的粗糙度也相应增加,掺杂对薄膜光学带隙的影响在一定程度取决于金属薄膜的氧化程度,氧化充分可以使光学带隙变宽,反之则变窄。     

Rapid determination of volatile organics using a nanoporous zinc oxide microsphere-coated quartz crystal microbalance

The organic vapor sensing properties of nanoporous ZnO microspheres coated on a quartz crystal microbalance were characterized. The ZnO nanoparticles were aggregated by aqueous synthesis into micrometer diameter spheres. The porous structure of the microspheres provided sufficient surface area for vapor adsorption and diffusion for gas exchange. The reversible response suggests that complete desorption without contamination was achieved. Sensing films on a quartz crystal microbalance (QCM) were characterized using five volatile organic compounds with different functional groups to compare the differences in selectivity between polyisobutylene (PIB) and nanoporous ZnO. The response time for nanoporous ZnO was half the value of the PIB-coated sensor. The results show that nanoporous ZnO microspheres are an alternative that provide selectivity and rapid response for QCM.     

Supported metal sulphide nanoclusters studied by HAADF-STEM

The morphology of MoS₂ and WS₂ nanoclusters supported on high‐surface area graphitic carbon was investigated using high angular annular dark field scanning transmission electron microscopy (HAADF‐STEM). Most of the MoS₂ (WS₂) nanoclusters contain only a single S‐Mo‐S (S‐W‐S) layer and the most commonly encountered morphology is truncated triangular. This is in contrast to the hexagonal morphology of macroscopic MoS₂ (WS₂) crystals. When in addition to molybdenum (tungsten), nickel is also present, the regular nanoclusters are truncated to a larger extent, indicating that Ni has influenced the morphology by the formation of so‐called Ni‐Mo‐S (Ni‐W‐S) structures. For these structures, the additional truncations are observed to lead to dodecahedral‐like shapes.     

Tribological behaviour of the adduct of bis(O,O′-dibutyldithiophosphato)-nickel (II) with isoquinoline

The bis(isoquinoline) adduct of bis(O,O′-dibutyldithiophos-phato)nickel (II), Ni(dtp)₂ · 2IQ, has been prepared; its crystal structure reveals that the nickel atom is bonded to four sulphur atoms of the dithiophosphate molecule, and two nitrogen atoms in the isoquinoline ring, to form a six-coordinated complex. Evaluation of the adduct's properties as an extreme-pressure (EP) and antiwear (AW) additive was conducted using a fourball machine. The results show that Ni(dtp)₂ · 2IQ exhibits better load-carrying capacity than Ni(dtp)₂ and Zn(dtp)₂, but poorer antiwear abilities. SEMs show that a wear scar surface on the ball lubricated with the adduct was much rougher than for those with isooctanol, Ni(dtp)₂ and Zn(dtp)₂, respectively. Further, energy dispersive X-ray (EDX) spectra indicates that the sulphur concentration in the wear scar lubricated with the adduct is much less than that of Ni(dtp)₂, which leads to a lesser wear reducing ability.     

Energy-loss near-edge structure (ELNES) and first-principles calculation of electronic structure of nickel silicide systems

The electronic structures of nanometre-sized nickel silicide systems, Ni(2)Si and NiSi, have been studied by energy-loss near-edge structure (ELNES) and first-principles band structure calculations. Experimental ELNES of Ni L(3)- and Si L(2,3)-edges could be explained well using theoretical spectra calculated for the ground state without the core hole, suggesting metallic properties for both silicides. It was shown that a slight difference in ELNES spectra of Ni(2)Si and NiSi comes from the coupling among the Ni d and Si p, d states in the unoccupied bands. The density of states and the contour plots of all the valence electron densities for Ni(2)Si, NiSi together with NiSi(2) show that Ni(2)Si has the bond with the strongest covalent character between Ni and Si atoms and the most transition metal-like character of the Ni 3d band among the three silicides.     

High efficiency slotted photonic crystal waveguides for the determination of gases using mid-infrared spectroscopy

We present the design and analysis of a high efficiency slotted photonic crystal waveguide for gas sensing applications in the mid-infrared wavelength range. We designed the slotted photonic crystal waveguide structure by engineering the interfaces between the input and output slot waveguides and a resonant coupler. Coupling and transmission spectra of the sensor have been modeled using the three-dimensional finite-difference time domain method. The sensing principle is based on the shift of the upper band edge of the sensor output transmission spectrum which arises due to changes in the ambient refractive index. Transmission spectrum and sensitivity of the proposed sensor are analyzed by tuning the radii of the air holes localized on each side of the slot. The results show that a change of the refractive index of the gas by 10^?4 leads to a shift of the upper band edge wavelength by 540?pm which corresponding to a sensitivity of 1720?nm per refractive index unit. The proposed design may be an ideal platform for developing mid-infrared gas sensing devices characterized by high coupling efficiencies and high sensitivities.     

Effect of heat treatment on the microstructure and properties of Ni based soft magnetic alloy

A Ni‐based alloy was heat treated by changing the temperature and ambient atmosphere of the heat treatment. Morphology, crystal structure, and physical performance of the Ni‐based alloy were characterized via SEM, XRD, TEM, and PPMS. Results show that due to the heat treatment process, the grain growth of the Ni‐based alloy and the removal of impurities and defects are promoted. Both the orientation and stress caused by rolling are reduced. The permeability and saturation magnetization of the alloy are improved. The hysteresis loss and coercivity are decreased. Higher heat treatment temperature leads to increased improvement of permeability and saturation magnetization. Heat treatment in hydrogen is more conducive to the removal of impurities. At the same temperature, the magnetic performance of the heat‐treated alloy in hydrogen is better than that of an alloy with heat treatment in vacuum. The Ni‐based alloy shows an excellent magnetic performance on 1,373 K heat treatment in hydrogen atmosphere. In this process, the µ_m, B_s, P_u, and H_c of the obtained alloy are 427 mHm^?1, 509 mT, 0.866 Jm^?3, and 0.514 Am^?1, respectively. At the same time, the resistivity of alloy decreases and its thermal conductivity increases in response to heat treatment.     

Ni/Al多层板的复合法制备及放热性能

在纯铝箔上化学镀镍得到微米级厚度的镍层,再将该镀镍铝箔堆垛热压后进行累积叠轧(1~7道次),得到Ni/Al多层板,研究了该多层板的组织结构及放热性能。结果表明:化学镀镍层为非晶态,在热压过程中发生晶化;随着叠轧道次的增加,镍层逐渐发生颈缩和断裂,其碎片镶嵌在铝中,增加了镍和铝的接触面积,从而提高了Ni/Al多层板的放热性能,其能量密度由1道次的520.27J·g^-1增大到7道次的1203.4J·g^-1,达到理论值的87.15%;不同道次叠轧Ni/Al多层板的起始反应温度均高于475℃,说明该多层板具有良好的室温稳定性。     

Self-Lubricating Cold-Sprayed Coatings Utilizing Microscale Nickel-Encapsulated Hexagonal Boron Nitride

It is often beneficial to modify surfaces to gain desirable properties such as improved wear and friction resistance. Self-lubricating coatings can improve the performance of contacting surfaces and extend component lifetimes by reducing the coefficient of friction and/or improving resistance to specific wear modes. With these goals in mind, self-lubricating coatings of hexagonal boron nitride (hBN) particles in a deposited nickel matrix were investigated and optimized for friction and wear. These self-lubricating coatings were created via high-velocity particle consolidation or cold spray using micrometer-sized hBN powder encapsulated by nickel and nickel phosphorous alloys. Relatively thick nickel encapsulation via electrolesss Ni plating was required to aid in coating bonding/formation by “tricking” the hBN into acting as monolithic Ni during deposition. Once deposited on aluminum substrates, the coatings were analyzed and found to exhibit enhanced mechanical and tribological properties such as high bond strength and microhardness, a relatively low coefficient of friction, and improved reciprocating wear behavior relative to pure cold-sprayed Ni coatings. Furthermore, the encapsulation process was found to be both scalable and amenable to relatively small hBN particles.     

Laser melt injection of BN powders on tool steels I:Microhardness and structure

A 5 kW continuous wave CO₂ gas laser, operating in an oscillating square beam mode, was utilized to melt inject hexagonal BN powders into the surfaces of AISI T1 and M₂ tool steels. Optical metallography, scanning electron microscopy, Auger spectroscopy and Vickers' microhardness tests were employed to characterize the melt layers. Both the hardness and the BN concentration of laser-processed layers were increased with an increase in the number of superimposing laser passes. A Vickers hardness of 2150 HV (maximum) was obtained in the specimen that was BN injected ten times. Microstructural features included fine cellular-dendritic structures and complex precipitates of metal boronitrides. The melt layers were nearly free from cracks and pores.     

Peculiarities of diamonds formed in alkaline carbonate-carbon melts at pressures of 8–10 GPA: Scanning electron microscopy and cathodoluminescence data

Diamond crystallization with both spontaneous and seeded nucleation was realized in the system Na₂Mg(CO₃)₂-K₂Mg(CO₃)₂-C (graphite) at 8–10 GPa and 1700–1800°C. The crystallization products were transparent colorless diamond single crystals of octahedral habit up to 100–150 μm in size. Scanning electron microscopy (SEM) showed that the growing diamond material was precipitated on both octahedral {111} and cubic { 100 } faces of synthetic and natural diamond seed crystals by layers of octahedral orientation, much like the growth of the natural diamond. The physicochemical conditions for diamond crystallization are interpreted as a crystal growth from carbon solutions in alkaline-carbonate melts. Color cathodoluminescence scanning electron microscopy (CCL-SEM) and cathodoluminescence (CL) spectroscopy studies suggested specific peculiarities of the synthetic “carbonate-carbon”(CC) diamonds resembling natural crystals in comparison with diamonds produced by metal-carbon (MC) synthesis. The main feature of the CC product is the lack, for both spontaneous and seed stimulated diamonds, of surface color cathodoluminescence as in the case for natural diamonds with lower concentrations of nitrogen impurity (type II). The CL spectra of the CC diamonds showed the simultaneous luminescent three-band system - H3, 575 nm, and a weak blue A-band - the H3 band structure of which resembles that of natural diamonds of type IIa.     

Study on the c-axis preferred orientation of ZnO film on various metal electrodes

ZnO thin film was deposited on various metal electrodes by reactive sputtering, and c-axis preferred orientation of the film has been studied. ZnO, which has high piezoelectricity, is promising for oscillators or filter devices such as surface acoustic wave (SAW) device, gas sensor, and film bulk acoustic resonator (FBAR). But, for the application of ZnO film for these devices, the film should be grown with c-axis normal to the electrode. In this study, Pt, Al, and Au were deposited on Si wafer, and the surface roughness and crystal structure of the ZnO film on the electrode were investigated using AFM, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Columnar structures of ZnO films were grown with c-axis normal to all electrodes, and among them Pt electrode showed the highest preferred orientation of ZnO film.     

The structure and continuous stoichiometry change of 1DTbBrx@SWCNTs

HRTEM and HAADF STEM of 1DTbBr_x@SWCNT meta‐nanotubes reveal three structural modifications of 1D nanocrystals within single wall carbon nanotube channels attributed to a different stoichiometry of the guest crystal. For SWCNTs with diameters D_m > 1.4 nm a most complete tetragonal unit cell is observed. When crystallization occurs inside SWCNT with D_m < 1.4 nm 1D TbBr_x crystal deforms a nanotube to elliptical shape in cross section. In this case the 1D crystal unit cell becomes monoclinic, with possible loss of a part of bromine atoms. Two modifications of a monoclinic unit cell appear. One of them is characterized by single or pair vacancies in the structure of the 1D crystal. Another structure is explained by peripheral and central bromine atoms loss. An appearance of such modifications can be stimulated by electron irradiation. The loss of bromine atoms is in agreement with chemical analysis data. Electronic properties of obtained meta‐nanotubes are investigated using optical absorption and Raman spectroscopy. It is shown that intercalation of terbium bromide into SWCNTs leads to acceptor doping of SWCNTs. According to local EDX analysis and elemental mapping this doping can arise from significant stoichiometry change in 1D nanocrystal indicating an average Tb:Br atomic ratio of 1:2.8 ± 0.1.