Multivariate curve resolution alternating least squares in the quantitative determination of sulfur using overlapped S(Kα)–Mo(Lα) emission peaks by wavelength dispersive X‐ray fluorescence spectrometry

Spectral line overlap is a serious problem in quantitative X‐ray fluorescence analysis. In this study multivariate curve resolution alternating least squares (MCR‐ALS) approach was used to resolve the effect of overlapping S(K_α)–Mo(L_α) emission lines generated by standard‐less software of a wavelength dispersive X‐ray fluorescence spectrometer (WDXRF) for the quantitative monitoring of sulfur in mineral samples. Scan channel set contained Ge crystal, 550‐µm collimator, flow detector (Ar + CH₃) and rhodium (Rh) tube. The 18 calibration and 10 validation samples contain 0.00%–10.98% sulfate (SO₃) and 0.00%–92.40% MoO₃. The digitized spectral data were extracted in the range between 109° and 113.9° (2θ) at every 0.1 degree. Lack of fit percentage (LOF%) for experimental data and the variance explained at the optimum condition () were 2.32 and 99.94, respectively. The values of the root mean square error of prediction (RMSEP) for analyzing of sulfur were 0.23. MCR‐ALS was also compared with partial least squares (PLS) method for determination of sulfur in the presence of molybdenum. To evaluate the resolution and quantification performance of MCR‐ALS procedure, the method was used to determine sulfur in presence of molybdenum in two synthetic soil samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Local structure around Zn and Ga in solution‐processed In–Ga–Zn–O and implications for electronic properties

We study by X‐ray absorption spectroscopy the local structure around Zn and Ga in solution‐processed In–Ga–Zn–O thin films as a function of thermal annealing. Zn and Ga environments are amorphous up to 450 °C. At 200 °C and 450 °C, the Ga atoms are in a β‐Ga₂O₃ like structure, mostly tetrahedral gallium oxide phase. Above 300 °C, the Zn atoms are in a tetrahedral ZnO phase for atoms inside the nanoclusters. The observed formation of the inorganic structure above 300 °C may be correlated to the rise of the mobility for IGZO TFTs. The Zn atoms localized at the nanocluster boundary are undercoordinated with O. Such ZnO cluster boundary could be responsible for electronic defect levels. Such defect levels were put in evidence in the upper half of the band gap. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Growth of nanostructures of Zn/ZnO by thermal evaporation and their application for room-temperature sensing of H<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>S gas

ZnO micro- and nanostructures were prepared by thermal evaporation of Zn and a mixture of ZnO with graphite. On heating Zn powder in a quartz tube at temperatures between 600 °C to 800 °C, radial growth of nanowires was observed on the source. On increasing the temperature to 900 °C, various interesting micro- and nanostructures of Zn and ZnO were observed to have deposited all over the quartz tube. On the other hand, when ZnO was heated in the presence of graphite, predominant growth of ZnO nanotetrapods was observed. Nanowires and tetrapods of ZnO were characterized by photoluminescence measurements and were found to show significantly improved response for detection of H₂S gas at room temperature when compared with earlier studies. The response was seen to improve with increase in oxygen vacancies in the material. PACS 78.55.Et; 07.07.Df     

ac conductivity of Na-Ag β” -alumina polycrystalline samples

The results of ac conductivity measurements carried out on ceramic samples of Li₂O and NiO-Li₂O-doped β7rdquo;-alumina with Na⁺, Ag⁺ and Na⁺ -Ag⁺ mobile ions are presented. The modifications of doping only slightly influenced either bulk or grain boundary conductivity in Na β” -alumina. The activation energies of conduction in Na β”-alumina equal to 0.28 eV at low temperatures decreased to 0.14–0.15 eV at temperatures above 200°C. The Arrhenius plots for Ag β” -alumina were found to be linear in whole 20–450°C temperature range with the activation energies of 0.19 eV (Li₂O) and 0.24 eV (NiO-Li₂O). The conductivity measurements done on partially exchanged samples revealed the presence of the mixed alkali effect.     

Low‐temperature synthesis and Raman scattering of Mn‐doped ZnO nanopowders

Nanocrystalline Mn‐doped zinc oxides Zn_1−xMn_xO (x = 0–0.10) were synthesized by the sol–gel technique at low temperature. The calcination temperature of the as‐prepared powder was found at 350 °C using differential thermal analysis. A thermogravimetric analysis showed that there is a mass loss in the as‐prepared powder till 350 °C and an almost constant mass till 800 °C. The X‐ray diffraction patterns of investigated nanopowders calcined at 350 °C correspond to the hexagonal ZnO structure without any foreign impurities. The average grain size of the nanocrystal that was observed around ∼25–40 nm from transmission electron microscopy matched well with the crystallite size calculated from the line shape of X‐ray diffraction. The chemical bonding structure in Zn_1−xMn_xO nanopowders was examined using X‐ray photoelectron spectroscopy techniques, which indicate substitution of Mn²⁺ ions into Zn²⁺ sites in ZnO lattice. Micro Raman spectroscopy confirmed the insertion of Mn ions in the ZnO host matrix, and similar wurtzite structure of Zn_1−xMn_xO (x < 10%) nanocrystals. Temperature‐dependent Raman spectra of the nanocrystals displayed suppression of luminescence and enhancement in full width at half maximum in pure ZnO nanocrystals with increase in temperature, which suggests an enhancement in particle size at elevated temperature. Copyright © 2009 John Wiley & Sons, Ltd.     

Acceptors related to group I elements in ZnO ceramics

ZnO ceramics doped with Li, Na or K were sintered in air for 4 h at 1000 °C. Electrical conductivity as well as photoluminescence (PL), PL excitation and photoconductivity spectra were measured and compared with those in undoped samples. The influence of both fast and slow cooling of the samples from 1000 °C on measured characteristics was investigated. The yellow–orange PL bands associated with the deep acceptors Li_Zn, Na_Zn and K_Zn were observed and the corresponding PL excitation spectra were determined. These acceptors were found to form some complexes with other lattice defects.     

Polarity control and residual strain in ZnO epilayers grown by molecular beam epitaxy on (0001) GaN/sapphire

We report on the polarity control of ZnO grown by plasma assisted molecular beam epitaxy on Ga polar (0001) GaN/sapphire templates simply via the oxygen‐to‐Zn (VI/II) ratio during the growth of a thin nucleation layer at 300 °C. Following Zn pre‐exposure, the ZnO layers nucleated with low VI/II ratios (<1.5) exhibited Zn‐polarity. Those nucleated with VI/II ratios above 1.5, exhibited O‐polarity. Supported by scanning transmission electron microscopic imaging, we have unequivocally demonstrated that polarity inversion takes place without formation of any vertical inversion domains and within one monolayer of presumably non‐stoichiometric GaO_x formed at the ZnO/GaN interface. A direct correlation between polarity and strain sign of ZnO layers has been found. The Zn‐polar ZnO layers were under tensile biaxial strain, whereas the O‐polar material exhibited compressive strain. Moreover, the amount of residual strain varied linearly with VI/II ratio used during the low‐temperature nucleation layer growth. Strain control with VI/II ratio has been explained by the potential formation of Zn interstitials.     

Sonochemical synthesis and characterization of three nano zinc(II) coordination polymers; Precursors for preparation of zinc(II) oxide nanoparticles

Nanostructures of three Zinc(II) coordination polymers, [Zn(NNO)₂(H₂O)₄]_n (1), [Zn(PNNO)₂(H₂O)₂]_n (2) and [Zn(H₂O)₆]·(INNO)₂ (3) {NNO: Nicotinic acid N-oxide, PNNO: Picolinic acid N-oxide and INNO: Isonicotinic acid N-oxide}, have been synthesized by a sonochemical process and reaction of ligands with Zn(CH₃COO)₂. The Zinc(II) oxide nano-particles have been synthesized from thermolysis of [Zn(NNO)₂(H₂O)₄]_n (1), [Zn(PNNO)₂(H₂O)₂]_n (2) and [Zn(H₂O)₆]·(INNO)₂ (3) at two different methods (with surfactant and without surfactant) and two temperatures (200 and 600 °C). The ZnO nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Comparison of the SEM images of ZnO nano-particles at two different methods and temperatures shows that higher temperature results in an increasing of agglomeration and thus small and spherical ZnO particles with good separation were produced by thermolysis of compounds at 200 °C and by use of surfactant.     

Raman spectroscopy of Cu doping in Zn1−xCoxO diluted magnetic semiconductor

The room‐temperature ferromagnetism and the Raman spectroscopy of the Cu‐doped Zn_1−xCo_xO powders prepared by the sol–gel method are reported. The x‐ray diffraction (XRD) data confirmed that the wurtzite structure of ZnO is maintained for ZnO doped with Co below 10 at%. The magnetization–field curves measured at room temperature demonstrated that all Co‐doped ZnO powders were paramagnetic. Ferromagnetic ordering is observed for the samples doped with Cu in Zn_0.98Co_0.02O and strongly depends on the concentration of Cu. The relative strength of the second‐order LO peak to the first‐order one in the Raman spectra, which is related to the carrier concentration, of the Cu‐doped Zn_0.98Co_0.02O powder is strongly correlated with the saturation magnetic moment of the system. This seems to be in favor of the Ruderman‐Kittel‐Kasuya‐Yosida (RKKY) or double exchange mechanism of the ferromagnetism in this system. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of polarity inversion on the electrical properties of Ga‐doped ZnO thin films

This study investigates how polarity inversion influences the relationship between the electrical properties of heavily Ga‐doped ZnO (GZO) films deposited by RF magnetron sputtering and their thickness. The electrical properties observed in very thin films are correlated with a change of polarity from O‐polar to Zn‐polar face upon increasing the film thickness based on results of valence band spectra measured by X‐ray photoelectron spectroscopy. It is found that the electrical properties of very thin GZO films deposited on Zn‐polar ZnO templates are significantly improved compared to those deposited on O‐polar face. A low resistivity of 2.62 × 10^–4 Ω cm, high Hall mobility of 26.9 cm²/V s, and high carrier concentration of 8.87 × 10²⁰ cm^–3 being achieved with 30 nm‐thick GZO films using Zn‐polar ZnO templates on a glass substrate. In contrast, the resistivity of 30 nm‐thick GZO films on bare glass that shows more likely O‐polar is very poor about 1.44 × 10^–3 Ω cm with mobility and carrier concentration are only 11.9 cm²/V s and 3.64 × 10²⁰ cm^–3, respectively. It is therefore proposed that polarity inversion plays an important role in determining the electrical properties of extremely thin GZO films. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Short‐circuit current improvement of CuGaSe2 solar cells with a ZnS/(Zn,Mg)O buffer combination

CuGaSe₂ (CGS) thin‐film solar cells were prepared with an in‐line co‐evaporation process and the established buffer combination CdS/i‐ZnO was replaced by ZnS/(Zn,Mg)O. We obtained functional CGS solar cells with a strong gain in the short‐circuit current density as compared to the CdS/i‐ZnO buffer reference cells. The enhanced current density is a result of improved transmission in the wavelength region between 330 nm and 550 nm of the ZnS/(Zn,Mg)O buffer combination as compared to CdS/i‐ZnO. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

CdSe nanocrystals in novel phosphate glass matrix

The CdSe nanoparticles have been prepared in the novel glass matrix P₂O₅–Na₂O–ZnO–Li₂O. The prepared nanoparticles and glass matrix are characterized by differential thermal analysis, X-rays diffraction, UV–vis optical absorption, and infrared spectroscopy. X-rays diffraction and optical absorption show that both of the annealing temperature and time play an important role in nanoparticles’ growth. The well-annealed and high-temperature-annealed samples suggest Zn atoms to substitute Cd atoms to form an additional ZnSe–CdSe system. Infrared spectroscopy confirms the decrease of the Zn-content in the host glass due to growing of nanoparticles, causing long phosphate chains within.     

Electrical properties of CoO,NiO, CuO and ZnO doped beta″-alumina

The measurements of ionic conductivity of sintered beta″-alumina samples doped with CoO, NiO, CuO and ZnO were caried out. It was found that conductivities of these samples are lower than conductivity of Li₂O stabilized beta″-alumina. For CoO, NiO, CuO as well as Li₂O stabilized beta″-alumina the bending of Arrhenius plots was observed. For samples doped with ZnO the plots were linear in whole 20°C–450°C temperature range. The doping effect on bulk conductivity was stronger than on grain boundary conductivity.     

Synthesis of α‐Willemite Nanoparticles by Post‐calcination of Flame‐made Zinc Oxide/Silica Composites

Composite ZnO/SiO₂ nanoparticles were made by flame spray pyrolysis (FSP). Characteristics of the product powder and its crystallization behavior on post‐calcination were evaluated. Polyhedral aggregates of nano‐sized primary particles consisting of ZnO nano‐crystals 1–3 nm in size and amorphous SiO₂ were obtained by FSP. A short residence time in the flame can result in the co‐existence of the ZnO and SiO₂ clusters without substitution or reaction hindering each other's grain growth. There was almost no change in the XRD pattern by calcination at 600 °C for 2 h, suggesting a high thermal stability of the ZnO nano‐crystals in the composite particles. A pure α‐willemite phase was obtained at 900 °C. At this calcination temperature, d_C and d_BET of the powder were 63 and 44 nm, respectively. The nano‐composite structure of the FSP‐made particles can suppress crystalline growth of ZnO during calcination to maintain a high reactivity of ZnO with SiO₂, obtaining pure α‐willemite with high specific surface area at low calcination temperatures.     

Hydrothermal synthesis and gas sensing properties of?single-crystalline ultralong ZnO nanowires

Ultralong ZnO nanowires were successfully synthesized by a simple hydrothermal reaction of Zn foil and aqueous Na₂C₂O₄ solution at 140°C. The as-synthesized ZnO nanowires are single crystalline with the wurtzite structure and grow in the [0001] direction. The role of Na₂C₂O₄ in the formation of ultralong ZnO nanowires was investigated, and a possible mechanism was also proposed to account for the formation of the ultralong ZnO nanowires. The gas sensor fabricated on the basis of the ultralong ZnO nanowires showed excellent response characteristics towards NH₃ and N(C₂H₅)₃ vapors with low concentration, and its detection limits for NH₃ and N(C₂H₅)₃ are about 0.2 and 0.15 ppm at the working temperature of 180°C, respectively. This result suggests potential applications of the ultralong ZnO nanowires in monitoring flammable, toxic and corrosive gases.     

Utilization of standardless analysis algorithms using WDXRF and XRD for Egyptian iron ore identification

On the basis of fundamental parameter approaches, the validity of standardless wavelength dispersive X‐ray fluorescence (WDXRF) and X‐ray powder diffraction algorithms was confirmed for analyzing Egyptian iron ore samples collected from two different locations, Aswan and Baharyia. The studied Egyptian iron ores represent different depositional environments and consequently exhibit variable mineralogical and chemical compositions. In the case of WDXRF analysis, the ground powders of iron ore samples were mixed and pressed with low contamination binder in a mass ratio of wax: sample = 4: 0.9 g at 120 kN cm^?2. A standardless method for quantitative WDXRF was employed, which requires accurate determination of the amount of organic material in the sample. On the basis of differential thermal analysis, a new method is introduced for the determination of loss of ignition. With the application of the proposed method and standardless quantitative analysis, results for 12 elements in iron ores were obtained: Fe, Mn, Mg, Si, Al, Ca, Na, K, S, Ba, Zn, and Cl. The reliability and precision of the adopted procedure were tested against a standard reference material ‘Iron ore concentrate (SRM 690, NIST, USA)’. The quantitative analysis results of the certified reference material were found acceptable. Depending on the WDXRF results, the powder samples were directly introduced to X‐ray powder diffraction goniometry, and the phase compositions were quantitatively determined by using a standardless analysis program based on Rietveld method. The main phases of all iron ore samples are the hematite and goethite, whereas other phases are found with varying ratios, namely quartz, nordstrandite, rhodochrosite, kaolinite, todorokit, bassanit, andydrite, and hydroxyapatite. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of the reaction conditions on the formation of the ZnO nanostructures

ZnO nanorods were synthesized through a simple chemical method by reacting Zn(C₂H₃O₂)₂·2H₂O and NaOH at low temperature and the effects of changing the order of addition of reactants on the morphological evolution of ZnO nanorods were investigated. The samples were characterized by using XRD, SEM, EDX, TEM, BET and Raman techniques. Optical properties of the ZnO nanostructures were too investigated by UV–Vis spectroscopy at room temperature.The hexagonal wurtzite phase of ZnO was confirmed by X-ray diffraction (XRD) for all the samples. SEM and TEM analysis indicated that different morphologies were obtained by changing the order of addition of reactants.     

Ultra‐high long‐term stability of oxide‐TTFTs under current stress

In this letter the stability of transparent thin‐film transistors (TTFTs) based on the ZnO–SnO₂ (ZTO) material system is investigated. Bottom‐gate devices have been subject to electrical stress via a gate–source bias of 10 V and a drain‐source bias of 10 V leading to a drain–source current of 188 µA. In optimized TTFTs with a composition of [Zn]:[Sn] = 36:64 the relative change of the saturated field effect mobility was less than 1% and the threshold voltage shift was about 320 mV after 1000 hours of operation. This extraordinary stability of ZTO TTFTs underlines their suitability as drivers in active matrix OLED displays. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Controllable Preparation of Hierarchical ZnO Nanocages and its Oxygen Vacancy through the Nanoscale Kirkendall Process

The synthesis of ZnO with tailorable shapes and point defects is important for its potential applications. Here, a facile approach is demonstrated to prepare ZnO nanocages with controllable porous shell structures though sintering a Zn‐based cyanide‐bridged coordination polymer under different temperatures. The transformation of ZnCP microspheres into ZnO nanocages is based on two types of nanoscale Kirkendall effect, which are related to low temperature solid–solid interfacial oxidation and high temperature solid–gas interfacial reaction, respectively. At low temperature (around 300 °C) and before the ZnCP decomposition, the novel “hierarchical ZnO bigger nanocages embedded with smaller nanocages with 10 nm nanocrystals” can be generated. By contrast, when coming to the total decomposition of ZnCP at 800 °C, ZnO nanocages with significantly increased sizes and large cavities are generated, and large amounts of oxygen vacancies (V_O) are created at the same time, leading to the dramatic increased luminescence intensities of the UV peak due to V_O at 540 nm. Thus, the luminescence intensities versus defect concentration in the prepared ZnO nanocages can also be controlled by tuning the sintering temperatures.     

Fast piezoresistive sensor and UV photodetector based on Mn‐doped ZnO nanorods

A low cost hydrothermal synthesis method to synthesize Mn‐doped ZnO nanorods (NRs) with controllable morphology and structure has been developed. Ammonia is used to tailor the ammonium hydroxide concentration, which provides a source of OH^– for hydrolysis and precipitation during the growth instead of HMT. The morphological, chemical composition, structural, and electronic structure studies of the Mn‐doped ZnO NRs show that the Mn‐doped ZnO NRs have a hexagonal wurtzite ZnO structure along the c‐axis and the Mn ions replace the Zn sites in the ZnO NRs matrix without any secondary phase of metallic manganese element and manganese oxides observed. The fabricated PEDOT:PSS/Zn_0.85Mn_0.15O Schottky diode based piezoresistive sensor and UV photodetector shows that the piezoresistive sensor has pressure sensitivity of 0.00617 kPa^–1 for the pressure range from 1 kPa to 20 kP and 0.000180 kPa^–1for the pressure range from 20 kPa to 320 kPa with relatively fast response time of 0.03 s and the UV photodetector has both relatively high responsivity and fast response time of 0.065 A/W and 2.75 s, respectively. The fabricated Schottky diode can be utilized as a very useful human‐friendly interactive electronic device for mass/force sensor or UV photodetector in everyday living life. This developed device is very promising for small‐size, low‐cost and easy‐to‐customize application‐specific requirements. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)