Effect of annealing and composition on crystal structure,surface morphology and optical absorption of chemically deposited Cd1‐xSnxS films

Cd_1‐xSn_xS thin films were successfully deposited on suitably cleaned glass substrate by chemical bath deposition method at 74 °C. Hydrated Stannous Chloride (SnCl₂.2H₂O) in aqueous solution was added to the CdS growing solution in different proportions. The experimental results indicate, a successful doping for lower concentration of Sn, saturation for intermediate doping levels, and a degradation of the doping process for higher concentration of Sn. Indirect (X‐ray diffraction) and Direct (Scanning electron microscopy) measurements were performed to characterize the growth and the nature of crystallinity of the different Cd_1‐xSn_xS films. The effect of annealing on the crystal structure and morphology of the deposited films has also been discussed. The X‐ray diffraction spectra show that the thin films are polycrystalline and have both cubic and hexagonal structure. The Interplanar spacing, lattice constant, grain size, strain, and dislocation density were calculated for as‐deposited and annealed films. The grain size was found to decrease from 5 nm to 0.89 nm with doping concentration of Sn. The grain size further decreased due to annealing at 400 °C. SEM studies show layered growth and long needle like structures along with some voids. After annealing the densification and smaller size of the particles was also observed. The optical absorption spectra show shifting of absorption peaks towards lower wavelength side (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and magnetic properties of Nd‐doped ZnO nanoparticles

Nd‐doped ZnO nanoparticles with different concentration were synthesized by sol‐gel method. The structures, magnetic and optical properties of as‐synthesized nanorods were investigated. X‐ray diffraction (XRD) and x‐ray photoelectron spectroscopy (XPS) results demonstrated that Nd ions were incorporated into ZnO lattice; but Zn_1‐xNd_xO nanoparticles with Nd concentration of x = 0.05 showed Nd₂O₃ phase, so the saturation concentration of Nd in Zn_1‐xNd_xO is less than 5 at%. Vibrating sample magnetometer (VSM) measurements indicated that Nd doped ZnO possessed dilute ferromagnetis behaviour at room temperature. Photoluminescence spectroscopy (PL) showed that Nd ions doping induced a red slight shift and decrease in UV emission with increase of Nd concentration.     

Experimental and first‐principle investigation of Cu‐doped ZnO ferromagnetic powders

Zn_1‐xCu_x O powders were synthesized by using sol‐gel method. Electronic band structure and ferromagnetic properties of Zn_1‐xCu_x O powders were studied experimentally and theoretically. The simulations are based upon the Perdew‐Burke‐Ernzerhof form of generalized gradient approximation within the density functional theory. Zn_1‐xCu_x O shows dilute ferromagnetism, as a saturated magnetization of 0.9×10^‐3emu/g was observed for Zn_0.95Cu_0.05O powders. The strong p ‐d hybridization between Cu and its four neighbouring O atoms is responsible for the ferromagnetism. Comparing with ZnO whose Fermi level locates at the valence band maximum, the Fermi level of the Zn_1‐xCu_x O shifts upward into the valence band and hence the Zn_1‐xCu_x O system exhibits theoretically a p ‐type metallic semiconducting property. The Zn_1‐xCu_x O system may be a potential candidate in spintronics. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Co nanoclusters as origin of ferromagnetism in sol‐gel synthesized Zn1‐xCoxO (x = 0.05, 0.10 and 0.15) samples

We report on the structural and magnetic properties of the polycrystalline samples of Zn_1‐xCo_xO (x = 0.05, 0.10 and 0.15) synthesized via sol‐gel route. The air sintered samples of all compositions exhibit paramagnetic behaviour at room temperature, on the other hand the same samples on annealing in Ar/H₂ atmosphere show room temperature ferromagnetism (RTFM) with enhanced magnetization. The value of magnetization increases with the Co concentration (x) in both the air sintered and Ar/H₂ annealed samples. The observed ferromagnetism in the Ar/H₂ annealed Zn_1‐xCo_xO (x = 0.05, 0.10 and 0.15) samples is attributed to the presence of Co nanoclusters as detected by XRD and FESEM‐EDAX. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of hexagonal ferrites BaFe12‐2xZnxTixO19 (0 ≤ x ≤ 2) by thermal decomposition of freeze‐dried precursors

Substituted barium hexaferrites, BaFe_12‐2xZn_xTi_xO₁₉ (0 ≤ x ≤ 2), have been synthesized by thermal decomposition of freeze‐dried acetate precursors. Decomposition and phase formation were investigated by means of thermal analysis, XRD and IR spectroscopy. The initially amorphous decomposed precursor reacts to the substituted hexaferrite via a spinel‐like maghemite (γ‐Fe₂O₃) and Zn/Ti containing spinel ferrites. The synthesis method allows a decrease of the reaction temperature and time, necessary for producing a single phase hexaferrite. At relative low reaction temperatures, the substitution rate x shows remarkable differences at different iron sublattices. For x ≤ 0,8 this selective substitution results in an increase of magnetization as x grows. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural properties of Zn1–xMgxO nanomaterials prepared by sol‐gel method

The mixed oxides Zn_1‐xMg_xO (ZMO) were prepared as nano‐polycrystalline powders and thin films by a simple sol–gel process and dip coating method. Thermogravimetric (TG) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structural and microstructural analysis was carried out applying x‐ray diffraction (XRD) and Rietveld method. Analysis showed that for x < 0.25, Mg replaces Zn substitutionally yielding ZMO single phase, while for x ≥ 0.25 two phases are identified ZMO and MgO. Replacing Zn²⁺ by Mg²⁺ distorts the cation tetrahedrons and decreases the lattice constants ratio c/a of the wurtzite ZMO which deviate the lattice gradually from the hexagonal structure as Mg⁺² increases. These distortions are attributed to the difference in electronic configuration of the two cations which suppress the paraelectric‐ferroelectric phase transition in the ZMO wurtzite. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and photoluminescence properties of CdS solid solution semiconductor

Photoluminescence (PL) emitted from Cd_1‐xZn_xS and CdS_1‐ySe_y solid solution semiconductor was significantly stronger than PL from the pure CdS and CdSe semiconductor. The samples were prepared using an improved Se‐S‐Na₂S flux route. Photoluminescence in Cd_1‐xZn_xS crystal was brightly yellow at the room temperature under VU radiation. The phase and composition of the solid solution was measured by the XRD and was confirmed by UV‐NIS spectrum as x of 0.3 and y of 0.2. The enhanced photoluminescence was presumably due to the introduction of extra defect (vacancies) by solid solution action and consequently the increasing of luminescence center concentration. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and optical properties of Mg‐doped ZnO nanoparticles by polyacrylamide method

Mg‐doped ZnO (Mg_xZn_1‐xO) nanoparticles with precise stoichiometry are synthesized through polyacrylamide polymer method. Calcination of the polymer precursor at 650 °C gives particles of the homogeneous solid solution of the (Mg_xZn_1‐xO) system in the composition range (x < 0.15). ZnO doping with Mg causes shrinkage of lattice parameter c. The synthesized Mg_xZn_1‐xO nanoparticles are typically with the diameter of 70–85 nm. Blue shift of band gap with the Mg‐content is demonstrated, and photoluminescence (PL) from ZnO has been found to be tunable in a wide range from green to blue through Mg doping. The blue‐related PL therefore appeared to be caused by energetic shifts of the valence band and/or the conduction band of ZnO. Mg_xZn_1‐xO nanoparticles synthesized by polyacrylamide‐gel method after modified by polyethylene glycol surfactant have a remarkable improvement of stability in the ethanol solvent, indicating that these MZO nanoparticles could be considered as the candidate for the application of solution–processed technologies for optoelectronics at ambient temperature conditions.     

X‐ray powder diffraction structural characterization of Ba1‐xEuxTiO3 ternary oxides

The single‐phase Ba_1‐xEu_xTiO₃ (0.1≤x≤0.4) samples have been synthesized by solid state reaction under high pressure and ‐temperature. X‐ray powder diffraction data was determined by MS Modeling using Reflex Powder Indexing technique. The Ba_1‐xEu_xTiO₃ series exhibited an interesting orthorhombic‐tetragonal‐cubic structural transformation as Eu composition increases, the distinct change of the X‐ray diffraction peak profile in the vicinity of 45.5º is characteristic of structural transformation. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and magnetic studies of Mn‐doped ZnO

The bulk samples of Mn‐doped ZnO were synthesized with the nominal compositions Zn_1‐xMn_xO (x = 0.02, 0.05, 0.10, 0.15) by the solid‐state reaction and sol‐gel methods. In both the methods the samples were finally sintered at ∼700 °C in air. The X‐ray diffraction (XRD) studies of the samples synthesized by the solid‐state reaction method exhibit the presence of wurtzite (hexagonal) crystal structure similar to the parent compound (ZnO) in all the samples, suggesting that doped Mn ions sit at the regular Zn sites. However, same studies spread over the samples with Mn content ≥5% and synthesized by the sol‐gel method reveal the occurrence of some secondary phase in addition to the majority wurtzite phase. The magnetic measurements by vibrating sample magnetometer (VSM) clearly indicate ferromagnetic interaction at room temperature in all the samples. The Curie temperatures (T_c) and magnetization vary with concentration of Mn ions in the samples. However, the samples synthesized by sol‐gel method were found to have lower Tc values and also lower magnetization as compared to the corresponding samples synthesized by solid‐state reaction method. It could possibly be due to the presence of antiferromagnetic islands and smaller crystallite sizes in the samples prepared by sol‐gel method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multimode phonon structure of Be‐containing II ‐ VI mixed crystals determined by IR spectroscopic ellipsometry

Spectroscopic ellipsometry in the infrared spectral range 250‐5000 cm^‐1 is used for analysis of the dielectric response of Zn_1‐x‐yBe_xMg_ySe and Zn_1‐x‐yBe_xMn_ySe crystals grown by a high‐pressure Bridgman method. Ellipsometric spectra display features in the spectral range 390‐500 cm^‐1 associated with BeSe‐type phonon modes. In the optical spectra of Zn_1‐x‐yBe_xMg_ySe crystals both BeSe‐type and MgSe‐type lattice absorption bands are detected. The MgSe‐like modes are located at approximately 300 cm^‐1. The complex dielectric functions can be reproduced using a model with two or three and one or two classical damped oscillators corresponding to the BeSe‐like and the MgSe‐like transverse‐optical phonon modes, respectively. The frequencies of longitudinal‐optical phonons have been derived from the dielectric loss functions. A red‐shift of the BeSe‐like phonons frequencies with a mean rate 0.42 cm^‐1 (0.50 cm^‐1) per mole percent of Mg (Mn) incorporated to the alloy has been found for examined concentration range x, y ≤ 0.25. A noticeable damping the intensities of BeSe‐type modes with increasing fraction of Mg and Mn dopant is observed in comparison to the strengths of BeSe‐type modes in Zn_1‐xBe_xSe crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and optical property of BexZn1‐xO nanorod arrays

Be_xZn_1‐xO nanorod arrays with high crystalline quality were fabricated on Si substrate by a simple, low‐cost hydrothermal method. The effect of Be‐corporation on the structure, morphology and optical property of ZnO nanorod arrays was investigated. The diameter of Be_xZn_1‐xO nanorods gradually decreased and the length of them increased with increasing Be concentration. Edge emissions of the Be_xZn_1‐xO nanorods show a obvious blue shift upon the increase of the Be content.     

XRD,IR, and Raman investigations of structural properties of Dy2‐xHox O3 prepared by sol gel procedure

The Rare earth mixed oxides Dy_2‐xHo_x O₃ (0.0 ≤ x ≤ 2.0) solid solution was synthesized by a sol–gel process. X‐ray diffraction (XRD) data were collected and crystal structure and microstructure analyses were performed applying Rietveld refinement method. Infrared and Raman spectroscopy were used to define the microstructure and to locally probe the structure of the samples. The cationic distribution over the two non‐equivalent sites 8b and 24d of the space group Ia3 is found to be randomly. The crystallite size and microstrain as well as Raman modes positions are influenced by Ho³⁺ concentration. The apparent size is isotropic but significant anisotropy is found for the microstrain with its largest value along the crystallographic direction [h00]. Inspite the single phase solid solution confirmed by Rietveld analysis for all samples, Raman spectra detected the coexistence of two phases; cubic and distorted monoclinic of too small amount or highly disordered, i.e. amorphous like, to be detected by XRD. The result indicates the ability of Raman spectroscopy to detect minor phases in solid solutions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and XRD analysis of the diluted magnetic semiconductor Zn1‐xNixO

Diluted magnetic semiconductor compound Zn_1‐xNi_x O (x =0.01, 0.02, 0.03, 0.04 and 0.05) was prepared by sol‐gel method and characterized using powder XRD for the distribution of electrons and bonding in the unit cell. The electronic structural studies of this material were carried out by maximum entropy method (MEM) for the quantitative and qualitative measurement on the inclusion and the effect induced on bonding by Ni doping. The spatial arrangement of charge and the bonding behavior of this material were analyzed from 3D, 2D and 1D density distributions. The evidence for the addition of Ni in the host lattice of Zn is realized. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of post-annealing temperature on structural,optical, and electrical properties of MgxZn1−xO films by RF magnetron sputtering

Mg_xZn_1?xO thin films were deposited on quartz substrates by RF magnetron sputtering. The effect of post-annealing temperature on structural, optical, and electrical properties was investigated with the annealing temperatures increasing from 450 to 750 °C. The crystallinity of Mg_xZn_1?xO film annealed at 650 °C was significantly improved while the film annealed at 750 °C showed little improvement. The electrical properties degraded with the increase of annealing temperature. The annealing temperature seemed to impact the E_g value of Mg_xZn_1?xO thin films because of the variation of carrier concentration.     

Preparation and investigation of (CuInSe2)x(2ZnSe)1‐x and (CuInTe2)x(2ZnTe)1‐x solid solution crystals

The (CuInSe₂)_x(2ZnSe)_1‐x and (CuInTe₂)_x(2ZnTe)_1‐x solid solution crystals prepared by Bridgman method and chemical vapor transport have been studied. The nature of the crystalline phases, the local structure homogeneity and composition of these materials have been investigated by X‐ray diffraction (XRD) and Electron Probe Microanalysis (EPMA) methods. The analysis revealed the presence of chalcopyrite‐sphalerite phase transition between 0.6 ≤ X ≤ 0.7. Lattice constants, value of σ position parameter and bond length between atoms were also calculated. It was found that the lattice parameters exhibit a linear dependence versus composition. The transmission spectra of solid solution crystals in the region of the main absorption edge were studied. It was established that the optical band gap of these materials changes non‐linearly with the X composition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical and optical properties of Cd1−xZnxS (0x0.18) grown by chemical bath deposition

Cd_1−xZn_xS films with 0x0.18 were grown by chemical bath deposition technique on glass substrates from an aqueous solution containing cadmium and zinc sulfate, ammonia and thiourea. Microstructural features, obtained from X-ray diffraction and scanning electron microscopy (SEM) measurements, reveal a predominance of Wurtzite structure and an homogenous microstructure formed by densely microcrystallines for all the samples studied. Cd_1−xZn_xS semiconductor was found to be resistive and of n-type. Also, the electron density decreases with increased x and the mobility reaches a maximum around x=0.12. Which means that the Cd_1−xZn_xS films at this composition are of high crystalline quality, i.e. having reduced intrinsic defect concentrations.     

Structure and morphological stability of (Lu1–xEux)2O3 thin films

(Lu_1–xEu_x)₂O₃ smooth, crack‐free, transparent films were prepared by the Pechini sol–gel method and a spin‐coating technique. Thermogravimetric analysis, differential thermal analysis and FITR spectroscopy were used to study the chemical processes during annealing of the films. Film structure, morphology and optical properties were investigated. X‐ray diffraction (XRD) analysis reveals the cubic phase of (Lu_1–xEu_x)₂O₃ films annealed in the 600–1000 °C temperature range. Smooth and crack‐free films with thicknesses of 250–1000 nm were obtained in the 600–800 °C temperature range. The thickness upper limit (1000 nm) of morphological stability of films (Lu_1–xEu_x)₂O₃ on sapphire substrates has been studied.     

Structure and electrical properties of Mg‐doped ZnO nanoparticles

Mg_xZn_1‐xO (x=0.01‐0.3) nanoparticles were synthesized by the sol‐gel technique using solutions of Mg and Zn based organometalic compounds. The electrical properties of Mg doped zinc oxide (ZnO) were studied within wide temperature range from 300 to 500 K under the N₂ gas flow (flow rate: 20 sccm) and in the frequency range from 40 Hz to 1 MHz for ac electrical measurements. The dc conductivities and the activation energies were found to be in the range of 10^‐9‐10^‐6 S/cm at the room temperature and 0.26‐0.86 eV respectively depending on doping rate of these samples. The ac conductivity was well represented by the power law Aω^s. The conduction mechanism for all doped ZnO could be related to correlated barrier hopping (CBH) model. The complex impedance plots (Nyquist plot) showed the data points lying on a single semicircle, implying the response originated from a single capacitive element corresponding to the nanoparticle grains. The crystal structures of the Mg_xZn_1‐xO nanoparticles were characterized using X‐ray diffraction. The calculated average particle sizes values of Zn_1‐xMg_xO samples are found between 29.72 and 22.43 nm using the Sherrer equation. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Paramagnetic behavior of Zn1−xMnxO at room temperature

Mn‐doped ZnO were synthesized by solid state reaction and sol‐gel method respectively. It was found that samples synthesized by solid state reaction containing Mn₂O₃ and MnO₂ are a mixture of ferromagnetic and paramagnetic phases. Contrary, samples without second phases were found to be paramagnetic at room temperature. According to previous report, interface effects between Zn‐rich Mn₂O₃ and MnO₂ interfaces may be the origin of the ferromagnetic behavior observed in our samples prepared by solid reaction, so the alloy of Zn_1−xMn_xO may be paramagnetic at room temperature. Prepared by sol‐gel technique, the samples without second phases in the XRD patterns are also room‐temperature paramagnetic. Therefore we believe that the magnetism of Zn_1−xMn_xO is paramagnetic at room temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)