The photocatalytic activity of sprayed Zn1 − xMgxO thin films

ZnO has received much attention in the degradation and complete mineralization of environmental pollutants. For the purpose of increasing the photocatalytic efficiency of ZnO, Mg was doped into ZnO thin films.Zn_1 − xMg_xO thin films were prepared by spray pyrolysis method on glass substrates. The deposition temperature was 500 °C. Mg concentration was varied in the range of 0.0 to 0.3 in intervals of 0.05. The pure ZnO films were polycrystalline with preferred orientation (100). Zn_1 − xMg_xO becomes amorphous with increasing Mg concentration. The optical band gap of Zn_1 − xMg_xO changes from 3.26 to 3.59 eV with increasing Mg content. Also, the photocatalytic activity increased with Mg, and the film with x = 0.3 showed the best result.     

Fabrication and properties of p-type K doped Zn1−xMgxO thin film

A series of K doped Zn_1−xMg_xO thin films have been prepared by pulsed laser deposition (PLD). Hall-effect measurements indicate that the films exhibit stable p-type behavior with duration of at least six months. The band gap of the K doped Zn_1−xMg_xO films undergoes a blueshift due to the Mg incorporation. However, photoluminescence (PL) results reveal that the crystallinity decreased with the increasing of Mg content. The fabricated K doped p-type Zn_0.95Mg_0.05O thin film exhibits good electrical properties, with resistivity of 15.21 Ω cm and hole concentration of 5.54 × 10¹⁸ cm⁻³. Furthermore, a simple ZnO-based p-n heterojunction was prepared by deposition of a K-doped p-type Zn_0.95Mg_0.05O layer on Ga-doped n-type ZnO thin film with low resistivity. The p-n diode heterostructure exhibits typical rectification behavior of p-n junctions.     

Effect of Ag-doping on crystal structure and high temperature thermoelectric properties of c-axis oriented Ca3Co4O9 thin films by pulsed laser deposition

Ag-doped Ca₃Co₄O₉ thin films with nominal composition of Ca_3−xAg_xCo₄O₉ (x = 0∼0.4) have been prepared on sapphire (0 0 0 1) substrates by pulsed laser deposition (PLD). Structural characterizations and surface chemical states analysis have shown that Ag substitution for Ca in the thin films can be achieved with doping amount of x ≤ 0.15; while x > 0.15, excessive Ag was found as isolated and metallic species, resulting in composite structure. Based on the perfect c-axis orientation of the thin films, Ag-doping has been found to facilitate a remarkable decrease in the in-plane electrical resistivity. However, if doped beyond the substitution limit, excessive Ag was observed to severely reduce the Seebeck coefficient. Through carrier concentration adjustment by Ag-substitution, power factor of the Ag-Ca₃Co₄O₉ thin films could reach 0.73 mW m⁻¹ K⁻² at around 700 K, which was about 16% higher than that of the pure Ca₃Co₄O₉ thin film.     

Preparation, structure and electrical conductivity of the pyrochlore-type phase Sm2Zr2O7 codoped with bivalent magnesium and trivalent dysprosium cations

The pyrochlore-type phases with the compositions of SmDy_1−xMg_xZr₂O_7−x/2 (0 ≤ x ≤ 0.20) have been prepared by pressureless-sintering method for the first time as possible solid electrolytes. The structure and electrical conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics have been studied by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy measurements. SmDy_1−xMg_xZr₂O_7−x/2 (x = 0, 0.05, 0.10) ceramics exhibit a single phase of pyrochlore-type structure, and SmDy_1−xMg_xZr₂O_7−x/2 (x = 0.15, 0.20) ceramics consist of pyrochlore phase and a small amount of the second phase magnesia. The total conductivity of SmDy_1−xMg_xZr₂O_7−x/2 ceramics obeys the Arrhenius relation, and the total conductivity of each composition increases with increasing temperature from 673 to 1173 K. SmDy_1−xMg_xZr₂O_7−x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The highest total conductivity value is about 8 × 10⁻³ S cm⁻¹ at 1173 K for SmDy_1−xMg_xZr₂O_7−x/2 ceramics.     

Effects of Mg substitution on the structural, optical, and electrical properties of CuAlO2 thin films

Mg-doped CuAlO₂ thin films are prepared by the chemical solution method. The XRD results show that the solid solubility of Mg species on Al sites in CuAlO₂ lattice is lower than 2 at.%. When less than 2 at.% of Mg is added to the CuAlO₂ film, the surface roughness of the films was reduced with Mg substitution. Moreover, the c-axis orientation of the films improves because the in-plane fusion between CuAlO₂ crystallites is hindered. Optical and electrical measurements show that substituting Al³⁺ in the films with Mg²⁺ increases both their transmittance in the visible region and their optical band gaps. As well, their electrical conductivity is enhanced. At 300 K, the conductivity of the 1 at.% Mg-doped sample is up to 5.2 × 10⁻³ S/cm. Thus, Mg-doped CuAlO₂ films may have potential applications as transparent conductive oxides.     

Structural, morphological and optical properties of Bi2−xSbxSe3 thin films grown by electrodeposition

Ternary single-phase Bi_2−xSb_xSe₃ alloy thin films were synthesized onto Au(1 1 1) substrates from an aqueous solution containing Bi(NO₃)₃, SbCl₃, and SeO₂ at room temperature for the first time via the electrodeposition technique. The electrodeposition of the thin films was studied using cyclic voltammetry, compositional, structural, optical measurements and surface morphology. It was found that the thin films with different stoichiometry can be obtained by controlling the electrolyte composition. The as-deposited films were crystallized in the preferential orientation along the (0 1 5) plane. The SEM investigations show that the film growth proceeds via nucleation, growth of film layer and formation of spherical particles on the film layer. The particle size and shape of Bi_2−xSb_xSe₃ films could be changed by tuning the electrolyte composition. The optical absorption spectra suggest that the band gap of this alloy varied from 0.24 to 0.38 eV with increasing Sb content from x = 0 to x = 0.2.     

Effect of lanthanum doping on linear and nonlinear-optical properties of Bi3TiNbO9 thin films

Lanthanum doped Bi₃TiNbO₉ thin films (LBTN-x, La³⁺ contents x = 5%, 15%, 25% and 35 mol.%) with layered perovskite structure were fabricated on fused silica by pulsed laser deposition method. Their linear and nonlinear optical properties were studied by transmittance measurement and Z-Scan method. All films exhibit good transmittance (>55%) in visible region. For lanthanum doping content are x = 5%, 15% and 25 mol.%, the nonlinear absorption coefficient of LBTN-x thin films increases with the La³⁺ content, then it drops down at x = 35 mol.% when the content of La³⁺ in (Bi₂O₂)²⁺ layers is high enough to aggravate the orthorhombic distortion of the octahedra. We found that, 25 mol.% is the optimal La³⁺ content for LBTN-x thin films to have the largest nonlinear absorption coefficient making the LBTN-x film a promising candidate for absorbing-type optical device applications.     

Structural and optical analysis of ZnBeMgO powder and thin films

We here report the structural and optical studies of Zn_1−x−yBe_xMg_yO (0 ≤ x ≤ 0.15; 0 ≤ y ≤ 0.20) powders and thin films. From the Rietveld refinement of the powder X-ray diffraction (XRD) patterns it was revealed that the value of ‘a’ lattice parameter remains almost unchanged whereas ‘c’ parameter reduces with Be and Mg co-doping in ZnO. The Zn-O bond length also decreases in co-doped samples. Raman studies of the pure ZnO powder showed all the characteristic peaks of the wurtzite hexagonal structure and with (Be, Mg) co-doping new modes appeared which can be attributed to arise as a result of substitution. The XRD of the films prepared from the powders using pulsed laser deposition (PLD) technique exhibited the preferential orientation and with increase in co-doping the (0 0 0 2) peak also shifts to higher 2θ values suggesting the incorporation of Be/Mg at the Zn-site. From the UV-visible optical transmittance measurement it was noticed that the band gap of the pristine ZnO film is 3.3 eV which enhanced up to 4.51 eV for Zn_0.7Be_0.1Mg_0.2O film which lies in the solar blind region and is very useful in the realization of deep UV detectors.     

Heat treatment induced phase separation and phase transformation of ZrNxOy thin films deposited by ion plating

Nanocrystalline ZrN_xO_y thin films were deposited on p-type Si (100) substrates using hollow cathode discharge ion-plating (HCD-IP) and the films were annealed at 700 and 900 °C in the controlled atmosphere. The purpose of this study was to investigate the phase separation, phase transformation and the accompanying change of properties of the heat-treated ZrN_xO_y films deposited by ion plating. With the increase of oxygen flow rate ranging from 0 to 10 sccm, the primary phase of the as-deposited films evolved from ZrN to nearly amorphous structure and further to monoclinic ZrO₂ (m-ZrO₂). After heat treatment at 700 and 900 °C, phase transformation occurred in the samples deposited at 8 and 10 sccm O₂, where a stoichiometric crystalline Zr₂ON₂ was found to derive from m-ZrO₂ with dissolving nitrogen (m-ZrO₂(N)). The hardness of the ZrN_xO_y thin films could be correlated to the fraction of Zr₂ON₂ + m-ZrO₂. The film hardness decreased significantly as the fraction of ZrO₂ + Zr₂ON₂ exceeded ~ 60%, which was due to phase transition by increasing oxygen flow rate or phase transformation induced by heat treatment. The phase separation of m-ZrO₂ from ZrN with dissolving oxygen (ZrN(O)) may relieve the residual stress of the ZrN_xO_y specimens deposited at 5 and 8 sccm O₂, while direct formation of m-ZrO₂ increased the stress of the film deposited at 10 sccm O₂. On the other hand, the phase transformation from m-ZrO₂(N) to Zr₂ON₂ by heat treatment at both 700 and 900 °C may effectively relieve the residual stress of the ZrN_xO_y films.     

Preparation of delafossite-type CuCrO2 films by sol-gel method

High-quality c-axis oriented delafossite-type CuCrO₂ films were successfully prepared by a simple sol-gel method. The microstructure, optical properties as well as room temperature resistivity were studied. It was found that the grain sizes of CuCrO₂ films pretreated with different temperatures are different; the films were smooth and consisted of fine particles. The maximal transmittance of CuCrO₂ films can reach 70% in the visible region. Optical transmission data of CuCrO₂ films indicate a direct band gap and an indirect-gap of about 3.15 eV and 2.66 eV, respectively. The carrier mobility of the films pretreated at 300 °C is smaller than that of the films pretreated at a higher temperature, because of the stronger carrier scattering.     

Growth and characterization of chemical bath deposited Cd1−xZnxS thin films

Cd_1−xZn_xS (0 ≤ x ≤ 1) thin films have been deposited by chemical bath deposition method on glass substrates from aqueous solution containing cadmium acetate, zinc acetate and thiourea at 80 ± 5 °C and after annealed at 350 °C. The structural, morphological, compositional and optical properties of the deposited Cd_1−xZn_xS thin films have been studied by X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) and UV-vis spectrophotometer, respectively. X-ray diffraction analysis shows that for x < 0.8, the crystal structure of Cd_1−xZn_xS thin films was hexagonal structure. For x > 0.6, however, the Cd_1−xZn_xS films were grown with cubic structure. Annealing the samples at 350 °C in air for 45 min resulted in increase in intensity as well as a shift towards lower scattering angles. The parameters such as crystallite size, strain, dislocation density and texture coefficient are calculated from X-ray diffraction studies. SEM studies reveal the formation of Cd_1−xZn_xS films with uniformly distributed grains over the entire surface of the substrate. The EDX analysis shows the content of atomic percentage. Optical method was used to determine the band gap of the films. The photoluminescence spectra of films have been studied and the results are discussed.     

Relationships between Zr substitution for Ti and microwave dielectric properties in Mg(ZrxTi1−x)O3 ceramics

The influence of Zr substitution for Ti on the microwave dielectric properties and microstructures of the Mg(Zr_xTi_1−x)O₃(MZ_xT) (0.01 ≤ x ≤ 0.3) ceramics was investigated. The quality factors of Mg(Zr_xTi_1−x)O₃ ceramics with x = 0.01-0.05 were improved because the solid solution of a small amount of Zr⁴⁺ substitution in the B-site could increase density and grain size. An excess of Zr⁴⁺ resulted in the formation of a great deal of secondary phase that declined the microwave dielectric properties of MZ_xT ceramics. The temperature coefficient of resonant frequency (τ_f) of Mg(Zr_xTi_1−x)O₃ ceramics slightly increased with increasing Zr content, and the variation in τ_f was attributed to the formation of secondary phases.     

Effect of Nb doping on the phase transition and optical properties of sol-gel TiO2 thin films

Various content Nb-doped TiO₂ thin films were prepared by sol-gel process. XRD analysis shows that the existence of crystalline TiO₂ in anatase and rutile form depends on the Nb content in the examined samples. It is observed that Nb promotes the anatase to rutile phase transition but has a depression effect on the anatase grain growth. It is found that incorporation of about 4 at.% of Nb completely transforms anatase TiO₂ to the rutile form at a calcination temperature as high as 900 °C. The mechanism is proposed. Optical analyses show that the films have an average of 60% transmission in visible region. The energy gap values using Tauc's formula have also been estimated. The band gap of rutile Ti_1−xNb_xO₂ solid solutions increases with increasing x.     

Mg-substituted ZnNb2O6-TiO2 composite ceramics for RF/microwaves ceramic capacitors

Microstructure and microwave dielectric properties of Mg-substituted ZnNb₂O₆-TiO₂ microwave ceramics were investigated. Mg acted as a grain refining reagent and columbite phase stabilization reagent. With an increasing Mg content, the amount of ixiolite (Zn, Mg) TiNb₂O₈ decreased, and the amount of (Zn_0.9Mg_0.1)_0.17Nb_0.33Ti_0.5O₂ and columbite increased. ZnO-Nb₂O₅-1.75TiO₂-5 mol.%MgO exhibited excellent dielectric properties (at 950 °C): ?_r = 35.6, Q × f = 16,000 GHz (at 5.6 GHz) and τ_f = −10 ppm/°C. The material was applied successfully to make RF/microwaves ceramic capacitor, whose self-resonance frequency was 19 GHz at low capacitance of 0.13 pF.     

Evidence of room temperature ferromagnetism in Co-doped transparent CuAlO2 semiconductor

We synthesized CuAl_1−xCo_xO₂ (x = 0.00-0.07) thin films by solid-state reaction from Cu₂O and Al₂O₃ on a sapphire (0 0 1) substrate by a simple and cost-effective spin-on technique. X-ray diffraction and Raman spectroscopy confirm the formation of single impurity-free delafossite CuAlO₂ structure for all the compositions. We observed diamagnetism for pristine CuAlO₂ and ferromagnetism for Co-doped CuAlO₂ at room temperature. Specially, the coercivity (H_c) and saturation magnetization (M_s) are significantly enhanced with Co composition from 1 at.% to 5 at.% but show the reverse tendency with higher Co content.     

Electrical properties of binder-free thick film BaYxBi1−xO3 NTC thermistors

The microstructure and electrical properties of BaY_xBi_1−xO₃ thick film negative temperature coefficient thermistors, fabricated by screen printing, were investigated. The sintered thick films were the single-phase solid solutions of the BaY_xBi_1−xO₃ compounds with a monoclinic structure. The added Y₂O₃ led to a significant decrease in the grain size of the thermistors. The resistivity and coefficient of temperature sensitivity for the BaY_xBi_1−xO₃ (0 ≤ x ≤ 0.15) thick film NTC thermistors decreased first with increasing x in the range of x < 0.04 and then increased with further increase in x.     

Preparation and characterization of Mg-doped CaCu3Ti4O12 thin films

Mg-doped CaCu_3?xMg_xTi₄O₁₂ (x=0, 0.05, 0.1, 0.15, 0.2, at.%) thin films were prepared by a modified sol?gel method. A comparative study on the microstructure and electrical properties of Mg-doped CaCu₃Ti₄O₁₂ (CCTO) thin films was carried out. The grain sizes of the Mg-doped CCTO thin films were smaller in comparison to the undoped CCTO films. Furthermore, compared to undoped CCTO films, Mg-doped CCTO thin films obtained higher dielectric constant as well as excellent frequency stability. Meanwhile, Mg doping could reduce the dielectric loss of CCTO thin films in the frequency range of 10⁴?10⁶ Hz. The results showed that the Mg-doped CCTO thin films had the better electrical characteristics compared with the undoped CCTO films. The nonlinear coefficient of Mg-doped CCTO thin films at x=0.15 and x=0.1 was improved to 7.4 and 6.0, respectively.     

Nickel-lithium oxide alloy transparent conducting films deposited by spray pyrolysis technique

In this research, nickel oxide (NiO) transparent semiconducting films are prepared by spray pyrolysis technique on glass substrates. The effect of Ni concentration in initial solution and substrate temperature on the structural, electrical, thermoelectrical, optical and photoconductivity properties of NiO thin films are studied. The results of investigations show that optimum Ni concentration and suitable substrate temperature for preparation of basic undoped NiO thin films with p-type conductivity and high optical transparency is 0.1 M and 450 °C, respectively. Then, by using these optimized deposition parameters, nickel-lithium oxide ((Li:Ni)O_x) alloy films are prepared. The XRD structural analysis indicate the formation of the cubic structure of NiO and (Li:Ni)O_x alloy films. Also, in high Li doping levels, Ni₂O₃ and NiCl₂ phases are observed. The electrical measurements show that the resistance of the films decreases with increasing Li level up to 50 at%. For these films, the optical band gap and carrier concentration are obtained to be 3.6 eV and 10¹⁵-10¹⁸ cm⁻³, respectively.     

Quantum confinement effects and band gap engineering of SnO2 nanocrystals in a MgO matrix

Nanocrystal formation of SnO₂ in xSnO₂-(100 − x)MgO (x in mol.%) nanocrystalline composite thin films is reported. SnO₂ and MgO exhibit strong immiscibility behavior below 750 °C, leading to controllable particle size of SnO₂ in the MgO matrix by changing their composition. The particle size of SnO₂ can also be controlled by increasing the annealing temperature. Above 750 °C MgO and SnO₂ react to yield a MgO-Mg₂SnO₄-SnO₂ composite in which the size of the SnO₂ nanophase increases with increasing temperature. By controlled choice of the composition and annealing conditions the band gap of SnO₂ can be continuously increased from 3.89 to 4.5 eV. We discuss this behavior in terms of the quantum confinement effect. The method provides a generic approach to tuning the band gap in nanocomposite systems over a wide energy range.     

Nano-grain Al2O3 crystals grown by sputtering of aluminium on CoCrPt thin films for potential application in ultra-high-density recording media

Designing supraceramic assemblies based on Al₂O₃ has remained a challenge due to the problems associated with the suitable dispersion in neat compounds and ability to control the preferred orientation in a unique fashion. Herein, granular HCP-(CoCrPt)_100−X(Al₂O₃)_X (X represents the percent weight) thin films with Si(1 0 0) substrates have been fabricated using sputtering technique followed by annealing treatment. Structural and magnetic properties of thin film have been investigated for potential application in magnetic recording media. It was shown that coercivity increased from 0.5 to 2.5 kOe by increasing the nano-grain Al₂O₃ content in the CoCrPt magnetic layers. In CoCrPt-Al₂O₃ thin films coercivity of 2.5 kOe has been obtained with increasing the Al₂O₃ content from 3 to 13 wt.% in the annealed thin films. The structural properties of the samples were studied using X-ray diffraction (XRD) and transmission electron microscope (TEM) equipped with selected area electron diffraction (SAED). The magnetic properties of the samples were measured with a vibrating sample magnetometer (VSM). The VSM results showed that the HCP-CoCrPt-Al₂O₃ granular films are a promising candidate for ultra-high-density recording media because of its low Al₂O₃ content and simple manufacturing process.