Probing into the optical and electrical properties of hybrid Zn<Subscript>1−x</Subscript>Co<Subscript>x</Subscript>Se thin films

Probing into the elemental composition, structural, morphological, optical and electrical transport properties of chemically deposited Zn_1?xCo_xSe (0?≤?x?≤?0.275) thin films with a special emphasis given to the Co²⁺-concentration is presented in this paper. Elemental and structural analysis confirmed the successful realization of Co(ZnSe) thin films. Addition of Co²⁺ into ZnSe host lattice caused morphological changes from globule like morphology to the formation of leaf like appearance composing the disc-decked micro-flakes elongated in size. The optical studies done in the range of wavelengths between 350 to 1200 nm showed a slight red shift in the optical spectrum with increased Co²⁺ concentration in the ZnSe matrix. Effect of increased impurity addition is also reflected in the band gap measurements that a decrease in the bandgap, typically from 2.71 to 1.96 eV, is observed for an increase in Co²⁺ concentration from x?=?0–0.275. The other optical parameters namely, refractive index, extinction coefficient, power factor and dielectric constants were determined from these studies and other variations are adequately explained as a special reference to the Co-concentration. The composition dependence of the electrical transport characteristics were studied using the two-probe and Hall measurement techniques. The effect of Co-concentration on the transport characteristics has been studied and mechanism of an electrical conduction is discussed. A continuous increase in an electrical conductivity with n-type conduction has been observed for these samples.     

Structural and electrical studies of Cd<Subscript>1−x</Subscript>Zn<Subscript>x</Subscript> Te thin film by vacuum evaporation technique

Cd_1−xZn_xTe (where x = 0.02, 0.04, 0.06, 0.08) thin film have been deposited on glass substrate at room temperature by thermal evaporation technique in a vacuum at 2 × 10⁻⁵ torr. The structural analysis of the films has been investigated using X-ray diffraction technique. The scanning electron microscopy has been employed to know the morphology behaviour of the thin films. The temperature dependence of DC electrical conductivity has been studied. In low temperature range the thermal activation energy corresponding to the grain boundary—limited conduction are found to be in the range of 38–48 μeV, but in the high temperature range the activation energy varies between 86 and 1.01 meV. The built in voltage, the width of the depletion region and the operating conduction mechanism have been determined from dark current voltage (I–V) and capacitor-voltage (C–V) characteristics of Cd_1−xZn_xTe thin films.     

Effect of deposition ambient on structural and optical properties of Mg<Subscript>x</Subscript>Zn<Subscript>1−x</Subscript>O alloy thin films grown by RF sputtering

Mg_xZn_1−xO thin films were deposited on Corning eagle 2,000 glass substrates by a RF magnetron sputtering using a ceramic target. The effect of Ar/O₂ ratios on structural and optical properties was investigated. The XRD results showed that the film demonstrated the best structural properties when the Ar/O₂ ratio equal 7:3. Sputtering ambient seemed to have minor effect on the optical properties of Mg_xZn_1−xO thin films.     

Theoretical and experimental approaches to measuring mechanical properties of Zn<Subscript>1−x</Subscript>Co<Subscript>x</Subscript>O binary tetrahedral bulk semiconductors

We prepared a \({{\text{Zn}}_{1 - {\text{x}}}}{{\text{Co}}_{\text{x}}}{\text{O}}\) system as polycrystalline nanoparticles with various compositions \((x=0.01, 0.02, 0.03, 0.04, 0.05, {\text{and}} \; 0.10)\) using sol–gel techniques and use zinc acetate dihydrate and cobalt acetate tetrahydrate as precursors. Nanoparticles were pressed under a pressure of 4 tons for 5 min into 2 mm thick disk shaped compacts 10 mm in diameter, which were then annealed at 500 °C for 30 min under a 5B Ar atmoshpere. We carried out X-ray diffraction, scanning electron microscopy, and Vickers microhardness analyses of Co doped \({\text{Zno}}\)-based nano bulk materials in detail, focusing especially on theoretical and experimental mechanical analyses. We found that calculated values were higher than the Vickers microhardness experimental results. Doping ZnO with Co did not lead to significant changes in the a and c axes. The calculated hardness values are larger than those from the experiments. Acoording to the SEM and EDS images grain size decreases as Co doping increases and the amount of Zn decreases with Co doping, respectively.     

Chemical,morphological, structural,optical, and magnetic properties of Zn<Subscript>1−x</Subscript>Nd<Subscript>x</Subscript>O nanoparticles

In the present investigation, we made an endeavor to fabricate the ZnO nanoparticles and achieved the tunable properties with Nd doping. The Nd-doped ZnO nanoparticles were characterized via X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) studies that confirmed the successful doping of Nd ions in the ZnO crystal lattice without amending its hexagonal phase. The particle morphology revealed nearly spherical particles with uniform size distribution. The band gap of these samples was determined using diffuse-reflectance spectra (DRS) and was found to vary from 3.17 to 3.21 eV with increasing Nd concentration. A broad and intense emission band at 1083 nm for Nd doped ZnO nanoparticles is observed and is assigned to corresponding emission transition ⁴F_3/2?→?⁴I_11/2 of Nd³⁺ ions. Furthermore, the magnetic studies indicate that the Nd doping altered the magnetic behavior of nanocrystalline ZnO particles from diamagnetic to ferromagnetic at 300 K and that the magnetization of these samples decreased with increasing Nd concentration. The tunable optical band gap as well as room-temperature ferromagnetism of these samples may find applications in both optoelectronics and spintronics.     

Structural,optical and electrical properties of ZnTe<Subscript>1−<Emphasis Type=Italic>x</Emphasis></Subscript>Se<Subscript><Emphasis Type=Italic>x</Emphasis></Subscript> thin films

ZnTe_1−x Se _x films were deposited on glass substrates kept at 200 °C by the electron beam evaporation technique. These films exhibited cubic structure and the lattice parameter increased with increase of Tellurium concentration in the films which confirmed the solid solution formation. The grain size is found to increase with Te content. The dislocation density and lattice strain show a decreasing trend with increasing of Te content. Band gap values of 2.73 eV, 2.63 eV, 2.52 eV and 2.41 eV have been calculated for the films of composition ‘x’ = 0.2, 0.4, 0.6 and 0.8, respectively, which confirmed the formation of solid solution between ZnSe and ZnTe. Refractive index of the films increased from 2.535 to 2.826 as the concentration of Te increased. All the films showed high resistivity values. Laser Raman spectral studies of ZnTe_1−x Se _x revealed LO phonon frequencies whose values are located in between the LO phonon frequencies of ZnSe and ZnTe.     

Characterization and electrical conductivity of La<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>CrO<Subscript>3</Subscript> NTC ceramics

The La_1?xSr_xCrO₃ (x?=?0–0.1) negative temperature coefficient (NTC) ceramics have been prepared by the traditional solid state reaction method. X-ray diffraction (XRD) analysis has revealed that the as-sintered ceramics crystallize in a single perovskite structure. Scanning Electron Microscope (SEM) images show that the doped Sr²⁺ contributes to in the decrease in porosity. X-ray photoelectron spectroscopy (XPS) analysis indicates the existence of Cr³⁺ and Cr⁶⁺ ions on lattice sites, which result in hopping conduction. The presence of the Cr⁶⁺ is one of the key factors that affect the electrical conductivity of La_1?xSr_xCrO₃. Resistance–temperature characteristics were studied in the range of ?80 to 10?°C for the ceramic samples, the electrical characterizations show that the electrical resistivity and material constant B decrease with the increase of the strontium content.     

Modulation of microstructure and interface properties of co-sputter derived Hf<Subscript>1−x</Subscript>Ti<Subscript>x</Subscript>O<Subscript>2</Subscript> thin films with various Ti content

Hf_1?xTi_xO₂ dielectric thin films were deposited on Si (100) substrates by RF reactive co-sputtering with the variation in RF power of Ti target. The compositional, morphological, structural and optical properties of Hf_1?xTi_xO₂ films with various Ti concentration were systematically investigated by X-ray photoelectron spectroscopy (XPS), Field emmission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman spectroscopy techniques respectively. The electrical properties of the co-sputtered thin films were studied by capacitance–voltage and current density–voltage measurements. The XRD study has shown the enhancement in the the crystalline property of Hf_1?xTi_xO₂ film up to 60 W of Ti target power and amorphous like behaviour was observed for higher RF power. The Ti content in Hf_1?xTi_xO₂ was calculated from the XPS measurements, where the Ti content was found to be increased with rise in RF power. FESEM micrographs depict the increase in grain size upto the RF power 60 W. The Raman spectrum of the Hf_1?xTi_xO₂ film has shown that the major generated phase was titanium-substituted monoclinic phase of HfO₂. The flatband voltage (V_fb) and oxide charge density (Q_ox) were extracted from the high frequency (1 MHz) C–V curve. The D_it has a minimum value for the film deposited at 60 W RF power of Ti target. The leakage current density of the Hf_1?xTi_xO₂ films was found to be minimum for the RF power 60 W.     

Optical and electrical properties of Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O thin films by sol–gel method

Mg _x Zn_1−x O (0 ≤ x ≤ 0.35) thin films have been deposited by sol–gel technique and the composition related structural, electrical, and optical properties are investigated. All the films have hexagonal wurtzite structure and the separation of MgO phase occurs when x = 0.3 and 0.35. With the increase of Mg content, the densification of the films decrease and band gap values increase. The maximum band gap value reaches 3.56 eV when x = 0.15. After Mg doping the conductivities of the Mg _x Zn_1−x O films are reduced greatly and the electrical current–voltage (I–V) characteristics show nonlinearity for x > 0.15.     

Investigation on the synthesis of (Zn<Subscript>1−x</Subscript>Mg<Subscript>x</Subscript>)TiO<Subscript>3</Subscript> and the modulation effect of CaTiO<Subscript>3</Subscript>

(Zn_1−xMg_x)TiO₃ (x = 0.1–0.5) solid solutions were synthesized by solid-state reaction using ZnO, (MgCO₃)₄·Mg(OH)₂·5H₂O and TiO₂ as raw materials. The influences of Zn: Mg ratio and calcining temperature on the properties of (Zn_1−xMg_x)TiO₃ were studied. By adding CaTiO₃ into (Zn_1−xMg_x)TiO₃, the microwave properties and sintering behavior were improved. The ceramics could be sintered at 1150 °C, and the ceramics with excellent microwave properties of τ_f ≈ ±10 ppm/°C, ε ≈ 24, Q × f > 45000 GHz (8 GHz) were obtained.     

Characterization of In<Subscript>1 − x</Subscript>Cd<Subscript>x</Subscript>S,In<Subscript>2</Subscript>S<Subscript>3</Subscript> and CdS thin films grown by SILAR method

Successive Ionic Layer Adsorption and Reaction (SILAR) technique was used to deposit In_1???xCd_xS, In₂S₃ and CdS thin films on glass substrate at room temperature. The crystal structure and crystal size of the thin films were characterized by X-ray diffraction (XRD) method. Scanning Electron Microscopy (SEM) was used to determine morphology and composition of the films. Optical and electrical properties of these films have been investigated as a function of temperature. The photoluminescence measurements were carried out at room temperature and absorption measurements were carried out in the temperature range 10–320 K with a step of 10 K. The band gap energies for CdS, In_0.8Cd_0.2S, In_0.6Cd_0.4S, In_0.4Cd_0.6S, In_0.2Cd_0.8S and In₂S₃ thin films were found as 2.22 eV, 2.56 eV, 2.52 eV, 2.46 eV, 2.38 eV, and 2.72 eV, respectively. The refractive indices (n), optical static and high frequency dielectric constants (\({\in }_{0}\), \({\in }_{{\infty}}\)) values have been calculated by using the energy bandgap values. The electrical resistivity of CdS, Cd_0.5In_0.5S and In₂S₃ thin films have been determined using a ‘dc’ two probe method, in the temperature range of 300–450 K. The electrical resistivity values have been calculated at 300 K.     

Microstructure and electrical properties of (Na<Subscript>1.015−x</Subscript>K<Subscript>x</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoceramics

In order to obtain the morphotropic phase boundary (MPB) and good piezoelectric properties, lead-free (Na_1.015−xK_x)NbO₃ (x = 0.32–0.35) piezoceramics were synthesized by conventional solid state sintering. The x-ray diffraction results show that the lattice parameters of the monoclinic primitive cell peak at x = 0.34. The scanning electron microscopy and energy dispersive spectroscopy reveal that the excess sodium may be an important reason for the abnormal growth of the grains larger than 20 μm. All the samples exhibit double-like hysteresis loops and it may also be attributed to the excess Na⁺. Although the salient microstructure was found in the studied range, the piezoelectric and ferroelectric properties changed slightly with increasing x from 0.32 to 0.35. The values of piezoelectric coefficient d ₃₃ obtained in this study are as high as about 75 pC/N which is close to that of normally prepared (Na_0.5K_0.5)NbO₃ ceramics with MPB structure.     

Microstrucutre and thermoelectric properties of rapidly prepared Sn<Subscript>1−x</Subscript>Mn<Subscript>x</Subscript>Te alloys

Sn_1?xMn_xTe (x?=?0, 0.09, 0.15, 0.20) bulk materials were prepared by melt spinning combined with spark plasma sintering process. Nanoscale grains were obtained, and the solid solubility of Mn was much enhanced by the ultrafast-cooling synthesis technique. The maximum of Seebeck coefficient and power factor are 242 µVK^?1 and 19.97 µW cm^?1K^?2 at 873 K with the doping concentration of 15 at% Mn. A large amount of grain boundaries and doped atoms improve the scattering of heat-carrying phonons in a wide range of frequencies, and the scattering mechanisms are also explained by theoretical calculation. As a result, the minimum of lattice thermal conductivity is 0.66 µVK^?1 at 873 K, the corresponding figure of merit is 1.26 for Sn_0.85Mn_0.15Te sample. This value is improved by 35% comparing with previously reported result. Our work indicates that melt spinning process is effective to develop SnTe related thermoelectric materials with excellent thermoelectric properties, which has the widespread commercial value and the prospects for development.     

Effects of Mg<Superscript>2+</Superscript> ion substitution on the structural and electric studies of spinel structure of Co<Subscript>1−x</Subscript>Mg<Subscript>x</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>

In this work, we have prepared Mg substituted CoFe₂O₄ from the transition metals by Sol–Gel Auto combustion method for different concentration (0.00, 0.05, 0.10, 0.15, 0.20 and 0.30) the aqueous materials involved Cobalt Nitrate, Magnesium Nitrate, Ferric nitrate and used a citric acid as a fuel. The final product was calcinated at 850 °C. Powder XRD studies confirmed the crystal structure, FTIR revealed the presence of various functional groups, FE-SEM showed the morphology of the prepared sample. EDAX shows percentage of chemical composition in series of Co ferrites. Dielectric constant, AC Conductivity, Cole–Cole plots, Activation Energy were analysed for the prepared nanoparticles for various frequencies at different temperatures. The dielectric constant values are higher for Mg substituted CoFe₂O₄. The activation energies were also calculated which ranged from 0.1552 to 0.1753 eV for CoFe₂O₄ and Co_1?xMg_xFe₂O₄ materials.     

Electrical and oxygen sensing properties of Nd<Subscript>1−x</Subscript>Ba<Subscript>x</Subscript>CoO<Subscript>3</Subscript> ceramics

Nd_1?xBa_xCoO₃ (0?≤?x?≤?0.2) ceramics was synthesized by solid state reaction. All the samples have an orthorhombic perovskite structure (Space group P n m a). The electrical transport property indicates that Ba doped NdCoO₃ ceramics goes through semiconductor–metal phase transition. The electrical resistivity of Nd_1?xBa_xCoO₃ (0?≤?x?≤?0.15) ceramics decreases, while the electrical resistivity of Nd_0.8Ba_0.2CoO₃ ceramics increases with the increase of temperature. The chemical-sensing property shows that Nd_1?xBa_xCoO₃ ceramics is very sensitive to oxygen. Also, increasing Ba²⁺ doping concentration can reduce the oxygen desorption rate and increase the sensitivity of resistivity. These results indicate that Ba²⁺ doped NdCoO₃ ceramics is not only the good candidate of the cathode materials of solid fuel cells but also the good materials of gas sensor devices.     

Laser and electromagnetic loss properties of Perovskite SmNi<Subscript>x</Subscript>Fe<Subscript>1−x</Subscript>O<Subscript>3</Subscript>

SmNi_xFe_1?xO₃ (0?≤?x?≤?0.5) with perovskite-type structure has been successfully prepared by conventional solid-state reaction as a microwave and laser multi-functional material. The optimized synthesis temperature and the effects of Ni doping on the reflectivity, electromagnetic loss properties were investigated in details. XRD results shown that synthesis temperature did not change the perovskite structure of SmFeO₃. The reflectivity at 1.06 μm was about 0.33% at 1200–1300?°C. Doping Ni did not cause the change of perovskite structure. The incorporation of Ni in SmFeO₃ contributed to the decrease of reflectivity at a wider wavelength, SmNi_0.3Fe_0.7O₃ possessed the lowest reflectivity at 1.06 μm. Moreover, electromagnetic property was very sensitive to Ni content. The real and imaginary parts of complex permeability were enhanced remarkably at a certain frequency. The changes in magnetic performance provided possibility of choosing specific frequency of magnetic loss. The difference in electric and magnetic losses caused by Ni concentration could result in microwave absorption at different frequency. In a word, SmNi_xFe_1?xO₃ could be a promising candidate for a multi-functional material with compatible camouflage capability for radar and laser waveband.     

Structural and optical absorption studies of cobalt substituted strontium ferrites,SrCo<Subscript>x</Subscript>Fe<Subscript>12−x</Subscript>O<Subscript>19</Subscript> (x = 0.1, 0.2 and 0.3)

Cobalt substituted strontium ferrites SrCo_xFe_12?xO₁₉ (x = 0.1, 0.2 and 0.3) were synthesized via sol–gel method and the dried gel obtained was annealed at 800 °C. The powder X-ray diffraction studies helped in the determination of the crystallite size that measured ≈ 12–14 nm. The optical properties of the powdered nanoparticles were determined by means of the UV–Vis absorption spectra of their dispersed solutions in liquid media. Despite these measurements, it was difficult to determine their band gap (E_g) precisely. However, the Kubelka–Munk treatment on the diffuse reflectance spectra of the powdered nanoparticles was used in order to extract their E_g unambiguously. The Co substituted strontium hexaferrites are used for optical studies. The energy band gap for all the ferrite compositions was found to be ≈ 1.46–1.78 eV. The study made on the dielectric behaviour of the substituted SrFe₁₂O₁₉ is also discussed in this paper.     

Synthesis of Cu<Subscript>2</Subscript>ZnSn(S<Subscript>x</Subscript>Se<Subscript>1−x</Subscript>)<Subscript>4</Subscript> thin films directly on transparent conductive glass substrates by solvothermal method

In this paper, the single-step solvothermal method was proposed to grow directly Cu₂ZnSn (S_xSe_1?x)₄ (CZTSSe) thin films on FTO substrates. The composition ‘x’ was varied by changing the molar ratios of thiourea to selenourea in the precursor solutions. The effects of the molar ratios of thiourea to selenourea on the structure, morphology and optical properties of CZTSSe thin films were investigated by X-ray diffraction, Raman spectroscopy, scanning electronic microscopy, energy dispersive spectrometry and UV–Vis spectrophotometry. The results indicated that CZTSSe thin films are composed of a large number of uniform sphere-like particles, and the diameter of particles varies from 600 to 280 nm when the molar ratios is changed from 1 to 0. The major XRD diffraction peaks shift towards lower diffraction angles, the Raman peak position of A1 mode of CZTSSe thin films moves consecutively towards the lower frequency due to the S replacement by Se. CZTS and CZTSe thin films are single kesterite structure, however, CZTSSe thin films are mixture structure of kesterite and wurtzite. By varying the molar ratios of thiourea to selenourea in the precursor solution, the atom ratios of S/Se in CZTSSe NCs thin films can be well controlled over the whole range, resulting in tunable optical band gap from 1.54 to 1.38 eV.     

Growth,characterization and transport properties of Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S mixed crystals

The polycrystalline Pb _x Zn_1−x S semiconductor powder with (0 ≤ x ≤ 0·5) has been prepared by controlled co-precipitation method from an alkaline medium using thiourea as a sulphide ion source. Pellets are made with these powders applying 10 ton/sq.cm. pressure and sintered at 800°C for 2 h in nitrogen atmosphere. X-ray studies of these samples have indicated that the compounds are polycrystalline in nature with mixed hexagonal and cubic structure of ZnS and cubic structure of PbS. Lattice parameters (a and c) of all the compounds are determined from the X-ray data and are found to decrease nonlinearly with increase in Pb concentration (x). It is also observed that the grain size of the crystallites increases in samples with x = 0−0·5. Scanning electron micrographs have shown that both cubic and hexagonal crystallites are present in the mixed crystals. The electrical conductivity in Pb _x Zn_1−x S is found to decrease with increase in composition (x = 0−0·5), whereas it increases at all temperatures in all samples. Mobility of charge carrier concentration is found to increase with increasing temperature. The increase in carrier mobility in Pb _x Zn_1−x S samples may be due to reduced grain boundary potential. In Pb _x Zn_1−x S samples with x = 0−0.3, the sum of the activation energy due to charge carriers and grain boundary potential is equal to the activation energy due to conductivity.