Preparation and electrochemical capacitance of MnO2 thin films doped by CuBi2O4

Manganese dioxide (MnO₂) and CuBi₂O₄-doped MnO₂ thin films with different nanostructures were deposited on indium tin oxide (ITO) glass and Ti foil substrates by using a chemical bath deposition (CBD) technique. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron microscopy (XPS). The effects of doping and substrates on electrochemical properties of MnO₂ and CuBi₂O₄-doped MnO₂ thin films on ITO glass and Ti foil were investigated. Capacitive properties of MnO₂ and CuBi₂O₄-doped MnO₂ thin films electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy in a three-electrode experimental setup using 0.1 M Na₂SO₄ aqueous solution as electrolyte. Specific capacitance, obtained from electrochemical measurement for the CuBi₂O₄-doped MnO₂, exhibited a higher value of 338 F g⁻¹ compared to the MnO₂ exhibiting value of 135 F g⁻¹. In addition, CuBi₂O₄-doped MnO₂ thin films on an ITO electrode had a better and satisfactory specific capacitance value, and exhibited more excellent electrochemical stability and reversibility than Ti foil substrates.     

Response time and mechanism of Pd modified TiO2 gas sensor

In this work, gas response properties of Pd modified TiO₂ sensing films are discussed when exposed to H₂ and O₂. TiO₂ films are surface modified in PdCl₂-containing solution by the dipping method and treated for different treatment times to get different surface states. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Kröger–Vink defect theory are used to characterize the sensing films. The gas response properties indicate that the sensor response time which related to the rate of change of sensor resistance is affected by the activation energy (E). In particular, the sensor treated at 900 °C for 2 h exhibits a response time of about 20–240 ms when exposed to H₂ and 40–130 ms when exposed to O₂ at 500–800 °C.     

Synthesis of highly selective and sensitive Cu-doped ZnO thin film sensor for detection of H2S gas

Copper (Cu) doped zinc oxide (ZnO) thin films were successfully prepared by a simple sol-gel spin coating technique. The effect of Cu doping on the structural, morphology, compositional, microstructural, optical, electrical and H₂S gas sensing properties of the films were investigated by using XRD, FESEM, EDS, FTIR, XPS, Raman, HRTEM, and UV–vis techniques. XRD analysis shows that the films are nanocrystalline zinc oxide with the hexagonal wurtzite structure and FESEM result shows a porous structured morphology. The gas response of Cu-doped ZnO thin films was measured by the variation in the electrical resistance of the film, in the absence and presence of H₂S gas. The gas response in relation to operating temperature, Cu doping concentration, and the H₂S gas concentration has been systematically investigated. The maximum H₂S gas response was achieved for 3 at% Cu-doped ZnO thin film for 50 ppm gas concentration, at 250 °C operating temperature.     

Aging characteristics of ZnO–V2O5-based varistors for surge protection reliability

The effect of sintering temperature on clamping characteristics and pulse aging behavior of V₂O₅/MnO₂/Nb₂O₅ co-doped zinc oxide varistors was systematically investigated at 875–950 °C. Experimental results related to varistor effect showed that the breakdown field decreased dramatically from 6830 to 968 V/cm with the increase in the sintering temperature and the non-ohmic coefficient exhibited a maximum (49.5) at 900 °C in the sintering temperature. Varistors sintered at 900 °C exhibited the best clamp characteristics for the pulse current of 1–100 A, with the clamp voltage ratio of K = 1.86–2.77. Varistors sintered at 875 °C exhibited the strongest stability; variation rates for the breakdown field, for the non-ohmic coefficient, and for the leakage current density were −14.2%, −63.6%, and 59.0%, respectively, after application of a multi-pulse current of 100 A.     

Characteristics of ZnOV2O5MnO2Nb2O5Er2O3 semiconducting varistors with sintering processing

The effects of sintering temperature on the microstructure, electrical properties, and dielectric characteristics of ZnOV₂O₅MnO₂Nb₂O₅Er₂O₃ semiconducting varistors have been studied. With increase in sintering temperature the average grain size increased (4.5–9.5 μm) and the density decreased (5.56–5.45 g/cm³). The breakdown field decreased with an increase in the sintering temperature (6214–982 V/cm). The samples sintered at 900 °C exhibited remarkably high nonlinear coefficient (50). The donor concentration increased with an increase in the sintering temperature (0.60×10¹⁸–1.04×10¹⁸ cm^?3) and the barrier height exhibited the maximum value (1.15 eV) at 900 °C. As the sintering temperature increased, the apparent dielectric constant increased by more than four-fold.     

Effect of thermal annealing on the structural,morphological and super capacitor behavior of MnO2 nanocrystals

Precursors of nanosized manganese dioxide were prepared through a chemical precipitation method. The synthesized precursors of MnO₂ were subjected to thermo gravimetric analysis. The thermal analysis results showed the MnO₂ formation at 500 °C. To study the effect of thermal treatments on the capacitive behavior of MnO₂, the precursors were annealed at different temperatures (300, 400 and 500 °C). The annealed products were characterized by X-ray diffraction (XRD), Fourier transforms infra-red spectroscopy (FT-IR) and cyclic Voltammetry (CV) analysis. Among the annealed products, MnO₂ annealed at 400 °C exhibits high specific capacitance. The morphologies of the products annealed at 400 and 500 °C were analyzed by a scanning electron microscope (SEM) and atomic force microscopy (AFM). The sample annealed at 500 °C shows spherical morphology with the inclusion of nanorods. To confirm the morphology of the annealed products, field emission transmission electron microscope (FE-TEM) measurements were carried out.     

Study of sensitivity and selectivity of α-Fe2O3 thin films for different toxic gases and alcohols

This paper presents a detailed study on the sensitivity and selectivity of α-Fe₂O₃ thin films produced by deposition of Fe and post-deposition annealed at two temperatures of 600 °C and 800 °C with flow of oxygen for application as a sensor for toxic gases including CO, H₂S, NH₃ and NO₂ and alcohols such as C₃H₇OH, CH₃OH, and C₂H₅OH. The crystallographic structure of the samples was studied by X-ray diffraction (XRD) method while an atomic force microscope (AFM) was employed for surface morphology investigation. The electrical response of the films was measured while they were exposed to various toxic gases and alcohols in the temperature range of 50–300 °C. The sample annealed at higher temperature showed higher response for different gases and alcohols tested in this work which can be due to the higher resistance of this sample. Results also indicated that the α-Fe₂O₃ thin films show higher selectivity to NO₂ gas relative to the other gases and alcohols while the best sensitivity is obtained at 200 °C. The α-Fe₂O₃ thin film post-deposition annealed at 800 °C also showed a good stability and reproducibility and a detection limit of 10 ppm for NO₂ gas at the operating temperature of 200 °C.     

Growth and characterization of indium oxide diodes prepared by reactive magnetron sputtering

The electrical properties of Cr/Pt/Au and Ni/Au ohmic contacts with unintentionally doped In₂O₃ (U-In₂O₃) film and zinc-doped In₂O₃ (In₂O₃:Zn) prepared by reactive magnetron sputtering deposition are described. The lowest specific contact resistance of Cr/Pt/Au and Ni/Au is 2.94 × 10⁻⁶ and 1.49 × 10⁻² Ω-cm², respectively, as determined by the transmission line model (TLM) after heat treatment at 300 °C by thermal annealing for 10 min in nitrogen ambient. The indium oxide diodes have an ideality factor of 1.1 and a soft breakdown voltage of 5 V. The reverse leakage current prior to breakdown is around 10⁻⁵ A.     

A study on MIS Schottky diode based hydrogen sensor using La2O3 as gate insulator

In this work, a Metal–Insulator–Semiconductor (MIS) based Schottky-diode hydrogen sensor was fabricated with La₂O₃ as a gate insulator. The electrical properties (current–voltage characteristics, change in barrier height and sensitivity) and hydrogen sensing performance (dynamic response and response time) were examined from 25 °C to 300 °C and towards H₂ with different concentrations. The conduction mechanisms were explained in terms of Fowler–Nordheim tunneling (below 120 °C) and the Poole–Frenkel effect at temperatures (above 120 °C). The results show that at an operating temperature of 260 °C, the sensitivity of the device can reach a maximum value of 4.6 with respect to 10,000-ppm hydrogen gas and its response time was 20 s.     

Fabrication and performance evaluation of symmetrical supercapacitor based on manganese oxide nanorods–PANI composite

Manganese oxide nanorods distributed over polyaniline (PANI) network was prepared by one step facile synthesis condition. pH of the reactant solution was tuned using sulfuric acid. Effect of pH on the morphology, chemical composition, structure and electrochemical performance of the prepared materials were studied. Thermal investigation reveals the decomposition of PANI at temperatures below 600 °C. Structural details and chemical composition of the compound was obtained from XRD, FTIR and XPS studies. α type MnO₂ was found to be crystallized in the prepared MnO₂–PANI composite. Single crystal manganese oxide nanorods distributed over the PANI network was cognizant from the FESEM and HRTEM investigations. Nanorods of average diameter 82 nm and length 482 nm were obtained without deploying any surfactants or templates. Electrochemical techniques like Cyclic Voltammetry (CV), Chronopotentiometry (CP) and Electrochemical Impedance Spectroscopy (EIS) were utilized. Study results indicate that the composites prepared shows excellent electrochemical performance. Among the prepared materials, MnP-46 exhibits a maximum specific capacitance of 687 Fg⁻¹ at 5 mV s⁻¹ scan rate and a capacitance retention of 95% over 2000 cycling. Promising performance of MnP-46 was further tested in a symmetrical two cell configuration. The cell was operative upto 1 V potential window. MnP-46 in a symmetrical arrangement demonstrates 179 Fg⁻¹ at 5 mV/s scan rate. High conductivity of the electrode material was confirmed from the Nyquist plot.     

Synthesis and gas sensing behavior of nanostructured V2O5 thin films prepared by spray pyrolysis

Nanocrystalline vanadium pentoxide (V₂O₅) thin films have been deposited by a spray pyrolysis technique on preheated glass substrates. The substrate temperature was changed between 300 and 500 °C. The structural and morphological properties of the films were investigated by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM). The influence of different substrate temperatures on ethanol response of V₂O₅ has also been investigated. XRD revealed that the films deposited at T_pyr=300 °C have low peak intensities, but the degree of crystallinity improved when the temperature was increased to 500 °C and films had orthorhombic structures with preferential orientations along the (0 0 1) direction. The fractal analysis showed a decreasing trend versus the pyrolysis temperature. Sensing properties of the samples were studied in the presence of ethanol vapor. The operating temperature of the sensor was optimized for the best gas response. The response increased linearly with different ethanol concentrations. It was found that films deposited at the lowest substrate temperature (300 °C) had the highest sensing response to ethanol.     

Nonohmic properties of V/Mn/Nb/Gd co-doped zinc oxide semiconducting varistors with low-temperature sintering process

The microstructure and nonohmic properties of the ZnO–V₂O₅–MnO₂–Nb₂O₅–Gd₂O₃ (ZVMNG) semiconducting varistors were systematically investigated at low sintering temperature. With increasing sintering temperature, the average grain size increased from 4.1 to 11.7 μm, the sintered densities decreased from 5.54 to 5.42 g/cm³, and the breakdown field decreased noticeably from 7138 to 920 V/cm. The sample sintered at 900 °C exhibited excellent nonohmic properties, which are 66.1 in the nonohmic coefficient and 77 μA/cm² in the leakage current density.     

Investigation of Si/SiGe/Si heterostructure implanted by H ion and annealed in vacuum and dry O2 ambient

The 20-nm-thick Si cap layer/74-nm-thick Si_0.72Ge_0.28 epilayer/Si heterostructures implanted by 25 keV H⁺ ion to a dose of 1×10¹⁶ cm⁻² were annealed in ultra-high vacuum ambient and dry O₂ ambient at the temperature of 800 °C for 30 min, respectively. Rutherford backscattering/ion channeling (RBS/C), Raman spectra, high-resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) were used to characterize the structural characteristics of the Si_0.72Ge_0.28 layer. Investigations by RBS/C demonstrated that the crystal quality of the Si/Si_0.72Ge_0.28/Si heterostructure sample implanted by 25 keV H⁺ in conjunction with subsequent annealing in dry O₂ ambient is superior to that of identical sample annealing in ultra-high vacuum ambient. The less strain relaxation of SiGe layer of the Si/Si_0.72Ge_0.28/Si heterostructures implanted by H ion and annealed in dry O₂ ambient at the temperature of 800 °C for 30 min could be doublechecked by Raman spectra as well as HRXRD, which was compared with that in an identical sample annealed in ultra-high vacuum ambient for identical thermal budget. In addition, the SiGe layer of the H-implanted Si/SiGe/Si heterostructural sample annealed in dry O₂ ambient accompanied by better crystal quality and less strain relaxation made its surface morphology superior to that of the sample annealed in ultra-high vacuum ambient at the temperature of 800 °C for 30 min, which was also verified by AFM images.     

Structural,magnetic and dielectric properties of nanocrystalline cobalt ferrite by wet hydroxyl chemical route

Nanopowders of CoFe₂O₄ are synthesized via wet chemical co-precipitation processing at pH 8. The synthesized nanoferrite powders are annealed at various temperatures (350 °C, 700 °C and 1050 °C) and are characterized. X-ray diffraction (XRD) patterns indicate the crystalline nature of CoFe₂O₄ nanopowders. Transmission electron microscope (TEM) investigations show, anisotropic shapes like cubic, hexagonal and spherical morphology of nanoparticles with average particle size 38–85 nm. Dielectric constant decreases as the frequency increases. Low value of dielectric loss at higher frequencies suggests the material is suitable for high frequency applications. AC conductivity increases with frequency. The saturation magnetization (M_s), remanant magnetism (M_R) and coercivity (H_C) increases with applied field.     

Effect of H2O2 concentration on electrochemical growth and properties of vertically oriented ZnO nanorods electrodeposited from chloride solutions

In this work, ZnO nanostructures are electrodeposited on a transparent conducting glass from chloride baths. The influence of H₂O₂ concentration on the electrochemical characteristics has been studied using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. From the analysis of the current transients on the basis of the Scharifker–Hills model, it is found that nucleation mechanism is progressive with a typical three-dimensional (3D) nucleation and growth process; independently with the concentration of H₂O₂. However, the nucleation rate of the ZnO changes with the increase of H₂O₂ concentration. The Mott–Schottky measurements demonstrate an n-type semiconductor character for all samples with a carrier density varying between 5.14×10¹⁸ cm⁻³ and 1.47×10¹⁸ cm⁻³. Scanning electron microscopy (SEM) observations show arrays of vertically aligned ZnO nanorods (NRs) with good homogeneity. The X-ray diffraction (XRD) patterns show that the ZnO deposited crystallises according to a hexagonal Würtzite-type structure and with the c-axis perpendicular to the electrode surface. The directional growth along (002) crystallographic plane is very important for deposits obtained at 5 and 7 mM of H₂O₂. The high optical properties of the ZnO NRs with a low density of deep defects was checked by UV–vis transmittance analyses, the band gap energy of films varies between 3.23 and 3.31 eV with transparency around 80–90%.     

Direct thermal decomposition synthesis and characterization of hematite (α-Fe2O3) nanoparticles

Hematite (α-Fe₂O₃₎ nanoparticles were prepared via direct thermal decomposition method using γ-Fe₂O₃ as a wet chemically synthesized precursor. The precursor was calcinated in air at 500 °C. Samples were characterized by Thermogravimetric analysis (TGA), X-ray diffraction, Infrared, Scanning electron microscopy, Transmission electron microscopy (TEM) and Photon correlation spectroscopy (PCS). TEM and PCS analyses revealed that the average particle size of the α-Fe₂O₃ nanoparticles synthesized at 500 °C are about 18±2 nm and 50±3 nm for 1 h and 24±2 nm and 82±3 nm for 2 h, respectively. The difference in average particle size determined by PCS and TEM analysis is due to the electrostatic forces between particles, and their agglomeration in PCS analysis. Magnetic properties have been detected by a Vibrating sample magnetometry at room temperature. The α-Fe₂O₃ nanoparticles exhibited a weak ferromagnetic behavior at room temperature.     

Ultra-low-energy ion-beam-synthesis of Ge nanocrystals in thin ALD Al2O3 layers for memory applications

Structural and electrical properties of ALD-grown 5 and 7 nm-thick Al₂O₃ layers before and after implantation of Ge ions (1 keV, 0.5–1 × 10¹⁶ cm^?2) and thermal annealing at temperatures in the 700–1050 °C range are reported. Transmission Electron Microscopy reveals the development of a 1 nm-thick SiO₂-rich layer at the Al₂O₃/Si substrate interface as well as the formation of Ge nanocrystals with a mean diameter of ～5 nm inside the implanted Al₂O₃ layers after annealing at 800 °C for 20 min. Electrical measurements performed on metal–insulator–semiconductor capacitors using Ge-implanted and annealed Al₂O₃ layers reveal charge storage at low-electric fields mainly due to location of the Ge nanocrystals at a tunnelling distance from the substrate and their spatial dispersion inside the Al₂O₃ layers.     

Influence of annealing temperature on the structural and optical properties of nanocrystalline zirconium oxide

Nanocrystalline zirconium oxide powder was prepared by sol-gel method using zirconyl chloride octahydrate (ZrOCl₂·8H₂O) and ethylenediaminetetraacitic acid (EDTA) in ammonium hydroxide (NH₄OH) solution. The as-synthesized complex product was annealed at 650 °C, 750 °C and 850 °C for 2 h to get fine ZrO₂ powder. These samples were further analyzed by Scanning electron microscopy (SEM), X- ray diffraction (XRD), Energy-dispersive X- ray spectroscopy (EDX), UV-vis analysis, Fourier transform infrared (FT-IR) spectroscopy, Photoluminescence spectroscopy (PL) and Raman Spectroscopy to study their structural and optical properties. The structural studies revealed that nanocrystalline ZrO₂ powder exhibits monoclinic phase with variation in crystallite size with annealing temperature. The UV–vis absorption band edge of ZrO₂ decreases from 514 nm to 451 nm as annealing temperature rises from 650 °C to 750 °C. It seems that the drastic reduction in band gap energy may be one of the novel unexpected characteristics of ZrO₂. The FTIR analyses further confirmed the formation of nanocrystalline monoclinic ZrO₂. PL analysis revealed the novel emission peaks at 305 and 565 nm. The Raman spectroscopy confirmed the transformation of amorphous zirconium hydroxide to m-ZrO₂ with increase in temperature from 650 °C to 850 °C.     

Structural and optoelectronic properties of nanostructured TiO2 thin films with annealing

About 480 nm thick titanium oxide (TiO₂) thin films have been deposited by electron beam evaporation followed by annealing in air at 300–600 °C with a step of 100 °C for a period of 2 h. Optical, electrical and structural properties are studied as a function of annealing temperature. All the films are crystalline (having tetragonal anatase structure) with small amount of amorphous phase. Crystallinity of the films improves with annealing at elevated temperatures. XRD and FESEM results suggest that the films are composed of nanoparticles of 25–35 nm. Raman analysis and optical measurements suggest quantum confinement effects since Raman peaks of the as-deposited films are blue-shifted as compared to those for bulk TiO₂ Optical band gap energy of the as-deposited TiO₂ film is 3.24 eV, which decreases to about 3.09 eV after annealing at 600 °C. Refractive index of the as-deposited TiO₂ film is 2.26, which increases to about 2.32 after annealing at 600 °C. However the films annealed at 500 °C present peculiar behavior as their band gap increases to the highest value of 3.27 eV whereas refractive index, RMS roughness and dc-resistance illustrate a drop as compared to all other films. Illumination to sunlight decreases the dc-resistance of the as-deposited and annealed films as compared to dark measurements possibly due to charge carrier enhancement by photon absorption.     

Properties of In2O3 films obtained by thermal oxidation of sprayed In2S3

In₂S₃ thin films were grown by the chemical spray pyrolysis (CSP) method using indium chloride and thiourea as precursors at a molar ratio of S:In=2.5. The deposition was carried out at 350 °C on quartz substrates. The film thickness is about 1 µm. The films were then annealed for 2 h at 550, 600, 650 and 700 °C in oxygen flow. This process allows the transformation of nanocrystal In₂O₃ from In₂S₃ and the reaction is complete at 600 °C. X-ray diffraction spectra show that In₂O₃ films are polycrystalline with a cubic phase and preferentially oriented towards (222). The film grain size increases from 19 to 25 nm and RMS values increase from 9 to 30 nm. In₂O₃ films exhibit transparency over 70–85% in the visible and infrared regions due to the thickness and crystalline properties of the films. The optical band gap is found to vary in the range 3.87–3.95 eV for direct transitions. Hall effect measurements at room temperature show that resistivity is decreased from 117 to 27 Ω cm. A carrier concentration of 1×10¹⁶ cm^?3 and mobility of about 117 cm² V^?1 s^?1 are obtained at 700 °C.