PdCl2–Polyaniline Composite for CO Detection Applications: Electrical and Optical Response

Different mass ratios of PdCl₂ were incorporated into polyaniline emeraldine base (PdCl₂–PANI) by sonication in acetonitrile. The Pd^II-doped PANI composites readily interact with CO gas at ambient conditions (1 atm, 27 °C) resulting in the reduction of Pd^II ions into metallic Pd⁰ and the release of HCl to afford Pd⁰–PANI·HCl. The dramatic structural changes associated with CO exposure were examined by different spectroscopic (UV–Visible, FT-IR), powder X-ray diffraction (P-XRD) and electrical conductivity (DC) techniques. The P-XRD data shows that the resulting nano-scale metallic Pd⁰ clusters (~10–15 nm) remain tightly bound to the PANI chains. The observed chemical transformation of PdCl₂–PANI into Pd⁰–PANI·HCl as a function of exposure to CO gas was exploited to monitor this poisonous gas in CO/air mixture; the optical and DC electrical response functions were examined in solution and solid state, respectively. The DC electrical response signal is relatively ten-fold more sensitive to CO exposure (% S_electrical = 471–496 %) compared to the corresponding optical response (%S_{optical at 460 nm} = 40–51 %). This responsive action demonstrates that PdCl₂–PANI composite can be employed as a feasible low-cost solid-state CO detecting material in chemical sensor devices.     

Low concentration CO gas sensor constructed from MoS2 nanosheets dispersed SnO2 nanoparticles at room temperature under UV light

In consideration of the different electron structure-associated physical properties and internal sensing merits of MoS₂ and SnO₂, this work reports a nanocomposite with unique structure of MoS₂ nanosheets dispersed SnO₂ nanoparticles. The sensing performance of MoS₂/SnO₂ sensor toward low concentration CO was investigated at room temperature under the UV light illumination. It was found that MoS₂/SnO₂ sensor shows improved CO gas response (R ~ 4.97 at 40 ppm CO) compared with pure SnO₂ (R ~ 3.27 at 40 ppm CO), which is due to the unique structure and the formation of heterostructure between MoS₂ and SnO₂. Moreover, the fabricated sensor also exhibits fast response and recovery time (43 s/36 s). The sensor provides a potential platform for monitoring CO gas at room temperature.     

Impact of Zn doping on the dielectric and magnetic properties of CoFe2O4 nanoparticles

Owing to its unique magnetic, dielectric, electrical and catalytic properties, ferrite nanostructure materials gain vital importance in high frequency, memory, imaging, sensor, energy and biomedical applications. Doping is one of the strategies to manipulate the spinel ferrite structure, which could alter the physico-chemical properties. In the present work, Co_1-xZn_xFe₂O₄ ($x$ = 0, 0.1, 0.2, 0.3, and 0.4 wt%) nanoparticles were prepared by sol-gel auto-combustion method and its structural, morphological, vibrational, optical, electrical and magnetic properties were studied. The structural analysis affirms the single-phase cubic spinel structure of CoFe₂O₄. The crystallite size, lattice constant, unit cell, X-ray density, dislocation density and hopping length were significantly varied with Zn doping. The Fe–O stretching vibration was estimated by FTIR and Raman spectra. TEM micrographs show the agglomerated particles and it size varies between 10 and 56 nm. The Hall effect measurement shows the switching of charge carriers from n to p type. The dielectric constant (ε′) varies from 0.2 × 10³ to 1.2 × 10³ for different Zn doping. The VSM analysis shows relatively high saturation magnetization of 57 and 69 emu/g for ZC 0.1 and ZC 0.2 samples, respectively than that of undoped sample. All the prepared samples exhibit soft magnetic behaviour. Hence, it can be realized that the lower concentration of Zn ion doping significantly alters the magnetic properties of CoFe₂O₄ through variation in the cationic distribution and exchange interaction between the Co and Fe sites of the inverse spinel structure of CoFe₂O_4.     

The influence of ZrO2 additive on sintering and microstructure of lithium and lithium-titanium-zinc ferrites

The effect of ZrO₂ addition (0–3?wt%) on sintering and microstructure of lithium and lithium-titanium-zinc ferrites was studied. The Vickers hardness and dc electrical resistivity were investigated and discussed in correlation with the structural properties. Ferrite powders with the chemical compositions of LiFe₅O₈ and Li_0.65Fe_1.6Ti_0.5Zn_0.2Mn_0.05O₄ were prepared by the conventional ceramic technique. The synthesized ferrites were doped with various amount of ZrO₂ and then were sintered at 1050?°C for 2?h. Dilatometric studies showed that the zirconia addition affects the densification process of ferrite ceramics so that the shrinkage rate of pressed ferrite powders during their heating decreased with an increase in ZrO₂ content. The bulk density of the sintered ferrites varied slightly as the concentration of the additive was increased from 0 to 2?wt%, while the density of ferrite doped with 3?wt% ZrO₂ significantly decreased. X-ray diffraction and scanning electron microscopy analyses showed that the lattice parameter of ferrites increases and their average grain size decreases as the additive content grows. It was established that small amounts of ZrO₂ additive (up to 2?wt%) improve significantly the hardness and the electrical resistivity of ferrites.     

Improvement of flux pinning ability by tungsten oxide nanoparticles added in YBa2Cu3Oy superconductor

In this study, series of superconductor-tungsten oxide (WO₃) nanoparticles composites, YBa₂Cu₃O_7-δ/(WO₃)_x, were produced via the solid-state reaction process. The structural, morphological, chemical compositions, electrical and magnetic properties were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) along with EDX system and physical properties measurement system (PPMS), respectively. The XRD, SEM and EDX analyses showed the successful formation of the Y-123 orthorhombic phase. The electrical resistivity measurements proved the occurrence of superconductivity in different samples. The magnetic results showed an improvement of critical current density (J_c) and pinning ability in WO₃ nanoparticles added Y-123 products. The dominant pinning mechanisms and the strength of pinning centers in various sintered products were examined and discussed. The measurements of zero-field-cooled (ZFC) and field-cooled (FC) magnetization versus temperature (M-T) indicated an increase in the magnitude of diamagnetic signal with the addition of WO₃ nanoparticles in the Y-123 superconductor.     

Field assisted sintering of electro-conductive ZrO2-based composites

In order to reveal the fundamentals of the field assisted sintering technique (FAST), also known as spark plasma sintering (SPS), the evolution of the current density and temperature distribution in the punch-die-sample set-up during FAST of ZrO₂–TiN powder mixtures was modeled by finite element calculations supported by in situ measured electrical and thermal input data. The thermal and electrical properties of partially sintered composite powder compacts were estimated using theoretical mixture rules, allowing to calculate the current density and temperature distribution inside the tool and the specimen during the FAST sintering process. The electrical properties of the sintering composite powder compact, and hence the thermal distribution in the sinter set-up, changed drastically during densification once percolation occurred. Based on the calculated thermal distribution inside the composite powder compact, an optimal tool-powder compact design was determined in order to process electrically conductive ZrO₂–TiN composites from electrical insulating powder compacts within minutes with high reproducibility.     

Enhanced NO2 sensing properties of Pt/WO3 films grown by glancing angle deposition

In this work, WO₃ films were synthesized by glancing angle deposition (GLAD) and conventional planar deposition respectively. By depositing Pt on WO₃ by GLAD, the NO₂ sensitivity of WO₃ films were significantly improved. The structural characteristics and NO₂ sensing properties of the films were investigated in order to establish the enhancement mechanism. The results show WO₃ films prepared by GLAD have porous nanorod-like structure, and isolated Pt clusters are distributed on WO₃. The nanostructured Pt/WO₃ films show high sensitivity to NO₂ at 150 °C, detecting as low as 80 ppb NO₂ with a response of 1.23. Meanwhile, the films also exhibit high NO₂ selectivity against NH₃, CO, acetone and ethanol. The excellent NO₂ sensing properties of the Pt/WO₃ films can be explained due to large specific surface area of nanorod-like WO₃, catalysis of Pt and Schottky barriers at interfaces. The reliable Pt/WO₃ nanostructure prepared by GLAD could be potentially applied in low-temperature, highly sensitive NO₂ sensor for micro-electro-mechanical system (MEMS).     

Electrical properties of nanoporous F doped SiO2 low-k thin films prepared by sol-gel method with catalyst HF

Using hydrofluoric acid as acid catalyst, F doped nanoporous low-k SiO₂ thin films were prepared through sol-gel method. Compared with the hydrochloric acid catalyzed film, the films showed better micro structural and electrical properties. The capacitance-voltage and current-voltage characteristics of F doped SiO₂ thin films were then studied based on the structures of metal-SiO₂-semiconductor and metal-SiO₂-metal, respectively. The density of state (DOS) of samples deposited on metal is found to decrease to a level of 2 × 10¹⁷ eV^?1 cm^?3. The values of mobile ions, fix positive charges, trapped charges and the interface state density between the SiO₂/Si interfaces also decrease obviously, together with the reduction of the leakage current density and the dielectric constant, which imply the improvement of the electrical properties of thin films. After annealing at a temperature of 450^°C, the lower values of the leakage current density and dielectric constant could be obtained, i.e. 1.06 × 10^?9 A/cm² and 1.5, respectively.     

CO Adsorption Characteristics on Impurity Substituted In<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanostructures: A Density Functional Theory Investigation

The structural stability, adsorption characteristics of CO on In₂O₃ base material and electronic properties of pure, N and Ga substituted cubic In₂O₃ nanostructures are optimized and simulated successfully using density functional theory with B3LYP/LanL2DZ basis set. The structural stabilities of In₂O₃ nanostructures are discussed using calculated energy. The electronic properties of In₂O₃ nanostructures are studied in terms of HOMO–LUMO gap, electron affinity and ionization potential. Point symmetry and dipole moment of In₂O₃ nanostructures are also reported. Adsorption characteristics of CO can be fine-tuned with proper substitution impurities such as N and Ga on In₂O₃ nanostructure. The adsorption characteristics of CO are explored with density of states and Mulliken population analysis. Moreover, nitrogen substituted In₂O₃ nanostructure enhances CO adsorption characteristics on In₂O₃ nanostructures. The proper adsorption sites of CO on cubic In₂O₃ nanostructures are identified and reported. The results of the present work give a clear vision on the adsorption characteristics of CO on In₂O₃ nanostructures.     

Importance of finding the proper ratio of alkaline earth oxide in a lithium-bismuthate-phosphate glass in order to enhance the tailoring of structural and electrical properties

Structural features of the glass family xLi₂O- yMgO (4.8 Bi₂O₃ 47.6 P₂O₅) obtained by melt quenching technique were studied taking into account the density, FTIR and UV–vis spectra and also the electrical response observed by impedance spectroscopy. In this work it becomes clarified how the alkaline earth oxides stabilize the glassy matrix and also, the fundamental importance of determining the optimal proportion in order to obtain a flabby easily polarizable matrix to enhance the electrical behavior due to a boosted cation mobility. It is evidenced that when the glass composition becomes complex it is needed to take into account a larger number of structural parameters to understand, to predict or to design the resulting physical properties.     

Flower-shaped ZnO nanomaterials for low-temperature operations in NOX gas sensors

In this study, we synthesized nanostructured zinc oxide (ZnO) by using various concentrations (0–0.05 M) of cetyltrimethylammonium bromide (CTAB) as a surfactant to optimize its morphology for gas sensor applications. The optimization process was used to elucidate the morphology effects (rod-shaped and flower-shaped morphologies). The morphologies were investigated through scanning electron microscopy, in which the assembly of nanorods leading to a spherical microstructure with a CTAB concentration of 0.005 M was observed. Brunauer–Emmett–Teller isotherm measurements revealed a surface area of 7.928 g/m² for the flower-like morphology, which was relatively higher than those of other CTAB-assisted morphologies. Such morphological features were expected to contribute toward high-performance gas-sensing. The effect of morphology variation on the resistance of ZnO microstructures was used for gas measurements. Among the varied morphologies, a sample with a spherical flower-shaped morphology exhibited a very high response at low temperatures (~29 at 25 °C) toward NO_X gas (0.75 ppm) and a high selectivity toward NO_x among ammonia (NH₃), toluene (C₆H₅CH₃), carbon monoxide (CO), acetone (CH₃COCH₃), and ethanol (C₂H₅OH). Raman and photoluminescence spectroscopy analyses unraveled the presence of a high density of oxygen vacancies in the sample, thereby suggesting a close link between the defective nature of the sample and the high response of the flower-like ZnO at low temperatures.     

Ab initio Modeling of the Electronic Structures and Physical Properties of a‐Si1−xGexO2 Glass (x = 0 to 1)

The amorphous silica (a‐SiO₂) and germania (a‐GeO₂) have a wide range of applications in glass industry. Based on a previously constructed near‐perfect continuous random network model with 1296 atoms and periodic boundary conditions, we extend our study to amorphous Si_1?xGe_xO₂ models of homogeneous random substitution of Si by Ge with x ranging from 0 to 1. We have calculated the structural, electronic, mechanical, and optical properties for the series by using the first‐principles density functional theory methods. The x‐dependence of the variations in the properties is analyzed and critically compared with available experimental data. The mass density, volume, total bond order density, bulk mechanical properties, and refractive index are found to vary linearly as a function of x. For x = 0.5, we have also constructed six different kinds of particle immersion models to test the effect of inclusion of spherical particles of one glass of different sizes in the medium of the other glass on their physical properties. It is shown that particle sizes do affect the properties of particle immersion. Our calculations provide deep insight on the properties of mixture and nanocomposites of a‐SiO₂ and a‐GeO₂ glasses.     

Highly stable and selective ethanol sensor based on α-Fe2O3 nanoparticles prepared by Pechini sol–gel method

In the present work, α-Fe₂O₃ nanoparticles were successfully synthesized by Pechini sol–gel (PSG) method following annealing at 550 °C. The morphology and microstructure of the prepared α-Fe₂O₃ nanoparticles were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman analysis. The electrical and sensing properties were also investigated. The α-Fe₂O₃ based sensor showed good sensitivity and selectivity towards ethanol at the optimal temperature of 225 °C. Moreover, the sensor displayed good electrical and sensing stability. These results suggest the potential applications of α-Fe₂O₃ synthesized by Pechini sol–gel method as a sensor material for ethanol detection.     

Effect of sintering temperature on the transport properties of La2Ce2O7 ceramic materials

La₂Ce₂O₇ (LCO) based materials are of a paramount importance since they can be utilized for ammonium production, thermal barrier application, catalysts, hydrogen production and solid oxide fuel cells (SOFCs). In this work, a nano crystalline LCO powder was prepared using glycine-nitrate combustion method and then its properties were comprehensively characterized. The structural analysis of the synthesized LCO was carried out using conventional X-ray diffraction (XRD) and Raman spectroscopy. In a disordered phase, LCO is a biphasic mixture composed of C- and F-type phases. Densification studies were performed by sintering LCO pellets at different sintering temperatures. A densification of ≥95% was observed in all the samples with a very little variation. Sintering temperature had a marked effect on the electrical conductivity of LCO. The LCO sintered at 1100 °C showed the highest conductivity (3.68 mS/cm at 700 °C in air). The electrical conductivity was found to be decreasing with an increase in sintering temperature from 1100 to 1400 °C. To understand the behavior, the analysis of distribution function of relaxation times (DFRTs) utilized for correct separation of grain and grain boundary resistances. The presence of C- and F- type phases calculated from Raman spectra plays a crucial role in deciding conduction behavior of LCO. The results suggest a strong relationship between history of the ceramics preparation and their electrical properties.     

Electrical properties of nanoporous F doped SiO2 low-k thin films prepared by sol-gel method with catalyst HF

Using hydrofluoric acid as acid catalyst, F doped nanoporous low-k SiO₂ thin films were prepared through sol-gel method. Compared with the hydrochloric acid catalyzed film, the films showed better micro structural and electrical properties. The capacitance-voltage and current-voltage characteristics of F doped SiO₂ thin films were then studied based on the structures of metal-SiO₂-semiconductor and metal-SiO₂-metal, respectively. The density of state (DOS) of samples deposited on metal is found to decrease to a level of 2 × 10¹⁷ eV⁻¹ cm⁻³. The values of mobile ions, fix positive charges, trapped charges and the interface state density between the SiO₂/Si interfaces also decrease obviously, together with the reduction of the leakage current density and the dielectric constant, which imply the improvement of the electrical properties of thin films. After annealing at a temperature of 450^∘C, the lower values of the leakage current density and dielectric constant could be obtained, i.e. 1.06 × 10⁻⁹ A/cm² and 1.5, respectively.     

Highly conducting and transparent antimony doped tin oxide thin films: the role of sputtering power density

Sb doped SnO₂ thin films were deposited on quartz substrates by magnetron sputtering at 600 °C and the effects of sputtering power density on the preferential orientation, structural, surface morphological, optical and electrical properties had been studied. The XRD analyses confirm the formation of cassiterite tetragonal structure and the presence of preferential orientation in (2 1 1) direction for tin oxygen thin films. The dislocation density analyses reveal that the generated defects can be suppressed by the appropriate sputtering power density in the SnO₂ lattice. The studies of surface morphologies show that grain sizes and surface roughness are remarkably affected by the sputtering power density. The resistivity of Sb doped SnO₂ thin films gradually decreases as increasing the sputtering power density, reaches a minimum value of 8.23×10⁻⁴ Ω cm at 7.65/cm² and starts increasing thereafter. The possible mechanisms for the change in resistivity are proposed. The average transmittances are more than 83% in the visible region (380–780 nm) for all the thin films, the optical band gaps are above 4.1 eV. And the mechanisms of the variation of optical properties at different sputtering power densities are addressed.     

TPD study of the reaction of CH3CH2SH and (CH3CH2)2S2 on ZnO(0001) and ZnO

Superior activation of on 1 wt% Pt/TiO₂ catalysts for the oxidation of CO was attained by loading a large amount of Fe-oxide (100 wt%) and TiO₂. In situ IR spectra of CO proved that the structural transformation is brought about on the Pt-sites by loading of Fe-oxide, where predominant Pt-sites giving linear CO change to highly reactive bridge CO Pt-sites. In contrast, no transformation of the linear CO sites to the bridge CO sites takes place by loading of TiO₂ but the environment of Pt-sites for linear CO is changed.     

Microstructure,optical, electrical properties,and leakage current transport mechanism of sol–gel-processed high-k HfO2 gate dielectrics

Deposition of high-k HfO₂ gate dielectric films on n-type Si and quartz substrates by sol–gel spin-on coating technique has been performed and the structural, optical and electrical characteristics as a function of annealing temperature have been investigated. The structural and optical properties of HfO₂ thin films related to annealing temperature are investigated by X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–vis), and spectroscopic ellipsometry (SE). Results indicate that the monoclinic form of HfO₂ appears when temperature rises through and above 500 °C. The reduction in band gap is observed with the increase of annealing temperature. Moreover, the increase of refractive index (n) and density and the decrease of the extinction coefficient with the increase of annealing temperature are obtained by SE measurements. Additionally, the electrical properties based on Al/Si/HfO₂/Al capacitor are analyzed by means of the high frequency capacitance–voltage (C–V) and the leakage current density–voltage (J–V) characteristics. And the leakage current conduction mechanisms as functions of annealing temperatures are also discussed.     

Synthesis and Structural Elucidation of NSC Auxiliary Dispersing Agents

The synthesis, characterization, structural elucidation, and application of the dispersant (NSC) obtained from condensation of β-naphthalene sulphonic acid and formaldehyde are described. The one pot process from naphthalene, sulphuric acid, and formaldehyde leads to reproducible condensate products with n = 13 and 14 naphthalene nuclei. The ¹H and ¹³C NMR spectra were recorded in D₂O (representative spherical shape) and DMSO (representative rod-like shape). Bleaching leads to the recovery of excellent super pure material.     

Hydrogen sensing properties and mechanism of NiO-Nb2O5 composite nanoparticle-based electrical gas sensors

A simple hydrothermal method was used to prepare NiO-Nb₂O₅ composite nanoparticle electrical sensors for the detection of hydrogen (H₂) at room temperature. To investigate the morphology and crystal structure of the synthesized powders, the synthesized nanoparticles were characterized by scanning electron microscopy and X-ray diffraction. The NiO-Nb₂O₅ composite nanoparticle sensor showed stronger and faster response to H₂ than the pristine Nb₂O₅ one at room temperature. Only weak responses were observed to carbon monoxide, methane and ethanol, indicating that the NiO-Nb₂O₅ composite nanoparticle sensor could be a potential candidate as a practical gas detector. In this study, the H₂ sensing properties and mechanism of NiO-Nb₂O₅ composite nanoparticle-based electrical gas sensors are discussed in detail.