Ethanol and LPG sensing characteristics of SnO<Subscript>2</Subscript> activated Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> thick film sensor

The sensing response of pure and SnO₂ activated Cr₂O₃ to ethanol vapours and liquefied petroleum gas (LPG) has been investigated. Fine particles of commercial chromium oxide powder were selected and deposited as thick film to act as a gas sensor. The sensor surface has been activated by tin dioxide, on surface oxidation of tin chloride. The concentration of tin chloride solution, used as activator, was varied from 0 to 5% and its effect on gas response, selectivity and operating temperature has been studied. It was found that response to ethanol vapours significantly improved, whereas response to LPG remained unaffected. Moreover, operating temperature remains unchanged both for LPG and ethanol vapours.     

Highly sensitive and selective ethanol sensor based on micron-sized zinc oxide porous-shell hollow spheres

Zinc oxide (ZnO) porous-shell hollow spheres (PHS) were prepared by thermally oxidizing high-purity zinc powder in an oxygen-containing atmosphere, and its ethanol gas sensing properties were measured in the concentration range of 10–400 ppm. At the optimum operating temperature of 350 °C, a sensitivity of 0.25/ppm was obtained and the response–concentration curve was of high linearity. The response and recovery times were measured to be ～5–12 s and 8–13 s, respectively. The sensor was proved to be highly selective to ethanol. Our results indicate that ZnO PHS might be a promising material for fabricating practical ethanol sensors.     

The properties of ethanol gas sensor based on Ti doped ZnO nanotetrapods

An ethanol gas sensor was fabricated based on Ti doped ZnO nanotetrapods which were prepared by chemical vapor deposition (CVD) of ZnO nanotetrapods followed by co-annealing with TiO₂ powder. X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM) were used to characterize the morphology and structure of the as-obtained sample and the ethanol-sensing characteristics of the device were investigated. ZnO:Ti sensors show higher gas response than ZnO counterparts towards 100 ppm ethanol gas at a temperature of 260 °C. The recovery times of the devices are 3.1 min for ZnO:Ti and 10.1 min for ZnO, respectively. The enhancement of sensing properties of ZnO:Ti tetrapods indicates the potential application for fabricating low power and highly sensitive gas sensors.     

Performance evaluation of ZnO–CuO hetero junction solid state room temperature ethanol sensor

A semiconductor ethanol sensor was developed using ZnO–CuO and its performance was evaluated at room temperature. Hetero-junction sensor was made of ZnO–CuO nanoparticles for sensing alcohol at room temperature. Nanoparticles were prepared by hydrothermal method and optimized with different weight ratios. Sensor characteristics were linear for the concentration range of 150–250 ppm. Composite materials of ZnO–CuO were characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR) and high-resolution transmission electron microscopy (HR-TEM). ZnO–CuO (1:1) material showed maximum sensor response (S = R_air/R_alcohol) of 3.32 ± 0.1 toward 200 ppm of alcohol vapor at room temperature. The response and recovery times were measured to be 62 and 83 s, respectively. The linearity R² of the sensor response was 0.9026. The sensing materials ZnO–CuO (1:1) provide a simple, rapid and highly sensitive alcohol gas sensor operating at room temperature.     

Preparation and characterization of copper nanoparticles/zinc oxide composite modified electrode and its application to glucose sensing

We report a new method for selective detection of d(+)-glucose using a copper nanoparticles (Cu-NPs) attached zinc oxide (ZnO) film coated electrode. The ZnO and Cu-NPs were electrochemically deposited onto indium tin oxide (ITO) coated glass electrode and glassy carbon electrode (GCE) by layer-by-layer. In result, Cu-NPs/ZnO composite film topography was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. SEM and AFM confirmed the presence of nanometer sized Cu-NPs/ZnO composite particles on the electrode surface. In addition, X-ray diffraction pattern revealed that Cu-NPs and ZnO films were attached onto the electrode surface. Indeed, the Cu-NPs/ZnO composite modified electrode showed excellent electrocatalytic activity for glucose oxidation in alkaline (0.1 M NaOH) solution. Further, we utilized the Cu-NPs/ZnO composite modified electrode as an electrochemical sensor for detection of glucose. This glucose sensor showed a linear relationship in the range from 1 × 10^? 6 M to 1.53 × 10^? 3 M and the detection limit (S/N = 3) was found to be 2 × 10^? 7 M. The Cu-NPs/ZnO composite as a non-enzymatic glucose sensor presents a number of attractive features such as high sensitivity, stability, reproducibility, selectivity and fast response. The applicability of the proposed method to the determination of glucose in human urine samples was demonstrated with satisfactory results.     

Physical/chemical properties of tin oxide thin film transistors prepared using plasma-enhanced atomic layer deposition

Thin film transistors (TFTs) with tin oxide films as the channel layer were fabricated by means of plasma enhanced atomic layer deposition (PE-ALD). The as-deposited tin oxide films show n-type conductivity and a nano-crystalline structure of SnO₂. Notwithstanding the relatively low deposition temperatures of 70, 100, and 130 °C, the bottom gate tin oxide TFTs show an on/off drain current ratio of 10⁶ while the device mobility values were increased from 2.31 cm²/V s to 6.24 cm²/V s upon increasing the deposition temperature of the tin oxide films.     

Microwave-assisted hydrothermal synthesis of zinc oxide particles starting from chloride precursor

Zinc oxide (ZnO) was synthesized using a microwave assisted hydrothermal (MAH) process based on chloride/urea/water solution and under 800 W irradiation for 5 min. In the bath, Zn²⁺ ions reacted with the complex carbonate and hydroxide ions to form zinc carbonate hydroxide hydrate (Zn₄CO₃(OH)₆·H₂O), and the conversion from Zn₄CO₃(OH)₆·H₂O to ZnO was synchronously achieved by a MAH process. The as-prepared ZnO has a sponge-like morphology. However, the initial sponge-like morphology of ZnO could change to a net-like structure after thermal treatment, and compact nano-scale ZnO particles were finally obtained when the period of thermal treatment increased to 30 min. Pure ZnO nanoparticles was obtained from calcination of loose sponge-like ZnO particles at 500 °C. The analysis of optical properties of these ZnO nanoparticles showed that the intensity of 393 nm emission increased with the calcination temperature because the defects were reduced and the crystallinity was improved.     

Effect of reaction temperature on crystallite size and sensing response of chromium oxide nanoparticles

Nanoparticles of chromium oxide have been synthesized following a precipitation technique at reaction temperatures 5, 27 and 65 °C. Synthesized powders were characterized using X-ray diffraction, transmission electron microscope and Brunauer–Emmett–Teller techniques to carry out structural and morphological analysis. The reaction temperature has been found to be playing a crucial role in controlling particle size. It has been observed that Cr₂O₃ nanoparticles synthesized at 27 °C were smaller as compared to those synthesized at 5 and 65 °C. Chromium oxide samples thus prepared were deposited as thick films on alumina substrates to act as gas sensors and their sensing response to ethanol vapour was investigated at different operable temperatures. It has been observed that all the sensors exhibited optimum response at 250 °C. The investigations revealed that sensing response of Cr₂O₃ nanoparticles synthesized at 27 °C was exceptionally higher than that of Cr₂O₃ nanoparticles synthesized at 5 and 65 °C.     

Structural and optical characterization of tin dioxide nanoparticles prepared by a surfactant mediated method

In this study tin dioxide nanoparticles were synthesized using a cationic surfactant (cetyl-trimethyl ammonium bromide) as the organic template and the hydrous tin chloride and liquid ammonia as the inorganic precursor. Samples were characterized by X-ray diffraction, transmission electron microscopy and UV–visible absorption, photoluminescence and Raman spectroscopy. The X-ray diffraction pattern of the as prepared sample is indexed to rutile phase of tin dioxide without any trace of an extra phase and particle size 7–8 nm which is further confirmed by electron microscopy. The UV–visible spectrum shows that the absorption edge is blue shifted and the band gap of the prepared sample is 4.0 eV which is larger than the bulk tin dioxide (3.6 eV).     

Preparation of poly(vinyl alcohol)/tin glycolate composite fibers by combined sol–gel/electrospinning techniques and their conversion to ultrafine tin oxide fibers

Ultrafine composite fibers made from poly(vinyl alcohol) (PVA)/tin glycolate — a moisture-stable tin oxide containing compound — were prepared by a combined sol–gel processing and electrospinning technique. These fibers were subsequently converted to ultrafine tin oxide fibers by calcination treatment, with the aim of producing tin oxide fiber with a high surface area-to-mass ratio and a high specific conductivity value. The acidity of spinning solution plays an important role to the morphology and size of the obtained fibers. The average diameters of the obtained composite fibers were in the range of 87–166 nm. It was found that the ultrafine tin oxide fiber showed the high conductivity value of 1.59 × 10³ S cm^?1 at calcinations temperature of 600 °C, and the BET surface area was in a range of 71 and 275 m² g^?1. Moreover, the effect of calcinations temperature on the phase and the size of the tin oxide fibers were investigated in this study.     

Synthesis,characterization, electrical and sensing properties of ZnO nanoparticles

The present study investigates the electrical and sensing properties of mechanically compacted pellets of nanosized zinc oxide powders synthesized by chemical method at room temperature in alcohol base using Triethanolamine (TEA) as capping agent. Synthesized ZnO particles has been characterized for its optical, structural, morphological properties using UV–VIS spectrophotometer, X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The ZnO particles have hexagonal wurtzite structure and the particles are of 20–30 nm in size. The electrical properties of the prepared material have been investigated with Impedance Spectroscopy at different temperatures and frequencies and other laboratory setup. Resistivity, I–V curves, AC impedance of ZnO nanoparticles pellets with temperature was investigated and response was compared with commercial ZnO. Piezoelectric and oxygen sensing property of ZnO were also examined. Dynamic hysteresis of sintered ZnO pellet using axis ACCT TF analyzer 2000HS did not show polarization retention by sample. Oxygen sensing of ZnO pellet has been investigated for different concentrations of oxygen for the temperature range of 200–350 °C. The decrease of the current flow through the ZnO pellet with increasing oxygen concentration indicates the application of ZnO in oxygen sensing. The prepared ZnO particles were also used for preparing nanofluids of different concentrations and were characterized by measuring thermal conductivity using hot wire method which shows sigmoidal behavior over a temperature range of 10–50 °C.     

New natively textured surface Al-doped ZnO-TCOs for thin film solar cells via magnetron sputtering

Natively textured surface aluminum doped zinc oxide (ZnO:Al) thin films were directly deposited via pulsed direct current (DC) reactive magnetron sputtering on glass substrates. During the reactive sputtering process, the oxygen gas flow rate was varied from 8.5 sccm to 11.0 sccm. The influences of oxygen flow rate on the structural, electrical and optical properties of naturally textured ZnO:Al TCO thin films with milky surface were investigated in detail. Gradual oxygen growth (GOG) technique was developed in the reactive sputtering process for textured ZnO:Al thin films. The light-scattering ability and optical transmittance of the natively textured ZnO:Al TCO thin films can be improved through gradual oxygen growth method while maintaining a low sheet resistance. Typical natively textured ZnO:Al TCO thin film with crater-like surface exhibits low sheet resistance (R_s ～ 4 Ω), high transmittance (T_a > 85%) in visible optical region and high haze value (12.1%).     

Application of nanostructured ZnO films for electrochemical DNA biosensor

Nanostructured zinc oxide (nsZnO) films have been fabricated onto conducting indium–tin–oxide (ITO) coated glass plate, by cathodic electro-deposition to immobilize probe DNA specific to M. tuberculosis via physisorption based on strong electrostatic interactions between positively charged ZnO (isoelectric point = 9.5) and negatively charged DNA to detect its complementary target. Electrochemical studies reveal that the presence of nano-structured ZnO results in increased electro-active surface area for loading of DNA molecules. The DNA–nsZnO/ITO bioelectrode exhibits interesting characteristics such as detection range of 1 × 10^?6 ? 1 × 10^?12 M, detection limit of 1 × 10^?12 M (complementary target) and 1 × 10^?13 M (genomic DNA), reusability of about 10 times, response time of 60s and stability of up to 4 months when kept at 4°C.     

Synthesis,strong room-temperature PL and photocatalytic activity of ZnO/ZnWO4 rod-like nanoparticles

Zinc oxide (ZnO)/zinc tungstate (ZnWO₄) rod-like nanoparticles with diameters in the range of 6–11 nm and length of about 30 nm were synthesized by a low temperature soft solution method at 95 °C in the presence of non-ionic copolymer surfactant. It was found that their crystallinity was enhanced with the increase of heating time from 1 h up to 120 h. The photoluminescence (PL) measurements showed very strong, narrow UV band peaked at 3.30 eV and a broad visible band peaking at 2.71 eV with a shoulder at about 2.53 eV, for λ_exc < 300 nm. Quite large variations in the intensities of the two PL bands were observed for different excitation wavelengths. The intensity of the main visible band decreases with decreasing excitation energy and disappears when samples are excited λ = 320 nm (E_exc = 3.875 eV). We found that observed optical properties originate from ZnO phase. UV band gap PL had high intensity for all applied excitations, probably induced by ZnWO₄ phase presence on the surface. In addition, two values were found for direct band-gap energy of ZnO/ZnWO₄ rod-like nanoparticles 3.62 and 3.21 eV, determined from reflectance spectrum. The photocatalytic behaviour of ZnO is strongly dependent on the formation of ZnWO₄ phase, of the obtained rod-like nanoparticles.     

Antireflection and band gap extension effects of ZnO nanocrystalline films grown on ITO-coated glasses by low temperature process

Zinc oxide (ZnO) nanocrystalline films coated on indium tin oxides (ITO, 90:10 wt%) glasses were prepared by low temperature process. The thin films were composed of uniform nanoparticles with average diameter around 8.4 nm. All samples exhibited excellent optical antireflective phenomena, and the maximum transmission reached 92.8% for the sample spin coated at 1500 rpm at 453 nm, improved by 21.5%. The antireflective results were explained by the coherence theory. And the antireflective effects were induced by the ITO and ZnO films. The calculated thicknesses of the ZnO films agreed well with the experimental results. The theoretical calculated band gap from the average diameter of ZnO nanoparticles was also well consistent with the experimental ones obtained from the optical transmission spectra. This result was promising for applications in organic solar cells.     

ZnO films and nanorod/shell arrays electrodeposited on PET-ITO electrodes

In this work, ZnO films, nanorod and nanorod/shell arrays were synthesized on the surface of PET-ITO electrodes by electrochemical methods. ZnO films with high optical transmittance were prepared from a zinc nitrate solution using a pulsed current technique with a reduced pulse time (3 s). The X-ray diffraction pattern of ZnO film deposited on PET-ITO electrode showed that it has a polycrystalline structure with preferred orientations in the directions [0 0 2] and [1 0 3]. ZnO nanorods were synthesized on electrochemical seeded substrate in an aqueous solution containing zinc nitrate and hexamethylenetetramine. In order to increase the stability of PET-ITO electrode to electrochemical and chemical stresses during ZnO nanorods deposition the surface of the electrode was treated with a 17 wt% NH₄F aqueous solution. Electrochemical stability of PET-ITO electrode was evaluated in a solution containing nitrate ions and hexamethylenetetramine. ZnO nanorod/shell arrays were fabricated using eosin Y as nanostructuring agent. Photoluminescence spectra of ZnO nanorod and ZnO nanorod/shell arrays prepared on the surface of PET-ITO electrode were discussed comparatively. By employing the 1.5 μm-length ZnO nanorod/shell array covered with a Cu₂O film a photovoltaic device was fabricated on the PET-ITO substrate.     

Preparation and characterization of the bismuth sodium titanate (Na0.5Bi0.5TiO3) ceramic doped with ZnO

This study investigates effects of the zinc oxide (ZnO) addition and the sintering temperature on the microstructure and the electrical properties (such as dielectric constant and loss tangent) of the lead-free piezoelectric ceramic of bismuth sodium titanate (Na_0.5Bi_0.5TiO₃), NBT, which was prepared using the mixed oxide method. Three kinds of starting powders (such as Bi₂O₃, Na₂CO₃ and TiO₂) were mixed and calcined. This calcined NBT powder and a certain weight percentage of ZnO were mixed and compressed into a green compact of NBT–ZnO. Then, this green compact of NBT–ZnO was sintered to be a disk doped with ZnO, and its characteristics were measured. In this study, the calcining temperature was 800 °C, the sintering temperatures ranged from 1000 to 1150 °C, and the weight percentages of ZnO doping included 0.0, 0.5, 1.0, and 2.0 wt%. At a fixed wt% ZnO, the grain size increases with increase in the sintering temperature. The largest relative density of the NBT disk obtained in this study is 98.3% at the calcining temperature of 800 °C, the sintering temperature of 1050 °C, and 0.5 wt% ZnO addition. Its corresponding dielectric constant and loss tangent are 216.55 and 0.133, respectively.     

Structural and microstructural behaviour of SnO2 dense ceramics doped with ZnO and WO3

SnO₂-based varistors doped with ZnO and WO₃ were prepared by mixed oxide method. Experimental evidence shows that the increase in ZnO amount increases the volume and microstrain of unit cell while the WO₃ promotes a decrease. The effect of ZnO and WO₃ additives could be explained by the substitution of Sn^4 +  by Zn^2 +  and W^6 + . The addition of WO₃ inhibits the grain growth due to the segregation in the grain boundary without influence in the densification of the samples. Besides that, an increase in the electrical resistance of the SnO₂–ZnO–WO₃ system was observed independent of the WO₃ concentration.     

One-step large-scale synthesis of porous ZnO nanofibers and their application in dye-sensitized solar cells

A one-step thermal evaporation and vapor-phase transport method was utilized to synthesize porous ZnO nanofibers in large scale. The synthesized nanofibers are highly porous, with diameters in the range of 200–700 nm and lengths of several micrometers. The addition of the CuCl₂·2H₂O into the Zn precursor powder was proved to be critical for the formation of the porous structures, which were proposed to be resulted from the decomposition of the unstable Cl-containing intermediate products such as zinc hydroxide chloride or zinc oxide chloride hydrate phases. In addition, a demonstration of applying the porous ZnO nanofibers as the photoanode of dye-sensitized solar cells is provided.     

Electrical and optical characteristics of surface treated ZnO nanotubes

Vertical ZnO nanotubes were electrochemically deposited onto an indium doped tin oxide glass substrate. These nanotubes were surface treated with zinc acetate and annealed at 450 °C, resulting in a nanotubes/nanoparticles composite layer. Scanning electron microscopy of the surface treated samples showed nanoparticles been dispersed uniformly along the ZnO tubular matrix, which was confirmed by X-ray diffractrometry. Photoluminescence and fluorescence microscopy showed untreated ZnO nanotubes exhibiting blue emission, while the treated samples exhibited green emissions. Ultra-violet spectroscopy of treated samples revealed lower band gap values compare to their untreated counterparts. Lifetime measurements showed higher excitonic lifetimes in treated samples. Conductance studies using atomic force microscopy showed significant improvement in the conductance values for the treated samples. A significant increase in photocurrent was observed in treated samples when used as photo-anodes in dye sensitized solar cells.