Effects of seed layers on structural, morphological, and optical properties of ZnO nanorods

We studied the effects of seed layers on the structural and optical properties of ZnO nanorods. ZnO and Ag-doped ZnO (ZnO:Ag) seed layers were deposited on glass substrates by magnetron co-sputtering. ZnO nanorods were grown on these seed layers by the chemical bath deposition in an aqueous solution of Zn(NO3)2 and hexamethyltetramine. SEM micrographs clearly reveal that ZnO nanorods were successfully grown on both kinds of seed layers. The XRD patterns indicate that crystallization of ZnO nanorods is along the c-axis. Meanwhile, the packing density and the vertical alignment of the ZnO nanorods on the ZnO seed layer are better than those of the ZnO nanorods on ZnO:Ag. The enhanced growth of nanorods is thought to be due to the fact that the ZnO layer exhibits a higher crystalline quality than the ZnO:Ag layer. According to the low-temperature photoluminescence spectra, the ZnO nanorods on the ZnO seed layer show a narrow strong ultraviolet emission band centered at 369 nm, while those on ZnO:Ag exhibit multiple bands. These results are thought to be related with the crystallinity of ZnO nanorods, the morphologies of ZnO nanorods, and the reflectivities of seed layers. More detailed studies for clarification of the seed layer effect on the growth of ZnO nanorods are desirable.     

Switching in structural, optical, and magnetic properties of self-assembled Co-doped ZnO: effect of Co-concentration

Here, we report on the self-assembled Co-doped ZnO nanoparticles synthesized by using sol–gel technique. It has been observed that when Co is introduced in the solution, nanoparticles arrange themselves into a particular pattern. This self-assembly of Zn_1?xCo_xO, were found to be consistent with the change in Co-doping concentration. Using electron microscopy these systems were studied to confirm the assembly formation with doping. Optical study of these assemblies suggests the decrease in direct band gap of these systems with the increase in doping concentration. In addition to it, the Urbach energy was found to be increased, indicating the redistribution of states in between conduction and valence band with doping. Magnetic measurement shows the introduction of paramagnetic behavior with Co-doping in this self-assembled Co-doped ZnO.     

Studies on the structural and optical properties of zinc oxide nanobushes and Co-doped ZnO self-aggregated nanorods synthesized by simple thermal decomposition route

Pure and Co-doped zinc oxide nanomaterials were prepared by a simple low temperature synthesis and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution-transmission electron microscopy (HR-TEM), diffused reflectance spectroscopy (DRS) and electron paramagnetic resonance (EPR) techniques. The results showed the formation of nanobushes that consists of several nanowires for pure ZnO and the nanorods formed by self-aggregation for Co-doped ZnO. The presence of Co²⁺ ions replacing some of the Zn²⁺ in the ZnO lattice was confirmed by EPR and DRS studies. The mechanism for the formation of self-aggregated and self-aligned ZnO rods after the incorporation of cobalt in the lattice by the building block units is discussed in this study. Morphological studies were carried out using SEM and HR-TEM, which supports the validity of the proposed mechanism for the formation of ZnO nanobushes and Co-doped ZnO nanorods. The synthesized nanomaterials were found to have good optoelectronic properties.     

Influence of thallium doping on structural,electrical, and optical properties of ZnO nanorods for TCO applications

Journal of Materials Science: Materials in Electronics - Thallium (Tl)-doped ZnO nanorods were prepared (the doping ratios were between 0 and 5 mol %) in two stages. Combined sol–gel...     

Effect of In incorporation on the structural, electrical, and gas sensing properties of ZnO films

In this paper, we report some comparative results on the structural, electrical, and gas sensing properties of undoped, In-doped ZnO, and ZnO–In₂O₃ thin films, respectively. The oxide films were obtained by thermal oxidation (flash oxidation) of metallic films, deposited by thermal evaporation under vacuum. X-ray diffraction patterns reveal that oxidized films are polycrystalline, the crystallites being preferentially oriented with (002) planes parallel with the substrate. It was observed that the films’ morphology, investigated by atomic force microscopy and scanning electron microscopy, is influenced by the In amount. The temperature dependence of electrical conductivity was studied and obtained results indicate that In-doped ZnO and ZnO–In₂O₃ films exhibit an enhancement of electrical conductivity with four orders of magnitude by comparison with undoped ZnO film. Gas sensitivity measurements were performed for four different gases (ammonia, methane, acetone, and ethanol), and it was observed that all investigated films are more sensitive to ammonia. Also, it was observed that gas sensitivity is visibly increased for In-doped ZnO and ZnO–In₂O₃ samples by comparison with undoped ZnO film.     

Structural,optical and morphological properties of La,Cu co-doped SnO2 nanocrystals by co-precipitation method

Sn_0.96−xLa_0.04Cu_xO₂ (0 ⩽ x ⩽ 0.03) nanocrystals have been successfully synthesized by employing a simple co-precipitation method. The crystal structure of the synthesized nanocrystals was found to be tetragonal rutile of tin oxide by using X-ray diffraction technique and was not affected by doping. The change in lattice parameters was discussed based on the secondary phase formation and presence of Cu²⁺/Cu³⁺ in LaSnO₂ lattice. The variation in size and shape of the nanocrystals by Cu-doping was discussed using scanning electron microscope. The chemical stoichiometry of Sn, Cu, La and O was confirmed by energy dispersive X-ray spectra. The best optical transparency and lower absorption observed at Sn_0.97La_0.02Cu_0.01O₂ nanocrystals seems to be optimal for industrial applications especially as transparent electrode. The initial blue shift of energy gap from 3.65 eV (Cu = 0%) to 3.78 eV (Cu = 1%) (ΔE_g ≈ 0.13 eV) is due to the distortion in the crystal structure of the host compound and generation of defects. The red shift of energy gap after Cu = 1% is due to the charge-transfer transitions between the metal ions d-electrons and the SnO₂ conduction or valence band. Lattice mode of SnO₂ at 686 cm⁻¹ in Sn_0.98La_0.02O₂ nanocrystals and anti-symmetric SnOSn stretching mode of the surface bridging oxide around 634–642 cm⁻¹ in Cu doped Sn_0.98La_0.02O₂ nanocrystals was confirmed by Fourier transform infrared spectra.     

Effect of thickness on structural,optical, electrical and morphological properties of nanocrystalline CdSe thin films for optoelectronic applications

This paper presents effect of thickness on the physical properties of thermally evaporated cadmium selenide thin films. The films of thickness 445 nm, 631 nm and 810 nm were deposited employing thermal evaporation technique on glass and ITO coated glass substrates followed by thermal annealing in air atmosphere at temperature 300 °C. The as-deposited and annealed films were subjected to the XRD, UV–Vis spectrophotometer, source meter, SEM and EDS to find the structural, optical, electrical, morphological and compositional analysis respectively. The structural analysis shows that the films have cubic phase with preferred orientation (1 1 1) and nanocrystalline nature. The structural parameters like inter-planner spacing, lattice constant, grain size, number of crystallites per unit area, internal strain, dislocation density and texture coefficient are calculated. The optical band gap is found in the range 1.69–1.84 eV and observed to decrease with thickness. The electrical resistivity is found to increase with thickness for as-deposited films and decrease for annealed films. The morphological studies show that the as-deposited and annealed films are homogeneous, smooth, fully covered and free from crystal defects like pin holes and voids. The grains in the as-deposited films are densely packed, well defined and found to be increased with thickness.     

Low-temperature sintering and electrical properties of Co-doped ZnO varistors

ZnO–Bi₂O₃–B₂O₃-based varistors doped with each kind of cobalt oxides were prepared by conventional ceramic processing. The effects of CoO, Co₂O₃ and Co₃O₄ on the microstructure and the electrical characteristics of varistor samples sintered at 880 °C were investigated separately. Analysis of microstructure indicated the cobalt cations were distributed both in grain regions and grain boundary regions and no crystalline phases containing cobalt were detected in XRD patterns for the samples with various cobalt oxides. All these cobalt oxides could effectively enhance the varistor performance by effectively increasing the nonlinear coefficient and lowing the leakage current, while the breakdown voltage fields increased slightly. Capacitance–voltage characteristics showed the potential barriers of varistor samples increased with the addition of each cobalt oxide. It was found that the addition of same amount of cobalt cations in various cobalt oxides had a different effect on the varistor samples. Best electrical properties were obtained for the varistor sample containing Co₃O₄, in which the nonlinearity coefficient is 28.5, the leakage current density is 3.4 μA and the breakdown voltage field is as low as 260 V/mm.     

On the structural, morphological, optical and electrical properties of sol-gel deposited ZnO:In films

Indium-doped zinc oxide thin films deposition was performed by the sol-gel technique using homogeneous and stable solutions of zinc acetate 2-hydrate and indium chloride in ethanol. Films were spin coated onto glass substrates. After drying and after a heat treatment at 450 °C, highly transparent (80%-90%) films were obtained. The effect on the structural, morphological, optical and electrical thin films properties of the dopant concentration was investigated. The temperature dependencies of the electrical conductivity under vacuum and in open atmosphere were analysed and discussed.     

Preparation of ZnO nanoparticles using electrodeposition and co-precipitation techniques for dye-sensitized solar cells applications

Zinc oxide thin films have been successfully prepared by co-precipitation and electrodeposition methods onto Fluorinated tin oxide substrate using zinc nitrate aqueous solutions at various bath temperatures (25–75 °C). The deposition of electrodeposition method was conducted using both using linear sweep voltammetry and Chronoamperometric techniques. The effects of solution composition, agitation and bath temperature on the electrochemical measurements and ZnO film characteristics were fully analyzed. The findings reveal that temperature and nitrate ion concentration have a strong promoting effect on ZnO film formation. Moreover, the obtained powders were investigated by X-ray diffraction, Field emission scanning electron microscopy and UV–Vis Spectroscopy. Structural characterization by X-ray diffraction indicates the formation of ZnO phase and the deposited film exhibits the Zincite structure with crystallite size around 51 nm. The photovoltaic performance of dye-sensitized solar cells based on both ZnO prepared by co-precipitation and electrodeposition methods was investigated. A power conversion efficiency (η) of 3.5 % was achieved for the DSSC with co-precipitation ZnO, which is higher than that of the cell with electrodeposition ZnO (2.5 %). Explanations are substantiated by incident photon to electron conversion efficiency curves.     

Effect of Al dopants on the structural,optical and gas sensing properties of spray-deposited ZnO thin films

Undoped and Al-doped ZnO thin films were deposited on glass substrates by the spray pyrolysis method. The structural, morphological and optical properties of these films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–Vis spectroscopy, photoluminescence (PL) and photoconductivity (PC) measurements, respectively. XRD analyses confirm that the films are polycrystalline zinc oxide with the hexagonal wurtzite structure, and the crystallite size has been found to be in the range 20–40 nm. SEM and AFM analyses reveal that the films have continuous surface without visible holes or faulty zones, and the surface roughness decreases on Al doping. The Al-doped films have been found to be highly transparent (>85%) and show normal dispersion behavior in the wavelength range 450–700 nm. The doped films show only ultraviolet emission and are found to be highly photosensitive. Among all the films examined, at 300 °C the 1.0 at% Al-doped film shows the selective high response (98.2%) to 100 ppm acetone concentration over to methanol, ethanol, propan-2-ol, formaldehyde and hydrogen.     

Fabrication and characterization of nanoporous ZnO layers for sensing applications

In this contribution we employ a low temperature method for the deposition of thin and highly porous layers based on ZnO nanocrystallites. The method is based on coating of a substrate with ZnO suspension and thereafter the application of quasi static pressure on the sample. A high temperature step becomes redundant and the temperature does not exceed 120 °C during the whole process. The porosity, the specific surface area and the pore size distribution can be influenced by the variation of the process pressure. The influence of oxygen and water vapor on the photoresponse is investigated and a model explaining the observed behavior is discussed.     

Surface morphological properties of sol-gel derived SiO2 fiber

In this study, sol-gel derived SiO₂ fibers were prepared by mixing tetraethyl orthosilicate, ethanol, water and hydrochloric acid. Fibrous SiO₂ was drawn by using a viscous solution. Dried gel fibers were final heat-treated at 1000, 1100, 1200 and 1300°C for 1 h in air. Crystallinity of the SiO₂ fiber after annealing was measured by X-ray diffraction analysis. A field emission—scanning electron microscope and an atomic force microscope were used to evaluate surface properties. SiO₂ fiber heat-treated at high temperature, i.e., 1300°C, exhibited inhomogeneous surface structure.     

Influence of surfactants on structural,morphological, optical and antibacterial properties of SnO2 nanoparticles

Tin oxide (SnO₂) nanoparticles were synthesised using various surfactants of different charges (n‐cetyl trimethyl ammonium bromide, sodium dodecyl sulphate and TRITON X‐100) by the co‐precipitation method. The synthesised nanomaterials were characterised using different techniques to study their structural, surface morphological, optical and anti‐bacterial activities. X‐ray diffraction patterns revealed the formation of a tetragonal rutile structure in pure and surfactants‐aided SnO₂ nanoparticles and the results show good agreement with JCPDS data [41‐1445]. The crystallite size of SnO₂ nanoparticles was found to decrease with the addition of surfactants. Scanning electron microscopy images exhibit spherical shape morphology with an average diameter of 30–75 nm for pure and surfactants‐aided SnO₂ nanoparticles. The band gap energy of the prepared materials was estimated from the UV–visible absorption spectra and a considerable increase in band gap energy was observed in surfactants‐aided SnO₂ nanoparticles (3.487, 3.57, 3.50 and 3.3 eV). The antibacterial activities of the synthesised nanoparticles were studied against Escherichia coli and Staphylococcus aureus bacteria.Inspec keywords: visible spectra, precipitation (physical chemistry), ultraviolet spectra, nanofabrication, tin compounds, X‐ray diffraction, crystallites, titanium compounds, particle size, antibacterial activity, surfactants, nanoparticles, energy gap, scanning electron microscopy, surface morphology, semiconductor materials, optical constants, semiconductor growthOther keywords: SnO₂ , co‐precipitation method, anti‐bacterial activities, X‐ray diffraction patterns, tetragonal rutile structure, spherical shape morphology, band gap energy, sodium dodecyl sulphate surfactant, surface morphology, surfactant‐aided SnO₂ nanoparticles, crystallite size, scanning electron microscopy, UV–visible absorption spectra, Escherichia coli, Staphylococcus aureus bacteria, TRITON X‐100 surfactant, n‐cetyl trimethyl ammonium bromide surfactant     

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.