The structural and optical properties of ZnO nanorods via citric acid-assisted annealing route

ZnO nanorods with diameters ranging from 25 to 88 nm and with length up to 1 μm were obtained via citric acid-assisted annealing route. The sample was characterized by X-ray diffraction, field-emission scanning electron microscopy (FE-SEM), Raman spectrometer, FTIR spectrophotometer, ultraviolet visible (UV–VIS) spectroscopy, and photoluminescence (PL) spectroscopy. It demonstrates that the sample is composed of ZnO with hexagonal structure and the ZnO nanorods are of excellent optical quality.     

Growth of aligned ZnO nanorods on transparent electrodes by hybrid methods

The fabrication of ZnO (80 nm) thin film was achieved by hybrid atomic layer deposition (ALD) to prevent the reaction between the reactants and conductive layer of the substrates. ZnO nanorods (ZnO-NRs) growth over the substrates was performed by wet chemical procedure in which Zn(NO₃)₂ and hexamethylenetetramine were used as the precursors. HR-TEM, SAED, FE-SEM, X-ray diffraction (XRD), and UV–Vis spectroscopy were employed to characterize the ZnO-NRs samples on the substrates. XRD and HR-TEM analyses confirmed that the ZnO nanorod structure is hexagonal wurtzite type with growth in the [0001] direction. Length and thickness of the ZnO-NRs ranged between 45  and 90 nm and 480  and 600 nm, respectively. It was observed that the growth rate of NRs in [0001] direction is 10 times higher than in [1000] direction. The growth mechanism and resulted dimensions of nanorods are function of the synthesis parameters (in hybrid ALD process) such as reaction time, temperature, precursor molar ratio, and thickness of ZnO film.     

Fabrication and growth mechanism of hexagonal zinc oxide nanorods via solution process

This article presents, the fabrication of perfectly hexagonal zinc oxide nanorods performed via solution process using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (HMT) at various concentrations of i.e. 1 × 10⁻³ to 10 × 10⁻² M in 50 mL distilled water and refluxed at 100 °C for 1 h. We used HMT because it acts as a template for the nucleation and growth of zinc oxide nanorods, and it also works as a surfactant for the zinc oxide structures. The X-ray diffraction patterns clearly reveal that the grown product is pure zinc oxide. The diameters and lengths of the synthesized nanorods lie in the range of 200–800 nm and 2–4 μm, respectively as observed from the field emission scanning electron microscopy (FESEM). The morphological observation was also confirmed by the transmission electron microscopy (TEM) and clearly consistent with the FESEM observations. The chemical composition was analyzed by the FTIR spectroscopy, and it shows the ZnO band at 405 cm⁻¹. On the basis of these observations, the growth mechanism of ZnO nanostructures was also proposed.     

Synthesis and characterization of anatase and rutile TiO2 nanorods by template-assisted method

Well-aligned anatase and rutile TiO₂ nanorods and nanotubes with a diameter of about 80–130 nm have successfully been fabricated via sol-gel template method. The prepared samples were characterized by using thermogravimetric (TG) and differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The XRD results indicated that the TiO₂ nanorods were crystallized in the anatase and rutile phases, after annealing at 400–800 °C for different periods of time from 0.2 to 10 h.     

Rapid growth of nanotubes and nanorods of würtzite ZnO through microwave-irradiation of a metalorganic complex of zinc and a surfactant in solution

Large quantities of single-crystalline ZnO nanorods and nanotubes have been prepared by the microwave irradiation of a metalorganic complex of zinc, in the presence of a surfactant. The method is simple, fast, and inexpensive (as it uses a domestic microwave oven), and yields pure nanostructures of the hexagonal würtzite phase of ZnO in min, and requires no conventional templating. The ZnO nanotubes formed have a hollow core with inner diameter varying from 140–160 nm and a wall of thickness, 40–50 nm. The length of nanorods and nanotubes varies in the narrow range of 500–600 nm. These nanostructures have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods and nanotubes are found by SAED to be single-crystalline. The growth process of ZnO nanorods and nanotubes has been investigated by varying the surfactant concentration and microwave irradiation time. Based on the various results obtained, a tentative and plausible mechanism for the formation of ZnO nanostructures is proposed.     

Facile ultrasound-assisted synthesis of ZnO nanorods in an ionic liquid

ZnO nanocrystals have been synthesized by ultrasound-assisted synthesis from Zn(CH₃COO)₂2H₂O and NaOH in the neat room-temperature ionic-liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C₄mim][Tf₂N]. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the formed ZnO nanocrystals are of rod like shape with lengths from 50 to 100 nm and diameters of about 20 nm. X-ray diffraction (XRD) confirms the crystallinity as well as the sample purity. The band gap of the as-prepared ZnO nanorods was estimated to be 3.31 eV from UV–Vis absorption measurements. The photoluminescence spectrum shows the characteristic greenish emission of ZnO at room temperature (λ_max = 563 nm). The ZnO bonding levels have been determined by X-ray photoelectron spectroscopy (XPS). Nitrogen adsorption–desorption measurements show typical samples to have a specific surface area of 49.93 m²/g.     

Photocatalytic activity of TiO2-capped ZnO nanoparticles

Using a combined hydrothermal and sol–gel route, TiO₂ -capped ZnO nanoparticles with an average size of 60 nm were prepared. The titania shell was amorphous with a thickness of ~10 nm. Formation of Zn₂TiO₄ phase at higher calcination temperature was noticed. Effects of Ti/Zn molar ratio and coating time on the thickness of TiO₂ shell and the photoactivity of the particles for decolorization of Methylene Blue (MB) under UV lamp irradiation (3 mW/cm²) were investigated. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, fourier-transform infrared spectrometry (FTIR), diffuse reflectance spectroscopy (DLS), and atomic absorption spectroscopy. Analysis of the photoactivity results according to Langmuir–Hinshelwood model revealed a two-step decolorization process with a high kinetics rate at the early stage followed by a slower step. The capped nanoparticles synthesized under specific conditions exhibited higher photodecolorization yield and faster kinetics in comparison to the uncoated ZnO and P25-Degussa TiO₂ nanoparticles.     

Growth of compact arrays of optical quality single crystalline ZnO nanorods by low temperature method

We report the synthesis and optical properties of compact and aligned ZnO nanorod arrays (dia, ∼ 50–200 nm) grown on a glass substrate with varying seed particle density. The suspension of ZnO nanoparticles (size, ∼ 15 nm) of various concentrations are used as seed layer for the growth of nanorod arrays via selfassembly of ZnO from solution. We studied the effect of various growth parameters (such as seeding density, microstructure of the seed layer) as well as the growth time on the growth and alignment of the nanorods. We find that the growth, areal density and alignment of the nanorods depend on the density of seed particles which can be controlled. It is observed that there is a critical density of the seed particles at which nanorod arrays show maximum preferred orientation along [002] direction. The minimum and maximum radius of the aligned nanorods synthesized by this method lie in the range 50–220 nm which depend on the seeding density and time of growth. These nanorods have a bandgap of 3.3 eV as in the case of bulk crystals and show emission in the UV region of the spectrum (∼ 400 nm) due to excitonic recombination and defect related emission in the visible region.     

Room temperature ferromagnetism in solvothermally synthesized pure CdSe and CdSe:Ni nanorods

We report here room temperature ferromagnetism in CdSe and Ni-doped CdSe nanorods. Pure and 3% Ni-doped CdSe nanorods are synthesized by using low temperature solvothermal process by using ethylenediamine as solvent. X-ray diffractogram depicts the wurtzite (hexagonal) structure of the CdSe nanorods. From Transmission Electron Microscopy analysis, it is found that the average diameter of the CdSe nanorods is about 4–5 nm having length of about 50 nm. Magnetic studies are made by the analysis of M–H curves, obtained by using Superconducting Quantum Interference Device. The room temperature ferromagnetic behaviour has been shown by both pure CdSe as well as Ni-doped CdSe nanorods.     

Synthesis of ZnO nanorods from aqueous solution

In the present work, crystalline one-dimensional ZnO nanorods were synthesized by a PVP (polyvinylpyrrolidone)-assisted hydrothermal process with zinc acetate as the precursor. The major advantage of this technique is the use of water as the solvent: cheaper and more environmentally friendly than alcohol. The as-synthesized ZnO nanorods have diameters of 50-200 nm and lengths up to 5 μm. X-ray powder diffractometry (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED), Fourier transmission infrared spectroscopy (FTIR) were used to characterize the structural and the chemical features of the ZnO nanorods.     

Effect of ammoniating temperature on microstructure of one-dimensional GaN nanorods with Tb intermediate layer

GaN nanorods have been successfully synthesized on Si (111) substrates by magnetron sputtering through ammoniating Ga₂O₃/Tb thin films. The influence of ammonating temperatures on microstructure, morphology and light emitting properties of GaN nanorods was ananlyzed in detail using X-ray diffraction, X-ray photoelectron spectroscopy, FT-IR spectrophotometer, scanning electron microscopy, high- resolution transmission electron microscopy, and photoluminescence spectroscopy. The results demonstrate that the GaN nanorods are single crystalline and exhibit hexagonal wurtzite symmetry. The highest crystalline quality was achieved at 950 °C for 15 min with the size of 100–150 nm in diameter, which have an excellent light emitting properties. A small red-shift occurs due to band-gap change caused by the tensile stress.     

Effect of annealing on the magnetic properties of solution synthesized Zn1−xMnxO nanorods

Mn-doped ZnO nanorods with ～30 nm in diameter and ～200 nm in length were synthesized by a seed-mediated solution method. The structures, magnetic properties, as well as the annealing effect were characterized by transmission electron microscopy, electron energy loss spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectrum and physical properties measurement system. Magnetic properties measurement revealed that the Zn_0.97Mn_0.03O nanorods exhibited ferromagnetism with a saturation magnetization of 0.005 emu g^?1 and a coercivity of 110 Oe at 305 K. After annealing the samples at 900 °C for 2 h in air, the nanorods were transformed into nanoparticle aggregates. The coercivity and saturation magnetization increased obviously. Detailed analyses proved that a phase-separation process was happened at the high temperature. In this process, most of the particles preserved the wurtzite ZnO structure, while a few small ones evolved into spinel-structured particles. The increasing of the ferromagnetism of the annealed sample is attributed to the formation of secondary phase Zn_xMn_3?xO_4.     

Quenching of photocatalytic activity and enhancement of photostability of ZnO particles by polydimethysiloxane coating

ZnO particles with a size range of 50–150 nm were coated with polydimethylsiloxane (PDMS) with a thin film thickness of 3–4 nm using a simple ambient-pressure chemical vapor deposition method. Surfaces consisting of the PDMS-coated ZnO nanoparticles were found to be superhydrophobic with a water contact angle >160°. The superhydrophobicity was sustained in the presence of UV light. Photocatalytic activity and photocorrosion of ZnO were nearly completely quenched in the presence of PDMS-coating. It is suggested that our PDMS-coating can be of potential interest for the application of ZnO in UV protection agents and energy and electronic devices.     

Synthesis of violet light emitting single crystalline ZnO nanorods by using CTAB-assisted hydrothermal method

ZnO nanorods were grown by cetyl trimethylammonium bromide assisted hydrothermal technique from a single molecular precursor. The phase and structural analysis were carried out by X-ray diffraction technique and Raman spectroscopy, respectively. The phase and structural analysis has suggested that as prepared nanorods have hexagonal wurzite structure. Morphology of the nanorods was investigated by electron microscopy techniques which showed the formation of well dispersed nanorods of 100 ± 10 nm in diameter and 900 ± 100 nm in length. Optical properties were investigated by photoluminescence spectroscopy. As prepared ZnO nanorods have shown intense room temperature photoluminescence peak in the violet region at 403 nm. Absence of defect mediated green luminescence peak suggests the formation of well crystalline ZnO nanorods without any impurities or structural defects.     

Effect of hydrothermal duration on synthesis of WO<Subscript>3</Subscript> nanorods

Among different type of transition metal oxides, tungsten trioxide (WO₃) is a suitable candidate for electronic device fabrication due to its n-type property and wide band gap. Herein, one-dimensional tungsten trioxide (WO₃) nanorods were achieved from an aqueous solution of sodium tungstate dihydrate (Na₂WO₄·2H₂O) and sodium chloride (NaCl) in an acidic media by a time-optimized hydrothermal synthesis in autoclave at 180°C or different synthesis durations. For studying morphology and size of obtained powder, X-ray diffraction (XRD), scanning electron microscope (SEM), and high resolution transmission electron microscope (HRTEM) were applied. Finally, WO₃ nanorods of about 2–3 μm in length and 100–200 nm in diameter were obtained during 3 h hydrothermal process.     

Analysis of growth parameters for hydrothermal synthesis of ZnO nanoparticles through a statistical experimental design method

Nanocrystalline ZnO particles were synthesized from an aqueous solution composed of zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O) and urea (H₂NCONH₂). A precipitating precursor, basic zinc carbonate (Zn₅(CO₃)₂(OH)₆), was first formed by hydrothermally treating the solution at 120 °C for 2–4 h. Nanocrystalline ZnO particles were then obtained by calcining the precursors at 350–650 °C for 0.5–2 h. The synthesis products were characterized using thermogravimetry–differential scanning calorimetry–mass spectrometry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence techniques. Based on the experimental results, a possible reaction mechanism for the ZnO formation was proposed. The effects of experimental parameters (namely, the hydrothermal treatment time, the calcination time, and the calcination temperature) on the characteristics of the resulting ZnO products (i.e., the crystalline size and the photoluminescence properties) were analyzed by the Taguchi method to attain the optimum synthesis conditions. By using the appropriate parameters derived from this method, we verified that the optimized synthesis provided a yield of ~70% and that the resulting ZnO particles possessed the characteristics of a ~25 nm crystalline size and a satisfactory photoluminescence property.     

Synthesis and electrocatalytic activity of multi-walled carbon nanotubes/Cu–Ag nanocomposites

Cu–Ag bimetallic nanoparticles with atomic ratio of 2.1:1 and diameter in the range of 15–30 nm were decorated on acid-treated multi-walled carbon nanotubes by a chemical reduction method, which was characterized by transmission electron microscope (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). The Cu–Ag/MWNTs nanocomposites were used to construct a modified electrode toward biosensing of H₂O₂ with a high sensitivity. The catalytic ability of MWNTs/Cu–Ag toward H₂O₂ was much better than that of MWNTs/Cu and MWNTs/Ag, which indicated that there is a cooperation effect between Cu and Ag.     

In situ thermal residual stress evolution in ultrathin ZnO and Ag films studied by synchrotron x-ray diffraction

Residual-stress evolution in sputtered encapsulated ZnO/Ag/ZnO stack has been studied in-situ by synchrotron x-ray diffraction when heat treated. The ZnO/Ag/ZnO stack encapsulated into Si₃N₄ layers and deposited on (001) Si substrates was thermally heated from 25 °C to 600 °C and cooled down to 25 °C. X-ray diffraction 2D patterns captured continuously during the heat treatment allowed monitoring the diffraction peak shifts of both Ag (15 nm thick) and ZnO (10 nm and 50 nm thick) sublayers. Due to the mismatch between the coefficients of thermal expansion, the silicon substrate induced compressive thermal stresses in the films during heating. We first observed a linear increase of the compressive stress state in both Ag and ZnO films and then a more complex elastic-stress evolution starts to operate from about 100 °C for Ag and about 250 °C for ZnO. Thermal contraction upon cooling seems to dominate so that the initial compressive film stresses relax by about 300 and 700 MPa after thermal treatment for ZnO and Ag, respectively. The overall behavior is discussed in terms of structural changes induced by the heat treatment.     

Numerical calculation of plasmonic field absorption enhancement in CdSe-quantum dot sensitized ZnO nanorods by Ag nanoparticle periodic arrays

Plasmonic field absorption enhancement (PFAE) of Ag nanoparticles (Ag NPs) periodic arrays in CdSe-quantum dot (QD) sensitized ZnO nanorods was numerically investigated by the three-dimensional finite difference time domain (FDTD). The Ag NPs with spherical morphology were found to have an optimum PFAE compared to other Ag NP morphologies such as cubic and pyramidal. The results also showed that PFAE intensity in CdSe-QD-sensitized ZnO nanorods is increased with the reduction of Ag NP diameter until 10 nm and decreases thereafter. Moreover, the optimum density of spherical Ag NPs for optimum PFAE was observed as 20%. PFAE in CdSe-QD-sensitized ZnO nanorods is improved with increasing space between ZnO nanorods until 180 nm and reduces thereafter. Finally, the results showed that PFAE of Ag NPs for the high distance between ZnO nanorods is dependent on radiation angle; while for the low distance between ZnO nanorods it is free of radiation angle.     

Synthesis,structural and optical characterization of Ni-doped ZnO nanoparticles

Nanocrystalline Zn_1−x Ni _x O (x = 0.00, 0.02, 0.04, 0.06, 0.08) powders were synthesized by a simple sol–gel autocombustion method using metal nitrates of zinc, nickel and glycine. Structural and optical properties of the Ni-doped ZnO samples annealed at 800 °C are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis using X-rays (EDAX), UV–visible spectroscopy and photoluminescence (PL). X-ray diffraction analysis reveals that the Ni-doped ZnO crystallizes in a hexagonal wurtzite structure and secondary phase (NiO) was observed with the sensitivity of XRD measurement with the increasing nickel concentration (x ≥ 0.04). The lattice constants of Ni-doped ZnO nanoparticles increase slightly when Ni²⁺ is doped into ZnO lattice. The optical absorption band edge of the nickel doped samples was observed above 387 nm (3.20 eV) along with well-defined absorbance peaks at around 439 (2.82 eV), 615(2.01 eV) and 655 nm (1.89 eV). PL measurements of Ni-doped samples illustrated the strong UV emission band at ~3.02 eV, weak blue emission bands at 2.82 and 2.75 eV, and a strong green emission band at 2.26 eV. The observed red shift in the band gap from UV–visible analysis and near band edge UV emission with Ni doping may be considered to be related to the incorporation of Ni ions into the Zn site of the ZnO lattice.