Growth temperature dependent properties of ZnO nanorod arrays on glass substrate prepared by wet chemical method

In this work, ZnO nanorod arrays were grown on glass substrate by the wet chemical method, and the effect of synthesis temperature on the properties was investigated. The grown nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman and Photoluminescence (PL) measurements. XRD pattern showed that nanorod prepared at 80 °C and 90 °C has high crystallinity with wurtzite structure and orientated along the c-axis. However, nanorods were not formed at 60 °C and 70 °C due to less energy supply for the growth of the ZnO. FE-SEM results showed that the morphology and the size of ZnO can be effectively controlled. In particular, as the temperature increased, diameter of the nanorod was increased while length decreased. Raman scattering spectra of ZnO nanorod arrays revealed the characteristic E₂^high mode that is related to the vibration of oxygen atoms in the wurtzite ZnO. Room-temperature PL spectra of the ZnO nanorods revealed a near-band-edge (NBE) emission peak. The NBE (UV light emission) band at ~383 nm might be attributed to the recombination of free exciton. The narrow full-width at half-maximum (FWHM) of the UV emission indicated that ZnO nanorods had high crystallinity.     

Synthesis and cathodoluminescence of ZnO tetrapods prepared by a simple oxidation of Zn powder in air atmosphere

Tetrapod-shaped ZnO crystals were synthesized by an oxidation process of Zn powder at temperatures over 930 °C in air. The ZnO crystals were formed in an alumina crucible in which metallic Zn powder was put. X-ray diffraction patterns revealed that the tetrapods were ZnO with wurtzite structure. Any impurities including Zn were not detected, indicating that the ZnO crystals were of high quality. As the oxidation temperature increased, the size of tetrapods was getting larger and longer. However at 1100 °C, tetrapod morphology was disappeared and changed to irregular shape. Strong UV emission at 380 nm was observed in the CL spectra taken for the ZnO tetrapods. The increase in the intensity of green emission at 510 nm was also observed with increased oxidation temperature.     

Photoluminescence of zinc oxide nanopowder synthesized by a combustion method

Zinc oxide (ZnO) nanopowder was synthesized by a simple and quick combustion method using zinc nitrate as a precursor and glycine as a fuel material. The starting materials were mixed at room temperature and spontaneous ignition of which resulted into the ZnO nanopowder. The synthesized nanopowder was characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM), Infrared (IR) spectrophotometer and spectroflurometer in order to study the structural, morphological, compositional and photoluminescence (PL) properties. The ZnO powder shows polycrystalline nature with preferential peak (101) having crystallite size 25 nm. A significant band at 532 cm⁻¹ in the IR spectrum corroborates the presence of characteristic band of ZnO. Room temperature photoluminescence spectrum of the synthesized nanopowder exhibits a dominant, sharp and strong ultraviolet (UV) emission with a suppressed deep-level emission indicating good crystal quality and optical properties.     

ZnO纳米棒水热法生长与表征

采用两步法在FTO导电玻璃衬底上制备ZnO纳米棒,首先利用浸渍-提拉法在FTO导电玻璃衬底上制备ZnO晶种层,然后把有ZnO晶种层的FTO衬底放入盛有生长溶液的反应釜中利用水热法制备ZnO纳米棒.研究了生长溶液的浓度、生长温度和生长时间对所制备的对ZnO纳米棒阵列的微结构和光致发光性能的影响,利用X射线衍射(XRD)、扫描电子显微镜(SEM)和光致发光谱(PL)研究了ZnO样品的结构、形貌和光学性质.实验结果表明:所制备的ZnO纳米棒呈现六方纤锌矿结构,沿(002)晶面择优取向生长,纳米棒的平均直径约为100 nm,长度约为2.5 μm.所制备的ZnO纳米棒在390 nm附近具有很强的紫外发光峰和在550 nm附近有较弱的宽绿光发光峰.     

CdWO4 nanorods: Ultrafast synthesis via a PEG-1000 polymer-assisted enhanced microwave synthesis route and their photoluminescence property

Cadmium tungstate (CdWO₄) nanorods have been successfully ultrafast synthesized in several minutes under enhanced microwave irradiation conditions and characterized by XRD, SEM, TEM, and photoluminescence. The products show a very strong photoluminescence peak at 475 nm with the excitation wavelength of 350 nm and a short decay time.     

Synthesis and characterization of Mn-doped ZnO nanorods grown in an ordered periodic honeycomb pattern using nanosphere lithography

We report a study of the structural, optical and magnetic properties of undoped and Mn-doped ZnO nanorods grown by chemical bath deposition in a periodic honeycomb lattice formation. Mn-doping is accomplished by a diffusion process at a constant time of 8 h for different temperatures of 500 °C, 600 °C and 700 °C. Undoped and Mn-doped ZnO nanorods had a hexagonal wurtzite structure with a (0 0 2) preferred orientation. From SEM results, it was seen that Mn-doped ZnO nanorods grew vertically in the honeycomb lattice with lengths of 0.8 μm. XPS results showed that Mn³⁺ ions was successfully incorporated in the ZnO matrix by substituting for Zn²⁺ ions and that Mn-doping increased the number of oxygen vacancies in ZnO compared to undoped ZnO. This result was also supported by photoluminescence data at 10 K. Magnetic data showed that all the samples exhibited ferromagnetic character. Although the origin of undoped ZnO is related to oxygen vacancy-induced d⁰ ferromagnetism, bound magnetic polarons are responsible from the ferromagnetism of Mn-doped ZnO samples which have T_c values above the room temperature.     

Synthesis of flower-like 3D ZnO microstructures and their size-dependent ethanol sensing properties

Flower-like 3D ZnO microstructures constructed from nanorods of different sizes were prepared by a microwave hydrothermal (MH) process in the presence of o-, m- and p-nitrobenzoic acid, respectively. Well-crystallized flower-like ZnO microstructures were obtained after 10 min MH treatment. The X-ray powder diffraction (XRD) test indicated that all the products were consistent with the hexagonal ZnO phase, and scanning electron microscopy (SEM) investigation revealed that the flower-like 3D ZnO microstructures were built with sword-like nanorods 60-100 nm in width and several micrometers in length. The formation mechanism of these flower-like 3D ZnO microstructures is discussed briefly. The gas sensitivity of the as-prepared ZnO microstructures to ethanol at different operation temperatures and concentrations was also studied. The results indicated that the gas sensitivity of the ZnO microstructures was influenced by the particle size and microcosmic configuration, the larger particles with crowded nanorods having higher gas sensitivity.     

A catalyst-free growth of aluminum-doped ZnO nanorods by thermal evaporation

The growth of Al:ZnO nanorods on a silicon substrate using a low-temperature thermal evaporation method is reported. The samples were fabricated within a horizontal quartz tube under controlled supply of O₂ gas where Zn and Al powders were previously mixed and heated at 700°C. This allows the reactant vapors to deposit onto the substrate placed vertically above the source materials. Both the undoped and doped samples were characterized using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) measurements. It was observed that randomly oriented nanowires were formed with varying nanostructures as the dopant concentrations were increased from 0.6 at.% to 11.3 at.% with the appearance of ‘pencil-like’ shape at 2.4 at.%, measuring between 260 to 350 nm and 720 nm in diameter and length, respectively. The HRTEM images revealed nanorods fringes of 0.46 nm wide, an equivalent to the lattice constant of ZnO and correspond to the (0001) fringes with regard to the growth direction. The as-prepared Al:ZnO samples exhibited a strong UV emission band located at approximately 389 nm (E _g  = 3.19 eV) with multiple other low intensity peaks appeared at wavelengths greater than 400 nm contributed by oxygen vacancies. The results showed the importance of Al doping that played an important role on the morphology and optical properties of ZnO nanostructures. This may led to potential nanodevices in sensor and biological applications.     

n-ZnO nanorods/p-CuSCN heterojunction light-emitting diodes fabricated by electrochemical method

n-ZnO nanorods/p-CuSCN heterojunction light-emitting diodes (LEDs) have been fabricated using low-temperature electrochemical method. The I-V characteristics of the heterojunction LEDs show obvious rectifying behavior. The typical room-temperature electroluminescence spectra obtained from this heterostructure device under forward bias exhibit a strong visible emission across the spectral region from 350 to 600 nm centered at 530 nm. The intensity of the visible emission rises more quickly than that of the ultraviolet emission with the increasing bias. Photocurrent and Raman spectra reveal that the growth process of CuSCN can induce more surface states and defects in the ZnO nanorods, which confirms the enhancement of visible emission from the ZnO nanorods/p-CuSCN heterostructure. Compared with the ZnO-only LEDs, a p-type CuSCN layer used as a hole-transporting material can balance the electrons and holes injection rates in the heterojunction LEDs. The processing procedure in this work is a low-cost, low-temperature and convenient way to fabricate ZnO-based heterojunction light-emitting diodes.     

Sol–gel synthesis of Pd doped ZnO nanorods for room temperature hydrogen sensing applications

A sol–gel spin coating technique was described for the synthesis of Pd doped ZnO nanorods for hydrogen sensing applications. The nanorods were hexagonal in shape, 50–100 nm in diameter and uniform in distribution. They exhibited homogeneous surface morphology, c-axis orientation and excellent crystalline properties. The synthesized nanorods were used to sense and detect hydrogen in a homemade gas chamber. The fabricated sensor successfully detected as low as 40 ppm hydrogen at room temperature with a very low level of power supply (16.16 μA) under a mixed background. Dynamic and repeated responses were observed with a wide range of hydrogen concentrations (40–360 ppm) at 200 °C. The developed sensor was at least 25 fold more sensitive over the literature documented Pd doped ZnO nanorods in detecting hydrogen at ambient temperature. The simplicity, low-cost, high sensitivity and high stability of the sensor materials suggested that the synthesized Pd doped ZnO nanorods could be used in hydrogen and chemical sensing devices where Pd-mediated catalysis is involved.     

Enhanced Fluorescence and Local Vibrational Mode in Near‐White‐Light‐Emitting ZnO:Mg Nanorods System

We report exciton and phonon properties of ZnO:Mg nanorods of different Mg doping concentration. X‐ray diffraction studies (XRD) confirm the growth of wurtzite phase ZnO nanostructures. XRD reveals doping‐induced shift in peaks and formation of secondary phase related to Mg. Optical properties of the prepared nanorods are investigated by using UV‐Visible absorption and photoluminescence spectroscopic techniques. Optical absorption studies show strong free excitonic absorption of ZnO and extra absorption bands related to the defect centers of the secondary phase (MgO) formed after Mg doping. Photoluminescence studies show sharp band in UV region and defects‐related broad band emission in the visible range. Gaussian‐fitted photoluminescence spectra show that the emission is composed of free exciton recombination and its longitudinal optical (LO) phonon replica. In addition, Mg‐related local vibrational mode observed in Raman and FTIR spectra after Mg doping, indicates the incorporation of Mg into the lattice positions of wurtzite ZnO.     

Ultrafast photoluminescence spectroscopy of H- and O-terminated nanocrystalline diamond films

We use femtosecond photoluminescence spectroscopy to study the light-induced changes in the sub-gap energy states of nanocrystalline diamond samples (thickness ~ 500 and 1000 nm) prepared on a spectral-grade fused silica substrate by microwave plasma enhanced chemical vapour deposition technique. The decay of photoluminescence in the visible spectral interval excited by blue femtosecond light pulses (405 nm,70 fs) shows that photoexcited charge carrier dynamics depend strongly on the ambient air pressure and on the light irradiation by the laser pulses. Specifically, at lower ambient air pressure (0.5-300 Pa) the irradiation leads to the peak photoluminescence intensity increase and to its faster decay. At higher air pressures (> 600 Pa) the photoluminescence intensity slightly decreases with no change in decay rates. O- and H-termination of nanocrystalline diamond films had negligible effect on their photoluminescence dynamics. The photoluminescence decay curves are described very well by the power-law decay reflecting the importance of the carrier trapping in the dynamics. Based on our results we propose a model of surface and sub-surface structure of nanodiamond films.     

A simple electrochemical deposition route for the controllable growth of Ce-doped ZnO nanorods

Here we report that the various Ce⁴⁺-doped ZnO nanorods can be successfully synthesized by electrochemical deposition route, which represents a simple, quick and economical method for the controllable growth of Ce⁴⁺-doped ZnO nanorods. The high-resolution transmission electron microscopy (HRTEM) and the selected area electron diffraction (SAED) both proved that the prepared Ce⁴⁺-doped ZnO nanorods consisted of single crystal with preferential growth in the [0 0 0 1] direction. The morphology and size of the nanorods can be tailored by optimizing the synthetic parameters. Furthermore, the flowerlike Ce⁴⁺-doped ZnO nanorod clusters can also be successfully prepared. An obvious blue-shifted absorption peak of Ce⁴⁺-doped ZnO nanorod compared with that of the bulk ZnO phase was observed.     

Solvothermal synthesis of microsphere ZnO nanostructures in DEA media

Microsphere ZnO nanostructures (ZnO-MNs) were synthesized via solvothermal method in diethanolamine (DEA) media. DEA was utilized to terminate the growth of ZnO nanoparticles which forms the ZnO-MNs. The ZnO-MNs were characterized by a number of techniques, including X-ray diffraction analysis (XRD) and field emission scanning electron microscopy (SEM). The ZnO-MNs prepared by solvothermal process at the temperature of 150 °C for 6, 12, 18, and 24 h exhibited a hexagonal (wurtzite) structure with sizes ranging from 2 to 4 μm. The growth mechanism and morphology of the ZnO-MNs were also investigated, and it was found that the ZnO-MNs were formed by ZnO nanoparticles with average particle size of 25 ± 5 nm. To show role of DEA in the formation of Zn-MNs, effect of MEA (monoethanolamine) and TEA (triethanolamine) on morphology of the final product are also investigated. The results showed that DEA is a good polymerization agent that can be used as a stabilizer in the solvothermal technique for preparing fine ZnO powder.     

Sol−gel-based hydrothermal method for the synthesis of 3D flower-like ZnO microstructures composed of nanosheets for photocatalytic applications

Self-assembled 3D flower-like ZnO microstructures composed of nanosheets have been prepared on a large scale through a sol−gel-assisted hydrothermal method using Zn(NO₃)₂·6H₂O, citric acid, and NaOH as raw materials. The product has been characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The optical properties of the product have been examined by room temperature photoluminescence (PL) measurements. A possible growth mechanism of the 3D flower-like ZnO is proposed based on the results of experiments carried out for different hydrothermal treatment times. Experiments at different hydrothermal treatment temperatures have also been carried out to investigate their effect on the final morphology of the ZnO. The photocatalytic activities of the as-prepared ZnO have been evaluated by photodegradation of Reactive Blue 14 (KGL) under ultraviolet (UV) irradiation. The experimental results demonstrated that self-assembled 3D flower-like ZnO composed of nanosheets could be obtained over a relatively broad temperature range (90−150 °C) after 17 h of hydrothermal treatment. All of the products showed good photocatalytic performance, with the degree of degradation of KGL exceeding 82% after 120 min. In particular, the sample prepared at 120 °C for 17 h exhibited superior photocatalytic activity to other ZnO samples and commercial ZnO, and it almost completely degraded a KGL solution within 40 min. The relationship between photocatalytic activity and the structure, surface defects, and surface areas of the samples is also discussed.     

Selective growth of ZnO nanorods on microgap electrodes and their applications in UV sensors

Selective area growth of ZnO nanorods is accomplished on microgap electrodes (spacing of 6 μm) by using a facile wet chemical etching process. The growth of ZnO nanorods on a selected area of microgap electrode is carried out by hydrothermal synthesis forming nanorod bridge between two electrodes. This is an attractive, genuine, direct, and highly reproducible technique to grow nanowire/nanorod onto the electrodes on selected area. The ZnO nanorods were grown at 90°C on the pre-patterned electrode system without destroying the electrode surface structure interface and geometry. The ZnO nanorods were tested for their application in ultraviolet (UV) sensors. The photocurrent-to-dark (Iph/Id) ratio was 3.11. At an applied voltage of 5 V, the response and recovery time was 72 and 110 s, respectively, and the response reached 2 A/W. The deposited ZnO nanorods exhibited a UV photoresponse that is promising for future cost-effective and low-power electronic UV-sensing applications.     

Facile Synthesis of ZnO Nanorods by Microwave Irradiation of Zinc–Hydrazine Hydrate Complex

ZnO nanorods have been successfully synthesized by a simple microwave-assisted solution phase approach. Hydrazine hydrate has been used as a mineralizer instead of sodium hydroxide. XRD and FESEM have been used to characterize the product. The FESEM images show that the diameter of the nanorods fall in the range of about 25–75 nm and length in the range of 500–1,500 nm with an aspect ratio of about 20–50. UV–VIS and photoluminescence spectra of the nanorods in solution have been taken to study their optical properties. A mechanism for microwave synthesis of the ZnO nanorods using hydrazine hydrate precursor has also been proposed.     

Preparation and electrochemical performances of ZnO nanowires as anode materials for Ni/Zn secondary battery

ZnO nanowires were synthesized by a hydrothermal route without any substrate or template. Structure analyses through XRD, SEM, TEM and HRTEM indicated that ZnO nanowires had high purity and perfect crystallinity, and grew along [0 0 0 1]. The diameter was 50-80 nm, the length was about several micrometers and length-diameter ratio was more than 100. As electrode materials of Ni/Zn batteries, ZnO nanowires showed the obviously improved cycle stability, average discharge capacity of 609 mAh g⁻¹, higher discharge voltage/lower charge voltage. Slow rate cyclic voltammetry showed that electrochemical activity of ZnO nanowires was superior to that of the conventional ZnO. The improvements of electrochemical performance were ascribed to the unique nanowire structure. During the charging/discharging cycles, nanowires were broke, grew in diameter, and changed into nanorods. Nanowires lying parallel to the anodes could suppress the growth of dendrite clusters perpendicular to the anodes.     

Effect of deposition temperature and quality of free-standing diamond substrates on the properties of RF sputtering ZnO films

Highly c-axis oriented ZnO film is often deposited on diamond substrates by RF magnetron sputtering and widely used for high frequency surface acoustic wave (SAW) devices. Deposition temperature is a key factor affecting the quality of the ZnO film. Different quality polished free-standing diamond films prepared by DC Arc Plasma Jet were used as the substrates to deposit ZnO films at different temperatures. Effect of the deposition temperature and the quality of the diamond films on the properties of the ZnO films were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that highly c-axis oriented ZnO films can be much easier deposited on the optical-grade diamond films with < 111> preferred orientation than the tool-grade diamond films with < 220> preferred orientation. The optimal deposition temperature is 200 °C for highly c-axis oriented and lower roughness ZnO films. Acoustic phase velocity of more than 10,000 m/s for the SAW devices based on the ZnO/optical-grade free-standing diamond films was obtained.     

Cu-doped ZnO nanorod arrays: the effects of copper precursor and concentration

Cu-doped ZnO nanorods have been grown at 90°C for 90 min onto a quartz substrate pre-coated with a ZnO seed layer using a hydrothermal method. The influence of copper (Cu) precursor and concentration on the structural, morphological, and optical properties of ZnO nanorods was investigated. X-ray diffraction analysis revealed that the nanorods grown are highly crystalline with a hexagonal wurtzite crystal structure grown along the c-axis. The lattice strain is found to be compressive for all samples, where a minimum compressive strain of −0.114% was obtained when 1 at.% Cu was added from Cu(NO₃)₂. Scanning electron microscopy was used to investigate morphologies and the diameters of the grown nanorods. The morphological properties of the Cu-doped ZnO nanorods were influenced significantly by the presence of Cu impurities. Near-band edge (NBE) and a broad blue-green emission bands at around 378 and 545 nm, respectively, were observed in the photoluminescence spectra for all samples. The transmittance characteristics showed a slight increase in the visible range, where the total transmittance increased from approximately 80% for the nanorods doped with Cu(CH₃COO)₂ to approximately 90% for the nanorods that were doped with Cu(NO₃)₂.