Field emission property of printed CNTs-mixed ZnO nanoneedles

ZnO nanoneedles were synthesized via thermal evaporation method without any catalyst. Scanning electron microscopy and transmission electron microscopy investigations showed that these products presented a nanoneedle structure. To enhance the field emission (FE) properties of screen printed ZnO nanoneedles, a given amount (0.05 g) carbon nanotubes (CNTs) mixed with (0.5 g) ZnO nanoneedles paste via screen printed method and heat-treatment at (600 °C, 500 °C and 450 °C) was presented. The CNTs-mixed ZnO nanoneedles heat-treated at 450 °C had the lowest turn-on field of 3.75 V/μm, highest field emission current of 0.16 mA at 7.5 V/μm and highest β of 830. An efficiency FE enhancement of 450 °C sample was attributed to melioration of conductance between ZnO nanoneedles and ITO surface by CNTs.     

Effects of annealing temperature on the structure, photoluminescence and ferromagnetism properties of Cr-implanted ZnO nanowires

Room temperature ferromagnetism was observed in Cr-implanted ZnO nanowires annealed at 500, 600, and 700 °C. The implantation dose for Cr ions was 1×10¹⁶ cm^?2, while the implantation energies were 100 keV. Except for ZnO (100), (002), and (200) orientations, no extra diffraction peaks from Cr-related secondary phase or impurities were observed. With the increasing of annealing temperatures, the intensity of the peaks increased while the FWHM values decreased. The Cr 2p_1/2 and 2p_3/2 peaks, with a binding energy difference of 10.6 eV, appear at 586.3 and 575.7 eV, can be attributed to Cr³⁺ in ZnO nanowires. For the Cr-implanted ZnO nanowires without annealing, the band energy emission disappears and the defect related emission with wavelength of 500–700 nm dominates, which can be attributed to defects introduced by implantation. Cr-implanted ZnO nanowires annealed at 500 °C show a saturation magnetization value of over 11.4×10^?5 emu and a positive coercive field of 67 Oe. The origin of ferromagnetism behavior can be explained on the basis of electrons and defects that form bound magnetic polarons, which overlap to create a spin-split impurity band.     

Ion beam synthesis and carrier dynamics of ZnO nanoparticles embedded in a SiO2 matrix

Zinc oxide (ZnO) nanostructures have been synthesized by the implantation of ZnO molecular ions into SiO₂ followed by high temperature thermal annealing. 35 keV ZnO^? ions were implanted to a fluence of 5×10¹⁶ ions/cm² into SiO₂ at room temperature (RT). The implanted sample was annealed in an oxygen environment to allow the growth of ZnO precipitates. In the as-implanted sample, Zn nanoparticles up to 4.5 nm in diameter were observed and were distributed throughout the implanted depth in the SiO₂. The highest concentration of Zn from the implantation was at a depth of 25 nm. During annealing, Zn diffused into the substrate and combined with oxygen to form ZnO. ZnO nanostructures thus formed had diameters up to 8 nm, embedded in SiO₂. Donor-bound exciton (D, X), acceptor-bound exciton (A, X), and donor–acceptor-pair (DAP) transitions were observed in low temperature photoluminescence (PL) measurements on an annealed sample. RT-PL measurement showed band-edge emission in the ultraviolet region with a full width at half maximum of 121 meV. Time-resolved PL measurements performed at 4 K revealed an excitonic lifetime of 160 ps.     

Synthesis and optical properties of pencil-like and shuttle-like ZnO microrods

The pencil-like and shuttle-like ZnO microrods have been fabricated on Si (100) substrates by chemical vapor deposition. Structure characterization results show that the microrods are perfect single crystals with the wurtzite structure along the [0001] growth direction and have diameters ranging from 100 nm to 2 μm and lengths up to 10 μm. Room-temperature photoluminescence measurements of ZnO microstructures exhibit an intensive ultraviolet peak at 390 nm and a broad peak centered at about 526 nm, which can be attributed to the free exciton emission and the deep level emission, respectively. Cathodoluminescence measurements show the same ultraviolet and green emissions as seen in the photoluminescence results. A possible growth mechanism of ZnO microrods is finally proposed.     

Effect of annealing temperature on optical and electrochemical properties of chitosan–ZnO nanostructure

Chitosan–ZnO nanostructures were prepared by chemical precipitation method using different concentration of zinc chloride and sodium hydroxide solutions. Nanorod-shaped grains with hexagonal structure for samples annealed at 300 °C and porous structure with amorphous morphology for samples annealed at 600 °C were revealed in SEM analysis. X-ray diffraction patterns confirmed the hexagonal phase ZnO with crystallite size found to be in the range of ~24.15–34.83 nm. Blue shift of UV–Vis absorption shows formation of nanocrystals/nanorods of ZnO with marginal increase in band gap. Photoluminescence spectra show that blue–green emission band at 380–580 nm. The chitosan–ZnO nanostructures used on surface of a glassy carbon electrode gives the oxidation peak potential at ~0.6 V. The electrical conductivity of chitosan–ZnO composites were observed at 2.1?×?10^?5 to 2.85?×?10^?5?S/m. The nanorods with high surface area and nontoxicity nature of chitosan–ZnO nanostructures observed in samples annealed at 300 °C were suitable as a potential material for biosensing.     

Enhanced Field Emission from Vertical ZnO Nanoneedles on Micropyramids

Vertical ZnO nanoneedles with sharp tips are secondarily grown on tips of primarily grown ZnO micropyramids by a vapour transport process. The field emission （FE） properties exhibit a lower turn-on electric field and a higher field enhancement factor as compared with vertical ZnO microrods. This result indicates that ZnO nanoneedles have good optimum shapes for FE due to electron accumulation at sharp tips.     

ZnO three-dimensional hedgehog-like nanostructure: synthesis,growth mechanism and optical enhancement

The 3D hedgehog-like ZnO nanostructures were synthesized on Si substrate through chemical vapor deposition process. The morphology and structure of the products were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, as well as transmission electron microscopy. The ZnO 3D hedgehog-like architectures were found to consist of a central nucleus and multiple side-growing nanowires with diameter of 100–250 nm and length up to 10 µm. The growth mechanism of the hedgehog-like ZnO nanostructures was studied. It revealed a three-step process during the entire growth. Finally, room temperature photoluminescence spectra of ZnO 3D nanostructures showed that the center excitation would render much stronger PL emission intensity. Furthermore, simulation results indicated that the enhanced emission came from light-trapping-induced excitation light field enhancement.     

One-pot synthesis of ferromagnetic Fe2.25W0.75O4 nanoparticles as a magnetically recyclable photocatalyst

ZnO nanostructures, including nanowires, nanorods, and nanoneedles, have been deposited on GaAs substrates by the two-step chemical bath synthesis. It was demonstrated that the O₂-plasma treatment of GaAs substrates prior to the sol?Cgel deposition of seed layers was essential to conformally grow the nanostructures instead of 2D ZnO bunches and grains on the seed layers. Via adjusting the growth time and concentration of precursors, nanostructures with different average diameter (26?C225?nm), length (0.98?C2.29???m), and density (1.9?C15.3?×?10⁹?cm^?2) can be obtained. To the best of our knowledge, this is the first demonstration of ZnO nanostructure arrays grown on GaAs substrates by the two-step chemical bath synthesis. As an anti-reflection layer on GaAs-based solar cells, the array of ZnO nanoneedles with an average diameter of 125?nm, a moderate length of 2.29???m, and the distribution density of 9.8?×?10⁹ cm^?2 has increased the power conversion efficiency from 7.3 to 12.2?%, corresponding to a 67?% improvement.     

Controllable vertically aligned ZnO nanorods on flexible polyethylene naphthalate (PEN) substrate using chemical bath deposition synthesis

Zinc oxide (ZnO) nanorods were successfully grown on polyethylene naphthalate substrates with a seed layer using a wet chemical bath deposition method at a low temperature. Using various precursor concentrations, the diameter, length, and density of the ZnO nanorods were controlled, and their optical and crystallinity properties were investigated. X-ray diffraction and field emission scanning electron microscopy were used to examine the structure and morphology of the ZnO nanorods. The obtained ZnO nanorods were hexagonal and grew vertically from the substrate in the (002) direction along the c-axis. The low compressive strain values confirmed the high-quality crystal structure of the synthesized ZnO nanorods. A 0.050 M precursor concentration resulted in nanorods with a uniform diameter along their entire length and diameters ranging from 10 nm to 40 nm. The photoluminescence results indicated that the ZnO nanorods grown using a 0.050 M precursor concentration exhibited the sharpest and most intense PL peaks in the UV range compared with the other samples. Therefore, the precursor concentration considerably influenced the growth of the ZnO nanorods. These ZnO nanorods can be greatly applied for the development of flexible, elastic electronic, and optoelectronic devices.     

Quantum cutting effect and photoluminescence emission at about 1,000 nm from Er–Yb co-doped ZnO nanoplates prepared by wet chemical precipitation method

ZnO nanoplates with Er-doping concentrations varying in the range from 3 to 7 wt% and co-doped with (Er–Yb) (7 + 7 wt%) were successfully prepared by wet chemical precipitation method. The effects of doping on the structural and optical properties of ZnO nanostructures have been systematically investigated. The structural morphology of the prepared nanostructures was found to change with increasing Er-doping concentrations. The visible photoluminescence and infrared photoluminescence of the prepared nanostructures were measured at room temperature. The intensity of visible emission spectra was found to increase with increasing Er-doping concentrations and was further enhanced for (Er–Yb) co-doped ZnO nanoplate samples. Additionally, Er-doped (7 wt%) and Yb-doped (7 wt%) ZnO nanoplates showed an enhanced emission peak at 950 nm, whereas two enhanced emission peaks at 950 and 980 nm have been found for (Er–Yb)-co-doped (7 + 7 wt%) ZnO nanoplates samples when excited at 310, 365 and 371 nm excitation wavelengths.     

Controlled growth and field emission properties of zinc oxide nanopyramid arrays

Single-crystalline, pyramidal zinc oxide nanorods have been synthesized in a large quantity on p-Si substrate via catalyst-free thermal chemical vapor deposition at low temperature. SEM investigations showed that the nanorods were vertically aligned on the substrate, with diameters ranging from 60 to 80 nm and lengths about 1.5 μm. A self-catalysis VLS growth mechanism was proposed for the formation of the ZnO nanorods. The field emission properties of the ZnO nanopyramid arrays were investigated. A turn-on field about 3.8 V/μm was obtained at a current density of 10 μA/cm², and the field emission data was analyzed by applying the Fowler-Nordheim theory. The stability of emission current density under a high voltage was also tested, indicating that the ZnO nanostructures are promising for an application such as field emission sources.     

Catalyst-free highly vertically aligned ZnO nanoneedle arrays grown by plasma-assisted molecular beam epitaxy

This work describes the growth of highly vertically aligned ZnO nanoneedle arrays on wafer-scale catalyst-free c-plane sapphire substrates by plasma-assisted molecular beam epitaxy under high Zn flux conditions. The photoluminescence spectrum of the as-grown samples reveals strong free exciton emissions and donor-bound exciton emissions with an excellent full width at half maximum (FWHM) of 1.4 meV. The field emission of highly vertically aligned ZnO nanoneedle arrays closely follows the Fowler–Nordheim theory. The turn-on electric field was about 5.9 V/µm with a field enhancement factor β of around 793.     

Direct fabrication of graphene/zinc oxide composite film and its characterizations

Graphene-based composites represent a new class of materials with potential for many applications. Graphene can be attached to a metal, a semiconductor, or any polymer for enhancing properties. In this work, a new mixed dispersion approach for graphene-based composite has taken on. Graphene flakes (<4 layers) and a well-known semiconductor zinc oxide (ZnO) (<50 nm particle size) have dispersed in N-methyl-pyrrolidone. We deposited graphene/ZnO composite thin film by a simple, low-cost, environmentally friendly and non-vacuum electrohydrodynamic atomization process on silicone substrate. Experiments have been carried out by changing flow rate and applied potential while keeping stand-off distance and substrate velocity constant, to discover the optimum conditions for obtaining a high-quality thin film. It has been explored that high-quality thin composite film is obtained at optimum flow rate of 300 μl/h at 6.3 kV applied potential after curing for 2 h at 300 °C. Graphene/ZnO thin composite film has been characterized using Field emission scanning electron microscopy, Ultra-violet Visible near Infra Red spectroscopy, X-ray diffraction, Raman Spectroscopy and 3D-Nanomap. For electrical behavior analysis, a simple diode Indium tin oxide/(poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/polydioctylfluorene-benzothiadiazole(F8BT)/(Graphene/ZnO) has fabricated. It is observed that at voltage of 0.3 V, the current in organic structure is at low value of 1.20 × 10^?3 Amp/cm² and after that as further voltage was applied, the device current increased by the order of 110 and reaches up to 1.32 × 10^?1 Amp/cm² at voltage 2 V.     

Morphological effects on the field emission characteristics of zinc oxide nanotetrapods films

The direct growth of a tetrapod-like ZnO nanostructure has been accomplished by using a thermal oxidation method without any catalysts. Studies on the field emission properties of the ordered ZnO nanotetrapods films found that the shape of the ZnO nanotetrapods has considerable effect on their field emission properties, especially the turn-on field and the emission current density. Compared with the rod-like legs ZnO nanotetrapods, the nanotetrapods with acicular legs have a lower turn-on field of 2.7 V/μm at a current density of 10 μA/cm², a high field enhancement factor of 1830, and an available stability. More importantly, the emission current density reached 1 mA/cm² at a field of 4.8 V/μm without showing saturation. The results could be valuable for using the ZnO nanostructure as a cold-cathode field-emission material.      

ZnO纳米棒的低温溶液法制备、光电特性研究及其在有机/无机复合电致发光中的应用

利用水热法制备了垂直于衬底的定向生长的ZnO纳米棒,利用扫描电子显微镜及光致发光的方法对其形貌及光学特性进行了表征,利用场发射性能测试装置对ZnO纳米棒的场发射性能进行了测试.结果表明:利用水热法在较低的温度(95 ℃) 下生长了具有较好形貌和结构的ZnO纳米棒,并表现出了较好的场发射特性,当电流密度为1 μA/cm²时,开启电场是2.8 V/μm,当电场为6.4 V/μm时,电流密度可以达到0.67 mA/cm²,场增强因子为3360.稳定性测试表明,在5 h内,4.5 V/μm的电场下,其波动不超过25%.将制备的ZnO纳米棒应用到有机/无机电致发光中,其中ZnO纳米棒为电子传输层,m-MTDATA(4,4',4″-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine) 为空穴传输层,得到了ZnO的342 nm的紫外电致发光,此发光较ZnO纳米棒光致发光的紫外发射有约40 nm的蓝移. 关键词： ZnO纳米棒 场发射 水热法 有机/无机复合电致发光     

Defect-dominated optical emission and enhanced ultraviolet photoconductivity properties of ZnO nanorods synthesized by simple and catalyst-free approach

We report on the defect-dominated light emission and ultraviolet (UV) photoconductivity characteristics of ZnO nanorods (NRs) fabricated using a facile, cost-effective, and catalyst-free thermal decomposition route under varying reaction temperatures. The morphological and structural studies reveal the formation of homogeneous quality nanorods in large scale at the highest reaction temperature of 600 ^°C. The luminescence feature of the nanorods is dominated by the defect related emission over the typical band edge emission. The variation of band-edge and native defect-related emission response of the samples has been correlated to the morphology and microstructure. In photoconductivity studies, the I–V characteristics of the ZnO NRs prepared at different reaction temperatures in dark and under UV illumination (λ=365 nm) follow the power law, i.e., IαV ^r . An enhanced ultraviolet photodetection has been observed in the nanorods fabricated at the highest reaction temperature of 600 ^°C. The sample prepared at highest reaction temperature of 600 ^°C exhibits UV photosensitivity value (photo-to-dark current ratio) of around 1.18×10³, which is much higher in magnitude compared to that of the samples prepared at lower reaction temperatures. The enhanced photoconductivity may be assigned to the development of uniformity and homogeneity of the nanorods. Further development of such ZnO nanostructures can form the basis of promising prototype luminescent and UV photodetecting devices.     

Optical Analysis of Er3+:Boro-Fluoro-Phosphate Glasses

This paper deals with the preparation and optical analysis of Er³⁺ (0.2 mol%) boro-fluoro-phosphate glasses in the following glass compositions:

• Series A: 69.8 B₂O₃–10 P₂O₅–10(ZnO/CdO/TeO₂)–10 AlF₃

• Series B: 69.8 B₂O₃–10 P₂O₅–10(ZnO/CdO/TeO₂)–10 LiF

Measured Vis-NIR absorption spectra of Er³⁺:boro-fluoro-phosphate glasses have revealed nine absorption bands at 377 nm, 405 nm, 450 nm, 486 nm, 519 nm, 543 nm, 649 nm, 973 nm and 1529 nm, which correspond with the transitions of ⁴I_15/2 → ⁴G_11/2, (²G_9/2,⁴H_9/2), ⁴F_5/2, ⁴F_7/2, ²H_11/2, ⁴S_3/2, ⁴F_9/2, ⁴I_11/2, and ⁴I_13/2, respectively. With an excitation at λ _exci = 375 nm, a bright green emission (⁴S_3/2 → ⁴I_15/2) at 547 nm has been observed from these erbium glasses. Judd–Ofelt characteristic intensity Ω_λ (λ = 2, 4, 6) parameters are obtained from the absorption spectra, and these results were used to compute the radiative properties of Er³⁺:boro-fluoro-phosphate glasses. The NIR emission (⁴I_13/2 → ⁴I_15/2) at 1547 nm from these glasses was measured with an Ar⁺ laser (514.5 nm) as an excitation source.     

Growth and optical characterization of diamond-shaped zinc oxide nanostructures deposited by pulsed laser ablation

We report on the growth of zinc oxide diamond-shaped nanostructured thin films by pulsed laser deposition technique on silicon substrate at different substrate temperatures (room temperature to 600  $^{\circ }$ C) and at fixed background pressure of oxygen using Nd:YAG laser at a wavelength of 532 nm. The influence of substrate temperature on the grain size, surface morphology and optical properties is characterized by x-ray diffraction, field-emission scanning electron microscope, photoluminescence and Raman spectroscopy. x-ray diffraction results show that the grain size increases with increasing substrate temperature during the growth of ZnO thin films due to improved crystallinity but at 450  $^{\circ }$ C the crystallinity degrades. It is attributed to the formation of diamond-shaped ZnO nanostructures as supported by the field emission scanning electron microscope images. Consequently, increase in photoluminescence and Raman intensities is also attributed to the formation of diamond-shaped structures. The growth of diamond-shaped structure is discussed in the light of growth of various planes in the hexagonal structure of ZnO.     

Synthesis and electrochemical investigation of highly dispersed ZnO nanoparticles as anode material for lithium-ion batteries

Highly dispersed ZnO nanoparticles were prepared by a versatile and scalable sol-gel synthetic technique. High-resolution transmission electronic microscopy (HRTEM) showed that the as-prepared ZnO nanoparticles are spherical in shape and exhibit a uniform particle size distribution with the average size of about 7 nm. Electrochemical properties of the resulting ZnO were evaluated by galvanostatic discharge/charge cycling as anode for lithium-ion battery. A reversible capacity of 1652 mAh g^?1 was delivered at the initial cycle and a capacity of 318 mAh g^?1 was remained after 100 cycles. Furthermore, the system could deliver a reversible capacity of 229 mAh g^?1 even at a high current density of 1.5 C. This outstanding electrochemical performance could be attributed to the nano-sized features of highly dispersed ZnO particles allowing for the better accommodation of large strains caused by particle expansion/shrinkage along with providing shorter diffusion paths for Li⁺ ions upon insertion/deinsertion.     

Synthesis and evaluation of the potential deleterious effects of ZnO nanomaterials (nanoneedles and nanoflowers) on blood components,including albumin,erythrocytes and human isolated primary neutrophils

The application of zinc oxide (ZnO) nanoparticles in biomaterials has increased significantly in the recent years. Here, we aimed to study the potential deleterious effects of ZnO on blood components, including human serum albumin (HSA), erythrocytes and human isolated primary neutrophils. To test the influence of the morphology of the nanomaterials, ZnO nanoneedles (ZnO-nn) and nanoflowers (ZnO-nf) were synthesized. The zeta potential and mean size of ZnO-nf and ZnO-nn suspensions in phosphate-buffered saline were ?10.73 mV and 3.81 nm and ?5.27 mV and 18.26 nm, respectively. The incubation of ZnO with HSA did not cause its denaturation as verified by the absence of significant alterations in the intrinsic and extrinsic fluorescence and in the circular dichroism spectrum of the protein. The capacity of HSA as a drug carrier was not affected as verified by employing site I and II fluorescent markers. Neither type of ZnO was able to provoke the activation of neutrophils, as verified by lucigenin- and luminol-dependent chemiluminescence and by the extracellular release of hydrogen peroxide. ZnO-nf, but not ZnO-nn, induced the haemolysis of erythrocytes. In conclusion, our results reinforce the concept that ZnO nanomaterials are relatively safe for usage in biomaterials. A potential exception is the capacity of ZnO-nf to promote the lysis of erythrocytes, a discovery that shows the importance of the morphology in the toxicity of nanoparticles.