Ultralong ZnO nanowire arrays synthesized by hydrothermal method using repetitive refresh

Long ZnO nanowire arrays (> or = 10 microm) were fabricated using the hydrothermal method and the refresh process of the reactant solution. The diameter of the synthesized nanowires was controlled by varying the solution concentration of the seed layers, without reducing their length. The maximum temperature in this process was 95 degrees C and the repeated refresh process at 95 degrees C provided the driving force for the growth of ultralong nanowires by exchanging the reactants. Interestingly, the diameter of the refreshed ZnO nanowires strongly depended on the solution temperature during refresh. The exchange of the reactant solution at the same temperature as the synthesis temperature induced the synthesis of ultralong nanowires and the length of the resultant nanowires can be controlled by varying the repetition number. The illumination of the ultraviolet light induced considerably enhanced current flow in the ultralong nanowires from mid 10(-10) to 10(-7) A at 5 V.     

水热法制备掺铝氧化锌纳米棒阵列及其光学特性

采用水热法,在ZnO种子层上制备出不同Al掺杂量的ZnO纳米棒阵列薄膜,利用XRD、SEM、TEM、PL等检测手段对样品进行结构、形貌和发光性能分析.结果表明,纳米棒属于六方纤锌矿结构,具有垂直基底沿[002]方向生长的特征,PL谱上存在强的近紫外辐射峰.随着掺杂量的增加,纳米棒直径略有减小,近紫外辐射峰蓝移,强度先增加后减小,证明掺杂会形成非辐射中心,探讨了Al掺杂ZnO纳米棒阵列的发光机理.     

Gas sensing properties of ZnO nanorods prepared by hydrothermal method

ZnO nanorods are prepared by a hydrothermal process with cetyltrimethylammonium bromide (CTAB) and zinc powder at 182°C. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The gas sensing properties of the materials have been investigated. The results indicate that the as-prepared ZnO nanorods are uniform with diameters of 40–80 nm and lengths about 1 μm, the relatively high sensitivity and stability of these sensors made from ZnO nanorods demonstrate the potential for developing a new class of stable and very sensitive sensors.     

Optical and magnetic properties of copper doped ZnO nanorods prepared by hydrothermal method

Surfactant free ZnO and Cu doped ZnO nanorods were synthesized by hydrothermal method. The formation of ZnO:Cu nanorods were confirmed by scanning electron microscopy, X-ray diffraction and Raman analysis. Diffuse reflectance spectroscopy results shows that band gap of ZnO nanorods shifts to red with increase of Cu content. The orange-red photoluminescent emission from ZnO nanorods originates from the oxygen vacancy or ZnO interstitial related defects. ZnO:Cu nanorods showed strong ferromagnetic behavior, however at higher doping percentage of Cu the ferromagnetic behavior was suppressed and paramagnetic nature was enhanced. The presence of non-polar E ₂ ^high and E ₂ ^low Raman modes in nanorods indicates that Cu doping didn’t change the wurtzite structure of ZnO.     

Investigations on structural, optical and electrical properties of p-type ZnO nanorods using hydrothermal method

Undoped and doped ZnO nanorods were grown from an aqueous solution at low temperature (90 °C) on sapphire (100) substrates coated with ZnO thin film annealed in air at 550 °C for 1 h. X-ray diffraction results show that these nanorods have wurtzite type structure, and they are oriented in the c-axis direction. The optical properties are examined by room temperature micro photoluminescence and Raman scattering analysis which confirm that the nanorods exhibit good optical and electrical properties. A strong enhancement of multiple-phonon Raman scattering process with longitudinal optical phonon overtone up to fifth order was observed. It is found that the thin film coating of ZnO plays an important role in the c-axis oriented growth of undoped and doped ZnO nanorods due to good lattice match between the thin film and nanorods.     

Optical properties of Ag doped ZnO nanocrystals prepared by hydrothermal and photodeposition method

Ag/ZnO nanocomposites have been synthesized by facile hydrothermal and photodeposition method. The effect of different concentration of Ag on the luminous intensity of ZnO was studied. The morphology, structure and optical properties of Ag/ZnO were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL), respectively. The XRD patterns show that intensities of diffraction peaks of Ag/ZnO were enhanced. The weak diffraction peak at 38.28° can be assigned to Ag₂O when the concentration of Ag increased to 0.09 M. PL results demonstrate that the UV luminous intensity of ZnO was significantly influenced by the concentration of Ag. The UV luminous intensity of Ag/ZnO nanocomposites increased by 11 times as compared with undoped ZnO when the concentration of Ag was 0.03 M due to the local surface plasma resonance effect of Ag nanoparticles.     

Effect of g-C3N4 on structural,optical, and photocatalytic properties of hexagonal cylinder-like twinned ZnO microcrystals prepared by the hydrothermal method

Journal of Materials Science: Materials in Electronics - The effect of g-C3N4 on the structural, optical, and photocatalytic properties of ZnO microcrystals under hydrothermal conditions was...     

Comparison of optical properties of Si and ZnO/CdTe core/shell nanowire arrays

The systematic computations of the short-circuit current density have been performed for Si and ZnO/CdTe core shell nanowire arrays of 1 μm height in order to optimize the structural morphology in terms of nanowire diameter and period. It is found that the best structural configuration for Si leading to the ideal short-circuit current density of 19.6 mA/cm² is achieved for a nanowire diameter and period of 315 nm and 350 nm, respectively. In case of ZnO/CdTe, the ideal short circuit current density is of 24.0 mA/cm², the nanowire diameter and period is of 210 nm and 350 nm, respectively. It is shown that the optimal configuration is more compact in the case of Si nanowire arrays than in the case of ZnO/CdTe nanowire arrays. Since Si has a smaller absorption coefficient than CdTe, a larger amount of material is needed and thus more compact nanowire arrays are required. It is also revealed that core–shell nanowire arrays made of ZnO/CdTe more efficiently absorb light than that of Si, making this device a good candidate for the next generation of nanostructured solar cells.     

Ordered ZnO/AZO/PAM nanowire arrays prepared by seed-layer-assisted electrochemical deposition

An Al-doped ZnO (AZO) seed layer is prepared on the back side of a porous alumina membrane (PAM) substrate by spin coating followed by annealing in a vacuum at 400 °C. Zinc oxide in ordered arrays mediated by a high aspect ratio and an ordered pore array of AZO/PAM is synthesized. The ZnO nanowire array is prepared via a 3-electrode electrochemical deposition process using ZnSO₄ and H₂O₂ solutions at a potential of − 1 V (versus saturated calomel electrode) and temperatures of 65 and 80 °C. The microstructure and chemical composition of the AZO seed layer and ZnO/AZO/PAM nanowire arrays are characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy (EDS). Results indicate that the ZnO/AZO/PAM nanowire arrays were assembled in the nanochannel of the porous alumina template with diameters of 110–140 nm. The crystallinity of the ZnO nanowires depends on the AZO seed layer during the annealing process. The nucleation and growth process of ZnO/AZO/PAM nanowires are interpreted by the seed-layer-assisted growth mechanism.     

Synthesis and photoluminescence of Eu-doped ZnO microrods prepared by hydrothermal method

Eu-doped ZnO microrods, with wurtzite structure and [0 0 0 1] growth direction have been successfully synthesized on Si (1 0 0) substrates by a simple hydrothermal method. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), lifetime decay curves, photoluminescence (PL) and photoluminescence excitation (PLE) spectra, respectively. These results indicate that Eu³⁺ ions are located in the distorted lattice sites near the surface of the ZnO microrods. Additionally, it is also suggested that the surface defects may act as a step in the process of energy transfer from ZnO to Eu³⁺ ions.     

沉积气压对磁控溅射制备ZnO薄膜的结构与光学性能影响

采用CS-400型射频磁控溅射仪在Si(111)和石英基底上成功的制备了ZnO薄膜,分别用XRD、SEM、紫外-可见光分光光度计和荧光分光光度计表征样品的结构和光学性质.实验表明,采用射频磁控溅射制备的ZnO薄膜具有六角纤锌矿结构的(002)峰和(101)峰的两种取向.在沉积气压>1.0Pa时所制备的ZnO薄膜具有(002)择优取向,并且十分稳定.SEM图表明,ZnO薄膜颗粒大小较为均匀,晶粒尺寸随着气压升高而变小,沉积气压不同时,薄膜样品的生长方式有所差异.在400～1000nm范围内,可以看出除O.5Pa下制备的ZnO薄膜外,其余ZnO薄膜在可见光区域的平均透过率超过80%,吸收边在380nm附近,所对应的光学带隙约为3.23～3.27eV,并随着沉积气压上升而变大.ZnO薄膜的PL谱上观察到了392nm的近紫外峰和419nm的蓝峰;沉积气压对Zno薄膜的发光峰位和峰强有影响.     

The synthesis and photoluminescence properties of selenium-treated porous silicon nanowire arrays

Here we prepared vertical and single crystalline porous silicon nanowire (SiNW) arrays using the silver-assisted electroless etching method. The selenization was carried out by annealing the samples in vacuum with selenium atmosphere. The selenization treatment at 700?°C is useful for investigating the photoluminescence (PL) properties of porous SiNWs, with an enhancement of 30 times observed. The observed PL peaks blue-shift to 650 nm and the decomposition of the spectrum reveals that three PL bands with different origins are obtained. It is proved that selenization treatment could remove the Si-H bonds on the surface and form Si-Se bonds, which could increase the absorbance of the SiNWs and also enhance the stability of the PL intensity. These Se-treated porous SiNWs may be useful as nanoscale optoelectronic devices.     

Seed-layer controlled synthesis of well-aligned ZnO nanowire arrays via a low temperature aqueous solution method

A simple and controllable method has been developed to synthesize well-aligned ZnO nanowire arrays on silicon and glass substrates in aqueous solution. A thin ZnO seed-layer coated with colloidal ZnO nanocrystals was introduced to control the density and orientation of ZnO nanowires. X-ray diffraction (XRD) and scanning electron microscopy (SEM) result show the high dense and well-aligned character of ZnO nanowires. The photoluminescence (PL) reveals the high crystal quality of the nanowires. It was found that the ZnO seed-layer can effect the size distribution, density and crystal structure of the nanowires. The growth mechanism of ZnO nanowires was also discussed.     

Fabrication and optical properties of mesoporous SnO2 nanowire arrays

Large-scale SnO2 mesoporous nanowires have been successfully synthesized by an improved sol-gel method within the nanochannels of porous anodic alumina templates. In this method, chloride of stannic and urea are used as precursors, chloride of stannic is acting as source of tin ions, and urea offers a basic medium through its hydrolysis. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction are used to characterize the SnO2 mesoporous nanowires. It is found that the as-prepared nanowires consist of SnO2 nanoparticles and pores. They can be indexed as rutile structures and diameters are about 50-70 nm. The growth mechanism of the mesoporous nanowires is also been discussed. The band gap of the as-prepared mesoporous nanowires is 3.735 eV, determined by UV/visible absorption spectral results. The SnO2 mesoporous nanowires show strong and stable photoluminescence with emission peak centered at 3.730 eV, which has never been reported in nanowires. It could be attributed to the exciton recombination.     

Facile synthesis of ZnO nanostructures and investigation of structural and optical properties

ZnO nanostructures were synthesized by chemical bath deposition method, using zinc nitrate [Zn(NO₃)₂] and hexa-methylene-tetra-amine [(HMT),C(H₂)₆N₄] as precursors. Controlled size and shape evolution of ZnO nanostructures were achieved by changing the HMT concentration from 0.025 M to 0.1 M, whereas Zn(NO₃)₂ concentration kept constant. X-ray diffraction (XRD) and Raman study confirmed the formation of single crystalline, hexagonal wurtzite ZnO structure. Sharp peaks in Raman spectra, corresponding to E₂(low) and E₂(high) referred to wurtzite structure with higher order of crystallinity. Transmission electron microscopy (TEM) revealed that the shape and size of the nanostructures reduced, with increasing concentration of HMT. Further, effect of structure's size was observed in the band gap (shift). Photoluminescence study showed two peaks at ~ 380 nm and ~ 540 nm corresponding to the band to band transition and defect transitions. Modifications of properties are explained in detail on the basis of shape and size change of the structures and possible mechanism is discussed.     

ZnO纳米线阵列的图形化生长

采用光刻和射频磁控溅射技术在Si衬底上制备了图形化的ZnO种子层薄膜。分别采用气相榆运和水热合成法，制备了最小单元为30μm的图形化的ZnO纳米线阵列。X射线衍射（XRD）分析显示单晶纳米线阵列具有高度的c轴[001]择优取向生长性质，从扫描电子显微镜（SEM）照片看出，阵列图形完整清晰，边缘整齐，纳米线阵列在室温下光致发光（PL）谱线中在380hm左右具有强烈的紫外发射峰，可见光区域发射峰得到了抑制，证明ZnO纳米线阵列氧空位缺陷少，晶体质量高。     

Temperature dependant structural and electrical properties of ZnO nanowire networks

In this paper, we report a successful growth of zinc oxide nanowire networks by simple thermal evaporation process using metallic zinc powder in the presence of oxygen. The morphological investigations of the synthesized nanowire networks are conducted by using field emission scanning electron microscopy (FESEM) which reveals that the grown products are in high-density over the whole substrate surface and possessing nanowire networks like structures. The structural and compositional properties of the grown nanowire networks are analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS), respectively which confirm that the synthesized products are well-crystalline, with wurtzite hexagonal phase ZnO. The as-grown ZnO nanowire networks grown on silicon substrate are utilized to fabricate n-ZnO/p-Si heterojunction diode and presented in this paper. The I-V characteristics of the fabricated heterojunction diode at different temperatures (77 K-477 K) are also investigated. High values of quality factor, which are obtained from this study, indicate a non-ideal behavior of the fabricated device. The mean barrier height of -0.84 eV is also estimated and presented in this paper.