Single-crystalline ZnO nanowires on zinc substrate by a simple hydrothermal synthesis method

A simple synthesis route to long ZnO nanowires with high aspect ratio of up to ∼ 1000 on zinc substrate in the NaOH aqueous solution was reported, without the assistance of any catalyst, templates or high temperature. We studied the key influencing factors including the reaction time and the solution concentration. With the increase of reaction time from 12 h to 24 h, the average length of ZnO nanowires would increase correspondingly. Through this synthesis route, we can obtain a mass of products and the method is both convenient and reproducible. The as-grown ZnO nanowires are single crystalline with a wurtzite structure.     

Structural and photoluminescence properties of aligned Sb-doped ZnO nanocolumns synthesized by the hydrothermal method

Aligned Sb-doped ZnO nanocolumns were synthesized by a simple hydrothermal method. Based on the analyses of the X-ray diffraction and photoluminescence result, it could be confirmed that the Sb has successfully doped in the ZnO crystal lattices to form an accepter energy level. At 85 K, the recombination of the acceptor-bound exciton was predominant in PL spectrum, which was attributed to the transition of the (Sb_Zn-2V_Zn) complex bound exciton. The acceptor binding energy had been calculated to be 123 meV.     

Structure, photoluminescence and wettability properties of well arrayed ZnO nanowires grown by hydrothermal method

Well aligned ZnO nanowire arrays with high crystal quality were grown on Si substrates at a low temperature (50 degrees C) by hydrothermal method using a pre-formed ZnO seed layer. ZnO seeds were prepared via radio-frequency magnetron sputtering onto Si substrates. The morphologies of the ZnO nanowire arrays were shown by field emission scanning electron microscopy. X-ray diffraction spectra showed that the full width at the half maximum of the (0002) peak of the nanowire arrays without any heat treatment was only 0.07 degrees, indicating very high crystal quality. Furthermore, the room-temperature photoluminescence spectra of the ZnO nanowire arrays exhibited excellent UV emission. The special micro/nano surface structure of the ZnO nanowire arrays can enhance the dewettability for surfaces modified via low surface energy materials such as long chain fluorinated organic compounds. The surface of the ZnO nanowire arrays is also found to be superhydrophobic with a contact angle of 165 degrees +/- 1 degrees, while the sliding angle is 3 degrees.     

Photoluminescence and field-emission characteristics of ZnO nanowires synthesized by two-step method

ZnO nanowires with excellent photoluminescence (PL) and field-emission properties were synthesized by a two-step method, and the ZnO nanowires grew along (0 0 2) direction. PL measurements showed that the ZnO nanowires have stronger ultraviolet emission properties at 376 nm and there is 3 nm blue shift after the nanowires were immersed in thiourea (TU) solution compared with those of without immersion. The immersed-ZnO nanowires show a turn-on field of 2.3 V/μm at a current density of 0.1 μA/cm and emission current density up to 1 mA/cm² at an applied field of 6.8 V/μm, which demonstrate that the immersed-ZnO nanowires posses efficient field-emission properties in contrast with those not immersed. The ZnO nanowires may be ideal candidates for making luminescent devices and field-emission displays.     

Fabrication and optical properties of needle-like ZnO array by a simple hydrothermal process

A simple low temperature hydrothermal process was employed to fabricate the needle-like ZnO array in the diluted butyl amine. The microstructure, morphology and the photoluminescence property of the as-prepared products were characterized by x-ray diffraction (XRD), transmission electron microscope (TEM), field emission environment scanning electron microscope (SEM) and photoluminescence spectrum (PL). The results show that the needle-like ZnO crystals are hexagonal wurtzite monocrystal with slender figure and smooth surface. A possible growth mechanism of the needle-like ZnO array related to the diluted butyl amine is proposed. The PL spectrum of the needle-like ZnO array shows a strong blue light emission at 437 nm and a relatively low ultraviolet emission at 377 nm.     

水热法合成氧化锌晶体形貌特征

本文采用水热法,在430℃,35%填充度,反应24h合成了ZnO晶体.当矿化剂浓度较低时,如1mol·L-1NaOH,只合成了ZnO微晶.提高矿化剂浓度可以合成出个体较大晶体,如采用5 mol·L-1NaOH作矿化剂时,合成晶体的长度达到500μm.以3mol·L-1 KOH作矿化剂时,合成晶体的长度为1500μm.以3 mol·L-1NaOH和1mol·L-1KBr作矿化剂时合成晶体的长度为700μm,直径200 μm,显露完整的晶面,显示晶体有较高的质量.除了大的晶体以外,合成产物中有大量的微晶和纳米晶簇.     

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.     

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.     

Growth and optical properties of ZnO nanorods by introducing ZnO sols prior to hydrothermal process

ZnO nanorods of 25 nm with quite homogeneous size and shape have been fabricated by introducing ZnO sols as nucleation centers prior to the hydrothermal reaction. The samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, photoluminescence and resonant Raman spectra. After ZnO sols are introduced, the width of the resulting nanorods decreases above an order of magnitude and the aspect ratio increases 5 times. The increase of the intensity ratio of ultraviolet to visible emissions in room-temperature photoluminescence spectrum and the decrease of the Raman linewidths show the improvement in the quality of ZnO nanorods. Influences of the number of seed nuclei and the aging time of ZnO sols on the morphology of ZnO nanorods are discussed.     

Characterization and magnetic properties of nanocrystalline nickel ferrite synthesized by hydrothermal method

Nanocrystalline nickel ferrite has been successfully synthesized through a simple hydrothermal process at 180 °C for 10 h. The as-synthesized powders were characterized by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) techniques. TEM image and HRTEM image revealed that the as-prepared crystals were well crystallized with grain size distribution from 50 to 80 nm. The magnetic properties were studied by vibrating sample magnetometer (VSM), it exhibited lower coercivity and higher saturation magnetization which came from high crystallinity and uniform morphologies.     

超细金属Zn纳米线的水热合成

用水热合成法制备了纤锌矿结构的超细金属Zn纳米线,X射线衍射结果分析表明所制备的金属Zn纳米线是单一的纤锌矿结构.扫描电子显微镜照片显示合成的纳米线长度达几微米,直径10～20nm,每一根纳米线都有一个锥形的顶部.进一步研究表明反应温度对合成产物的形貌有重要的影响,最后对纳米线的生长机制进行了初步分析.     

Field-emission triode of low-temperature synthesized ZnO nanowires

A field-emission triode based on the low-temperature (75/spl deg/C) and hydrothermally synthesized single-crystalline zinc-oxide nanowires (ZnO NWs) grown on Si substrate with a silicon dioxide (SiO/sub 2/) insulator was fabricated for the controllable field-emission device application. Field-emission measurement reveals that the ZnO NWs fabricated on the Si substrate exhibit a good emission property with the turn-on electric field and threshold electric field (current density of 1 mA/cm/sup 2/) of 1.6 and 2.1 V//spl mu/m, respectively, with a field enhancement factor /spl beta/ of 3340. The field-emission properties of the ZnO NW-based triode exhibit the controllable characteristics. The well-controlled field-emission characteristics can be divided into three parts: gate leakage region, linear region, and saturation region. Therefore, this study provides a low-temperature field-emission triode fabrication process that is compatible with the Si-based microelectronic integration, and the field-emission measurements also reveal that the emission behavior can be well controlled by adopting the triode structure.     

Single crystalline ZnO nanorods grown by a simple hydrothermal process

Single crystalline ZnO nanorods with wurtzite structure have been prepared by a simple hydrothermal process. The microstructure and composition of the products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, energy dispersive X-ray spectrum (EDS) and Raman spectrum. The nanorods have diameters ranging from 100 nm to 800 nm and length of longer than 10 µm. Raman peak at 437.8 cm^− 1 displays the characteristic peak of wurtzite ZnO. Photoluminescence (PL) spectrum shows a blue light emission at 441 nm, which is related to radiative recombination of photo-generated holes with singularly ionized oxygen vacancies.     

Partial conversion reaction of ZnO nanowires to ZnSe by a simple selenization method and their photocatalytic activities

A simple novel synthetic method for preparing ZnSe/ZnO heterostructured nanowire (NW) arrays via the selenization of ZnO NWs is reported. A hydrothermally grown ZnO NWs array on a glass substrate was reacted with selenium vapor to generate a 20–30 nm of zincblend ZnSe nanoparticles (NPs) on wurtzite ZnO NWs. A growth mechanism was proposed based on SEM, XRD, and TEM analysis to explain the partial chemical conversion of ZnO NW surfaces into ZnSe NPs. This mechanism is applicable to the synthesis of other chalcogenide compounds. The as-synthesized ZnSe/ZnO heterojunctions showed enhanced UV–visible light absorption properties. The materials exhibited excellent photocatalytic activity toward the decomposition of an organic dye compared to the bare ZnO due to enhanced light absorption and the type-II cascade band structure.     

Microstructure and luminescence properties of Co-doped SnO2 nanoparticles synthesized by hydrothermal method

Co-doped SnO₂ nanoparticles were synthesized by a simple hydrothermal method, and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), UV–Vis diffuse reflectance spectra (DRS) and Photoluminescence spectroscopy (PL). It is found that the SnO₂ crystallites with the tetragonal rutile structure formed directly during the hydrothermal process without calcination. The Co-doped SnO₂ nanoparticles were spheric and well-dispersed with narrow size distribution. The crystalline size of SnO₂ decreased from 5.98 to 2.22 nm when the Co content increased from 0% to 20%. A considerable red shift in the absorbing band edge was observed with increasing of Co dopant.     

Flower-like CuO synthesized by CTAB-assisted hydrothermal method

Flower-like CuO nanostructures have been synthesized by cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. Here, CuCl₂·2H₂O was used as copper raw material, and sodium hydroxide was used as precipitate. The resulting CuO powders were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). X-ray diffraction (XRD) pattern exhibited the nanocrystalline nature with monoclinic structure for the as-synthesized nanostructures. FESEM images indicated that the flower-like CuO nanostructures are composed of many interconnected nanosheets in size of several micrometres in length and width and 60–80 nm in thickness. The possible formation mechanism of flower-like CuO nanostructures was discussed.     

Structural characterization of silicon-substituted hydroxyapatite synthesized by a hydrothermal method

Silicon-substituted hydroxyapatite (Si-HA) was prepared successfully by hydrothermal method. The crystalline phase, microstructure, chemical composition, morphology and thermal stability of Si-HA were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results show that the substitution of the silicate groups for the phosphate groups causes some OH^- loss to maintain the charge balance and changes the lattice parameters of HA. Furthermore, the substitution of the silicate groups restrains the growth of Si-HA crystal. DSC analysis shows that the small amount of silicon incorporates into HA lattice does not influence the thermal stability of HA.     

Photoluminescence studies from ZnO nanorod arrays synthesized by hydrothermal method with polyvinyl alcohol as surfactant

Well-aligned ZnO nanorod arrays have been synthesized by a simple hydrothermal method with polyvinyl alcohol as surfactant on F:SnO₂ conductive glasses substrates. Visible violet photoluminescence has been observed at room temperature. A series of annealing treatments in different environments have been made in order to investigate the nature of these emissions. The violet emission shows no change after annealing in air, while shifts to the ultra-violet region after annealing in H₂. It is concluded that the violet emission is due to V_Zn⁻ defect formed at the surface of the ZnO nanorods.     

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.     

Microstructures and photoluminescence properties of three-dimensional multi-layered ZnO flowers by surfactant-free hydrothermal method

In this paper, a large-scale of three-dimensional multi-layered ZnO flowers constructed by porous nanosheets were fabricated on Zn foils through a surfactant-free hydrothermal method. The morphology and microstructures of precursors and the mesoporous ZnO flowers were revealed by scanning electron microscopy. Based on the urea hydrolyzation, a possible growth mechanism of etching-deposition was proposed. The quantities and sizes of ZnO petals can be turned by urea concentration variations. The optical properties of the multi-layered ZnO flowers prepared with variety urea contents were also investigated by room temperature photoluminescence spectroscopy and showed the lower urea added sample has better crystalline quality.