ZnO纳米棒阵列和薄膜的同步外延生长及其光电化学性能

使用化学气相沉积法在a面蓝宝石衬底上同步外延生长氧化锌(ZnO)竖直纳米棒阵列和薄膜,研究了阵列和薄膜的光电化学性能。结果表明,纳米结构中的竖直单晶纳米棒有六棱柱形和圆柱形,其底部ZnO薄膜使竖直纳米棒互相联通。与ZnO纳米薄膜的比较表明,这种纳米结构具有优异的光电化学性能,其入射光电流效率是ZnO纳米薄膜的2.4倍;光能转化效率是ZnO纳米薄膜的5倍。这种纳米结构优异的光电化学性能,可归因于其高表面积-体积比以及其底部薄膜提供的载流子传输通道。本文分析了这种纳米结构的生长过程,提出了协同生长机理：Au液化吸收气氛中的Zn原子生成合金,合金液滴过饱和后ZnO开始成核,随后在衬底表面生成了ZnO薄膜。同时,还发生了Zn自催化的气-固(VS)生长和Au催化的气-液-固(VLS)生长,分别生成六棱柱纳米棒和圆柱形纳米棒,制备出底部由薄膜连接的竖直纳米棒阵列。     

Elemental vapor-phase synthesis of nanostructured zinc oxide

We systematize experimental data on the elemental vapor-phase synthesis of zinc oxide nanocrystal arrays on substrates. This process may yield nanostructures differing in shape and dimensions, in particular, well-aligned ZnO nanorod arrays. A model is proposed in which aligned zinc oxide nanorod arrays may grow by the vapor-liquid-solid (VLS) mechanism, and liquid zinc nanodroplets forming on the substrate surface at the beginning of the process catalyze one-dimensional growth. The VLS process is accompanied by zinc oxide deposition onto the lateral surface of the nanorods from the vapor phase. The relative rates of these processes influence the shape of the nanorods and the thickness of the polycrystalline underlayer. Optimizing the deposition conditions, one can grow uniform arrays of aligned high-quality ZnO nanorods with no catalysts and with no special substrate preparation steps.     

低温水热法生长ZnO纳米棒阵列的电子结构及光学特性(英文)

使用低温水热法在Si衬底上生长ZnO纳米棒阵列.通过X射线衍射和扫描电子显微镜对ZnO纳米棒的结晶性和形貌进行观测.结果表明,六棱柱形ZnO纳米棒沿c轴方向的阵列性良好,且均匀致密的生长在衬底上.室温光致发光谱表明应用低温水热法可以得到光学性质良好的ZnO纳米棒阵列.使用同步辐射对ZnO纳米棒阵列的氧K带边进行X射线吸收近带边谱测量,研究了不同半径ZnO纳米棒阵列的局部电子结构及其半径对电子结构的影响.另外,对ZnO纳米棒及ZnO薄膜的局部电子结构进行了对比研究.     

Growth of well-aligned ZnO nanorod arrays on Si substrates by thermal evaporation of Cu-Zn alloy powders

Well-aligned ZnO nanorod arrays with uniform diameters and lengths have been fabricated on a Si substrate by simple thermal evaporation of Cu-Zn alloy powders in the presence of oxygen without using a template, catalyst, or pre-deposited ZnO seed layer. The ZnO nanorods are characterized by X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy and the growth mechanism is suggested. The nanorods have a single-crystal hexagonal structure and grow along the (0001) direction. Their diameters range from 200 to 400 nm and the lengths are up to several micrometers. The photoluminescence (PL) and Raman spectra disclose the optical properties of the products. The PL spectra show intense near-band ultraviolet emission at 378 nm from the nanorod arrays. The well-aligned ZnO nanorod arrays have a low turn-on field of 6.1 V/microm, suggesting good field emission properties. The simple synthesis methodology in conjunction with the good field emission and optical properties make the study both scientifically and technologically interesting.     

Fabrication of ZnS/ZnO hierarchical nanostructures by two-step vapor phase method

A simple two-step vapor phase method is presented to fabricate ZnS/ZnO hierarchical nanostructures in bulk quantities. That is ZnS nanobelts were first synthesized and then used as substrate for growth of ZnO nanorod arrays. Investigation results demonstrate that the polar surfaces of ZnS nanobelts could induce a preferred asymmetric growth of ZnO nanorods on the side surfaces. But it is believed that if the local concentration of ZnO was high enough, ZnO nanorods could also grow symmetrically on the top/bottom surface of the ZnS nanobelts. The optical property of the products was also recorded by means of photoluminescence (PL) spectroscopy.     

Controllable synthesis and photoluminescence properties of ZnO nanorod and nanopin arrays

Well-aligned ZnO nanorods and nanopins are synthesized on a silicon substrate using a one-step simple thermal evaporation of a mixture of zinc and zinc acetate powder under controlled conditions. A self-assembled ZnO buffer layer was first obtained on the Si substrate. The structure and morphology of the as-synthesized ZnO nanorod and nanopin arrays are characterized using X-ray diffraction, and scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. The influence of the background atmosphere on the two ZnO nanostructures has been studied. Two different growth mechanisms are mentioned to interpret the formation of ZnO nanorod and nanopin arrays in our work. The room-temperature PL features the ZnO nanorods exhibit only sharp and strong ultraviolet (UV) emission emissions, which confirms the better crystalline and optical quality than the ZnO nanopins.     

Growth of zinc oxide nanorod structures: pressure controlled hydrothermal process and growth mechanism

Zinc oxide (ZnO) nanorods of various morphologies are grown on zinc substrate by pressure-assisted hydrothermal process and the growth mechanism is investigated with the help of molecular dynamics (MD) simulation results. Hydrothermally reacted ZnO₂ nanostructure bottom-up formation from Zn substrate is a useful process employed here. A systematic study on the role of process control parameters such as pressure and temperature on nanorod growth has been carried out. Correlation among the process parameters to form ordered nanostructures is established. The effect of pressure on the diameter and length of the grown ZnO nanorod structures is studied, which is precisely tunable. With a decrease in pressure from 500 to 400 kPa, the nanorod diameter is reduced by 22.2 %, while its length is increased by 24.8 %. At lower vapor pressure, the nanorod tips are sharper, whereas at higher vapor pressure they are flat. These variations along with a detailed analysis of MD simulations helps us hypothesize that pressure plays an important role in governing the diffusion of oxygen atom onto zinc surface and generating wurtzite phase. Simulation results clearly show that ZnO nanorods lift off due to their interaction with the Zn atoms on the substrate and the resulting forces.     

Microstructural and optical characteristics of solution-grown Ga-doped ZnO nanorod arrays

Highly oriented Ga-doped zinc oxide (ZnO) nanorod arrays have been prepared on a ZnO-buffered silicon substrate in an aqueous solution, which is a mixture of methenamine (C(6)H(12)N(4)), zinc nitrate hexahydrate (Zn(NO(3))(2)·6H(2)O), and gallium nitrate hydrate (Ga(NO(3))(3)·xH(2)O). The microstructure characteristics and optical properties of the nanorod arrays were analyzed using different characterization techniques including field-emission scanning electron microscopy (FESEM), x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL). The experimental results show that the morphology, density, and surface compositions of ZnO nanorod arrays are sensitive to the concentration of gallium nitrate hydrate. The PL spectra of all ZnO nanorod arrays show three different emissions, including UV (ultraviolet), yellow, and NIR (near infrared) emissions. With the increase in the Ga doping level, the luminescence quality of ZnO nanorods has been improved. The peak of UV emission has a small redshift, which can be ascribed to the combined effect of size and Ga doping. Furthermore, Ga doping has caused defects that respond to NIR emission.     

Vertically aligned Fe-doped ZnO nanorod arrays by ultrasonic irradiation and their photoluminescence properties

A facile sonochemical route was demonstrated for the direct fabrication of Fe-doped ZnO nanorod arrays on a Si substrate under ambient conditions. By adding Fe³⁺ ions in reaction solution, Fe is readily in situ doped into ZnO nanorod arrays via ultrasound irradiation. The morphology and structural characteristic of the Fe-doped ZnO nanorods were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). And crystal structure was characterized by X-ray diffraction (XRD) spectroscopy. Inductively-coupled plasma atomic emission spectroscopy (ICP-AES) confirmed the Fe-doping of ZnO nanorod arrays with a concentration of 0.9 wt.%. In addition, Fe-doped ZnO nanorod showed the enhancement of photoluminescence (PL) intensity in green-yellow emission.     

基于氧化铝模板的有序ZnO纳米棒的合成及光学特性研究

利用高度有序的多孔氧化铝膜作为模板,使用简单的热蒸发Zn粉的方法,成功地制备出高度有序的ZnO纳米棒束,该方法克服了制备有序纳米结构通常需要的催化剂或复杂的合成过程.利用扫描电镜、透射电镜和X射线衍射研究了样品的形貌及其结构特性,其结果表明模板表面所制备的ZnO纳米棒具有更好的有序度和结晶质量,从而推断出模板表面有序ZnO纳米棒的形成应该同模板表面局域化负电荷的存在有关.同Si基片上所形成无序纳米棒的光致发光谱相比,模板表面所形成的有序ZnO纳米棒束具有更强的紫外峰,表明有序的ZnO纳米棒具有更好的结晶质量和光学特性.     

Zinc oxide nanorod growth on gold islands prepared by microsphere lithography on silicon and quartz

Gold islands, vapor deposited on silicon and quartz by microsphere lithography patterning, are used to nucleate arrays of ZnO nanorods. ZnO is grown on approximately 0.32 microm2 Au islands by carbothermal reduction in a tube furnace. Scanning electron microscopy (SEM) and energy dispersive atomic X-ray spectroscopy (EDS) confirm that the gold effectively controls the sites of nucleation of ZnO. Atomic force microscopy (AFM) shows that approximately 30 nm diameter nanorods grow horizontally, along the surface. Alloy droplets that are characteristic of the vapor-liquid-solid (VLS) mechanism are observed at the tips of the nanorods. The spatial growth direction of VLS catalyzed ZnO nanorods is along the substrate when they nucleate from gold islands on silicon and quartz. The energy of adhesion of the VLS droplet to the surface can account for the horizontal growth.     

化学浴沉积过程中的氧化锌微米棒与纳米棒研究

采用化学浴沉积法在氧化锌种子层上制备了整齐有序且具有c轴取向的氧化锌纳米棒,同时还出现了自由分布的微米棒,其生长速度高于纳米棒,且生长模式符合扩散控制"Ostwald熟化"机制,但纳米棒生长过程的影响因素除扩散过程外还有形核密度、生长界面的反应动力学等.并研究了氧化锌纳米棒的微观结构和光学性质.     

可见光诱导TiO2光催化及其机理研究进展

简述了二氧化钛的光催化机理。针对其禁带宽度较大,只能被小于387nm的紫外光所激发的缺点,综述了近年来国内外针对纳米TiO2可见光催化的改性方法和改性机理研究进展,包括离子掺杂、半导体复合、表面光敏化等方法。最后展望了提高纳米TiO2可见光光催化活性研究的前景。     

Sensitization of ZnO nanorods with CdSe quantum dots

We have optimized the low-temperature growth of aligned arrays of zinc oxide nanorods of controlled length and diameter on conductive substrates. Varying the solution concentration and growth time, we were able to tune the nanorod diameter and length in the ranges 40–600 nm and 0.5–15 μm, respectively. The grown zinc oxide nanorods were photosensitized with CdSe quantum dots (QDs) in an oleic shell, which was replaced by pyridine. We studied the optical and transport properties of the ZnO nanorod arrays, with and without CdSe QDs on their surface. The current-voltage characteristics of the ZnO nanorod arrays with CdSe QDs are significantly influenced by illumination with light at a wavelength under the absorption band of the QDs, which points to effective interaction between the QDs and ZnO matrix.     

Growth specificity of vertical ZnO nanorods on patterned seeded substrates through integrated chemical process

A simple and cost effective method has been employed for the random growth and oriented ZnO nanorod arrays over as-prepared and patterned seeded glass substrates by low temperature two step growth process and growth specificity by direct laser writing (DLW) process. Scanning electron microscopy (SEM) images and X-ray diffraction analysis confirm the growth of vertical ZnO nanorods with perfect (0 0 2) orientation along c-axis which is in conjunction with optimizing the parameters at different reaction times and temperatures. Transmission electron microscopy (TEM) images show the formation of vertical ZnO nanorods with diameter and length of ∼120 nm and ∼400 nm respectively. Photoluminescence (PL) spectroscopic studies show a narrow emission at ∼385 nm and a broad visible emission from 450 to 600 nm. Further, site-selective ZnO nanorod growth is demonstrated for its high degree of control over size, orientation, uniformity, and periodicity on a positive photoresist ZnO seed layer by simple geometrical (line, circle and ring) patterns of 10 μm and 5 μm dimensions. The demonstrated control over size, orientation and periodicity of ZnO nanorods process opens up an opportunity to develop multifunctional properties which promises their potential applications in sensor, piezoelectric, and optoelectronic devices.     

Synthesis of size-tunable ZnO nanorod arrays from NH3·H2O/ZnNO3 solutions

Well-aligned crystalline ZnO nanorod arrays were fabricated via an aqueous solution route with zinc nitrate and ammonia as precursors. Dip-coating was firstly utilized to form a ZnO film on ITO substrate as a seed layer for subsequent growth of ZnO nanorods. The effects of NH₃·H₂O/ZnNO₃ molar ratio, ZnNO₃ concentration, growth temperature and time on nanorod morphology were respectively investigated. It was found that the size of nanorod is mainly determined by the molar ratio and concentration. XRD demonstrates that ZnO nanorods are wurtzite crystal structures preferentially orienting in the direction of the c-axis. SEM confirms that ZnO nanorods grew up perpendicular to the substrate. The diameter and length were tunable in a broad range from 80 nm to 500 nm and 250 nm up to 8 μm, respectively. The aspect ratio changed from 3 to 17 mainly dependent on composition of the aqueous solution.     

Efficient dye-sensitized solar cells based on the combination of ZnO nanorods and microflowers

Well-aligned ZnO nanorod films were grown onto transparent conducting substrates by using an aqueous solution route. The presence of some reflections in the X-ray diffraction pattern of the ZnO films indicates the vertical alignment of the nanorods along the c axis of the wurtzite hexagonal structure. Well-aligned ZnO nanorods were observed by scanning electron microscopy. The presence of top ZnO microflower layers over the ZnO nanorod film was observed for all growth times studied. The ZnO nanorods with ZnO microflower top layers were applied as photoelectrodes in dye-sensitized solar cells. Higher photocurrent densities and photovoltages were observed with longer nanorod growth times. The high performance of the dye-sensitized solar cells might be associated to the combination of ZnO nanorods and microflowers in the same photoelectrode.     

A novel, substrate independent three-step process for the growth of uniform ZnO nanorod arrays

We report a three-step deposition process for uniform arrays of ZnO nanorods, involving chemical bath deposition of aligned seed layers followed by nanorod nucleation sites and subsequent vapour phase transport growth of nanorods. This combines chemical bath deposition techniques, which enable substrate independent seeding and nucleation site generation with vapour phase transport growth of high crystalline and optical quality ZnO nanorod arrays. Our data indicate that the three-step process produces uniform nanorod arrays with narrow and rather monodisperse rod diameters (∼ 70 nm) across substrates of centimetre dimensions. X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction were used to study the growth mechanism and characterise the nanostructures.     

ZnO纳米棒阵列膜的制备及其光电化学性能研究

采用化学溶液沉积法,在ZnO纳米颗粒膜修饰的FTO导电玻璃基底上,制备了ZnO纳米棒阵列。用X射线衍射仪（XRD）、场发射扫描电子显微镜（FESEM）、透射电子显微镜（TEM）对样品进行表征。研究结果表明所制备的ZnO纳米棒为六方纤锌矿相单晶结构,沿c轴择优取向生长,平均直径约为40nm,长度约为900nm;ZnO纳米棒阵列生长致密,取向性较一致。以曙红Y敏化的ZnO纳米棒阵列膜为光阳极制作了染料敏化太阳能电池原型器件,在光照强度为100mW/cm2下,其开路电压为0.418V,短路电流为0.889mA/cm2,总的光电转换效率为0.133%。     

Catalyst-free synthesis of ZnO nanorod arrays on InP (001) substrate by pulsed laser deposition

High-density well-aligned ZnO nanorod arrays were successfully fabricated on ZnO a seed-layer coated InP (001) substrate by using pulsed laser deposition (PLD) technique without metal catalyst. SEM image showed that uniformly distributed droplet-like ZnO seed-layer was formed on the InP wafer. Well-oriented ZnO nanorods were formed perpendicular to the seed-layer coated substrate and well-separated from each other. X-ray diffraction θ-2θ scanning measurements demonstrated that the ZnO nanorods exhibited a strong c-axis orientation with high crystalline quality. The photoluminescence (PL) spectrum measurement illuminated that the ZnO nanorods produced in this work had well optical quality. The well-aligned and separated ZnO nanorods fabricated by this comparatively simple technique shed light on further applications for nanodevices.