MWCNT/ZnO纳米线复合阴极薄膜的场发射特性

实验提出以多壁碳纳米管(MWCNT)/ZnO纳米线复合材料作为场发射阴极薄膜,研究其图形化制备工艺以及其场发射特性.用丝网印刷工艺制备图形化MWCNT/ZnO纳米线复合阴极薄膜,实验获得合适的浆料配比以及适合的烘烤和烧结温度.对MWCNT/ZnO纳米线样品进行SEM分析和场发射特性测试,发现图形化阴极设计提高了场发射电流,并且改善场发射发光均匀度;材料组分的低维化明显降低场发射开启电压;加电老练处理有效改善场发射特性.     

ZnO纳米线的制备及其光学性能

采用物理热蒸发ZnS粉的方法,制备出了大规模的线状和棒状ZnO纳米结构.借助扫描电子显微镜、透射电子显微镜、激光拉曼光谱仪以及荧光光谱仪研究了ZnO纳米线的表面形貌、内部结构及其光学性能.结果表明,所得到的ZnO纳米线是六方的单晶结构,而且具有较好的发光性能和良好的结晶性.纳米线长约2～5μm,直径约60nm,其生长机制为气-固(VS)机制.     

基于氧化锌纳米线表面传导场发射阴极的研究

利用热蒸发和丝网印刷技术在玻璃基底上成功制备了氧化锌纳米线表面传导场发射阴极阵列,并测试其场发射性能。扫描电镜表明,在氩气和氧气流量分别为60和1mL/min,反应温度550℃保温30min条件下制备的氧化锌纳米线均匀垂直生长在玻璃基底上,直径大约在80～200nm,长度〉7μm。场发射测试表明,在阳压2000V和阴阳间距为500μm时,ZnO纳米线表面传导场发射阴极的开启电压为70V;在栅压为96V时,电子发射效率为26.2%,高于传统报道的表面传导电子发射器件,在经过80min的老练后发射接近稳定,平均发射电流接近135μA,表明ZnO纳米线表面传导场发射阴极有着稳定高效的场发射性能。     

Ag纳米粒子修饰ZnO纳米线特性研究

利用水溶液法制备ZnO纳米线,使用真空热蒸发方法用Ag对ZnO纳米线进行表面修饰。用场发射扫描电子显微镜(FESEM)、X射线衍射(XRD)仪、吸收谱仪分析它们的表面形貌、物相结构及光学性质,同时分析了其场发射性能。结果表明,随着Ag修饰量的增加,ZnO纳米线表面上的Ag纳米粒子分布会由稀疏逐步到致密,最后Ag的纳米粒子几乎连在一起。测量吸收谱线发现修饰后的ZnO纳米线的吸收能力变强,但存在一个临界值,当修饰量超过临界值后,ZnO纳米线的光吸收能力会减弱。对修饰后ZnO纳米线的场发射性能进行初步测试,结果表明适当量的Ag修饰可以有效降低ZnO纳米线的场发射开启电压。     

Ag掺杂ZnO纳米线酒敏性能的研究

利用浸渍法将ZnO纳米线浸渍于AgNO3溶液中制备了Ag 掺杂的ZnO纳米线.借助X射线衍射仪(XRD)和场发射扫描电子显微镜(FESEM)对纳米线的晶体结构和形貌进行了表征.结果表明纳米线既含面心立方结构的Ag又含有六方纤锌矿结构的ZnO.三维网络结构的ZnO纳米线被一层致密的Ag颗粒包裹并在其表面形成了大量的具有高比表面剂的孔洞结构.将纯的和Ag掺杂的ZnO 纳米线都作为酒敏传感材料,在酒精浓度为0.001%,工作温度为150～400℃的范围内测试了它们的气敏特性,结果显示,Ag掺杂的ZnO纳米线的酒精灵敏度比纯ZnO纳米线提高了14.在工作温度为350℃的条件下测试了它们的响应-恢复时间.气敏元件的酒敏特性主要归结于表面吸附效应.     

利用静电纺丝技术制备ZnO纳米线

用电纺得到的ZnO／SiO2复合纤维膜,浸在溶胶-凝胶法制备的ZnO溶胶中2h,使其充当控制ZnO纳米线（棒）生长的先驱物种子,再采用溶液生长法制备ZnO纳米线。结果表明先驱ZnO薄膜可以控制生长的ZnO纳米线。     

MBE法生长ZnO纳米线阵列的结构和光学性能

在氧等离子体辅助的MBE系统中, 以1 nm厚的Au薄膜为催化剂, 基于气?液?固(VLS)机制实现了低温ZnO纳米线阵列在Si(111)衬底表面的生长. 通过场发射扫描电子显微镜(FE-SEM)可以观察到, ZnO纳米线阵列垂直生长在衬底上, 直径为20~30 nm. X射线衍射(XRD)和高分辨透射电镜(HRTEM)结果表明: ZnO纳米线为六方纤锌矿结构, 具有沿c轴方向的择优取向. 光致发光(PL)谱显示在380 nm附近有强烈ZnO本征发射峰, 475~650 nm可见光区域有较强的缺陷导致的发射峰.     

水热法在碳纤维表面生长ZnO纳米线及性能研究

采用水热法在碳纤维表面生长ZnO纳米线,通过扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和SmileView软件对ZnO纳米线进行分析。XPS结果确认碳纤维表面纳米线为ZnO纳米线,SEM图片说明T700碳纤维表面ZnO纳米线取向度高于T300碳纤维表面ZnO纳米线,关于生长时间的分析表明最优值为4h。此外,通过附着生长在碳纤维表面制备了改性的ZnO纳米线,XPS测试结果表明ZnO纳米线表面涂层为CoO。     

Ag(TCNQ)纳米线的制备和场发射性能研究

采用气-液-固反应方法在硅片上制备了取向金属有机配合物Ag(TCNQ)纳米线.样品的XRD特征峰与Ag(TCNQ)相对应;SEM形貌显示纳米线几乎垂直基片生长,直径在50～300nm,长度在2～50μm.初步对其场发射性能进行了研究,所得Ag(TCNQ)纳米线的最低场发射开启电压约为1.5Vμm-1,最大发射电流密度约为0.03mAcm-2,此时对应的电场约为2.5Vpm-1.由测量所得I-Ⅴ曲线得到的FoWler-Nordheim(F-N)曲线近似为一条直线,说明样品具有场发射性能.重复实验表明,Ag(TCNQ)纳米线的场发射具有一定的稳定性.结合纳米线制备工艺,初步分析了场发射性能的影响因素.     

生长温度对热蒸发法制备ZnO纳米线的结构与发光性能影响

采用无金属催化剂的简单热蒸发法,在Si(100)衬底上不同生长温度下成功地制备了高密度和大长径比的单晶ZnO纳米线。分别利用X射线衍射仪(XRD)、扫描电子显微镜(SEM-EDS)、透射电子显微镜(TEM)及荧光光谱仪表征样品的结构和发光性质。XRD和TEM研究表明,所制备的样品为沿C轴择优取向生长的单晶ZnO纳米线,具有六方纤锌矿结构。SEM和TEM研究表明,生长温度对ZnO纳米线的形貌及长径比的影响较大。当生长温度为700℃时,制备得到长径比为300(长度约为15μm,直径约为50nm)的ZnO纳米线。低于600℃时,形成花状ZnO纳米锥或 纳 米 棒。高 于700℃时,形 成 小 长 径 比 的ZnO纳米棒。此外,室温光致发光(PL)谱上出现一个强而尖锐的紫外发射峰以及一个弱而宽泛的蓝光发射峰。采用的热蒸发法制备ZnO纳米线基于气-固(VS)生长机理且该生长方法可用于大规模、低成本制备高纯度的单晶ZnO纳米材料。     

Reshaping the tips of ZnO nanowires by pulsed laser irradiation

Vertically aligned ZnO nanowires have been synthesized by a hydrothermal method. After being irradiated by a short laser pulse, the tips of the as-synthesized ZnO nanowires can be tailored into a spherical shape. Transmission electron microscopy revealed that the spherical tip is a single-crystalline piece connected to the body of the ZnO nanowire, and that the center of the sphere is hollow. The growth mechanism of the hollow ZnO nanospheres is proposed to involve laser-induced ZnO evaporation immediately followed by re-nucleation in a temperature gradient environment. The laser-irradiated ZnO nanowire array shows hydrophobic properties while the original ZnO nanowire array shows hydrophilicity. The as-grown ZnO nanowire arrays with hollow spherical tips can serve as templates to grow ZnO nanowire arrays with very fine tips, which may be a good candidate material for use in field emission and scanning probe microscopy.      

反应源温度对ZnO纳米线阵列定向性及发光性能的影响

以Au薄膜为催化剂、ZnO与碳混合粉末为反应源,采用碳热还原法在单晶Si衬底上制备了ZnO纳米线阵列.通过扫描电子显微镜( SEM)、X射线衍射仪(XRD)、荧光分光光度计对样品的表征,研究了反应源温度对ZnO纳米线阵列的定向性和光致发光性能的影响.样品在源温度920℃条件下沿(002)方向择优生长,定向性最好,温度过低不利于ZnO纳米线阵列密集生长,而温度过高导致Zn原子二次蒸发,因而也不利于纳米线阵列的定向和择优生长;样品在源温度880℃有最强的近紫外带边发射,表明温度过高和过低都不利于ZnO晶体结构的优化;由于ZnO纳米线在缺氧氛围下生长,氧空位是缺陷存在的主要形式,因此所有样品都有较强的绿光发射.温度升高导致纳米线生长速度提高而增加了氧空位缺陷数量,从而使样品绿峰强度增强并在源温度920℃时达最大值,但温度的进一步升高可导致ZnO纳米线表面Zn元素的蒸发而降低氧空位缺陷的数量,从而抑制绿峰强度.     

高压PLD法生长p型钠掺杂氧化锌纳米线阵列

采用高压脉冲激光沉积法(HP-PLD)研究了压强、金催化层厚度对钠掺杂氧化锌纳米线(ZnO:Na)生长的影响, 并制备了ZnO:Al薄膜/ZnO:Na纳米线阵列同质pn结器件。实验发现, 当金膜厚度为4.2 nm, 生长压强为3.33×10⁴ Pa, 生长温度为875℃时, 可在单晶Si衬底上生长c轴取向性良好的ZnO纳米线阵列。X射线衍射和X射线光电子能谱综合分析证实了Na元素成功掺入ZnO纳米线晶格中。在低温(15 K)光致发光谱中, 观测到了一系列由Na掺杂ZnO产生引起的受主光谱指纹特征, 如中性受主束缚激子峰(3.356 eV, A0X)、导带电子到受主峰(3.312 eV, (e, A0))和施主受主对发光峰(3.233 eV, DAP)等。通过在ZnO:Al薄膜上生长ZnO:Na纳米线阵列形成同质结, 测得I-V曲线具有明显的整流特性, 证实了ZnO:Na纳米线具有良好的p型导电性能。     

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.     

Direct synthesis of ZnO nanowire arrays on Zn foil by a simple thermal evaporation process

ZnO nanowire arrays were synthesized on zinc foil by a simple thermal evaporation process at relatively low temperature. Morphology and size controlled synthesis of the ZnO nanostructures was achieved by variation of the synthesis temperature, reaction time and the surface roughness of the substrate. A gas-solid and self-catalytic liquid-solid mechanism is proposed for the growth of nanowires at different temperatures. High-resolution transmission electron microscopy (HRTEM) showed that the as-grown nanowires were of single crystal hexagonal wurtzite structure, growing along the [101] direction. Photoluminescence exhibited strong UV emission at ～382?nm and a broad green emission at ～513?nm with 325?nm excitation. Raman spectroscopy revealed a phonon confinement effect when compared with results from bulk ZnO. The nanowire arrays also exhibited a field emission property.     

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.     

Synthesis and microstructure of vertically aligned ZnO nanowires grown by high-pressure-assisted pulsed-laser deposition

The microstructure and growth behavior for vertically aligned Zinc oxide (ZnO) nanowires, synthesized on a ZnO thin film template by pulsed-laser deposition (PLD), is reported. The nanowire growth proceeds without any metal catalyst for nucleation, although an epitaxial ZnO thin film template is necessary in order to achieve uniform alignment. Nanowire growth at argon or oxygen background pressures of 500-mTorr results in nanowire diameters as small as 50–90 nm, with diameters largely determined by growth pressure and temperature. Room temperature photoluminescence show both near-band-edge and deep-level emission. The deep-level emission is believed caused by oxygen vancancies formed during growth.     

Synthesis of ZnO nanowires by the hydrothermal method,using sol–gel prepared ZnO seed films

Zinc oxide (ZnO) nanowires with various morphologies are synthesized by the hydrothermal method on silicon substrates coated with ZnO thin films. The ZnO films are used as the seed layer and are prepared using the sol–gel technique. Experimental results demonstrate that the synthesis of ZnO nanowires is dependent on the crystalline properties of the ZnO seed-layer films. Sol concentration is the controlled parameter for the preparation of ZnO seed-layer films in this study. The ZnO films are found to have the hexagonal wurtzite structure with highly preferred growth along the c-axis at suitable sol concentrations. The vertically aligned ZnO nanowire arrays on the substrates are believed to be the result of the epitaxial growth of the ZnO seed layer. Scanning electron microscopy shows that nanowires with uniform distribution in length, diameter, and density are obtained. X-ray diffraction patterns clearly reveal that the ZnO nanowires are primarily grown along the c-axis direction. Transmission electron microscopy and selected-area electron diffraction measurements show that the nanowires have good crystalline properties. The well-aligned and high surface areas of the ZnO nanowires make them a potential candidate for applications in solar cells, field emission devices, and ultra-sensitive gas sensors.     

Thickness optimized nanocrystalline ZnO-coated silicon nanowires for cold cathode application

Silicon nanowire is an important material for the potential use as a cold cathode, but there are some bottlenecks like oxidation of the surface during field emission thereby degradation of its performance. To compete with carbon based nanostructures in this field the performance of Si nanowires as field emitter should be improved. Here, we report a simple technique for the significant improvement of field emission properties of Si nanowires by ZnO nanoparticle coating. Boron-doped p-type Si wafers were chemically etched to synthesize vertically aligned silicon nanowires and they were coated with different thicknesses of ZnO layer by radio frequency magnetron sputtering technique. The nanostructured thin films were studied by X-ray photoelectron spectroscopy for compositional and valence states information while their morphological information was obtained by a field emission scanning electron microscope and a high resolution transmission electron microscope. The field assisted electron emission performance of Si nanowires significantly improved for the thickness optimized ZnO coating. The photoluminescence spectra showed a peak at ~558 nm assigned to surface defect states of ZnO and the field emission from Si nanowires coated with ZnO for different times were correlated with the surface defect structures. The mechanism of such improvement is also discussed.