Aligned growth of ZnO nanowires and lasing in single ZnO nanowire optical cavities

Ordered ZnO nanowire arrays have been fabricated in N₂ background gas by catalyst-free nanoparticle-assisted pulsed-laser deposition. A single ZnO nanowire was collected in an electrode gap by dielectrophoresis. Under the optical pumping above an exciting laser (λ= 355 nm) threshold of ∼ 334 kW/cm², ultraviolet lasing action in a single ZnO nanowire was observed at room temperature, indicating that the as-synthesized nanowires in pure N₂ background gas are of high quality. The crystalline facets of both ends of the nanowire acted to form an optical cavity. Therefore, the mode spacings corresponding to cavity lengths of the respective nanowires were observed in photoluminescence spectra. PACS 78.66.Hf; 81.07.Bc; 78.67.-n; 81.16.Mk     

片上制备横向结构ZnO纳米线阵列紫外探测器件

将纳米技术与传统的微电子工艺相结合, 片上制备了横向结构氧化锌(ZnO)纳米线阵列紫外探测器件, 纳米线由水热法直接自组织横向生长于叉指电极之间, 再除去斜向的多余纳米线, 其余工艺步骤与传统工艺相同. 分别尝试了铬(Cr)和金(Au)两种金属电极的器件结构: 由于Cr电极对其上纵向生长的纳米线有抑制作用, 导致横向生长纳米线长度可到达对侧电极, 光电响应方式为受表面氧离子吸附控制的光电导效应, 光电流大但增益低, 响应速度慢, 经二次电极加固, 纳米线根部与电极金属直接形成肖特基接触, 光电响应方式变为光伏效应, 增益和速度得到了极大改善; 由于Au电极对其上纵向生长的纳米线有催化作用, 导致溶质资源的竞争, 相同时间内横向生长的纳米线不能到达对侧, 而是交叉桥接, 但却形成了紫外光诱导的纳米线间势垒结高度调控机理, 得到的器件特性为最优, 在波长为365 nm的20 mW/cm²紫外光照下, 1 V电压时暗电流为10^-9 A, 光增益可达8×10⁵, 响应时间和恢复时间分别为1.1 s和1.3 s.     

Synthesis and optical characterization of vertically grown ZnO nanowires in high crystallinity through vapor-liquid-solid growth mechanism

The gas-phase growth and optical characteristics of 1-dimensional ZnO nanostructure have been investigated. The ZnO nanowires (NWs) were grown vertically on Au coated silicon substrates by vapor-liquid-solid (VLS) growth mechanism using chemical vapor deposition (CVD). The ZnO NWs were grown in the crystal direction of [0 0 0 1]. The ZnO NWs exhibit the uniform size of less than 100 nm in diameter and up to 5 μm in length. Photoluminescence (PL) spectrum of ZnO NWs shows the strong band-edge emission at ∼380 nm (∼3.27 eV) without significant deep-level defect emission. The exciton lifetime of ZnO NWs was measured to be approximately 150 ± 10 ps.     

Experimental evidence for electron-hole liquid in ZnO

Measurements of optical gain in ZnO have been performed as a function of excitation intensity and temperature. The results are interpreted in terms of formation of an electron-hole liquid at temperatures below 70K. The liquid has a binding energy of 22 meV and a low temperature density of 0.98 × 10¹⁸cm^-3.     

Growth of self-assembled ZnO nanowire arrays

This paper reports on ZnO nanowires arrays synthesized using Sn as a catalyst. The Sn particles were produced from the reduction of SnO₂ powders via a vapour-solid growth process. Control of growth conditions led to the formation of ZnO nanowire arrays, radial nanowire ‘flowers’ and uniaxial fuzzy nanowires. ZnO nanowire–nanobelt junctions were also grown by changing the growth direction. As-grown nanowire arrays could be fundamental materials for investigating physical and chemical properties at nano-scale dimensions.     

Effect of Mn-doping on the growth mechanism and electromagnetic properties of chrysanthemum-like ZnO nanowire clusters

Chrysanthemum-like ZnO nanowire clusters with different Mn-doping concentrations are prepared by a hydrothermal process. The microstructure, morphology and electromagnetic properties are characterized by x-ray diffractometer high-resolution transmission electron microscopy (HRTEM), a field emission environment scanning electron microscope (FEESEM) and a microwave vector network analyser respectively. The experimental results indicate that the as-prepared products are Mn-doped ZnO single crystalline with a hexagonal wurtzite structure, that the growth habit changes due to Mn-doping and that a good magnetic loss property is found in the Mn-doped ZnO products, and the average magnetic loss tangent tanδ_m is up to 0.170099 for 3% Mn-doping, while the dielectric loss tangent tanδ_e is weakened, owing to the fact that ions Mn^{2 +} enter the crystal lattice of ZnO.     

Experimental evidence for the existence of biexcitons in ZnO

For the first time resonant two-photon Raman scattering via biexcitons in highly excited ZnO is reported. The existence of biexcitons is thus shown. Their binding energy is determined to be (20 ± 1) meV.     

Study on the defects of ZnO nanowire

The room-temperature photoluminescence property of ZnO nanowires was studied. It showed an ultraviolet peak and a visible light band in the PL spectrum. Through Gaussian fitting, it was found that the visible light band can be divided into two peaks at 2.37 eV and 2.53 eV, which was originated from oxygen antisite and oxygen vacancy defects, respectively. After being exposed to air or post-annealed in oxygen ambience, aging effect was observed and the peak at 2.53 eV disappeared due to the removal of oxygen vacancy defects. Therefore, it is suggested that oxygen antisite and oxygen vacancy coexist in ZnO and induce visible light emission.     

Diameter-independent kinetics in the vapor-liquid-solid growth of Si nanowires

We examine individual Si nanowires grown by the vapor-liquid-solid mechanism, using real-time in situ ultra high vacuum transmission electron microscopy. By directly observing Au-catalyzed growth of Si wires from disilane, we show that the growth rate is independent of wire diameter, contrary to the expected behavior. Our measurements show that the unique rate-limiting step here is the irreversible, kinetically limited, dissociative adsorption of disilane directly on the catalyst surface. We also identify a novel dependence of growth rate on wire taper.     

Contact welding study of carbon nanotube with ZnO nanowire

Study of proton beam induced welding of multiwall carbon nanotubes (MWCNTs) with ZnO nanowires (NWs) has been carried out by proton (H⁺) beam irradiation. The samples were irradiated by 70-keV proton (H⁺) ion beams at different substrate temperatures. The irradiation-induced defects in CNTs and ZnO NWs were greatly reduced at elevated temperature. The crystalline structure of ZnO NWs and MWCNTs were found to remain stable after the irradiation at 700 K. As a preparation step, a coupling of two parallel ZnO NWs with irradiation has also been demonstrated. The welding mechanisms of MWCNTs and ZnO NWs were also been suggested. These two welding processes between same and distinct nanostructures to form homo- and hetero-junctions have provided an opportunity to mass produce interconnecting one-dimensional structures used for the manufacturing of future nanowire-based electronic circuits and devices.     

Surface reconstruction of ZnO nanowire arrays via solvent-evaporation-induced self-assembly

Vertically aligned ZnO nanowires (NWs) can be reconstructed on large scales by a solvent-evaporation-induced method. The morphologies of the nanowires are regulated by changing the concentration of the solution. Possible mechanism, which the compressive residual stresses and wires/wires self-attraction can be responsible for the surface reconstruction, is addressed. Furthermore, we compare the structural properties of ZnO nanowires before and after reconstructed.     

Characterization of ZnO nanowire field-effect transistors and exposed to ultraviolet radiation

A ZnO nanowire (NW) field-effect transistor (FET) is fabricated and characterized, and its characterization of ultraviolet radiation is also investigated. On the one hand, when the radiation time is 5~min, the radiation intensity increases to 5.1~μ W/cm², while the saturation drain current (I_\rm dss) of the nanowire FET decreases sharply from 560 to 320~nA. The field effect mobility (μ ) of the ZnO nanowire FET drops from 50.17 to 23.82~cm²/(V.s) at V_\rm DS=2.5~V, and the channel resistivity of the FET increases by a factor of 2. On the other hand, when the radiation intensity is 2.5~μ W/cm^2 , the DC performance of the FET does not change significantly with irradiation time (its performances at irradiation times of 5 and 20~min are almost the same); in particular, the I_\rm dss of NW FET only reduces by about 50~nA. Research is underway to reveal the intrinsic properties of suspended ZnO nanowires and to explore their device applications.     

Inexpensive and highly controlled growth of zinc oxide nanowire: Impacts of substrate temperature and growth time on synthesis and physical properties

Zinc oxide nanowires (ZnO NWs) were synthesized using a simple reactive-evaporation method without the use of catalysts. The NWs growth was precisely controlled by adjusting the experimental conditions mainly growth times and substrate temperatures. These experimental parameters are crucial for the growth of NWs. The typical diameter and length of the highly crystalline NWs obtained are several tens and several hundred nanometers, respectively. The nature of early-stages growth, morphology, structure and photoluminescent properties of the NWs grown at low temperatures have been explained and give the basic reasons behind these growth mechanisms. Self-organized ZnO nuclei are primarily formed on FTO pits due to high density of Zn atoms. It can be ascribed to vapour-solid with an area selected growth of NWs which provide a continuous pathway for carrier transport due to direct contact with the substrate. These features are crucial for the application of electronic devices, solar cells, etc.     

Control growth of catalyst-free high-quality ZnO nanowire arrays on transparent quartz glass substrate by chemical vapor deposition

ZnO nanowire arrays have been successfully synthesized on transparent quartz glass substrate by chemical vapor deposition technique. Our work demonstrates the critical role of the growth temperature and the buffer layer on the effective control of the morphology of ZnO nanowires. A proper growth temperature and the thicker buffer layer could promise the good alignment and high density of the nanowires. The room-temperature photoluminescence spectrum shows that the buffer layer has also great effects on optical properties of ZnO nanowire arrays. The integrated intensity ratio [I_UV/I_{Visible band}] of the ZnO UV emission peak to visible band emission decreases with the increase of the thickness of the buffer layers. The obtained nanowire arrays have transmittance of above 50% in the visible region.     

Growth mechanism studies of ZnO nanowire arrays via hydrothermal method

Well-controlled ZnO nanowire arrays have been synthesized using the hydrothermal method, a low temperature and low cost synthesis method. The process consists of two steps: the ZnO buffer layer deposition on the substrate by spin-coating and the growth of the ZnO nanowire array on the seed layer. We demonstrated that the microstructure and the morphology of the ZnO nanowire arrays can be significantly influenced by the main parameters of the hydrothermal method, such as pH value of the aqueous solution, growth time, and solution temperature during the ZnO nanowire growth. Scanning electron microscopy observations showed that the well oriented and homogeneous ZnO nanowire arrays can be obtained with the optimized synthesis parameters. Both x-ray diffraction spectra and high-resolution transmission electron microscopy (HRTEM) observations revealed a preferred orientation of ZnO nanowires toward the c-axis of the hexagonal Wurtzite structure, and HRTEM images also showed an excellent monocrystallinity of the as-grown ZnO nanowires. For a deposition temperature of 90 °C, two growth stages have been identified during the growth process with the rates of 10 and 3 nm/min, respectively, at the beginning and the end of the nanowire growth. The ZnO nanowires obtained with the optimized growth parameters owning a high aspect ratio about 20. We noticed that the starting temperature of seed layer can seriously influence the nanowire growth morphology; two possible growth mechanisms have been proposed for the seed layer dipped in the solution at room temperature and at a high temperature, respectively.     

Control of ZnO nanowire arrays by nanosphere lithography (NSL) on laser-produced ZnO substrates

Nanosphere lithography (NSL) is a successful technique for fabricating highly ordered arrays of ZnO nanowires typically on sapphire and GaN substrates. In this work, we investigate the use of thin ZnO films deposited on Si by pulsed laser deposition (PLD) as the substrate. This has a number of advantages over the alternatives above, including cost and potential scalability of production and it removes any issue of inadvertent n-type doping of nanowires by diffusion from the substrate. We demonstrate ordered arrays of ZnO nanowires, on ZnO-coated substrates by PLD, using a conventional NSL technique with gold as the catalyst. The nanowires were produced by vapor phase transport (VPT) growth in a tube furnace system and grew only on the areas pre-patterned by Au. We have also investigated the growth of ZnO nanowires using ZnO catalyst points deposited by PLD through an NSL mask on a bare silicon substrate.     

表面修饰ZnO纳米线紫外光响应的增强效应

制备了基于单根ZnO纳米线的紫外光探测原型器件,并研究了聚苯乙烯硫酸钠表面修饰对器件紫外响应特性的影响.研究发现,在相同的紫外光照射条件下,表面修饰后的器件对紫外光的探测灵敏度比修饰前提高了3个数量级.I-V特性研究表明,修饰前后器件在光照时的电导没有明显变化,但修饰后器件的暗电导却下降了3个数量级.这说明通过表面修饰降低探测器的暗电导是提高紫外光探测器灵敏度的一条重要途径. 关键词： 紫外光探测器 纳米结构 ZnO 表面修饰     

单根砷掺杂氧化锌纳米线场效应晶体管的电学及光学特性

采用化学气相沉积（CVD）的方法在砷化镓基底上合成直径为20 nm左右、长约数十微米的氧化锌纳米线,然后采用热扩散的方法,将生长于砷化镓基底之上的氧化锌纳米线通过600 ℃,30 min的有氧退火处理后,获得了砷掺杂的氧化锌纳米线.将获得的掺杂后的氧化锌纳米线采用电子束曝光以及真空溅射镀膜的方法将钛/金合金作为接触电极引出,从而构建成场效应晶体管.文中研究了单根氧化锌纳米线砷掺杂前后的电学特性,证实了通过砷掺杂来获得p型的氧化锌纳米线的可行性.构建的p型砷掺杂氧化锌场效应晶体管的跨导为35 nA/V,载流 关键词： p型ZnO纳米线 砷掺杂 场效应晶体管 光致发光