Photovoltaic device on a single ZnO nanowire p-n homojunction

A photovoltaic device was successfully grown solely based on the single ZnO p-n homojunction nanowire. The ZnO nanowire p-n diode consists of an as-grown n-type segment and an in situ arsenic-doped p-type segment. This p-n homojunction acts as a good photovoltaic cell, producing a photocurrent almost 45 times larger than the dark current under reverse-biased conditions. Our results demonstrate that the present ZnO p-n homojunction nanowire can be used as a self-powered ultraviolet photodetector as well as a photovoltaic cell, which can also be used as an ultralow electrical power source for nanoscale electronic, optoelectronic and medical devices.     

Fast switching electrochromic display using a viologen-modified ZnO nanowire array electrode

We report an electrochromic (EC) display using a viologen-modified ZnO nanowire array as the EC electrode. The ZnO nanowire array was grown directly on an indium tin oxide (ITO) glass by a low temperature aqueous thermal decomposition method and then modified with viologen molecules. The ZnO nanowire electrochromic device shows fast switching time (170 and 142 ms for coloration and bleaching respectively for a 1 cm (2) cell), high coloration efficiency (196 C (-1) cm (2)) and good stability. The improved performance of the ZnO nanowires EC device can be attributed to the large surface area and high crystalline and good electron transport properties of the ZnO nanowire array.     

Near UV LEDs made with in situ doped p-n homojunction ZnO nanowire arrays

Catalyst-free p-n homojunction ZnO nanowire (NW) arrays in which the phosphorus (P) and zinc (Zn) served as p- and n-type dopants, respectively, have been synthesized for the first time by a controlled in situ doping process for fabricating efficient ultraviolet light-emitting devices. The doping transition region defined as the width for P atoms gradually occupying Zn sites along the growth direction can be narrowed down to sub-50 nm. The cathodoluminescence emission peak at 340 nm emitted from n-type ZnO:Zn NW arrays is likely due to the Burstein-Moss effect in the high electron carrier concentration regime. Further, the electroluminescence spectra from the p-n ZnO NW arrays distinctively exhibit the short-wavelength emission at 342 nm and the blue shift from 342 to 325 nm is observed as the operating voltage further increasing. The ZnO NW p-n homojunctions comprising p-type segment with high electron concentration are promising building blocks for short-wavelength lighting device and photoelectronics.     

Tunable electronic transport characteristics of surface-architecture-controlled ZnO nanowire field effect transistors

Surface-architecture-controlled ZnO nanowires were grown using a vapor transport method on various ZnO buffer film coated c-plane sapphire substrates with or without Au catalysts. The ZnO nanowires that were grown showed two different types of geometric properties: corrugated ZnO nanowires having a relatively smaller diameter and a strong deep-level emission photoluminescence (PL) peak and smooth ZnO nanowires having a relatively larger diameter and a weak deep-level emission PL peak. The surface morphology and size-dependent tunable electronic transport properties of the ZnO nanowires were characterized using a nanowire field effect transistor (FET) device structure. The FETs made from smooth ZnO nanowires with a larger diameter exhibited negative threshold voltages, indicating n-channel depletion-mode behavior, whereas those made from corrugated ZnO nanowires with a smaller diameter had positive threshold voltages, indicating n-channel enhancement-mode behavior.     

The growth and characterization of ZnO/ZnTe core-shell nanowires and the electrical properties of ZnO/ZnTe core-shell nanowire field effect transistor

Vertically aligned ZnO/ZnTe core-shell nanowires were grown on a-plane sapphire substrate by using chemical vapor deposition with gold as catalyst for the growth of ZnO core and then followed by growing ZnTe shell using metal-organic chemical vapor deposition (MOCVD). Transmission electron microscope (TEM) and Raman scattering indicate that the core-shell nanostructures have good crystalline quality. Three-dimensional fluorescence images obtained by using laser scanning confocal microscope demonstrate that the nanowires have good optical properties. The core-shell nanowire was then fabricated into single nanowire field effect transistor by standard e-beam photolithography. Electrical measurements reveals that the p-type ZnO/ZnTe FET device has a turn on voltage of -1.65 V and the hole mobility is 13.3 cm2/V s.     

Fabrication and characterization of directly-assembled ZnO nanowire field effect transistors with polymer gate dielectrics

We report the fabrication and electrical characterization of ZnO nanowire field effect transistors (FETs). Dielectrophoresis technique was used to directly align ZnO nanowires between lithographically prepatterned source and drain electrodes, and spin-coated polyvinylphenol (PVP) polymer thin layer was used as a gate dielectric layer in "top-gate" FET device configuration. The electrical characteristics of the top-gate ZnO nanowire FETs were found to be comparable to the conventional "bottom-gate" nanowire FETs with a SiO2 gate dielectric layer, suggesting the directly-assembled nanowire FET with a polymer gate dielectric layer is a useful device structure of nanowire FETs.     

ZnO纳米线阵列修饰对材料表面浸润性调控

采用溶胶-凝胶法制备了ZnO薄膜,利用溶剂热沉积法获得大面积均匀ZnO纳米线阵列。通过对水在ZnO材料表面的浸润性研究,发现薄膜材料表面的粗糙度对ZnO膜亲水性有增强作用,而周期性ZnO阵列微结构表面可以实现其疏水性质增强效果。同时从理论上分析了这两种现象的物理机制,讨论了空气填隙对ZnO纳米线阵列表面的浸润性质的敏感性。制备出ZnO纳米线阵列的表观接触角约为103°,具有较强的疏水性质,可为进一步的ZnO光流控研究提供实验基础。     

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.     

Nano-X-ray absorption spectroscopy of single Co-implanted ZnO nanowires

We report on the local structure of single Co-implanted ZnO nanowires studied using a hard X-ray nanoprobe. X-ray fluorescence maps show uniform Zn and Co distributions along the wire within the length scale of the beam size. The X-ray fluorescence data allow the estimation of the Co content within the nanowire. Polarization dependent X-ray absorption near edge structure shows no structural disorder induced neither in the radial nor axial directions of the implanted nanowires after subsequent annealing. Co2+ ions occupy Zn sites into the wurtzite ZnO lattice. Extended X-ray absorption fine structure data reveal high structural order in the host lattice without distortion in their interatomic distances, confirming the recovery of the radiation damaged ZnO structure through thermal annealing.     

ZnO纳米线的制备及场发射特性的研究进展

从ZnO纳米线的生长机制出发,重点讨论了催化剂在制备过程中的作用,比较了采用VLS和VS不同机制生长ZnO纳米线的优缺点,并结合二者特点发现采用金属自催化将是制备高质量ZnO纳米线阵列的一种有效方法.分析了几种有利于提高其场发射性能的后处理方法,经过适当的后处理ZnO纳米线晶体的结构将更加完善,场发射开启场、阈值场将进一步降低,电流密度和场增强因子也将随之大大提高.     

Highly sensitive ZnO nanowire CO sensors with the adsorption of Au nanoparticles

In this study, the growth of high density single-crystalline ZnO nanowires on patterned ZnO:Ga/SiO(2)/Si templates was reported. We also adsorbed Au nanoparticles onto nanowire surfaces and fabricated ZnO nanowire CO sensors. With 50?ppm CO gas, it was found that we could enhance the device sensitivities at 350?°C from 4.2% to 46.5% by the adsorption of Au nanoparticles. It was also found that measured sensitivities were around 30%, 37%, 46.5% and 53% when concentration of the injected CO gas was 5, 20, 50 and 100?ppm, respectively.     

Crabwise ZnO nanowires: growth and field emission properties

Crabwise ZnO nanowires with an average length of 5 microm and an average diameter of 30 nm were selectively grown on ZnO:Ga/glass templates. Cathodoluminescence measurement indicated that the crystal quality of the crabwise ZnO nanowires was good. With an applied voltage of 120 V, the crabwise ZnO nanowire field emitters gave an emission current of 0.1 mA/cm2. Moreover, the field enhancement factor, beta, of the crabwise ZnO nanowires was approximately 980.     

Noise Characteristics of ZnO-Nanowire Photodetectors Prepared on ZnO:Ga/Glass Templates

In this paper, we report the fabrication of vertically well-aligned ZnO nanowire ultraviolet (UV) photodetectors on ZnO:Ga/glass templates. With 1 V applied bias, it was found that dark current density of the device was only 1.37times10^-7 A/cm². It was also found that UV-to-visible rejection ratio of the fabricated photodetector was around 1000 with a maximum quantum efficiency of 12.6%. It was also found that noise equivalent power and normalized detectivity of the ZnO nanowire photodetector were 5.73times10^-11 W and 6.17times10⁹ cmHz^0.5W^-1, respectively.     

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。     

Strain modulation on graphene/ZnO nanowire mixed-dimensional van der Waals heterostructure for high-performance photosensor

The mixed-dimensional van der Waals (vdW) heterostructure is a promising building block for strained electronics and optoelectronics because it avoids the bond fracture and atomic reconstruction under strain.We propose a novel mixed-dimensional vdW heterostructure between two-dimensional graphene and a one-dimensional ZnO nanowire for high-performance photosensing.By utilizing the piezoelectric properties of ZnO,strain modulation was accomplished in the mixed-dimensional vdW heterostructure to optimize the device performance.By combining the ultrahigh electrons transfer speed in graphene and the extremely long life time of holes in ZnO,an outstanding responsivity of 1.87 × 105 A/W was achieved.Under a tensile strain of only 0.44％ on the ZnO nanowire,the responsivity was enhanced by 26％.A competitive model was proposed,in which the performance enhancement is due to the efficient promotion of the injection of photogenerated electrons from the ZnO into the graphene caused by the strain-induced positive piezopotential.Our study provides a strain-engineering strategy for controlling the behavior of the photocarriers in the mixed-dimensional vdW heterostructure,which can be also applied to other similar systems in the future.     

Synthesis and characterization of ZnO nanowires for nanosensor applications

In this paper we report the synthesis of ZnO nanowires via chemical vapor deposition (CVD) at 650 °C. It will be shown that these nanowires are suitable for sensing applications. ZnO nanowires were grown with diameters ranging from 50 to 200 nm depending on the substrate position in a CVD synthesis reactor and the growth regimes. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Raman spectroscopy (RS) have been used to characterize the ZnO nanowires. To investigate the suitability of the CVD synthesized ZnO nanowires for gas sensing applications, a single ZnO nanowire device (50 nm in diameter) was fabricated using a focused ion beam (FIB). The response to H₂ of a gas nanosensor based on an individual ZnO nanowire is also reported.     

超声喷雾热解法生长氧化锌同质p-n结及其电致发光性能研究

采用超声喷雾热解法在单晶GaAs(100) 衬底上生长ZnO同质p-n结. 以醋酸锌水溶液为前驱体, 分别以醋酸铵和硝酸铟为氮(N)源和铟(In)源, 通过氮--铟(N-In)共掺杂沉积p型ZnO薄膜, 以未故意掺杂的ZnO薄膜做为n型层获得ZnO基同质p-n结. 采用热蒸发工艺在ZnO层和GaAs衬底上分别蒸镀Zn/Au和Au/Ge/Ni电极而获得发光二极管原型器件, 在室温下发现了该器件正向电流注入下的连续发光现象.     

Room temperature electroluminescence from arsenic doped p-type ZnO nanowires/n-ZnO thin film homojunction light-emitting diode

The highly arrayed arsenic doped p-ZnO nanowires/n-ZnO thin film homojunction light-emitting diode was fabricated on semi-insulated Si substrate. The homojunction was consisted of high-quality n-ZnO thin film grown by metal–organic chemical vapor deposition technology following arsenic doped ZnO nanowires grown by chemical vapor deposition. The device shows good rectification characteristic with a turn-on voltage of ~4.8 V and reverse breakdown voltage of ~18 V. Moreover, two distinct electroluminescence bands centered at 2.35 and 3.18 eV are detected from this device under forward bias at room temperature.     

Facile route to well-aligned ZnO nanowire arrays

Well-aligned ZnO nanowire arrays were fabricated on the photoresist SPR6112-B coated (111) Si substrates by a facile vapor transport and condensation method. The structure and growth mechanism of the ZnO nanowire arrays were investigated in detail. It is found that the immiscibility of the zinc oxide-carbon system is responsible for the self-catalysis vapor-liquid-solid (VLS) growth of nanowire arrays. The photoluminescence measurement only presents a strong near-band-edge ultraviolet (UV) emission band centered at 379.6 nm (3.266 eV), exhibiting that the nanowire arrays are of stoichiometric composition and have good optical performance.     

Capillary-driven assembly of ZnO nanowire arrays into micropatterns

The vertically aligned ZnO nanowire arrays prepared by vapor transport process can be assembled into complex micropatterns under capillary force. The deflection of the flexible ceramic nanowire is closely related to the liquid tension coefficient, mechanical and structural properties of the ZnO nanowires. The bended nanowires are adhesive together because the solid adhesion energy is sufficient to withstand the restoring elastic force of the deformed nanowires. The size of the bundling pattern can be controlled by varying the aspect ratio of the nanowire. The deflection of the ZnO nanostructure composed of a nanowire and a base is multifarious.