Effect of textured seeds on the morphology and optical properties of solution- and vapor-grown ZnO nanorod arrays

This paper examines the growth of aligned ZnO nanorod arrays through chemical deposition from solution and the vapor phase. The nanorod alignment is ensured primarily by a thin layer of seeds—zinc oxide nanoparticles produced by decomposing zinc acetate directly on the substrate and aligned with their c axes normal to the substrate surface. The acetate route was used to produce nanorod arrays 1 × 1 mm in dimensions on substrates with photoresist.     

水热法制备掺铝氧化锌纳米棒阵列及其光学特性

采用水热法,在ZnO种子层上制备出不同Al掺杂量的ZnO纳米棒阵列薄膜,利用XRD、SEM、TEM、PL等检测手段对样品进行结构、形貌和发光性能分析.结果表明,纳米棒属于六方纤锌矿结构,具有垂直基底沿[002]方向生长的特征,PL谱上存在强的近紫外辐射峰.随着掺杂量的增加,纳米棒直径略有减小,近紫外辐射峰蓝移,强度先增加后减小,证明掺杂会形成非辐射中心,探讨了Al掺杂ZnO纳米棒阵列的发光机理.     

Effect of AZO seed layer on electrochemical growth and optical properties of ZnO nanorod arrays on ITO glass

We report the structural and optical properties of ZnO nanorod arrays (NRAs) grown by an electrochemical deposition process. The ZnO NRAs were grown on indium tin oxide (ITO) coated glass substrates with a thin sputtered Al-doped ZnO (AZO) seed layer and compared with ones directly grown without the seed layer. The growth condition dependence of ZnO NRAs was investigated for various synthetic parameters. The morphology and density of the ZnO NRAs were accordingly controlled by means of zinc nitrate concentration and growth time. From photoluminescence results, the ultraviolet emission was significantly enhanced after thermal treatment. For ZnO NRAs grown on ITO glass without the seed layer, the diffuse transmittance was enhanced despite the reduction in the total transmittance, indicating a high haze value. By using a thin AZO seed layer, the well-aligned ZnO NRAs on AZO/ITO glass are controllably and reproducibly synthesized by varying the growth parameters, exhibiting a total transmittance higher than 91% in the visible wavelength range as well as good optical and crystal quality.     

Effect of Sn doping on structural, optical, electrical and wettability properties of oriented ZnO nanorod arrays

Herein we present a modified sol gel route for the one step fabrication of oriented ZnO nanorod arrays. The method is seed layer free, and nanorods directly attach to a substrate. We also present the effect of tin (Sn) content on the crystallinity, microstructural, optical and electrical properties of the ZnO nanorod arrays. Thermo gravimetric (TG) curves of gel precursors showed that most of the organic groups and other volatiles were removed at about 450 °C. X-ray diffraction patterns confirmed that the films were polycrystalline in nature with (002) preferred orientation. The texture coefficient, grain size, dislocation density and lattice parameters of the ZnO arrays were determined. The SEM micrographs revealed that the undoped and 1 at.%Sn doped films were composed of nanorods and the concentration of 2 at.%Sn doping hindered the rod like structure growth and modulated into granular nature. UV-visible transmission spectroscopy indicated that the transparency of the films increased with Sn content. On Sn doping, the films also exhibited a red shift and slight shrinkage of band gap. The electrical studies revealed that 1 at.% of Sn doping enhanced electrical conduction in ZnO films and beyond that the distortion caused in the lattice reduced the conductivity. The contact angle of the ZnO nanostructures varied between 91° and 115° depending upon the Sn content. Therefore, 1 at.%Sn doping into ZnO nanorods improves the crystallinity, electrical conductivity and water contact angle.     

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.     

Effect of pulsed electromagnetic field on growth and structure properties of ZnO nanorod arrays

Well-aligned ZnO nanorod arrays had been prepared by hydrothermal methods assisted with pulsed electromagnetic field (PEMF). The effects of pulsed electromagnetic field on growth and structure properties of ZnO nanorod arrays were studied in detail. XRD and SEM analysis showed ZnO nanorod arrays had bigger length to diameter ratio and better verticality on the substrate. And the Raman analysis showed well-aligned ZnO nanorod arrays have highly crystallized wurtzite structure with much fewer defects after a pulsed electromagnetic field was introduced. At last, a possible mechanism of pulsed electromagnetic field acted on nanorod arrays was proposed.     

Optical and electrical properties of Ga-doped ZnO nanorod arrays fabricated by thermal evaporation

Well-aligned Ga-doped ZnO nanorod arrays with high optical and electrical property were fabricated by catalyst-free thermal evaporation on p-silicon substrate. As the Ga/Zn atom ratio in the source material was tuned from 0 to 0.2, wurtzite structure ZnO nanorod arrays were realized with length of -6 microm and growth direction along c-axis. With the addition of Ga, the intensity of the near-band-edge emission was enhanced and the deep-level emissions maintained neglectable. As the Ga/Zn atom ratio increased from 0 to 0.1, the red shift of the near-band-edge emission occurred due to Ga-doping induced band gap renormalization effect related with the enhancement of the carrier density, while the blue shifts of the emission were found once the Ga/Zn ratio is higher than 0.1 resulting from Burstein-Moss effect. The configuration of the vertical-aligned Ga-doped ZnO nanorod arrays on p-Si substrate makes it straightforward for the fabrication of p-n nanodiode, which shows an excellent rectifying characteristic with threshold voltage as low as -4.7 V with the Ga/Zn atomic ratio of 0.2.     

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.     

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.     

ZnO纳米棒阵列、纳米片及其发光和光催化特性

首先通过溶胶-凝胶法在Si片基底上制备1层ZnO纳米薄膜,作为纳米棒的晶种层,然后利用金属浴沉积法在ZnO纳米薄膜基础上制备择优取向的ZnO纳米棒阵列,最后通过水热法二次成核结晶形成纳米片。研究证明,ZnO纳米棒阵列和纳米片均沿着c轴取向。在Cu2+抑制极性面生长的作用下,形成的ZnO纳米片结构均匀,分布面积广,单片ZnO纳米片的厚度约为8 nm,面积呈平方微米级,较大的有40μm2左右。ZnO纳米结构的生长取向对其物理化学性能具有重要影响。高度沿c轴取向的ZnO纳米棒有利于紫外光发射和激光器的发展,但极性面的缩小不利于光催化反应。     

Influence of ZnO nanorod morphology on optical confinement--finite-difference time-domain numerical simulation study

We studied the influence of nanorod (NR) morphology on the optical confinement. In order to understand the optical field confinement by the ZnO NR, we obtained the spatial intensity distribution inside/outside the NR by solving Maxwell equations using the finite-difference time-domain numerical simulation. The hexagonal cylinder-shaped NR exhibits a strong confinement and the circular cylinder-shaped NR shows also similar confinement effect. Meanwhile, the rectangular cylinder-shaped NR, the tapered NR, and the NR with sharp cone show a weak confinement of optical field as compared to that of the hexagonal cylinder-shaped NR. Next, as the rod length and/or the rod diameter increase, the high intensity region increases. This suggests that longer nanorod will exhibit more efficient lasing action.     

The structural and optical properties of ZnO nanowire arrays prepared by hydrothermal synthesis method

ZnO nanowire arrays have been grown on the ZnO film-coated silicon (100) substrates by hydrothermal method, and the deposited nanowires are found to have a uniform size distribution with sharp hexagonal-shaped tips. The structural and optical properties of the nanowires were investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cathodoluminescence (CL) techniques. The XRD and SEM results demonstrate that the well-aligned ZnO nanowires are single crystalline structure formed along the c-axis orientation. TEM analysis further confirms that the ZnO nanowires are highly preferred grown along the (002) crystal plane. The spacing between adjacent (002) lattice planes is estimated as 0.52 nm. The optical properties of the nanowires were measured using CL after annealing in oxygen and nitrogen atmospheres at 550 °C for various times. The CL spectra in the visible spectrum exhibit two weak deep-level emission bands that may be attributed to the intrinsic or extrinsic defects. It can be observed that the ZnO nanowires show different optical behaviors after various annealing times. The dependence of the optical properties on the annealing conditions is also discussed.     

Fabrication of free-standing Cu nanorod arrays on Cu disc by template-assisted electrodeposition

Free-standing Cu nanorod arrays on Cu foil have been fabricated by a template-assisted method. Cu nanorods were potentiostatically deposited on mechanically polished Cu foil using anodized aluminum oxide templates as the deposition mask. Three electrolyte systems were compared, including two acid copper sulfate based solutions and one alkaline solution. The most uniform nanorods were achieved in the alkaline electrolyte. The weight gain per unit area after electrodeposition has been used as a direct measure of average length of deposited Cu nanorods. It was found that our control over the uniformity in nanorod length across the array is important in reaching the maximized aspect ratio without aggregation. Through controlling the weight change it was possible to control the aspect ratio of nanorods and to avoid aggregation of nanorods. Our capability to fabricate free-standing Cu nanorod arrays of uniform height with maximized aspect ratio on Cu foil is especially important in applying this nanostructured Cu as a current collector in Li ion batteries.     

Effect of phosphorus incorporation on morphology and optical properties of ZnO nanorods

Phosphorus-doped ZnO nanorods have been prepared on Si substrates by thermal evaporation process without any catalyst. X-ray photoelectron spectroscopy and Raman spectra indicate that phosphorus entering into ZnO nanorods mainly occupies Zn site rather than O one. The introduction of phosphorus leads to the morphological changes of nanorods from hexagonal tip to tapered one, which should be attributed to the relaxation of the lattice strain caused by phosphorus occupying Zn site along the radial direction. Transmission electron microscopy shows that phosphorus-doped ZnO nanorods still are single crystal and grow along [0 0 0 1] direction. The effect of phosphorous dopant on optical properties of ZnO nanorods also is studied by the temperature-dependent photoluminescence spectra, which indicates that the strong ultraviolet emission is connected with the phosphorus acceptor-related emissions.     

Study on the electron emission properties of ZnO nanorod arrays on different substrates

Large area well-aligned ZnO nanorod arrays on different substrates were synthesized by hydrothermal methods. The electron emission properties of the ZnO nanorod arrays on different substrates were investigated under both direct current (DC) and pulse electric fields. Owing to the excellent conductivity of substrates, the array on stainless steel substrate had better electron emission properties than that on silicon substrate. Under the DC and pulse electric fields, the electron emission of arrays had different production mechanisms which were pure field emission and plasma-induced emission respectively. During the plasma-induced emission, the plasma formed on the array surface, and the maximum emission current density of arrays on stainless steel was 118.87 A/cm2. The plasma-induced emission of ZnO nanorod arrays were always distributed uniformly. In this work, the results show that the ZnO nanorod arrays are expected to be applied to different electronic devices as electron beam sources under different electric fields.     

Effect of ZnO seed layer on the catalytic growth of vertically aligned ZnO nanorod arrays

We have grown vertically aligned ZnO nanorods and multipods by a seeded layer assisted vapor–liquid–solid (VLS) growth process using a muffle furnace. The effect of seed layer, substrate temperature and substrate material has been studied systematically for the growth of high quality aligned nanorods. The structural analysis on the aligned nanorods shows c-axis oriented aligned growth by homoepitaxy. High crystallinity and highly aligned ZnO nanorods are obtained for growth temperature of 850–900 °C. Depending on the thickness of the ZnO seed layer and local temperature on the substrate, some region of a substrate show ZnO tetrapod, hexapods and multipods, in addition to the vertically aligned nanorods. Raman scattering studies on the aligned nanorods show distinct mode at ∼438 cm⁻¹, confirming the hexagonal wurtzite phase of the nanorods. Room temperature photoluminescence studies show strong near band edge emission at ∼378 nm for aligned nanorods, while the non-aligned nanorods show only defect-emission band at ∼500 nm. ZnO nanorods grown without the seed layer were found to be non-aligned and are of much inferior quality. Possible growth mechanism for the seeded layer grown aligned nanorods is discussed.     

Structure and photoluminescence of S-doped ZnO nanorod arrays

Vertically aligned S-doped ZnO nanorod arrays have been successfully synthesized by hydrothermal method at 90 °C for 2 h. The obtained nanorod is ～ 70 nm in diameter and 1.2 μm in length. The XRD pattern and the Raman spectra indicate that the S-doped nanorod arrays are orientated at [001] and are single crystals with hexagonal wurtzite structure. The photoluminescence (PL) spectra show that S-doped ZnO nanorod arrays exhibit a relative weak ultraviolet (UV) emission, a violet emission and a strong green emission. The effects of S-doping on the structure and photoluminescence of ZnO nanorod arrays are discussed in detail.     

Zn/纳米棒阵列ZnO/聚噻吩复合电极的制备及光电化学性质

使用简单的水热法在锌片上生长ZnO纳米棒阵列,并用电化学共聚制备了ZnO纳米棒阵列与聚噻吩(Zn/ZnO/PTH)复合膜。通过X射线衍射(XRD)、扫描电子显微镜(SEM)等手段对ZnO的结构和形貌进行表征,XRD结果表明产物为六方纤锌矿型ZnO。SEM结果表明,在垂直锌片方向生长了包括纳米棒、纳米片、纳米线的表面光滑的ZnO纳米阵列,其中以纳米棒为主,其直径为30～100nm,长度1μm。用光电流作用谱、光电流-电势图研究了Zn/ZnO/PTH电极的光电转换性质。结果表明,PTH修饰ZnO/Zn电极可使光电流产生波长发生明显红移,使其光电转换效率提高了4倍,填充因子FF=33%,光电转换效率η=1.25%。     

Fabrication and characterization of Mg-doped ZnO nanorod arrays

Photoelectronic characteristics are investigated in well-aligned MgO-coated ZnO nanorods (MgO/ZnO nanocables) grown on Si substrates buffered with ZnO film at a low temperature by solution techniques. Transmission electron microscopy shows that a rough surface was observed for the MgO-coated ZnO nanorods due to deposition of MgO nanoparticles on the surface of the ZnO nanorods. However, after annealed at high temperatures, the surface of the MgO-coated ZnO nanorods was flattened to form Mg-doped ZnO nanorods. Photoluminescence spectra of Mg-doped ZnO nanorods displayed a blue shift of the near-band-edge emission with increasing annealing temperature indicative of an increase in the band gap of the MgZnO alloy due to diffusion of the Mg atoms into the ZnO nanorods. In contrast, no blue shift was detected for the samples annealed in H2/N2 (5%/95%) reduction atmosphere but a blue emission was detected at 800 degrees C, indicating that MgO diffusion process may produce a new luminescent center to emit the blue emission in H2/N2 reduction atmosphere.