Fabrication of highly oriented ZnO nanorod arrays by galvanostatic deposition

Highly oriented ZnO nanorod arrays were suecessfully prepared on the indium tin oxide (ITO) substrate using a galvanostatic electrodeposition method.The ITO substrate was pretreated with ZnO nanoparticles via simple low-temperature solution route.The crystallinity,microstructure of surface,and optical properties of the obtained ZnO were characterized by X-ray diffraction,scanning electron microscope,and transmittance spectrum.The results indicate that the average diameter of ZnO nanorod arrays is about 30 nm,and the narrow size distribution ranges from 20 to 50 nm The nanorod arrays are growing along [001] direction with an orientation perpendicular to the substrate.When the wavelength of incident is over 380 nm,the ZnO nanorod arrays show a high optical transmission of above 95%.Furthermore,the possible growth mechanism of the nanorod arrays was discussed.     

Pretreatment of glass substrates by Ar/O2 ion beams for the as-sputtered rough Al doped zinc oxide thin films

Textured TCO surfaces are required in silicon thin film solar cells to gain efficient light trapping. Nowadays, magnetron sputtered ZnO:Al films are usually etched in HCl solution to obtain textured surface. This study introduces a method to achieve as-grown rough ZnO:Al films by ion beam pretreatment of the glass substrate. The reference ZnO:Al films deposited on untreated glass are composed of well aligned columnar grains. In contrast, in the as-grown rough films, additional large conical grains are observed. The large grains exhibit faster growth rate than the surrounding columnar grains, and therefore overgrow the columnar grains gradually and finally cover the whole surface. In order to investigate the ZnO:Al film structural properties, transmission electron microscopy and X-ray diffraction are employed. The crystal orientations of these two types of grains are further analyzed by selected area diffraction patterns. The columns in the as-grown rough ZnO:Al are similarly textured as the reference ZnO:Al film on untreated glass. The c-axis is well aligned nearly perpendicular to the substrate surface, but a tilt of 10° was observed with respect to the growth direction. The large conical grains show no strong out of plane texture and random in plane orientation.     

Absorption-emission study of hydrothermally grown Al:ZnO nanostructures

The preparation, structural characterization and optical properties of aluminum doped ZnO (Al:ZnO) nanostructures grown under hydrothermal method are reported. One-dimensional (1-D) growth is achieved by the controlled addition of metal nitrate as precursors in the presence of long chain surfactant, poly-ethylene glycol (PEG) at 160 °C for 20 h. The as-synthesized ZnO rods are single crystalline, exhibiting an oriented growth along [001] direction. The Al6 rod has an aspect ratio of 3.2, which can be effectively applied in optoelectronic devices. Comprehensive structural analysis using X-ray diffraction method (XRD) and Energy dispersive X-ray analysis (EDX) indicate that the dopant Al atom occupies Zn sites in ZnO and the elemental composition of Al is consistent with the amount utilized in the hydrothermal synthesis. XRD shows that the Al:ZnO nanostructures from 1 to 9 atomic percent (at.%) has hexagonal wurtzite structure of ZnO. The Al dopant effects on lattice vibration and electronic transitions of the ZnO nanostructures have been investigated by Fourier transform Infrared spectroscopy (FT-IR), Ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) emission recorded at room temperature. The correlation existing between absorption and emission study tell that their characteristic band edge peak of doped ZnO shifts towards higher wavelength side for 3-9 at.% with respect to Al0 thus, exhibiting a red shift phenomenon with decrease in optical bandgap. The observed PL reveals two emission peaks centered at 374 nm and 530 nm. The near band edge (NBE) to defect emission ratio increases with dopant concentration indicating the linear enhancement in crystal quality and declination in zinc vacancies from 3 to 9 at.% of Al.     

Al diffusion in ZnO nanowalls investigated by atom probe tomography

Synthesis of ZnO nanowall structures using Ni catalyst was studied. ZnO nanowalls were grown by vapour-liquid-solid method. Ni as being a catalyst in the formation of ZnO nanowalls provided nucleation sites for the nucleation and the growth of ZnO nanowalls. Even though the sapphire system with ZnO has the high stability, the reactions between ZnO nanowalls and the sapphire substrate formed a 10-nm-thick interlayer during ZnO nanowall growth. Moreover, during the growth of the ZnO nanowalls, diffusion of Ni and Al was not expected as the Ni-Sapphire system is known to be non-reactive. Atom-probe tomography revealed that Al and Ni diffused into the NiO interface and sapphire substrate. Al diffused along the interface generated by the growth of ZnO nanowall, but Ni diffused into the interlayer between ZnO and sapphire.     

Site-specific synthesis of ZnO nanocrystalline networks via a hydrothermal method

ZnO nanocrystalline networks (NCNWs) consisting of percolating nanocrystals with irregular shape and size were synthesized using Al seed layers in a hydrothermal process. Various thicknesses of Al films were used to assess the effects of film thickness on the formation of ZnO NCNWs; the coverage and size of the ZnO nanocrystals increased with an increasing Al film thickness. In addition, by exploiting the seed layer-dependent crystal growth behaviors, two distinctly different ZnO nanostructures, nanorods on ZnO seed and NCNWs on Al seed, could be selectively achieved on the same substrate under the same growth conditions. Spectrally- and spatially-resolved investigations of these two ZnO nanostructures were performed using cathodoluminescence, which provided a significant opportunity to study the effect of the nanostructures on the luminescent characteristics. The ZnO NCNWs have an extremely high surface to volume ratio and sufficient inter-space, which enabled the conversion of the surface property from hydrophilic to superhydrophobic.     

简易种子调停法制备大小可调的三角形银纳米盘(英文)

通过柠檬酸钠还原银离子,以银纳米粒子为种子,在室温下制备出平均厚度约为5nm,尺寸40到500nm可调的三角形银纳米片。通过种子调停法可实现银纳米盘的面内偶极表面等离子体共振峰(SPR)从最初的520nm红移至1100nm。通过控制实验参数能够很好地理解其生长机制。柠檬酸根离子和增加到生长液里面的银纳米种子是2个重要的参数,可以控制银纳米盘的大小却不改变银纳米盘的厚度以及晶面结构。采用PVP作为包覆剂,其作用机理还不是很清楚,需要进一步的研究。     

电气石衬底温度对ZnO薄膜的结晶特征和光学特性的影响

利用超声雾化热解技术 (USP) 在不同温度的电气石和玻璃衬底上生长ZnO纳米片状薄膜。结构研究表明晶体为六方纤锌矿多晶结构。衬底温度越高,Raman特征峰越强,XRD结果给出（002）优势定向越明显,晶体结晶性能越好,晶粒尺寸越大。SEM图像显示片状ZnO晶体沿平行衬底方向叠加形成花状晶柱的微观形貌,沉积温度越高,晶柱宽度越大。UV-Vis表明电气石衬底上ZnO吸收峰强度高于玻璃衬底,最大吸收峰位置发生红移,高温下移动更大。     

还原剂与表面活性剂的覆盖效应在纳米片状银合成中的作用(英文)

研究还原剂与表面活性剂对于片状银形成的影响,考虑了两种弱还原剂:柠檬酸三钠、酒石酸钾,以及3种常用表面活性剂:聚乙烯吡咯烷酮、十二烷基磺酸钠、阿拉伯胶的影响。结果表明,以上弱还原剂与表面活性剂均具有可以与纳米银(111)面紧密结合的活性基团,从而产生覆盖效应阻止该晶面生长,最终达到形成片状银的目的。结果还显示,卤素离子的熟化作用在片状银生长过程中也存在一定的影响。     

Temperature effect on ZnO/Si thin film grown using metal organic chemical vapor deposition

We investigated the effect of deposition temperature on the growth and structural quality of ZnO films on Si (100) substrate using the metal organic chemical vapor deposition (MOCVD) technique. We revealed that highly c-axis oriented ZnO thin films were obtained at the temperature of 400°C. The film crystallinity improved and the surface smoothness decreased with increasing growth temperature.     

Interlayer growth at interfaces of Ti/Al–1%Mn,Ti/Al–4·6%Mg and Ti/pure Al friction weld joints by post-weld heat treatment

Abstract

The interlayer growth at interfaces of Ti/Al–1%Mn and Ti/Al–4·6%Mg weld joints was studied by postweld heat treatment. The heating temperatures ranged from 676 to 873 K (400–600°C) and maximum heating time was 360 ks (100 h). The basic mechanism of interlayer growth for pure Ti/pure Al friction weld joint was also estimated. The interlayer growth rate of Ti/Al–4·6%Mg joint was much faster than for the Ti/ Al–1%Mn joint. The interlayer mainly consisted of (Al,Si)₃Ti for the Ti/Al–1%Mn joint, and Al₁₈Mg₃Ti₂ for the Ti/Al–4·6%Mg joint. While the interlayer grew from Al alloy substrate to the Ti side for the Ti/Al–1%Mn joint, it grew from the Ti substrate to the Al alloy side for the Ti/Al–4·6%Mg joint. The interlayer growth stopped for several hours on heating for 36 ks (10 h). Neither linear nor parabolic time-dependence relations could be exactly fit to the interlayer growth rate for both joints. The interlayer growth of Ti/Al–1%Mn was proportional to heating time raised to approximately 0·85. The crystal direction of Al₃Ti interlayer growth of the Ti/Al joint was close to 〈001〉 and 〈111〉 directions obtained by OIM method. Nucleation and nuclei growth were observed at the interface of the Ti/Al joint. The nucleation and the nuclei growth are the reason for the phenomena (time dependence) described above.     

基片温度对Co掺杂ZnO薄膜室温铁磁性的影响

采用磁控共溅射法在Al2O3(0001)基片上沉积了Zn1-xCoxO(x=0.08～0.3%)薄膜,研究了基片温度对Co掺杂ZnO薄膜结构和磁性的影响.结果表明:Al2O3(001)基片很好地诱导了ZnCoO薄膜(002)取向生长,并且所有的薄膜均显示室温铁磁性.较低的基片温度不仅能有效抑制薄膜中Co2O3杂质相的产生,而且薄膜磁矩较大.紫外-可见光谱也表明,薄膜中Co2 取代了ZnO中Zn2 的位置.     

Growth and optical properties of ZnO nanorods prepared through hydrothermal growth followed by chemical vapor deposition

We report on the synthesis of high-quality ZnO nanorods by combining hydrothermal growth (HG) and chemical vapor deposition (CVD) processes. Vertically aligned and closely packed ZnO nanorods were grown by HG on a sputtered ZnO seed layer on a SiO₂/Si (0 0 1) substrate. The top surface of the HG-prepared ZnO nanorods showed very flat surfaces compared with that of the sputtered ZnO seed layer. Therefore, the HG-prepared ZnO nanorods were used as a new alternative seed material for the CVD growth of the ZnO nanorods. Vertical ZnO nanorods were grown by CVD on both the new HG-prepared nanorod seed material and the sputtered ZnO seed layer. The CVD-prepared ZnO nanorods on new HG-prepared nanorod seed material showed better crystalline quality and superior optical properties than the CVD-prepared ZnO nanorods on sputtered seed layer. The former showed negligible deep-level emissions at room temperature photoluminescence measurements. The intensity ratio of near-band-edge emissions to deep-level emissions from the former was about 910, but that from the latter was about 151. This implies that the HG-prepared ZnO nanorods can be used as a promising new seed material for nanostructure synthesis.     

Al/Ti液/固界面扩散溶解层形成机制及生长规律

采用镶嵌式扩散偶技术制备Al/Ti扩散偶,在Al熔点以上Ti熔点以下进行扩散热处理,研究Al/Ti液/固界面扩散溶解层的组织结构演变、形成机制及生长规律。实验结果表明,热处理后的扩散溶解层为TiAl3颗粒 和含少量Ti的铝基固溶体的混合组织;TiAl3相是热处理过程中最先出现也是唯一出现的新生相;扩散溶解层的生长机制和生长方向随热处理时间的延长发生了改变,在热处理开始后一段时间,扩散溶解层的生长受化学反应速度控制,与保温时间呈线性关系,之后,转变为受扩散控制,与保温时间呈抛物线关系,扩散溶解层的生长方向也由Ti基侧转变为Al基侧;扩散溶解层的厚度与热处理温度呈指数关系。     

Elaboration and characterization of Al doped ZnO nanorod thin films annealed in hydrogen

ZnO thin films doped with Al concentrations of 1.0, 2.0, 3.0, 4.0, 5.0 at% were prepared by a sol-gel spin-coating method on glass substrates and respectively annealed at 550 °C for 2 h in hydrogen and air. The X-ray diffraction and selected-area electron diffraction results confirm that the Al doped ZnO thin films are of wurtzite hexagonal ZnO. The scanning electron microscope results indicate that the Al doped ZnO nanorod thin films can be got by annealing in hydrogen rather than in air. The optical properties reveal that the Al doped ZnO thin films have obviously enhanced transmittance in the visible region. The electrical properties show that the resistivity of 1.0 at% Al doped ZnO thin films has been remarkably reduced from 0.73 Ω m by annealing in air to 3.2 × 10⁻⁵ Ω m by annealing in hydrogen. It is originated that the Al doped ZnO nanorod thin films annealed in hydrogen increased in electron concentration and mobility due to the elimination of adsorbed oxygen species, and multicoordinated hydrogen.     

Effects of pretreatment of substrates on the preparation of large scale ZnO nanotube arrays

Well-aligned hexagonal ZnO nanotubes (NTs) arrays were synthesized on pretreated indium fin oxide (ITO) substrates by a simple hydro-thermal method. The morphology and structure of the products were characterized by scanning electron microscopy (SEM) and X-my dif-fraction analysis (XRD). A new method of substrate pretreatment was introduced to prepare ZnO coated films. The size of ZnO seeds and the formation rote of ZnO NTs were investigated. Further, the mechanism of the preparation of ZnO NTs was discussed. The photoluminescence (PL) spectrum measurement shows fairly internal defects existing in ZnO nanotubes.     

The evolution behavior of structures and photoluminescence of K-doped ZnO thin films under different annealing temperatures

In this work, 1 at.% K-doped ZnO thin films were prepared by sol-gel method on Si substrates. The evolution behavior of the structures and photoluminescence of these films under different annealing temperatures was deeply studied. The crystal structures and surface morphology of the samples were analyzed by an X-ray diffractometer and an atomic force microscope, respectively. The photoluminescence spectra were used to study the luminescent behavior of the samples. The results showed that the films had a hexagonal wurtzite structure and were preferentially oriented along the c-axis perpendicular to the substrate surface. All the samples showed a strong ultraviolet emission and a weak blue emission. With the increase of annealing temperature, the ZnO grains gradually grew up; at the same time, the blue emission gradually decreased. The sample annealed at 500 °C showed the best crystalline quality and strongest ultraviolet emission. The authors think that the blue emission in these samples is mainly connected with K interstitial defects. When the 1 at.% K-doped ZnO thin film is annealed at high temperatures (≥600 °C), most of K interstitials move into ZnO lattice sites replacing Zn. As a result, the blue emission resulting from K interstitial defects also decreased.     

Conductivity enhancement in transparetn ZnO films via Al-dopping produced by CW-CO2 laser-induced evaporation

Highly conductive transparent aluminium-doped ZnO (ZnO:A1) films were successfully deposited by CW-CO₂ laser-induced evaporation. Optimisation of evaporation parameters was based on laser power, substrate temperature, O₂ partial pressure in the vacuum chamber and amount of Al in the ZnO source pellet. ZnO:A1 films with an electrical resistivity as low as 6.6 × 10⁻²Ω·cm and an optical transmission of 80% at 500nm were obtained at laser power of 15 W, substrate temperature of about 200°C, O₂ partial pressure of 6—7 × 10⁻⁴ Torr and 5wt.% Al. Conductivity of ZnO films can be increased one order via Al-doping in ZnO films. The films obtained by laser-induced evaporation have compared quite favorably with the high quality films obtained by sputtering.     

Catalyst-free synthesis of ZnO microrod arrays on SiC substrate and their tunable photoluminescence by erosion process

We present here the results on the preparation and characterization of highly oriented ZnO microrods fabricated on SiC substrate via a vapor solid route. These ZnO microrods grow along the c-axis perpendicularly to the substrate and are well separated from each other. Photoluminescence (PL) due to the band-gap emission (centered at 380 nm) and defect-related deep band emission (centered at 530 nm) were observed. Tunable PL intensities of these two bands were achieved by acid etching for varying durations.     

Relationship between the growth rate and Al incorporation of AlGaN by metalorganic chemical vapor deposition

The growth rate and its relationship with growth conditions of AlGaN alloy films by metalorganic chemical vapor deposition (MOCVD) are investigated. It is found that both parasitic reaction and competitive adsorption play important roles in determining the growth rate and Al incorporation in AlGaN. Low reactor pressure can weaken parasitic reactions, thus increasing the Al composition. In addition, a decrease of absolute amount of Ga atoms arriving on the substrate may lead to a lower Ga competitive power, and then a higher Al content in AlGaN film.     

ZnO nanocoral reef grown on porous silicon substrates without catalyst

Porous silicon (PS) technology is utilized to grow coral reef-like ZnO nanostructures on the surface of Si substrates with rough morphology. Flower-like aligned ZnO nanorods are also fabricated directly onto the silicon substrates through zinc powder evaporation using a simple thermal evaporation method without a catalyst for comparison. The characteristics of these nanostructures are investigated using field-emission scanning electron microscopy, grazing-angle X-ray diffraction (XRD), and photoluminescence (PL) measurements of structures grown on both Si and porous Si substrates. The texture coefficient obtained from the XRD spectra indicates that the coral reef-like nanostructures are highly oriented on the porous silicon substrate with decreasing nanorods length and diameter from 800-900 nm to 3.5-5.5 μm and from 217-229 nm to 0.6-0.7 μm, respectively. The PL spectra show that for ZnO nanocoral reefs the UV emission shifts slightly towards lower frequency and the intensity increase with the improvement of ZnO crystallization. This non-catalyst growth technique on the rough surface of substrates may have potential applications in the fabrication of nanoelectronic and nanooptical devices.