Effect of chromium interlayer deposition on periodic silver nanoparticle array structure fabricated by nanosphere lithography

Effect of chromium interlayer deposition on 2-dimensional, periodic silver nanoparticle array structure was systematically investigated. The silver nanoparticle array was fabricated by nanosphere lithography with assembled polystyrene nanospheres being as a deposition mask. The chromium interlayer was deposited by thermal evaporation either on the nanosphere mask or directly on the silicon substrate. The structures of the achieved silver nanoparticle arrays were characterized by scanning electron microscope and were compared with that of silver nanoparticle array without the interlayer. With analysis of the anomalies among the structures the critical role of the interlayer in the periodic nanoparticle array fabrication was revealed.     

Morphology control and electron field emission properties of high-ordered Si nanoarrays fabricated by modified nanosphere lithography

High-ordered silicon nanoarrays were prepared using direct nanosphere lithography combined with thermal oxidation. Atomic force microscope (AFM) images of the silicon arrays show that the patterns of polystyrene (PS) template are well transferred to the silicon surface. The size and morphology of the nanoarrays can be controlled effectively by varying the plasma-therm reactive ion etching (RIE) or thermal oxidation parameters. The field emission studies revealed that the typical turn-on field was about 7-8 V/μm with emission current reached 1 μA/cm². It is also found that the field emission current is highly dependent on the morphology of these Si nanoarrays.     

花状纳米金结构阵列的工艺制备与拉曼增强研究

基于纳米球光刻技术制备了一种花状纳米金结构阵列,经过PS509 nm球旋凃和ICP氧刻蚀,再通过镀金膜与高温退火工艺,纳米球阵列的表面被粗糙化,进而形成了一种鳞状的花状阵列 。FDTD仿真结果表明,制备的这种阵列具备很高的电磁场增强特性,主要的增强集中于纳间隙的边缘处。以罗丹明 6G染料为探针分子测试基底的拉曼效应,与金基底的拉曼信号相比,该纳米结构阵列拉曼增强效应明显,对罗丹明 6G的检测极限达到了10-6 mol/L的水平。     

Aqueous phase Ag nanoparticles with controlled shapes fabricated by a modified nanosphere lithography and their optical properties

We have developed a modified nanosphere lithography (NSL) process to fabricate surface-confined Ag nanoparticles (NPs) with controlled shapes. NPs with different shapes, such as triangular, quadrilateral, pentagon or trapezoidal with rounded tips or edges, can be fabricated by this process. These Ag NPs can be dislodged into water forming NPs in an aqueous environment. The developed process results in better NP shape retaining than those obtained using the routine NSL process. The UV-vis absorption of the surface-confined Ag NPs show distinct blue shift and reduced intensity after surface modification. The NPs produced by the modified NSL and dislodged in water have significantly less density of debris as observed by transmission electron microscopy and UV-vis absorption spectrum.     

纳米球刻蚀法制备的二维有序的CdS纳米阵列及其光学性质的研究

采用纳米球刻蚀(nanosphere lithography)技术,以自组装的聚苯乙烯纳米小球(polystyrene,PS小球)的单层膜为掩模,制备出二维有序的CdS纳米阵列.利用扫描电子显微镜(SEM)对样品结构进行了表征,用紫外—可见分光光度计对样品光学性质进行了分析.结果表明：制备的二维CdS纳米阵列是高度有序的,且与作为掩模的纳米小球的原始尺寸及排布结构一致;禁带宽度为2.60eV,相对于体材料的2.42eV,向短波长蓝移了0.18eV,表现出CdS材料在纳米结构点阵中的量子尺寸效应;CdS纳米 关键词： 纳米球刻蚀 二维CdS纳米有序阵列     

Vertically integrated nanogenerator based on ZnO nanowire arrays

We report a technique to construct a vertically integrated nanogenerator (VI‐NG) based on ZnO nanowire (NW) arrays. The VI‐NG consists of nine single NGs connected mixed parallel and serial by a layer‐by‐layer stacking. For the single layer NG, the peak output voltage and current are 0.045 V and 2.5 nA, respectively. The VI‐NG produces an output power density of 2.8 nW/cm² with a peak output voltage of 0.15 V and output current of 7.2 nA. The vertical integration of the multi‐NG provides a feasible technique for effectively converting mechanical energies to electricity from environment. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fabrication of large-scale periodic silicon nanopillar arrays for 2D nanomold using modified nanosphere lithography

We present a fabrication procedure that can form large-scale periodic silicon nanopillar arrays for 2D nanomold which determines the feature size of nanoimprint lithography, using modified nanosphere lithography. The size of silicon nanopillars can be easily controlled by an etching and oxidation process. The period and density of nanopillar arrays are determined by the initial diameter of polystyrene (PS) spheres. In our experiment, the smallest nanopillar has a full width half maximum (FWHM) of approximately 50 nm, and the density of silicon pillar is ∼10⁹/cm². Using this approach, it is possible to fabricate 2D nanoimprint lithography mask with 50 nm resolution.     

Room-temperature deposition of crystalline patterned ZnO films by confined dewetting lithography

In this work patterned ZnO films were prepared at room-temperature by deposition of ∼5 nm size ZnO nanoparticles using confined dewetting lithography, a process which induces their assembly, by drying a drop of ZnO colloidal dispersion between a floating template and the substrate. Crystalline ZnO nanoparticles exhibit a strong visible (525 nm) light emission upon UV excitation (λ = 350 nm). The resulting films were characterized by scanning electron microscopy (SEM) and atomic force microscope (AFM). The method described herein presents a simple and low cost method to prepare crystalline ZnO films with geometric patterns without additional annealing. Such transparent conducting films are attractive for applications like light emitting diodes (LEDs). As the process is carried out at room temperature, the patterned crystalline ZnO films can even be deposited on flexible substrates.     

热蒸发法制备的球棒状氧化锌晶体的形貌及生长过程

在不用催化剂的条件下,通过热蒸发锌粉的方法,一种新颖的球棒状的氧化锌纳米结构被沉积在硅基片上.每一根球棒状的氧化锌纳米棒("纳米球棒")由三部分构成,分别是六边形"球棒头"、"球棒把手"以及一个连接过渡的部分.高分辨率透射电镜和选区电子衍射结果表明,纳米棒呈单晶特性,沿着[0001]方向择优生长.根据对实验结果的分析,纳米球棒的生长过程可以利用气-固生长机制进行解释,合理地提出其生长模型.     

Morphological control of ZnO nanostructures on silicon substrates

ZnO nanostructures are grown on Au-catalyzed Si substrates by vapour phase transport between 800 and 1150 C. Nanostructures grown at 800 C are mainly rod-like in structure with diameters of <200 nm. Increasing growth temperature yields combination growth modes with 2D structures (nanowalls/nanosheets) connecting 1D nanorods at intermediate temperatures and a 3D growth mode of foam-like appearance at the highest temperatures. The present work indicates that it may be possible to systematically control the morphology of ZnO nanostructures by varying the growth temperature.     

Profile calculation of gold nanostructures by dispersed-nanosphere lithography through oblique etching for LSPR applications

Nanosphere lithography is an inexpensive method used to fabricate gold nanostructures on a substrate. Using dispersed-nanosphere lithography, in which the nanospheres are dispersed on a substrate, 2D or 3D nanostructures can be fabricated by obliquely depositing a gold film on the nanospheres and etching the gold film afterward. These nanostructures are tunable and acute, and are thus good emitting elements for the localized surface plasmon resonance applications. So far, for the fabrication of nanostructures on a substrate with dispersed nanospheres, only 2D nanostructures have been reported through perpendicular etching. We report in this paper that the 3D nanostructures fabricated by dispersed-nanosphere lithography are rigid non-conformal structures, and perpendicular gold etching can be expanded to oblique etching, which provides more possibilities for fabricating the gold nanostructures in various shapes. The profiles of gold nanostructures after several varying angle depositions, and their final profiles after perpendicular or oblique etching, are calculated in this paper. Our profile simulations are applicable for nanospheres (or microspheres) within the range of tens of nanometers to tens of micrometers, and are consistent with our fabricated nanostructures observed using scanning electron and atomic force microscopy. Electronic Supplementary Material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Growth and characterization of thin ZnO films deposited on glass substrates by electrodeposition technique

Electrodeposition technique was used in order to produce nanometric zinc oxide films on glass insulating substrates. The effect of electrolyte concentration and applied current density on the formation and growth of electrodeposited Zn thin films in aqueous solutions of ZnSO₄ were studied. After a thermal oxidation, a characterization of the structural morphology of the films deposited was carried out by optical microscopy (OM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and by grazing incidence X-rays diffraction (GIXD). These characterization techniques show that the grains size of the films after oxidation at temperature 450 °C is between 5 and 15 nm, as well as the structure is polycrystalline nature with several orientations. UV/vis spectrophotometry confirms that it is possible to obtain transparent good ZnO films with an average transmittance of approximately 80% within the visible wavelength region, as well as the optical gap of obtained ZnO films is 3.17 eV.     

Investigation of the luminescence properties of ZnO tetrapods and clusters grown on Si substrates

ZnO nanostructures are formed on Si substrates using Zn powder without catalyst. The substrate temperature was controlled from 450 to 600 °C, and the variation of structural and optical properties was investigated. From all samples both ZnO tetrapods and clusters were observed. Among them, no significant dispersion was observed from the ZnO tetrapods. However, ZnO clusters show considerable change in density and size. From the energy dispersive X-ray spectroscopy (EDX) results, atomic composition difference was observed. The clusters have considerable O-deficiencies, while tetrapods have almost stoichiometric composition. From all samples, strong luminescence, UV emission at 3.21 eV and green emission at 2.5 eV, were observed at room temperature. Cathodoluminescence measurements showed that the UV emission is closely related with tetrapods and the green emission is dominated from the clusters.     

Fabrication and photoluminescence of P doped ZnO nanobelts by thermal evaporation method

Uniform and flat single crystal ZnO:P nanobelts (NBs) were fabricated on Si (1 0 0) substrates by the thermal evaporation method. The growth process, free-catalyst self-assembly vapor-solid (V-S) mechanism, was described and investigated deeply in terms of thermodynamics and kinetics. Then, the photoluminescence (PL) properties of ZnO NBs were studied in a temperature range from 10 to 270 K. At 10 K the recombination of acceptor-bound exciton (A⁰X) was predominant in the PL spectrum, and was attributed to the transition of P_Zn−2V_Zn complex bound exciton. The active energy of A⁰X and acceptor binding energy were calculated to be 17.2 and 172 meV, respectively. The calculated acceptor binding energy of P doped ZnO nanostructure is in good agreement with that of P doped ZnO film.     

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.     

Emerging of Ag particles on ZnO nanowire arrays for blue-ray hologram storage

Noble-metal/metal-oxide-semiconductor nanostructures as an important material platform have been applied in massive data storage. ZnO exhibits excellent optical modulation ability. However, plasmon induced charge separation effect in Ag/ZnO systems is very weak due to the low chemical activity on surface of the oxide. Herein, we prepare ZnO nanowire arrays via the hydrothermal method, and measure their absorption spectra, photoluminescence spectra and electron paramagnetic resonance, proving the existence of oxygen defects in ZnO. Accordingly, an idea of "electron reverse transfer" is proposed such that blue-ray (403.4 nm) induces reduction of Ag⁺ ions through the excitation of ZnO. Rod-like and spherical silver nanoparticles emerge on the surface and in the gap of ZnO nanowire arrays, respectively, after the visible light stimulus. It is found that nanowire density, oxygen defects and surface roughness are dependent on hydrothermal time. The optimized diffraction efficiency of 0.08% is obtained for reconstructing hologram in the nanocomposite film. This work provides a bright way for construction of ZnO-based optoelectronic integrated devices.     

Enhanced formation of periodic arrays of low-resistivity NiSi nanocontacts on (0 0 1)Si0.7Ge0.3 by nanosphere lithography with a thin interposing Si layer

In this study, we demonstrated significant enhancement of the formation of low-resistivity NiSi nanocontacts with controlled size on (0 0 1)Si_0.7Ge_0.3 substrates by combining the nanosphere lithography with the use of a new Ni/a-Si bilayer nanodot structure. Low-resistivity NiSi with an average size of 78 nm was observed to be the only silicide phase formed in samples annealed at 350-800 °C. The presence of the interposing Si layer with appropriate thickness was found to effectively prevent Ge segregation and maintain the interface stability in forming NiSi nanocontacts on (0 0 1)Si_0.7Ge_0.3. As the annealing temperature was increased to 900 °C, amorphous SiO_x nanowires were observed to grow from silicide nanocontact regions. The NSL technique in conjunction with a sacrificial Si interlayer process promises to be applicable in fabricating periodic arrays of other low-resistivity silicide nanocontacts on Si_1−xGe_x substrates without complex lithography.     

基于直接胶体晶体刻蚀技术的高度有序纳米硅阵列的尺寸及形貌控制

以自组装单层胶体小球阵列为掩模，采用直接胶体晶体刻蚀技术在硅表面制备二维有序尺寸可控的纳米结构.在样品制备过程中，首先通过自组装法在硅表面制备了直径200nm的单层聚苯乙烯(PS)胶体小球的二维有序阵列；然后对样品直接进行反应离子刻蚀(RIE)，以氧气为气源，利用氧等离子体对聚苯乙烯小球和对硅的选择性刻蚀作用，通过改变刻蚀时间，制备出不同尺寸的PS胶体小球的有序单层阵列；接着以此二维PS胶体单层膜为掩模，以四氟化碳为气源对样品进行刻蚀；最后去除胶体球后得到二维有序的硅柱阵列.SEM和AFM的测量结果表明：改变氧等离子体对胶体球的刻蚀时间和四氟化碳对硅的刻蚀时间，可以控制硅柱的尺寸以及形貌，而硅柱阵列的周期取决于原始胶体球的直径. 关键词： 胶体晶体刻蚀 纳米硅柱阵列     

Synthesis and properties of ZnO hexagonal prisms synthesized on MgO-coated Si (111) substrates

ZnO hexagonal prisms have grown on MgO-coated Si (111) substrates by chemical vapor deposition. The process has two steps : the preparation of MgO-coated Si (111) substrates and the preparation of uniform ZnO hexagonal prisms. Some nucleation sites are provided on the Si substrates by the MgO layers, which have the capability to improve the growth of ZnO prisms in the heteroepitaxy. The prisms are single crystals with a preferential growth along the c axis and they are well-faceted at both the end and side surfaces. Room-temperature photoluminescence measurement of these ZnO prisms have shown a strong ultraviolet (UV) emission band centered at 393 nm and a weak green emission band centered at 507 nm, which may be provide an improvement in novel ultraviolet light-emitting devices. In addition, a possible mechanism for the prism growth is proposed based on the analysis by electron microscopy.     

Synthesis and properties of aligned ZnO microtube arrays

Two kinds of different aligned zinc oxide (ZnO) crystal microtube arrays were prepared on silicon (1 0 0) substrates by using of a simple thermal chemical reaction vapor transport deposition method. The synthesizing processes were done by using of heating the mixture of zinc oxide and graphite powders at 1150 °C in a quartz tube with one side opened to the air. The O₂ gas (99.9%) and air had been introduced as the assistant gases, respectively. Both the flow rates were 100 ml/min. And the temperature of the Si (1 0 0) substrate region was about 400 °C. There is no other metal catalyst on the Si wafers in the process. After growing for 30 min, one kind of synthesized sample is trumpet-shaped hexagonal microtube arrays assisted with O₂ gas and another produced sample is the uniform hexagonal microtubes only assisted with air. As the increasing of preparing time, their maximal lengths can range from several 10 μm to mm scale. The microstructure, room temperature photoluminescence properties and growth mechanism of both aligned microtube arrays were investigated and discussed.