热蒸发法Zn／ZnO叶状微米结构自组装生长及其发光特性

采用热蒸发法在ZnO缓冲层覆盖着Si衬底上合成了2D叶状的Zn晶枝结构,Zn的晶枝长度约为几十微米,厚度约为200nm,随后Zn晶枝在O2的气氛下热处理,在晶枝表面获得纤细、均匀的ZnO纳米线。晶枝按照无催化、自组装、汽相生长模式生长,晶枝最快生长方向是沿着载气气流的方向释放凝固潜热,XRD分析结果结果显示了Zn纳米线具有六角纤锌矿结构,Zn/ZnO的发光谱显示,在380nm处有一弱的UV近带边发射和中心在505nm处的强绿光发射,绿光发射归因于施主/受主对之间的辐射跃迁。     

Direct laser ablation of sub-100 nm line structures into polyimide

Periodic line structures with a period of 167 nm and linewidths varying from 30 to 100 nm have been produced in polyimide by direct ablation with a KrF laser using an interferometric technique. The characteristics of this interferometer as it applies to the ablation of these line structures, including linewidth and alignment sensitivity, are analyzed. The ability to control the linewidth by varying the average incident fluence is described theoretically and demonstrated experimentally. This externally generated period of 167 nm also prevents the spontaneous growth of laser induced periodic surface structures (LIPSS).     

Nd:YAG纳秒激光诱导硅表面微结构的演化

利用Nd:YAG纳秒激光(波长为532和355 nm)对单晶硅在真空中进行了累积脉冲辐照,研究了表面微结构的演化情况.在激光辐照的初始阶段,532和355 nm激光脉冲均在硅表面诱导出了波纹结构,后者辐照硅表面后形成了近似同心但稍显混乱的环形波纹结构.随着脉冲数的增加,波纹结构逐渐演化为一种类似珠形的凹凸结构,最后形成准规则排列的微米量级锥形结构,该微结构的生长依赖于表面张力波和结构自组织.分析发现,形成的交叉环形结构主要是在355 nm激光辐照硅的过程中,表面张力波导致波纹结构部分叠加的结果.     

One-pot sonochemical fabrication of hierarchical hollow CuO submicrospheres

Hierarchical hollow CuO submicrospheres have been fabricated on a large scale by a facile one-pot sonochemical process in the absence of surfactants and additives. The as-prepared products were investigated by XRD, FESEM, EDX, TEM, SAED, HRTEM and BET nitrogen adsorption-desorption isotherms. The results reveal that hollow pumpkin-shaped structures possess a monoclinic phase CuO with the diameters ranging from 400 to 500 nm, and their walls with around 45 nm in thickness are composed of numerous single crystalline CuO nanoribbons with a width of about 8 nm. The BET specific surface area of the as-synthesized CuO hollow structures was measured to be 59.60 m(2)/g, and the single point adsorption total pore volume was measured to be 0.1036 cm(3)/g. A possible growth mechanism for the formation of hierarchical hollow CuO structures was proposed, which is considered to be a sonohydrolysis - oriented aggregation - Ostwald ripening process. The novel hollow CuO spherical structures may utilize applications in biosensors, photonics, electronics, and catalysts.     

Structuring of Surfaces with Gold Nanoparticles by Using Bessel‐Like Beams

Here, the structuring of surfaces with gold nanoparticles by using Bessel‐like beam array is demonstrated. The experimental results show that the fabricated microring structures containing gold nanoparticles have a surface plasmon resonance in the spectral range of 520–540 nm, which can be tuned by selecting the laser treatment parameters. Fabricated microring structures exhibit a lower light transmittance comparing with the randomly distributed gold nanoparticles for wavelengths 500–570 nm due to the growth in the size of nanoparticles. In the spectral range of 600–700 nm, the light transmittance through microring structures is higher compared with the randomly distributed gold nanoparticles because of the removal of gold nanoparticles as gold has high reflectivity for wavelengths longer than 600 nm. The demonstrated method enables an easy fabrication of microring structures having tunable plasmonic properties.     

花状ZnO纳米结构的液相合成和光学性能

在常压下,以ZnCl2和NaOH为原料,不添加任何表面活性剂等有机物质,研究了用60℃恒温搅拌的湿化学法制备花状纳米ZnO。XRD、SEM和TEM分析结果表明:所得纳米ZnO是由平均直径约为80nm左右的纳米棒组成的花状结构,其平均长度可达1μm;利用紫外-可见分光光度计测试了光吸收性能,发现ZnO产物对300～380nm波长范围的光有强的吸收性;室温光致发光光谱显示:产物在462nm和620nm处分别出现了蓝光发射和较强较宽的红光发射。     

Synthesis and morphology of silicon oxide nanowires from a free jet activated by electron-beam plasma

Silicon oxide nanowires were synthesized from monosilane–argon–hydrogen mixture by the gas-jet electron-beam plasma chemical deposition method with simultaneous oxygen injection into the vacuum chamber. The synthesis was performed on monocrystalline silicon substrates covered with micron and nanometer tin catalyst particles. The nanowires are formed the via vapor–liquid–solid mechanism in the “catalyst-on-bottom” mode, in which many nanowires grow from one catalyst particle. The process of synthesizing nanowires on a substrate with catalyst consists of three stages: heating to synthesis temperature, hydrogen plasma treatment, and nanowire growth. In the substrate region corresponding to the jet axis, different structures are formed depending on the catalyst particle size. For catalyst particles under 100 nm, there are formed structures of chaotically oriented and interlaced bundles of silica nanowires. For catalyst particles of 0.3–1 micron, there are formed oriented arrays of cylindrically shaped nanowire bundles (“microropes”). Cocoon-like structures are formed for catalyst particles of more than 1 micron.We propose a model of nanowire growth by this method, which is based on nonuniform heating of a catalyst particle by a directed plasma flow. It was found that for synthesis of oriented microrope arrays the initial tin film thickness should be less than 100 nm and the synthesis process should include a hydrogen plasma treatment stage.     

Structural and morphological characterisation of hybrid Cu/Si(0 0 1) structures

The structural and morphological properties of epitaxial Cu/Si(0 0 1) type of structures have been investigated by a combination of electron, X-ray and scanning probe imaging techniques. Auger electron spectroscopy measurements indicate the presence of Si in the Cu layer for Cu thicknesses up to 10 nm. In addition, X-ray scattering results show that there is a mosaic spread in the Cu(0 0 1) crystal which decreases as the Cu thickness increases, from 8° at 15 nm to 4.5° at 100 nm. This behaviour is corroborated by reflection high energy electron diffraction patterns of the Cu surface measured during growth, which exhibit a twinning in the diffraction spots for the 15 and 30 nm Cu films. Atomic force and scanning electron microscopy imaging of Cu(4 nm)/Co(7,17 nm)/Cu(100 nm)/Si(0 0 1) structures allow one to visualise and characterise the sample surface in real space; from these measurements, an average roughness amplitude of ∼0.5 nm and a correlation length of ∼50 nm are obtained. Our results provide a better understanding of an important system which has been widely used as a template for the growth of epitaxial ultrathin magnetic films.     

Morphology engineering of ZnO nanostructures

Nanosized ZnO structures were grown by atmospheric pressure metalorganic chemical vapor deposition (APMOCVD) in the temperature range 200–500 °C at variable precursor pressure. Temperature induced evolution of the ZnO microstructure was observed, resulting in regular transformation of the material from conventional polycrystalline layers to hierarchically arranged sheaves of ZnO nanowires. The structures obtained were uniformly planarly located over the substrate and possessed as low nanowires diameter as 30–45 nm at the tips. The observed growth evolution is explained in terms of ZnO crystal planes free energy difference and growth kinetics. For comparison, the convenient growth at constant precursor pressure on Si and SiC substrates has been performed, resulting in island-type grown ZnO nanostructures. The demonstrated nanosized ZnO structures may have unique possible areas of application, which are listed here.     

Surfactant effects of indium on cracking in AlN/GaN distributed Bragg reflectors grown via metal organic vapor phase epitaxy

Aluminum Nitride (AlN) and Gallium Nitride (GaN) superlattice structures are often characterized by a network of cracks resulting from the large lattice mismatch and difference in thermal expansion coefficients, especially as the thickness of the layers increases. This work investigates the influence of indium as a surfactant on strain and cracking in AlN/GaN DBRs grown via Metal Organic Vapor Phase Epitaxy (MOVPE). DBRs with peak reflectivities ranging from 465 nm to 540 nm were grown and indium was introduced during the growth of the AlN layer. Image processing techniques were used to quantify the crack length per square millimeter and it was observed that indium has a significant effect on the crack formation and reduced the total crack length in these structures by a factor of two.     

Localization of 523 and 794 defects in diamond

Natural diamonds are studied via confocal scanning fluorescent spectroscopy. Defects 523 and 794 nm have a number of similar features and are associated with one another. Features of their localization in the (111) planes of the individual growth pyramids testify to their postgrowth origin and are the result of plastic deformations. The structure of the defects presumably contains dislocations. The participation of other impurities in the structures of the defects is doubtful.     

ZnO纳米带外延树枝状锯齿形缺口结构的制备及其发光特性

应用气固生长方式在没有催化剂的情况下合成出一种新奇的ZnO纳米结构．通过透射电子显微镜分析，发现这种ZnO纳米带外延晶枝直径约20 nm，在[0001]方向有着良好的外延生长取向．提出了一个模型来解释这种树枝状锯齿结构的生长．室温下光致发光测量表明这种ZnO纳米结构在382、491 nm处有一个紫外发光峰和绿光发光峰．     

SrTiO3基片的晶体质量及表面粗糙结构的X射线研究

用X射线双晶衍射摇摆曲线以及双晶X射线形貌对两个SrTiO₃基片的单晶质量进行了对比研究，并用X射线掠入射镜面反射及漫散射研究了它们的表面粗糙结构．结果表明，两个SrTiO₃基片中都存在镶嵌缺陷，其中一个样品的晶体质量相对较高．两个样品的表面粗糙结构相差很大，包括均方根粗糙度σ和横向相关长度ξ．σ分别为（0.5±0.1）和（1.3±0.1）nm，ξ分别为（1200±200）和（300±20）nm．样品的表面粗糙将增加Ｘ射线的漫散射强度而降低镜面反射的强度．晶体质 关键词：     

Process of fabricating semiconductor microcavities and photon crystals

A process of fabricating microcavities and photon crystals in GaAs structures by means of electron lithography and reactive ion etching is described. Two types of structures, with micropillars and with photon crystals, are considered. The latter structures have the form of a square or hexagonal array of holes in a planar waveguiding structure. The minimal diameter of the micropillars is 100 nm, and their height is 700 nm. The size of the holes in the photon crystals and the photon crystal period are controllably varied from 140 to 500 nm and from 400 to 1000 nm, respectively. The etch depth of the crystals is more than 350 nm.     

Fabrication and observation of nanowire-assemblages of Si-Ge

A few of the interesting structures made by the assemblage of Si-Ge nanowires fabricated by the floating-zone melting-vapor method have been observed. They reveal shapes that are similar to coral, jellyfish and sea anemones. The pre-sintered substrate bar has some large crystalline particles (1–15 μm), which produce sites that are energetically predisposed to nucleation. The peculiar structures created by the assemblage of Si-Ge nanowires form on favored nucleation sites that consist of numerous bundles of nanowires with diameters of 20–50 nm. The periodic variation in the diameter of the bundles of nanowires is a common feature of these structures. In addition, a growth mechanism assisted by the coexistence of Ge and Si-Ge oxides is suggested. The growth process of these assemblages opens up new possibilities for the study of the growth mechanism of Si-Ge nanowires. Received: 25 July 2002 / Accepted: 9 September 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: 81-298/59-2736, E-mail: HU.Quanli@nims.go.jp     

Selective growth of GaAs quantum dots and vertical quantum wires in two-dimensional V-grooves

We propose and demonstrate a novel technique for the fabrication of quantum dot (QD) structures using metal organic chemical vapor deposition (MOCVD). The GaAs quantum dots are grown at the bottom of the two-dimensional V-groove (2DVG) structures which are composed of (1 1 1)A and (1 1 1)B-facets on GaAs(1 0 0). The 2DVG is formed by MOCVD selective growth on a SiO₂ patterned substrate. It should be noted that the 2DVGs cannot be formed by a chemical wet etching technique because the facet's anisotropy of etching ratios are different. By changing the growth condition, we can obtain GaAs QD structures which have a size of less than 10 nm, and vertical GaAs quantum wires (V-QWRs) in 2DVGs. We have observed photoluminescence from each structure. We have also demonstrated stacking of GaAs QDs in the 2DVG on GaAs (1 0 0).     

Investigation of phosphorus surface segregation by X-ray scattering measurements

The surface segregation of phosphorus in silicon at low temperatures is studied by using δ doping structures grown by molecular beam epitaxy. The samples are characterized by X-ray crystal truncation rod (CTR) scattering using synchrotron radiation as the light source. The 1/e decay length of P segregation and segregation barrier energy are obtained by fitting the CTR curves within kinematical approximation of X-ray diffraction theory. The surface segregation of P is strong at a growth temperature of 450 °C, with a 1/e decay length of 14 nm, while for growth temperatures below 350 °C, P segregation is negligible with a 1/e decay length not larger than 4 nm. The segregation barrier energy is determined to be 0.43 eV.     

Optimization of Metamorphic InGaAs Quantum Wells on GaAs Grown by Molecular Beam Epitaxy

We investigate the molecular beam epitaxy growth of metamorphic InxGal-xAs materials （x up to 0.5） on GaAs substrates systematically. Optimization of structure design and growth parameters is aimed at obtaining smooth surface and high optical qualdty. The optimized structures have an average surface roughness of 0.9-1.8 nm. It is also proven by PL measurements that the optical properties of high indium content （55%） InGaAs quantum wells are improved apparently by defect reduction technique and by introducing Sb as a surfactant. These provide us new ways for growing device quality metamorphic structures on GaAs substrates with long-wavelength emissions.     

Correlation between green luminescence and morphology evolution of ZnO films

Photoluminescence and atomic force microscopy have been used to characterize ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD) at varied growth pressures. The surface morphology with different grain structures has strong influence on the green photoluminescence of ZnO. When large discrete islands or structureless overgrowth cover the rough surface, broad green emissions around 500 nm go beyond the ultraviolet (UV) emission band; whereas, when the surface is packed closely with small grains, only weak green emission is observed with a red-shift to 528 nm. This variation of green emissions is ascribed to changes in the charge states of oxygen vacancies, which is strongly dependent on the surface morphology and grain structures. Based on the grain boundary defect model, two possible recombination processes for the green emission are proposed and discussed in detail. PACS 68.55.Jk; 78.55.Et; 81.05.Dz     

Structures of Si and Ge nanowires in the subnanometer range

We report an ab initio investigation of several structures of pristine Si and Ge nanowires with diameters between 0.5 and 2.0 nm. We consider nanowires based on the diamond structure, high-density bulk structures, and fullerenelike structures. Our calculations indicate a transition from sp3 geometries to structures with higher coordination, for diameters below 1.4 nm. We find that diamond-structure nanowires are unstable for diameters smaller than 1 nm, undergoing considerable structural transformations towards amorphouslike wires. For diameters between 0.8 and 1 nm, filled-fullerene wires are the most stable. For even smaller diameters (approximately 0.5 nm), we find that a simple hexagonal structure is particularly stable for both Si and Ge.