SiO2胶体晶体的自组装结构及其带隙特征

光子晶体是一种具有光子带隙的新型功能材料.利用垂直沉积自组装法制成SiO2胶体晶体,并利用扫描电子显微镜和紫外分光度计对胶体晶体的显微形貌和光学特征进行了研究.结果表明,利用垂直沉积法自组装得到的SiO2胶体晶体具有面心立方结构;在可见光波段,胶体晶体在＜111＞面方向存在光子带隙.     

CdSe-SiO2光子晶体的垂直沉积及近红外变频特性

在氧化铟锡玻璃上电化学合成了CdSe薄膜,采用垂直沉积法首次在CdSe薄膜上制备了SiO2胶体晶体, 实现了CdSe表面介电常数的调节.扫描电镜观察表明,500nm微球在CdSe薄膜上呈面心立方密堆结构排列,在微米尺度上胶体晶体显示出一定的多晶序.与SiO2胶体晶体相比,CdSe-SiO2光子晶体的UV-vis-NIR透射谱只有一个较宽的光子带隙,带隙在近红外波段随入射角减小向短波方向移动.所得CdSe-SiO2光子晶体样品可作为地面目标针对红外卫星成像的伪装材料.     

光子晶体用二氧化硅胶体球的改性制备及其自组装

采用一步法制备了表面接枝甲基丙烯酰氧基三甲氧基硅烷(MPS)的单分散SiO2胶体球,并通过垂直沉积法在40℃、60%相对湿度下组装出有序性较好的密排结构的SiO2光子晶体.傅立叶红外光谱(FT-IR)和X射线光电子能谱(XPS)结果证明SiO2胶体球表面接枝上了MPS;扫描电子显微镜(SEM)结果表明改性后SiO2胶体球平均粒径为284nm,单分散性较高,平均标准偏差＜5%;制备出的光子晶体是面心立方(fcc)紧密堆积结构;吸收光谱表明,所制备的光子晶体在(111)方向具有光子晶体的带隙特性,带隙中心波长为646nm.     

NaCl改性SiO_2微球的制备及其自组装光子晶体研究

为提高SiO2微球的表面电荷密度,通过改进Stober法,引入电解质NaCl合成SiO2微球,并采用垂直沉积法制备出光子晶体.通过Zeta电位粒度仪、带EDS能谱仪的场发射扫描电子显微镜(SEM)和紫外-可见-近红外光谱仪对其电学性能、显微形貌和光学性能进行测试分析.Zeta电位测试结果显示改性SiO2:微球的Zeta电位平均提高11.39mV;EDS能谱分析表明微球中含有钠元素;SEM照片表明样品平均粒径为334 nm,平均标准偏差小于5%,所得光子晶体为面心立方密排结构;吸收光谱表明在725nm处具有光子晶体带隙.     

近红外光学带隙硅三维光子晶体的制备

用溶剂蒸发法将单分散SiO2微球组装成三维有序结构的胶体晶体模板,用低压化学气相沉积法填充高折射率材料硅,酸洗去除SiO2模板,获得了硅反蛋白石三维光子晶体.通过扫描电镜、X射线衍射仪和紫外-可见-近红外光谱仪对硅反蛋白石三维光子晶体的形貌、成分、结构和光学性能进行了表征.研究结果表明:Si在SiO2微球空隙内具有较高的结晶质量,填充致密均匀;通过控制沉积条件,可控制硅的填充率;制备的硅反蛋白三维光子晶体在近红外区(1.4μm左右)具有明显的光学反射峰,表现出光学带隙效应,测试的光学性能与理论计算基本吻合.     

硅槽内自组装二氧化硅光子晶体

采用溶剂蒸发法在硅片上微槽内对不同粒径的SiO2微球进行组装,尝试利用刻有微槽的硅片与平坦衬底间形成的毛细管池限制胶体晶体的生长厚度,获得了具有显著光子带隙特征的光子晶体线形阵列,并在此基础上比较了不同实验条件如微球直径、毛细管池物理限制作用等对微球排列方式及规整度的影响.     

Se-SiO2三维光子晶体的制备

报道了一种新的调节二氧化硅光子晶体带隙的方法;通过化学镀向SiO2胶体晶体中填充半导体材料Se,获得了Se-SiO2两种介质复合的三维光子晶体;采用扫描电子显微镜(SEM)、X射线衍射和紫外-可见光谱仪(UV-VIS)等对Se-SiO2三维光子晶体的形貌、结构和光学性能进行了观察测试.研究结果表明,Se以纳米晶粒的形式均匀地包覆在SiO2微球表面,形成了Se壳层,与相同晶格周期的SiO2光子晶体相比,Se-SiO2光子晶体的带隙发生了明显的红移.     

SiO2微球的制备及其自组装行为研究

采用Stober溶胶-凝胶法制备了粒径约为150～220nm的单分散SiO2微球,利用DLS、SEM等对样品进行了表征,并探讨了TEOS用量、氨水用量及去离子水量等因素对合成SiO2微球的影响.采用垂直沉积技术研究了SiO2微球的自组装行为,在相对湿度为70%、温度为25℃的稳定环境下成功地制备了大面积具有六方密堆结构的三维SiO2光子晶体.     

单分散SiO2胶体球制备及其胶体晶体组装

运用胶体化学法在乙醇介质中合成SiO2胶体球,将制得的样品在30℃下用双氧水浸泡处理48h.用扫描电子显微镜(SEM)、傅立叶红外光谱(FT-TR)、Zeta电位仪和标准氢氧化钠滴定法对其形貌、结构和表面电学性质进行分析.结果表明样品平均粒径为292nm,平均标准偏差小于5%;经双氧水浸泡处理后,SiO2胶体球表面羟基数目增多,在水溶液中的Zeta电位从-55.72mV提高到-63.26mV,表面电荷密度从0.19μC/cm2提高到0.28μC/cm2.通过垂直沉积法,在40℃和60%相对湿度条件下制备出有序性较好、密排结构的SiO2胶体晶体.在SEM下,观察到这种胶体晶体是面心立方(fcc)密排结构,其(111)晶面平行于基底.透射光谱表明,所制备的胶体晶体在(111)方向具有光子晶体的不完全带隙性质.     

SiO2/CdS光子晶体的制备及其光学性能

用化学浴沉淀法(CBD)在SiO2胶体晶体中生长了CdS半导体材料, 并用UV-VIS-NIR光谱仪和荧光光分度计测试了其光学性能.测试结果表明,在SiO2胶体晶体中随着CdS填充量的增加,光子带隙向长波段方向移动且变宽;当发射出的光与基体材料的光子带隙相匹配时,可控制半导体材料的光致发光,同时,可通过控制SiO2胶体颗粒粒经的大小来调节CdS的光致发光性能.     

Metal-coated colloidal particles

Procedures are described for coating of submicrometre ceramic powders with copper and nickel. The process required precoating of the core particles with a palladium catalyst. A precoating procedure was developed in which palladium chloride is reduced by sodium hypophosphite or stannous chloride on the powder surface in aqueous suspensions. Commercial electroless solutions were used to deposit copper and nickel on the catalysed powders. The effect of various experimental parameters on the effectiveness of the surface conditioning of the particles was also investigated.     

Nanolithographic self-assembly of colloidal nanoparticles

Technical Physics Letters - Methods of nanolithographic self-assembly of colloidal nanoparticles have been created, which are promising for the development of fractal nanolithography.     

Columnar self-assembly of colloidal nanodisks

The self-assembly of sterically stabilized colloidal copper sulfide nanodisks, 14-20 nm in diameter and 5-7 nm thick, was studied. The nanodisks were observed by electron microscopy and small-angle X-ray scattering to form columnar arrays when evaporated as thin films from concentrated dispersions. These superstructured nanomaterials might give rise to technologically useful properties, such as anisotropic electrical transport and electrorheological and optical properties.     

Hybrid colloidal plasmonic-photonic crystals

We review the recently emerged class of hybrid metal-dielectric colloidal photonic crystals. The hybrid approach is understood as the combination of a dielectric photonic crystal with a continuous metal film. It allows to achieve a strong modification of the optical properties of photonic crystals by involving the light scattering at electronic excitations in the metal component into moulding of the light flow in series to the diffraction resonances occurring in the body of the photonic crystal. We consider different realizations of hybrid plasmonic-photonic crystals based on two- and three-dimensional colloidal photonic crystals in association with flat and corrugated metal films. In agreement with model calculations, different resonance phenomena determine the optical response of hybrid crystals leading to a broadly tuneable functionality of these crystals.     

Nanomachining by colloidal lithography

Colloidal lithography is a recently emerging field; the evolution of this simple technique is still in progress. Recent advances in this area have developed a variety of practical routes of colloidal lithography, which have great potential to replace, at least partially, complex and high-cost advanced lithographic techniques. This Review presents the state of the art of colloidal lithography and consists of three main parts, beginning with synthetic routes to monodisperse colloids and their self-assembly with low defect concentrations, which are used as lithographic masks. Then, we will introduce the modification of the colloidal masks using reactive ion etching (RIE), which produces a variety of nanoscopic features and multifaceted particles. Finally, a few prospective applications of colloidal lithography will be discussed.     

Nanoparticle-controlled aggregation of colloidal tetrapods

Tetrapods are among the most promising building blocks for nanoscale self-assembly, offering various desirable features. Whereas these particles can be fabricated with remarkable precision, comparatively less is known about their aggregation behavior. Employing a novel, powerful simulation method, we demonstrate that charged nanoparticles offer considerable control over the assembly of tip-functionalized tetrapods. Extending these findings to tetrapods confined to a gas/liquid interface, we show that regular structures can be achieved even without functionalization.     

Three-dimensional nanoscopy of colloidal crystals

We demonstrate the direct three-dimensional imaging of densely packed colloidal nanostructures using stimulated emission depletion microscopy. A combination of two de-excitation patterns yields a resolution of 43 nm in the lateral and 125 nm in the axial direction and an effective focal volume that is by 126-fold smaller than that of a corresponding confocal microscope. The mapping of a model system of spheres organized by confined convective assembly unambiguously identified face-centered cubic, hexagonal close-packed, random hexagonal close-packed, and body-centered cubic structures.     

Defects in colloidal crystal

Colloidal crystal of polystyrene spheres of 0·53 μm diameter dispersed in water is prepared in a quartz container. Optical microscope, video camera and image processor are used to investigate the defects, their dynamics and the effect of shear in this colloidal crystal. Six layers of the crystal from the surface of the container are imaged sequentially, one after another, and the crystal is reconstructed. FCC structure with (111) planes parallel to the container surface is stable at high volume fraction whereas, at low volume fraction (100) planes also coexist. Vacancies, dislocations, grain boundaries, voids and particle aggregates are identified. The vibration of aggregates is sluggish as compared to that of a single particle. The nearest layer of particles to the container surface is better ordered than those in the interior layers. The container wall provides a stabilizing potential to the nearby layers of particles. The 2-D crystalline-like characteristics of the nearby layers are probed. The colloidal crystal is shear-melted by shaking the container. On resting it, the crystal-flow slows down. The flow is constrained to be parallel to the container surface and occurs along the layer in quantum jumps. During the flow, both (111) and (100) planes coexist in the layer. Flow at low rates anneals the defects created by the shear-melting.     

Study of lanthanum-based colloidal sols formation

Lanthanum-based colloidal sols have been studied in order to synthesize lanthanum oxychloride inorganic coatings or thin layers for catalytic applications. The singularity of this process leading to microporous coatings is based on the polymerization of lanthanum acetate species in aqueous solution. Sols are prepared from lanthanum chloride modified by acetate ions. The sol formation mechanism can be explained by La³⁺ hydrolysis, giving basic species (La (OH)_X with x = 1 or 2) which condense and lead to polycondensed hydroxo ions. In the pH range of sol formation, OH^– and CH₃COO^– are ligands competitive towards La³⁺; when acetate ions are present, the condensation rate is limited by lanthanum acetate complexation. Several distributions of lanthanum hydroxide and acetate species are given and related to experimental results (pH, Fourier transform infrared (FTIR) spectroscopy, turbidity and stability of sols, SEM and TEM analysis of coatings). FTIR spectroscopy has been revealed as useful to evidence a polymerization of acetate species in sols leading to translucent gels. These gels allow the preparation of almost fully dense LaOCl coatings after thermal treatment above 450°C. These results confirm the possible polymerization of lanthanum acetate complexes during the drying step and emphasize the great effect of acetate species on the final material texture.     

Magnetic manipulation of self-assembled colloidal asters

Self-assembled materials must actively consume energy and remain out of equilibrium to support structural complexity and functional diversity. Here we show that a magnetic colloidal suspension confined at the interface between two immiscible liquids and energized by an alternating magnetic field dynamically self-assembles into localized asters and arrays of asters, which exhibit locomotion and shape change. By controlling a small external magnetic field applied parallel to the interface, we show that asters can capture, transport, and position target microparticles. The ability to manipulate colloidal structures is crucial for the further development of self-assembled microrobots.