Colloidal monolayer self-assembly and its simulation via cellular automaton model

A wafer-scale colloidal monolayer consisting of SiO2 spheres is fabricated by a method combining spin coating and thermal treatment for the first time. Moreover, a new cellular automaton model describing the self-assembly process of the colloidal monolayer is introduced. Rather than simulate molecular self-assembly to establish the most energetically favored position, we reconstruct the self-assembly of the colloidal monolayer by adjusting several simple transition rules of a cellular automaton. This model captures the main self-assembly characteristics of SiO2 spheres, including experimental processing time, morphology, and some statistics. It possesses the advantage of less calculation and higher efficiency,paving a new way to simulate a mesoscopic system.     

Hollow graphene oxide spheres: facile synthesis and formation mechanism

In this work, we introduced a facile approach for preparing hollow graphene oxide spheres (HGOSs). By electrostatic self-assembly polystyrene (PS)/graphene oxide (GO), core/shell microspheres were synthesized. After removal of the sacrificial PS colloidal spheres by toluene solution treatment, HGOSs were prepared successfully. Based on the DLVO theory, van der Waals force and electric double layer repulsion were proposed to quantitatively analyze the self-assembly of the composite structure. The theoretical formulation for the resultant interaction force F versus separation between the surfaces d showed a significant low energy barrier for the aggregation of the GO and PS, which predicted the favorable HGOSs formation.     

Observations of defect propagation in [100]-oriented opal-type photonic crystals

Charged colloidal suspensions have been used as experimental models for the study of crystal nucleation. Here we propose that the technique of template-assisted colloidal self-assembly can be used to visualize the effects of defect propagation in atomic crystal films produced using epitaxial growth. Templates with periodic line defects were used to grow [100]-oriented three-dimensional photonic crystals by means of the template-assisted colloidal self-assembly method, aided by capillary and gravitational forces. The defect propagation in the [100]-oriented photonic crystal was observed using scanning electron microscopy, both at the surface of the crystal and on cleaved facets. This method is useful in the understanding of defect propagation in the growth of colloidal films on templates - and the same approach may also prove useful for the understanding of atomic crystal growth on substrates with defects. Additionally, the deliberate incorporation of line defects may prove valuable as a way of introducing waveguide channels into three-dimensional photonic crystals.     

A colloidal crystal double-heterostructure fabricated with the angle controlled inclined deposition method

A self-assembly method, named the angle controlled inclined deposition method, is developed for fabricating well-ordered silica and polystyrene colloidal crystals. A high-quality colloidal crystal with a flat and uniform surface over a large area can be produced rapidly using a minute quantity of suspension and without any additional equipment. By controlling the inclined angle, we can fabricate colloidal crystals with diverse numbers of layers. A colloidal crystal double-heterostructure (composed of three different colloidal photonic crystals) can be rapidly fabricated with this method. Both experimental and simulation results show that the photonic band gap of the double-heterostructure is not a simple superposition of that of the compositional colloidal crystals along the stacking direction.     

Experimental research of liquid refractive index sensing by optical fiber and colloidal crystal's photonic band-gap

We use the changes of colloidal photonic crystal photonic band-gap center wavelength to research the refractive index sensing by experiment. The changes in the center wavelength of the colloidal crystals photonic band-gap are analyzed. A mold is designed to obtain a controllable self-assembly method, colloidal crystals are observed by scan electronic microscope (SEM) and the band-gap is measured by infrared spectrometer. The results are agreed well with the theoretical analysis. An experimental device is designed to test liquid refractive index. The couple of the fibers are used to measure the band-gap of colloidal crystals and the results are also discussed in theory. The results show that the band-gap of colloidal crystals can be used to measure the liquid refractive index. The new sensing mechanism is formed and it provides a new application of colloidal crystals in the sensing.     

采用溶胶凝胶协同自组装与光刻相结合的方法在反蛋白石结构薄膜中引入二维缺陷

采用溶胶凝胶协同自组装与光刻相结合的方法,在光子晶体反蛋白石结构中引入缺陷,通过溶胶凝胶协同自组装方法在硅片上垂直沉积胶体晶体复合薄膜,把BP212正性光刻胶均匀旋涂在复合薄膜上,通过曝光、显影等光刻工艺,把掩膜版图案复制在复合薄膜上,用此样品再次垂直沉积一层复合薄膜,使图案被复合薄膜覆盖.最后去除胶体微球与光刻胶图案,从而在反蛋白石结构中引入缺陷,用扫描电子显微镜对样品进行表征.分析了光刻胶图案对胶体微球排列的影响.     

一种胶体光子晶体修饰的光纤

设计了一种胶体光子晶体修饰的光纤. 采用恒温快速蒸发法直接在经切割刀处理后的光纤端面生长胶体晶体,再与另一根切割后的光纤在毛细玻璃管中完成对接,制备成胶体光子晶体修饰的光纤. 用扫描电子显微镜和光谱分析仪对样品的形貌、结构以及光学特性进行分析. 实验结果表明,粒径为640 nm、体积分数约为0.5%的SiO₂胶体微球溶液在60 ℃的情况下沉积,大约12 h后可得到质量较高的胶体光子晶体. 在SEM下,观察到端面的胶体晶体为面心立方(fcc)结构. 透射光谱证明,该结构在(111)面上     

Three-dimensional structure of polystyrene colloidal crystal by synchrotron radiation X-ray phase-contrast computed tomography

Colloidal crystal with long-range ordered structure has attracted great attention for their applications in various fields. Although perfect colloidal crystals have been achieved by some fabrications for utilization, little is known about their exact structures and internal defects. In this study, we use synchrotron radiation (SR) phase-contrast computed tomography (CT) to noninvasively access the internal structure of polystyrene (PS) colloidal crystals in three dimensions (3D). The phase-attenuation duality Paganin algorithm phase retrieval was employed to achieve a satisfactory contrast and outline of the spheres. After CT reconstruction, the positions of individual PS particles and structural defects are identified in three dimensions, and the local crystal structure is revealed. Further quantitative analysis of the void system in colloidal crystal illustrates that single voids can be mostly attributed to tetrahedron void of sphere close packing, but the interconnected voids with large volume induce a sphere volume fraction of 59.39 % that reflects a metastable glass behavior of colloidal crystal arrangement. The void orientation result reveals that the 3D close-packing difficulty mainly lies in the stacking of interlayer.     

对流自组装2维胶体晶体成膜趋势和覆盖率

从自组装理论出发, 分析对流自组装2维胶体晶体中空白、条纹区域出现的机理,并在实验上予以验证。通过研究得知, 2维胶体晶体的自组装过程呈现空白、条纹、大面积单层、双层条纹的趋势。从胶体晶体覆盖率的角度出发研究2维胶体晶体的组装参数与质量之间的关系,结果表明:胶体晶体的总覆盖率与基片提拉速度倒数呈线性正比,和粒子体积分数呈反比例函数关系; 受到多种因素的影响,大面积2维胶体晶体总是伴随着一定比例的空白区域和双层区域出现,提拉法所能获得的最大单层覆盖率为95%。     

光纤表面自组装胶体晶体微结构的实验研究

利用自组装方法在普通单模光纤裸纤表面生长胶体晶体,采用自组装方法制备了一种新型的三维光子晶体微结构光纤。将单分散度小于2％的二氧化硅胶体微球超声分散于乙醇溶液,通过垂直沉积法在表面经湿法腐蚀处理的裸光纤表面组装胶体晶体。采用SEM对样品进行表征,胶体样品表面为六角密排列,晶体呈FCC结构,其（111）晶面平行于光纤表面。当微球直径远小于光纤直径时,在60℃温度下制备的胶体样品有较好的质量。     

采用溶胶凝胶协同自组装方法制备SiO2反蛋白石结构薄膜及其光学性质研究

研究了溶胶凝胶协同自组装制备大面积高质量SiO₂反蛋白石结构薄膜的方法. 向单分散的聚苯乙烯(PS)胶体溶液中添加SiO₂前驱物溶液,用垂直自组装法一步得到微球空隙中均匀填充有凝胶的 复合PS胶体晶体薄膜,在空气中烧结去除PS后得到SiO₂反蛋白石结构薄膜.通过对添加前驱物溶液比例、 自组装温度以及烧结温度等参数的研究,用不同粒径的PS微球制备了不同孔径的高质量SiO₂反蛋白石结构薄膜. 用扫描电子显微镜和X射线能量色散谱仪对制备得到的薄膜样品进行显微形貌和成分表征,并测试了其透射光谱. 结果表明:溶胶凝胶协同自组装法制备的SiO₂反蛋白石结构薄膜大面积高度有序,孔径可以控制且选择范围宽; 薄膜的透射光谱带隙明显,带隙中心波长与理论计算结果相符.     

高质量胶体晶体薄膜的快速制备及表征

通过控制温度和湿度，用垂直沉积法（vertical deposition method）快速制备出了可精确控制样品的厚度、在较大范围呈现好的有序性的密排结构的聚苯乙烯（PS）胶体晶体 薄膜.利用透射电子显微镜直观准确地确定了样品为面心（fcc）密排结构.通过控制样品干燥速度和加温处理，胶体颗粒排列更加有序,并且克服了胶体晶体干燥后易碎和在水等溶 剂中容易再分散等缺点，为胶体晶体实际应用创造了条件. 关键词： 胶体晶体薄膜 垂直沉积法 面心密排结构 再分散     

Observation of unconventional optical diffraction in <Emphasis Type="Italic">α</Emphasis>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Si two-dimensional photonic crystal slab fabricated by sol-gel method

The α-Fe₂O₃/Si two-dimensional (2D) photonic crystal (PC) with hexagonal honeycomb structure was fabricated by self-assembly and solution-dipping method based on colloidal monolayer template with 780 and 470 nm diameter polystyrene (PS) spheres. Optical diffraction measurement was carried out under wavelengths of 800, 532 and 400 nm. An interesting dispersion phenomenon with a hexagonal diffraction pattern composed of six elliptical spots is observed under specific wavelengths. Both theoretical and experimental calculations reveal that the diffraction can only occur when the incident wavelength is smaller than \(\sqrt{3}/2\) of lattice constant, and both the shape and distribution of these spots can be modified by the PC lattice constant and the incident wavelength. All these results reveal that optical properties of these 2D PC slabs are different from conventional diffractive devices.     

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     

亚微米聚苯乙烯微球在气-液界面组装的机理研究

系统地研究了亚微米聚苯乙烯微球在气-液界面的组装机理.聚苯乙烯微球在介质对流的带动下会到达悬浮液的表面并在气-液界面组装，气-液界面处聚苯乙烯微球间由弯液面产生的毛细管力是组装的推动力.界面处聚苯乙烯微球在干燥过程中其润湿性发生了转变，由完全润湿到部分润湿并最终变成不润湿，相应的聚苯乙烯微球与分散介质间接触角也逐渐增大.研究表明，只有接触角达到或超过某数值θ′_critical时，才能够出现气-液界面组装现象.考虑到PS胶粒晶体的表面是“规则”粗糙的表面，由Wenzel公式知θ′_critical大于测量值θ＝22°.聚苯乙烯微球润湿性的转变是界面组装发生和持续进行的关键性因素. 关键词： 自组装 胶粒晶体 聚苯乙烯微球 润湿性     

Influence of Gravity on Structure of Colloidal Crystal Using Simulated Microgravity

将重水(D2O)和水(H2O)以一定比例混合来匹配直径为110 nm的聚苯乙烯带电小球的密度,并利用Kossel衍射方法测量了胶体晶体的结构和晶格常数等参数．通过将密度匹配(g=0)和没有进行密度匹配(g=1)的实验结果的对比,发现重力将会使样品池中胶体晶体的晶格常数随高度的变低而变小．这一结果表明,在带电粒子胶体晶体的研究中有必要考虑重力的影响     

亚微米聚苯乙烯微球在气-液界面组装的机理研究

系统地研究了亚微米聚苯乙烯微球在气-液界面的组装机理.聚苯乙烯微球在介质对流的带动下会到达悬浮液的表面并在气-液界面组装，气-液界面处聚苯乙烯微球间由弯液面产生的毛细管力是组装的推动力.界面处聚苯乙烯微球在干燥过程中其润湿性发生了转变，由完全润湿到部分润湿并最终变成不润湿，相应的聚苯乙烯微球与分散介质间接触角也逐渐增大.研究表明，只有接触角达到或超过某数值θ′_critical时，才能够出现气-液界面组装现象.考虑到PS胶粒晶体的表面是“规则”粗糙的表面，由Wenzel公式知θ′_critical大于测量值θ＝22°.聚苯乙烯微球润湿性的转变是界面组装发生和持续进行的关键性因素. 关键词： 自组装 胶粒晶体 聚苯乙烯微球 润湿性     

低压化学气相沉积技术制备锗反蛋白石三维光子晶体

采用溶剂蒸发对流自组装法将单分散SiO2微球组装形成三维有序胶体晶体模板,用低压化学气相沉积法填充高折射率材料锗,酸洗去除SiO2模板,获得了锗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-近红外光谱仪对锗反蛋白石的形貌、成分、结构和光学性能进行了表征.结果表明：锗在SiO2微球空隙内具有较高的结晶质量,填充致密均匀.通过改变沉积工艺,可控制锗的填充率;制备的锗反蛋白三维光子晶体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.     

Three-dimensional binary superlattices of oppositely charged colloids

We report the equilibrium self-assembly of binary crystals of oppositely charged colloidal microspheres at high density. By varying the magnitude of the charge on near equal-sized spheres we show that the structure of the binary crystal may be switched between face-centered cubic, cesium chloride, and sodium chloride. We interpret these transformations in terms of a competition between entropic and Coulombic forces.     

Large-scale protein/antibody patterning with limiting unspecific adsorption

A simple synthetic route based on nanosphere lithography has been developed in order to design a large-scale nanoarray for specific control of protein anchoring. This technique based on two-dimensional (2D) colloidal crystals composed of polystyrene spheres allows the easy and inexpensive fabrication of large arrays (up to several centimeters) by reducing the cost. A silicon wafer coated with a thin adhesion layer of chromium (15 nm) and a layer of gold (50 nm) is used as a substrate. PS spheres are deposited on the gold surface using the floating-transferring technique. The PS spheres were then functionalized with PEG-biotin and the defects by self-assembly monolayer (SAM) PEG to prevent unspecific adsorption. Using epifluorescence microscopy, we show that after immersion of sample on target protein (avidin and anti-avidin) solution, the latter are specifically located on polystyrene spheres. Thus, these results are meaningful for exploration of devices based on a large-scale nanoarray of PS spheres and can be used for detection of target proteins or simply to pattern a surface with specific proteins.