Epitaxially Grown Ferroelectric PVDF‐TrFE Film on Shape‐Tailored Semiconducting Rubrene Single Crystal

Epitaxial crystallization of thin poly(vinylidene fluoride‐co‐trifluoroethylene) (PVDF‐TrFE) films is important for the full utilization of their ferroelectric properties. Epitaxy can offer a route for maximizing the degree of crystallinity with the effective orientation of the crystals with respect to the electric field. Despite various approaches for the epitaxial control of the crystalline structure of PVDF‐TrFE, its epitaxy on a semiconductor is yet to be accomplished. Herein, the epitaxial growth of PVDF‐TrFE crystals on a single‐crystalline organic semiconductor rubrene grown via physical vapor deposition is presented. The epitaxy results in polymer crystals globally ordered with specific crystal orientations dictated by the epitaxial relation between the polymer and rubrene crystal. The lattice matching between the c‐axis of PVDF‐TrFE crystals and the (210) plane of orthorhombic rubrene crystals develops two degenerate crystal orientations of the PVDF‐TrFE crystalline lamellae aligned nearly perpendicular to each other. Thin PVDF‐TrFE films with epitaxially grown crystals are incorporated into metal/ferroelectric polymer/metal and metal/ferroelectric polymer/semiconductor/metal capacitors, which exhibit excellent nonvolatile polarization and capacitance behavior, respectively. Furthermore, combined with a printing technique for micropatterning rubrene single crystals, the epitaxy of a PVDF‐TrFE film is formed selectively on the patterned rubrene with characteristic epitaxial crystal orientation over a large area.     

ZnO晶体生长新方法研究

基于ZnO-PbF₂高温溶液体系的相关系和析晶行为, 发展了一种通气诱导成核的助熔剂-坩埚下降法生长技术. 通过优化生长参数, 获得了尺寸为φ25mm×5mm的ZnO晶体. 该晶体具有纤锌矿结构, 晶格常数a=0.3252nm, b=0.5209nm. X射线定向确认其择优取向生长方向为[0001]. 实验结果表明, 助熔剂-坩埚下降法是ZnO晶体生长的一条新途径.     

A Compact Device for Colloidal Crystal Studies on Tiangong-1 Target Spacecraft

An experimental device with three crystallization cells, each with two working positions, was designed to study growth kinetics and structural transformation of colloidal crystals under microgravity condition. The device is capable of remote control of experimental procedures. It uses direct-space imaging with white light to monitor morphology of the crystals and reciprocal-space laser diffraction (Kossel lines) to reveal lattice structure. The device, intended for colloidal crystal growth kinetics and structural transformation on Tiangong-1 target spacecraft, had run on-orbit for more than one year till the end of the mission. Hundreds of images and diffraction patterns were collected via the on-ground data receiving station. The data showed that single crystalline samples were successfully grown on the orbit. Structural transformation was carefully studied under electric and thermal field. Using a backup device, control experiments were also performed on the ground under similar conditions except for the microgravity. Preliminary results indicated that the on-orbit crystals were more stable than the on-ground ones.     

Laser patterning and morphology of two-dimensional planar ferroelastic rare-earth molybdate crystals on the glass surface

The laser-induced crystallization method is applied to pattern two-dimensional planar crystals consisting of ferroelastic β′-(Sm,Gd)₂(MoO₄)₃ crystals (designated here as SGMO crystals) on the surface of Sm₂O₃–Gd₂O₃–MoO₃–B₂O₃ glass. By scanning Yb:YVO₄ fiber lasers (wavelength: 1080 nm) continuously with a small pitch (0.7 μm) between laser irradiated parts, planar SGMO crystals with periodic domain structures showing different refractive indices are patterned successfully, and a high orientation of SGMO crystals is confirmed from micro-Raman scattering spectrum and second harmonic intensity measurements. It is found that the crystal growth direction is perpendicular to the laser scanning direction. This relation, i.e., the perpendicular relation, is a different from the behavior in discrete crystal line patterning, where the crystal growth direction is consistent with the laser scanning direction. The present study proposes the possibility of the control of crystal growth direction in laser-induced crystallization in glasses.     

Improved liquid crystal pretilt angles by patterned dual alignment coating structures

The pretilt angles for the optically compensated bend (OCB) mode liquid crystals have been improved using novel patterned dual alignment coating structures in this study. The transition from the splay configuration to the bend configuration can thus be effectively reduced. The dual alignment coating structures consisted of a horizontal alignment polyimide (PI) and a patterned vertical alignment liquid crystal polymer (LCP). Three patterning masks were designed for the photolithography process. The pretilt angles were demonstrated to be increased to 34 degrees for the triangle lattice array-patterned cells. It became 31 degrees for the square lattice array-patterned cells, and 24 degrees for the honeycomb lattice array-patterned cells. The improved pretilt angles were illustrated by the force balance model that can be predicted by the LCP area ratio. The effective control over the pretilt angle could improve the response time to 2 ms when the voltage was ramped up to 5.5 V for the OCB mode liquid crystal devices.     

Inkjet Printing of Patterned,Multispectral, and Biocompatible Photonic Crystals

Patterning of photonic crystals to generate rationally designed color‐responsive materials has drawn considerable interest because of promising applications in optical storage, encryption, display, and sensing. Here, an inkjet‐printing based strategy is presented for noncontact, rapid, and direct approaches to generate arbitrarily patterned photonic crystals. The strategy is based on the use of water‐soluble biopolymer‐based opal structures that can be reformed with high resolution through precise deposition of fluids on the photonic crystal lattice. The resulting digitally designed photonic lattice formats simultaneously exploit structural color and material transience opening avenues for information encoding and combining functions of optics, biomaterials, and environmental interfaces in a single device.     

The Control on Size and Density of InAs QDs by Droplet Epitaxy (April 2009)

We report on the ability to grow InAs quantum dots (QDs) by droplet epitaxy (DE) using solid-source molecular beam epitaxy (MBE). In particular, the control of the size and density of InAs QDs at near room temperatures are achieved as a function of substrate temperature and crystallization condition. For a typical range of QD density ( ~10⁹ to 10¹⁰ cm^-2), the growth window is revealed to be fairly narrow ( ~20degC). In droplets are extremely sensitive to surface diffusion and arsenic background pressure even at near room temperatures. As a result, a very careful fabrication procedure is required to crystallize In droplets in order to fabricate desired shape of InAs QDs. For this purpose, we developed a double-step crystallization process, in which As background recovery and high-temperature crystallization are introduced. In addition, the results by DE are compared with QDs fabricated by Stranski-Krastanow (S-K) growth approach in terms of size and density. The results can find applications in optoelectronics as the fabrication of QDs by DE approach has more flexibility over S-K approach, i.e., more freedom of size and density control.     

Hierarchical nanofabrication of microporous crystals with ordered mesoporosity

Shaped zeolite nanocrystals and larger zeolite particles with three-dimensionally ordered mesoporous (3DOm) features hold exciting technological implications for manufacturing thin, oriented molecular sieve films and realizing new selective, molecularly accessible and robust catalysts. A recognized means for controlled synthesis of such nanoparticulate and imprinted materials revolves around templating approaches, yet identification of an appropriately versatile template has remained elusive. Because of their highly interconnected pore space, ordered mesoporous carbon replicas serve as conceptually attractive materials for carrying out confined synthesis of zeolite crystals. Here, we demonstrate how a wide range of crystal morphologies can be realized through such confined growth within 3DOm carbon, synthesized by replication of colloidal crystals composed of size-tunable (about 10-40 nm) silica nanoparticles. Confined crystal growth within these templates leads to size-tunable, uniformly shaped silicalite-1 nanocrystals as well as 3DOm-imprinted single-crystal zeolite particles. In addition, novel crystal morphologies, consisting of faceted crystal outgrowths from primary crystalline particles have been discovered, providing new insight into constricted crystal growth mechanisms underlying confined synthesis.     

Protein crystallization in space

The microgravity environment of space is an ideal place to study the complicated protein crystallization process and to grow good-quality protein crystals. A series of crystal growth experiments of 10 different proteins was carried out in space on a Chinese re-entry satellite FSW-2 in August, 1992. The experiments were performed for about two weeks at a temperature of 18.5 +/- 0.5 degrees C using a tube-like crystallization apparatus made in the Shanghai Institute of Technical Physics, Academia Sinica. More than half of 48 samples from 6 proteins produced crystals, and the effects of microgravity on protein crystal growth were observed, especially for hen-egg white lysozyme and an acidic phospholipase A2 from the venom of Agkistrodon halys Pallas. Analyses of the crystallization of these two enzymes in this mission showed that the microgravity environment in space may be beneficial to improve size, external perfection, morphology, internal order, and nucleation of protein crystals. Some of these positive microgravity effects were also demonstrated by the growth of protein crystals in gelled solution with the above two enzymes. A structural analysis of the tetragonal lysozyme crystal grown in space is in progress.     

Nanopatterning self-assembled nanoparticle superlattices by moulding microdroplets

Highly ordered arrays of nanoparticles exhibit many properties that are not found in their disordered counterparts. However, these nanoparticle superlattices usually form in a far-from-equilibrium dewetting process, which precludes the use of conventional patterning methods owing to a lack of control over the local dewetting dynamics. Here, we report a simple yet efficient approach for patterning such superlattices that involves moulding microdroplets containing the nanoparticles and spatially regulating their dewetting process. This approach can provide rational control over the local nucleation and growth of the nanoparticle superlattices. Using DNA-capped gold nanoparticles as a model system, we have patterned nanoparticle superlattices over large areas into a number of versatile structures with high degrees of internal order, including single-particle-width corrals, single-particle-thickness microdiscs and submicrometre-sized 'supra-crystals'. Remarkably, these features could be addressed by micropatterned electrode arrays, suggesting potential applications in bottom-up nanodevices.     

凝胶玻璃网络稳定性与析晶分析

利用溶胶-凝胶方法制备了：BaO-TiO2-Al2O3-SiO2体系的凝胶玻璃，以及其不同晶相的玻璃陶瓷。利用X-衍射分析确定凝胶玻璃析出的晶相。利用晶格能对凝胶玻璃的稳定性与析晶特性进行了定性分析。在凝胶玻璃的析晶过程中，品格能大者优先析晶。BaO-TiO-Al2O3-SiO2体系凝胶玻璃析出离子晶体的晶格能由大到小依次为BaTiO3、Ba2TiSi2O8、BaAl2Si2O8，这与实验结果的析晶次序一致。     

Direct visualization of dislocation dynamics in grain-boundary scars

Mesoscale objects with unusual structural features may serve as the analogues of atoms in the design of larger-scale materials with novel optical, electronic or mechanical behaviour. In this paper we investigate the structural features and the equilibrium dynamics of micrometre-scale spherical crystals formed by polystyrene particles adsorbed on the surface of a spherical water droplet. The ground state of sufficiently large crystals possesses finite-length grain boundaries (scars). We determine the elastic response of the crystal by measuring single-particle diffusion, and quantify the fluctuations of individual dislocations about their equilibrium positions within a scar by determining the dislocation spring constants. We observe rapid dislocation glide with fluctuations over the barriers separating one local Peierls minimum from the next and rather weak binding of dislocations to their associated scars. The long-distance (renormalized) dislocation diffusion glide constant is extracted directly from the experimental data and is found to be moderately faster than single-particle diffusion. We are also able to determine the parameters of the Peierls potential induced by the underlying crystalline lattice.     

Epitaxial and graphoepitaxial growth of materials on highly orientated PTFE substrates

The mechanism by which friction-deposited, highly orientated poly(tetrafluoroethylene) (PTFE) films promote orientated growth of materials was investigated. For this purpose, transmission electron microscopy was used to determine the orientation of polyethylene and 1,4-bis-2-(5-phenyloxazolyl)benzene (POPOP) crystals grown from the vapour phase onto the single crystal like PTFE films. Electron diffraction patterns revealed that the polyethylene crystals adopted an orientation that minimized the lattice mismatch at the interface between this material and the PTFE substrate. On the other hand, the POPOP crystals aligned in a fibre pattern, implying that orientated growth occurred because of the grating-shaped surface topography of the PTFE films. Evidently, the latter films were capable of promoting orientated growth of materials by a graphoepitaxial mechanism or conventional epitaxy, depending on the material used.     

Preparation of P(St-NMA) microsphere inks and their application in photonic crystal patterns with brilliant structural colors

Patterned photonic crystals with structural colors on textile substrates have attracted a special attention due to the great advantages in application, which currently become a research hot-spot. This study utilized an ink-jet printing technology to prepare high-quality photonic crystal patterns with structural colors on polyester substrates. The self-assembly temperature of poly(styrene-N-methylol acrylamide) (P(St-NMA)) microspheres set to construct photonic crystals were deeply optimized. Moreover, the structural colors of prepared photonic crystal patterns were characterized and evaluated. When the mass fraction of P(St-NMA) microspheres was 1.0 wt.%, the pH value ranged from 5 to 7, and the surface tension was in the range of 63.79 to 71.20 mN/m, inks could present the best print performance. At 60 °C, prepared P(St-NMA) microsphere inks were good for printing to obtain patterned photonic crystals with regular arrangement and beautiful structural colors. Specifically, photonic crystals with different colors could be constructed by regulating the diameter of microspheres in inks, and prepared structural colors exhibited distinct iridescent phenomenon. The present results could provide a theoretical basis for the industrial realization of patterned photonic crystals by ink-jet printing technology.     

Patterning Porous Oxides within Microchannel Networks

A continuing challenge for materials chemists and engineers is the ability to create multifunctional composite structures with well‐defined superimposed structural order from nanometer to micrometer length scales. Materials with three‐dimensional structures ordered over multiple length scales can be prepared by carrying out colloidal crystallization and inorganic/organic cooperative self‐assembly within microchannel networks. The resulting materials show hierarchical ordering over several discrete and tunable length scales ranging from several nanometers to micrometers. These patterned porous materials hold promise for use as advanced catalysts, sensors, low‐k dielectrics, optoelectronic and integrated photonic crystal devices.     

用于蛋白质结晶的形核剂研究综述

获取蛋白质晶体是蛋白质三维结构解析、医疗药品生产、自组装纳米体系构建等过程中重要的步骤。例如,利用X射线衍射技术对蛋白质进行三维结构解析时,首先需要通过结晶条件筛选,获得质量较高的蛋白质晶体,进而进行衍射得到蛋白质结构相关信息。蛋白质结晶需要经历从未饱和区经亚稳区至形核区的形核过程以及从形核区到亚稳区的生长成熟过程。在整个蛋白质结晶过程中,形核过程是至关重要的一步。均相形核过程中,结晶体系中各个部分形核概率相同,当蛋白质结晶体系中溶液的过饱和度足够克服形核势垒时,在形核区发生成核,因而在低浓度的结晶溶液体系中,均相形核存在一定的局限性。形核剂的添加使蛋白质晶体异相形核,相较于均相形核其需要克服的阻力小,形核势垒低。因而形核剂的使用对于难结晶蛋白或者起始浓度过低的蛋白质结晶具有重要意义。随着结构生物学的发展,形核剂在蛋白质结晶中的研究仍是结晶方法学领域的热点问题。多孔微球对蛋白质分子的吸附作用有利于无序蛋白质分子团簇的形成,进而促进蛋白质形核。添加多孔微球不但可以增加结晶条件筛选数,也可以提高晶体质量。促进蛋白质分子有序排列的形核剂籽晶的使用,使晶体的形核生长过程始终处于结晶体系溶液浓度较低的状态,而交联的籽晶因为稳定性更高而更有应用前景。新型交互扩散结晶板中,蛋白质结晶体系通过一个较缓慢的交互扩散过程实现蛋白质结晶溶液浓度的变化,并且结晶体系可达到共平衡,因而能显著提高蛋白质晶体结晶条件筛选数和晶体质量:蛋白酶K结晶条件数由39个提升至47个,分辨率由1.66提升至1.54。利用基底材料的一些特性,如静电作用、疏水作用和氢键,可以起到促进蛋白质分子聚集的功能,从而促进形核。本文从物理作用和化学作用两个角度详细总结了形核剂对蛋白质结晶的影响,并展望了该领域的发展前景及研究方向。     

用于晶体生长的地基无容器悬浮技术

空间微重力环境下几乎无对流和沉降,可为晶体生长提供一个相对稳定和均一的理想环境,易于得到尺寸较大的高质量单晶。但是,空间结晶实验成功率低,费用昂贵,实验机会受限。因此,研发各种空间微重力环境地基模拟技术具有重要意义。目前可用于晶体生长的地基无容器悬浮技术主要有空气动力悬浮、静电悬浮、电磁悬浮、液体界面悬浮、超声悬浮和磁场悬浮技术等。这些地基模拟技术可实现晶体的无容器悬浮生长,避免器壁对晶体生长的不良影响,提高晶体质量,为解决X射线单晶衍射技术中的瓶颈问题提供新途径,还可为在地基进行结晶动力学和机理研究提供简单易行的方法。从技术原理、优势、缺陷及在结晶(特别是蛋白质结晶)中的应用4个方面对这些技术逐一进行了介绍和评述。重点介绍了液体界面悬浮、超声悬浮和磁场悬浮技术这3种用于蛋白质晶体生长的较为成熟的地基无容器悬浮技术。     

Three-dimensional Si/Ge quantum dot crystals

Modern nanotechnology offers routes to create new artificial materials, widening the functionality of devices in physics, chemistry, and biology. Templated self-organization has been recognized as a possible route to achieve exact positioning of quantum dots to create quantum dot arrays, molecules, and crystals. Here we employ extreme ultraviolet interference lithography (EUV-IL) at a wavelength of lambda = 13.5 nm for fast, large-area exposure of templates with perfect periodicity. Si(001) substrates have been patterned with two-dimensional hole arrays using EUV-IL and reactive ion etching. On these substrates, three-dimensionally ordered SiGe quantum dot crystals with the so far smallest quantum dot sizes and periods both in lateral and vertical directions have been grown by molecular beam epitaxy. X-ray diffractometry from a sample volume corresponding to about 3.6 x 10(7) dots and atomic force microscopy (AFM) reveal an up to now unmatched structural perfection of the quantum dot crystal and a narrow quantum dot size distribution. Intense interband photoluminescence has been observed up to room temperature, indicating a low defect density in the three-dimensional (3D) SiGe quantum dot crystals. Using the Ge concentration and dot shapes determined by X-ray and AFM measurements as input parameters for 3D band structure calculations, an excellent quantitative agreement between measured and calculated PL energies is obtained. The calculations show that the band structure of the 3D ordered quantum dot crystal is significantly modified by the artificial periodicity. A calculation of the variation of the eigenenergies based on the statistical variation in the dot dimensions as determined experimentally (+/-10% in linear dimensions) shows that the calculated electronic coupling between neighboring dots is not destroyed due to the quantum dot size variations. Thus, not only from a structural point of view but also with respect to the band structure, the 3D ordered quantum dots can be regarded as artificial crystal.     

移动加热器法晶体生长工艺的研究进展

移动加热器法被认为是一种切实可行的生长大尺寸、高质量单晶体的方法,它结合了液相外延和区熔提纯的优点.本文阐述了移动加热器法晶体生长的基本原理、优缺点,综述了相关加热方式、晶体生长过程中的质量输运和热交换,并探讨了工艺条件(如重力场、磁场、强迫对流等和晶体生长速率)对移动加热器法生长晶体过程与晶体质量的影响,最后对移动加热器法的发展趋势进行了展望.     

DNA-controlled assembly of a NaTl lattice structure from gold nanoparticles and protein nanoparticles

The formation of diamond structures from tailorable building blocks is an important goal in colloidal crystallization because the non-compact diamond lattice is an essential component of photonic crystals for the visible-light range. However, designing nanoparticle systems that self-assemble into non-compact structures has proved difficult. Although several methods have been proposed, single-component nanoparticle assembly of a diamond structure has not been reported. Binary systems, in which at least one component is arranged in a diamond lattice, provide alternatives, but control of interparticle interactions is critical to this approach. DNA has been used for this purpose in a number of systems. Here we show the creation of a non-compact lattice by DNA-programmed crystallization using surface-modified Qβ phage capsid particles and gold nanoparticles, engineered to have similar effective radii. When combined with the proper connecting oligonucleotides, these components form NaTl-type colloidal crystalline structures containing interpenetrating organic and inorganic diamond lattices, as determined by small-angle X-ray scattering. DNA control of assembly is therefore shown to be compatible with particles possessing very different properties, as long as they are amenable to surface modification.