Crystal‐Growth‐Dominated Fabrication of Metal–Organic Frameworks with Orderly Distributed Hierarchical Porosity

Constructing architectures with hierarchical porosity has been widely considered as the most efficient way to bypass the problems related to slow mass transfer and inaccessibility of internal space in MOFs. Now, a crystal‐growth‐dominated strategy is proposed to fabricate hierarchically porous MOFs (HP‐MOFs). When the crystal growth is dominated by the monomer attachment, the aggregation of nonionic surfactant or polymer can be easily captured and released during the crystal growth process, resulting in the formation and ordering hierarchical pores along the radial direction. Owing to the accelerated mass diffusion and more exposed active sites of this design, HP‐MOFs exhibited an enhanced catalytic efficiency in styrene oxidation.     

Self-construction of core-shell and hollow zeolite analcime icositetrahedra: a reversed crystal growth process via oriented aggregation of nanocrystallites and recrystallization from surface to core

Zeolite analcime with a core-shell and hollow icositetrahedron architecture was prepared by a one-pot hydrothermal route in the presence of ethylamine and Raney Ni. Detailed investigations on samples at different preparation stages revealed that the growth of the complex single crystalline geometrical structure did not follow the classic crystal growth route, i.e., a crystal with a highly symmetric morphology (such as polyhedra) is normally developed by attachment of atoms or ions to a nucleus. A reversed crystal growth process through oriented aggregation of nanocrystallites and surface recrystallization was observed. The whole process can be described by the following four successive steps. (1) Primary analcime nanoplatelets undergo oriented aggregation to yield discus-shaped particles. (2) These disci further assemble into polycrystalline microspheres. (3) The relatively large platelets grow into nanorods by consuming the smaller ones, and meanwhile, the surface of the microspheres recrystallizes into a thin single crystalline icositetrahedral shell via Ostwald ripening. (4) Recrystallization continues from the surface to the core at the expense of the nanorods, and the thickness of the monocrystalline shell keeps on increasing until all the nanorods are consumed, leading to hollow single crystalline analcime icositetrahedra. The present work adds new useful information for the understanding of the principles of zeolite growth.     

An Energy Investigation into 1D/2D Oriented‐Attachment Assemblies of 1D Ag Nanocrystals

In the field of oriented‐attachment crystal growth, one‐dimensional nanocrystals are frequently employed as building blocks to synthesize two‐dimensional or large‐aspect‐ratio one‐dimensional nanocrystals. Despite recent extensive experimental advances, the underlying inter‐particle interaction in the synthesis still remains elusive. In this report, using Ag as a platform, we investigate the van der Waals interactions associated with the side‐by‐side and end‐to‐end assemblies of one‐dimensional nanorods. The size, aspect ratio, and inter‐particle separation of the Ag precursor nanorods are found to have dramatically different impacts on the van der Waals interactions in the two types of assemblies. Our work facilitates the fundamental understanding of the oriented‐attachment assembling mechanism based on one‐dimensional nanocrystals.     

铅基复合钙钛矿型弛豫铁电单晶的生长基元与生长机理Ⅰ.PMNT单晶的表面形貌、负晶结构及生长基元的组装与拆分

铅基复合钙钛矿型弛豫铁电单晶体PMNT的生长基元为多种[BO_6]配位八面体,晶体生长过程可视为多种八面体基元与Pb~(2 )的组装过程.这些生长基元向{111}面叠合时易采取法向生长机制,向{001}面叠合时易采取层状生长机制,由此决定了晶体生长速度的各向异性与晶体的形貌.Bridgman法生长的PMNT晶体在生长过程中由内向生长机制形成规则的负晶结构;在晶体生长过程中,在其自然表面上可形成正形与负形两种形貌;在高温退火过程中,由于PbO的分解,晶体表面上可形成类似“蚀象”的构型,这些可从[BO_6]八面体生长基元的组装或拆分方面获得解释.     

Crystal Growth Kinetics of Nanocrystalline ZnS under Surface Adsorption

The crystal growth mechanism,kinetics,and microstructure development play a fundamental role in tailoring the materials with controllable size and morphology. In this study,by introducing the strong surface adsorption of the concentrated NaOH,two-stage crystal growth kinetics of ZnS nanoparticles was observed. In the first stage,the primary particles grow into a size over a hundred times of the original volume and the growth is controlled by the crystal-lographically specific oriented attachment. The first stage data were fitted by the "multistep OA kinetic model" built based on the molecular collision and reaction. In the second stage,following the dispersal of nanoparticles,an abrupt transition from asymptotic to parabola growth kinetics occurs,which can be fitted by a standard Ostwald ripening volume diffusion model. The presence of surface adsorption causes the two-stage growth kinetics and permits an almost exclusive OA-based growth to dominate in the first stage.     

The molecular orientation of para-sexiphenyl on Cu(110) and Cu(110) p(2x1)O.

Controlling the molecular growth of organic semiconductors is an important issue to optimize the performance of organic devices. Conjugated molecules, used as building blocks, have an anisotropic shape and also anisotropic physical properties like charge transport or luminescence. The main challenge is to grow highly crystalline layers with molecules of defined orientation. The higher the crystallinity, the closer these properties reach their full intrinsic potential, while the orientation determines the physical properties of the film. Herein we show that the molecular orientation and growth can be steered by the surface chemistry, which tunes the molecule-substrate interaction. In addition, the oxygen reconstruction of the surface, demonstrates the flexibility of the organic molecules to adopt a given surface corrugation and their unique possibility to release stress by tilting.     

Self‐Template‐Directed Formation of Coordination‐Polymer Hexagonal Tubes and Rings,and their Calcination to ZnO Rings

This template will self‐destruct : A unique particle‐growth mechanism involves growth of new coordination polymers on the surface of initially formed hexagonal blocks and concomitant dissolution of the blocks to form hexagonal tubes (see scheme and scanning electron, optical, and fluorescence microscopy images). Calcination of the tubes yields ZnO particles of the same shape.

     

Nanoporous Nanorods Fabricated by Coordination Modulation and Oriented Attachment Growth

A growing attachment : Porous coordination polymer (PCP) nanorods are synthesized by modulation of the coordination equilibria between framework components, which regulates the rate of framework extension and crystal growth. Investigation of the crystal growth mechanism by TEM indicates that face‐selective modulation on the surfaces of PCP crystals enhances the anisotropic crystal growth of nanorods by an oriented attachment mechanism.

     

Reversed Crystal Growth of RHO Zeolitic Imidazolate Framework (ZIF)

RHO zeolitic imidazolate framework (ZIF), Zn_1.33(O.OH)_0.33(nim)_1.167(pur), crystals with a rhombic dodecahedral morphology were synthesized by a solvothermal process. The growth of the crystals was studied over time using scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD) and Brunauer–Emmett–Teller (BET) analyses, and a reversed crystal growth mechanism was revealed. Initially, precursor materials joined together to form disordered aggregates, which then underwent surface recrystallization forming a core–shell structure, in which a disordered core is encased in a layer of denser, less porous crystal. When the growth continued, the shell became less and less porous, until it was a layer of true single crystal. The crystallization then extended from the surface to the core over a six‐week period until, eventually, true single crystals were formed.     

Effect of surface orientation on the segregation kinetics of Sb from a Cu single crystal

In a previous theoretical study it has been suggested that the bulk vacancy formation energy near a surface depends on the orientation of the surface. It has been suggested also that this dependency of the vacancy formation energy would influence the bulk diffusion coefficient near the surface. The experimental results presented in this paper support this hypothesis. The experimental results were obtained by measuring the bulk‐to‐surface segregation of Sb for a Cu(111) single crystal with 0.088 at.% Sb and for a Cu(110) single crystal with 0.082 at.% Sb. The experimental results were fitted with the vacancy‐modified Darken model and it was clear that the bulk diffusion coefficient beneath the (110) surface is higher than the bulk diffusion coefficient beneath the (111) surface. Copyright © 2003 John Wiley & Sons, Ltd.     

Observation of Twisting Growth of Branched Polyethylene Single Crystals Formed from the Melt

The twisting growth of a branched polyethylene single crystal formed from the melt was observed directly by means of transmission electron and atomic force miscroscopy. The surface stress asymmetry arising from the asymmetry of the surface‐fold structure and chain tilting resulted in the twisting growth of the single crystals. The handedness of the twisting lamellae was consistent with the chain‐tilting direction. When multilayer lamellae piled up in a thicker film, the lamellar twist would be inevitably causing screw dislocations.     

Observation of shish crystal growth into nondeformed melts

Thin films of isotactic polystyrene (iPS) were deformed on a carbon supported TEM grid at temperatures between 210 °C and 240 °C. The elongation of the supercooled polymer melt films is localized in a deformation zone due to the formation of cracks within the brittle carbon support film, whereas the adjoining areas stay in a relaxed state. Since the nucleation of fibrous (“shish”) crystals needs an orientation mechanism to align the molecular chains, their origin is located in the deformation zone. It is shown that the subsequent growth of the shish crystal can propagate into the relaxed melt although it has to surmount the adhesion to the carbon substrate. From these results the conclusion is drawn that the shish crystal growth can be an autocatalytic process, which induces a self‐orientation of the molecules in the growth front of the crystal tip and does not necessarily need an external flow field. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1183–1187, 2000     

Facile Synthesis of Hierarchical Nanosized Single‐Crystal Aluminophosphate Molecular Sieves from Highly Homogeneous and Concentrated Precursors

The synthesis of hierarchical nanosized zeolite materials without growth modifiers and mesoporogens remains a substantial challenge. Herein, we report a general synthetic approach to produce hierarchical nanosized single‐crystal aluminophosphate molecular sieves by preparing highly homogeneous and concentrated precursors and heating at elevated temperatures. Accordingly, aluminophosphate zeotypes of LTA (8‐rings), AEL (10‐rings), AFI (12‐rings), and ‐CLO (20‐rings) topologies, ranging from small to extra‐large pores, were synthesized. These materials show exceptional properties, including small crystallites (30–150 nm), good monodispersity, abundant mesopores, and excellent thermal stability. A time‐dependent study revealed a non‐classical crystallization pathway by particle attachment. This work opens a new avenue for the development of hierarchical nanosized zeolite materials and understanding their crystallization mechanism.     

A Porous Coordination Polymer with Accessible Metal Sites and its Complementary Coordination Action

Broken switch : Guest‐accessible metal sites are generated on the pore surface of a porous coordination polymer (see figure) through the complementary coordination‐bond rearrangement in a single‐crystal‐to‐single‐crystal fashion, which is triggered by the removal of coordinated water.

     

Laser‐Induced Crystallization and Crystal Growth

Recent streams of laser studies on crystallization and crystal growth are summarized and reviewed. Femtosecond multiphoton excitation of solutions leads to their ablation at the focal point, inducing local bubble formation, shockwave propagation, and convection flow. This phenomenon, called “laser micro tsunami” makes it possible to trigger crystallization of molecules and proteins from their supersaturated solutions. Femtosecond laser ablation of a urea crystal in solution triggers the additional growth of a single daughter crystal. Intense continuous wave (CW) near infrared laser irradiation at the air/solution interface of heavy‐water amino acid solutions results in trapping of the clusters and evolves to crystallization. A single crystal is always prepared in a spatially and temporally controlled manner, and the crystal polymorph of glycine depends on laser power, polarization, and solution concentration. Upon irradiation at the glass/solution interface, a millimeter‐sized droplet is formed, and a single crystal is formed by shifting the irradiation position to the surface. Directional and selective crystal growth is also possible with laser trapping. Finally, characteristics of laser‐induced crystallization and crystal growth are summarized.     

Oriented attachment kinetics for ligand capped nanocrystals: coarsening of thiol-PbS nanoparticles

In this work, the growth kinetics of thiol-capped PbS nanoparticles was studied. Two-stage growth process was observed, which was controlled first by oriented attachment (OA) mechanism and then by the hybrid Ostwald ripening (OR) and OA mechanism. Different from the NaOH-ZnS system, where OA will occur between any two multilevel nanoparticles, an OA kinetic model only considering the attachment related to original particles was fitted well with the experimental results. Analysis reveals that this model may be a universal one to describe the OA crystal growth process of nanocrystals capped with easily destroyed ligands, such as thiol-ZnS in the previous report. The OA crystal growth characteristics determined by the surface agent were discussed and compared. We propose that with stronger surface capping, the OR growth of nanocrystals is hindered, which facilitates the size controlling via OA kinetics during nanosynthesis.     

Motif Reconstruction in Clusters and Layers: Benchmarks for the Kawska–Zahn Approach to Model Crystal Formation

A recently developed atomistic simulation scheme for investigating ion aggregation from solution is transferred to the morphogenesis of metal clusters grown from the vapor and layers deposited on a substrate surface. Both systems are chosen as benchmark models for intense motif reorganization during aggregate/layer growth. The applied simulation method does not necessarily involve global energy minimization after each growth event, but instead describes crystal growth as a series of structurally related configurations which may also include local energy minima. Apart from the particularly favorable high‐symmetry configurations known from experiments and global energy minimization, we also demonstrate the investigation of transient structures. In the spirit of Ostwald’s step rule, a continuous evolution of the aggregate/layer structure during crystal growth is observed.     

Fabrication of oriented crystals as force measurement tips via focused ion beam and microlithography methods

Detailed knowledge of the forces between nanocrystals is very crucial for understanding many generic (eg, random aggregation/assembly and rheology) and specific (eg, oriented attachment) phenomena at macroscopic length scales, especially considering the additional complexities involved in nanocrystals such as crystal orientation and corresponding orientation‐dependent physicochemical properties. Because there are a limited number of methods to directly measure the forces, little is known about the forces that drive the various emergent phenomena. Here, we report on two methods of preparing crystals as force measurement tips used in an atomic force microscope: the focused ion beam method and microlithography method. The desired crystals are fabricated using these two methods and are fixed to the atomic force microscope probe using platinum deposition, ultraviolet epoxy, or resin, which allows for the orientation‐dependent force measurements. These two methods can be used to attach virtually any solid particles (from the size of a few hundreds of nanometers to millimeters). We demonstrate the force measurements between aqueous media under different conditions such as pH.     

搅拌条件下电流密度对Cu镀层的结构和表面形貌的影响

电沉积;晶体取向;搅拌条件下电流密度对Cu镀层的结构和表面形貌的影响     

The effect of voltage controlled orientation order of liquid crystals in non-acrylic polymer dispersed liquid crystals films

The nematic liquid crystals (LCs) are randomly dispersed material with random orientation order in polymer dispersed liquid crystal (PDLC) films. The LCs change their orientation from random to vertical as electric field is applied. This transformation of orientation order of nematic liquid crystals in the PDLC films is controlled by many factors operating simultaneously. For instance, some factors like the internal forces of attractions among the neighboring LC molecules, anchoring with polymeric matrix, ITO glass boundaries, and chemical structures of the materials are less studied. The learning of extent of vertical orientation of liquid crystal droplets in an electric field is essential to attain optimum electro optical properties of PDLCs. In this finding, bipolar and radial LCs droplets with random orientation have been observed in non-acrylic polymeric media. It is learned that with small increase of contents of external material, the extent of vertical orientation has been varied intensely. The extent of vertical orientation of LCs molecules increases as the contents of external non-acrylic polymeric material decreased. For this study, the orientations of LCs with respect to material type/contents, external applied force, and restoration of electric filed as hysteresis have been studied in details.