Crystal Growth Modifier Research Articles

Template-free synthesis of single-crystalline SmF3 rattle-structured sub-micropumpkins

Single-crystalline SmF3 sub-micropumpkins with a rattle-type structure have been successfully synthesized on a large scale by reaction of aqueous Sm3+ with ammonium fluoride in the presence of ethylenediaminetetraacetic acid (EDTA) at 110 °C for 16 h, which were confirmed by X-ray powder diffraction, energy dispersive X-ray analysis, transmission electron microscopy, and scanning electron microscopy. The reaction time and EDTA have been shown to play important roles in the formation of SmF3 rattle-structured sub-microcrystals. A mechanism for the formation of the SmF3 rattle-structured sub-micropumpkins via cooperation of an oriented aggregation process and Ostwald ripening has been proposed based on observations of time-dependent experiments. In addition, this crystal growth mode could be expanded to the synthesized Eu-doped SmF3 rattle-structured sub-microcrystals. It is believed that the results of the present investigation may provide a versatile approach for designing and fabricating a wide range of nano/microcrystals.

Effect of nucleation agents on the crystallization of poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB)

AbstractBoron nitride (BN), talc, hydroxyapatite (HA), and zinc stearate (ZnSt) were investigated as nucleation agents (NA) for nonfossil‐based poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) plastics. Nonisothermal crystallization behaviors of the P3/4HB/NA blends were examined by DSC. It revealed that BN is the most efficient nucleation agent to promote the crystallization rate, however, but not the crystallization degree. The lasting crystallization of P3/4HB was also removed. The nucleation effect was strengthened with increase of BN content up to 1% and then slackened deeply when further BN was added. Isothermal crystallization analysis revealed that the addition of nucleation agent BN does not alter the crystal growth mode of P3/4HB, with maintaining the Avrami parameter n value around 2.40. Talc did enhance the crystallization of P3/4HB with however milder crystal growth rate. HA and ZnSt did not promote, but depressed the crystallization of P3/4HB plastics. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Hierarchical ZnO Nanorod-Assembled Hollow Superstructures for Catalytic and Photoluminescence Applications

In this study, hierarchically complex hollow cage-like superstructures assembled by ZnO nanorods have been successfully constructed with water-soluble biopolymer sodium carboxymethyl cellulose as crystal growth modifiers. The number of the hollow cage could be adjusted from single-cage, double-cage, multi-cage to connected-cage. A possible formation mechanism of the hollow superstructures has also been proposed. The catalytic study shows that these ZnO superstructures have good abilities to enhance propellant combustion of ammonium perchlorate (an important oxidizer used in solid rocket propellants), by decreasing its decomposition temperature to as low as 285 °C. Photoluminescence studies reveal that the increase in the cage number leads to an increase in the relative photoluminescence intensity around 500 to 700 nm, which might be attributed to the increase in radiative defects at the interface of the components of the ZnO hollow structure with the growth in cage number.

Increase of the production rate and crystal growth mode ofGdBa2Cu3Oy-coated conductors using an in-plume growth technique for a reel-to-reel pulsed-laserdeposition system

We developed a new fabrication technique which we call the ‘in-plume growth (IPG)’ technique. AREBa2Cu3Oy layered film for a coated conductor (REBCO CC) is grown in the plume using a pulsed-laserdeposition (PLD) method with a short distance between the target and the substrate (dT−S) to increase the production rate. In general, the critical current density (Jc) of PLD-REBCO CCs using an RTR system decreases asdT−S decreases since the amount of the dead layer increases and the composition ofthe REBCO layer becomes off-stoichiometric. In this work, we fabricated high-Jc GdBa2Cu3Oy (GdBCO) CCs using the IPG technique by varying the target composition and the tapemoving speed to control the composition of the REBCO layer and to suppress the formation ofa-axis-oriented grains. As a result, the IPG-GdBCO CCs, which were fabricated at 2 m h−1 (depositionarea = 1-turn × 6.5 cm = 6.5 cm2, laserpower = 300 mJ,f = four-plumes × 30 Hz), showed the followingcharacteristics: Ic = 312 A cm−1 width (Jc = 2.6 MA cm−2)with 1.2 µm in thickness and 1 m length. The production speed and theJc value are 3.0 and 1.8 times higher, respectively, compared to those deposited understandard conditions without using the IPG technique. This result indicates that thePLD-REBCO CCs could be more competitive for production of CCs for practical electricpower applications in the near future.

The effects of vicinal sapphire substrates on the properties of AlGaN/GaN heterostructures

AlGaN/GaN heterostructures on vicinal sapphire substrates and just-oriented sapphire substrates (0001) are grown by the metalorganic chemical vapor deposition method. Samples are studied by high-resolution x-ray diffraction, atomic force microscopy, capacitance–voltage measurement and the Van der Pauw Hall-effect technique. The investigation reveals that better crystal quality and surface morphology of the sample are obtained on the vicinal substrate. Furthermore, the electrical properties are also improved when the sample is grown on the vicinal substrate. This is due to the fact that the use of vicinal substrate can promote the step-flow mode of crystal growth, so many macro-steps are formed during crystal growth, which causes a reduction of threading dislocations in the crystal and an improvement in the electrical properties of the AlGaN/GaN heterostructure.

Controlled Synthesis of CdClOH Sub‐nanocones by Low‐temperature Solution Process and Their Transformation into CdS Hollow Sub‐nanocones

AbstractNovel CdClOH sub‐nanocone crystals were successfully synthesized on a large scale by a facile solution‐based method using polymers as crystal growth modifiers. The crystals showed cone‐like morphology. Some factors affecting the morphology and size of the product, such as reaction temperature, concentrations of polyacrylamide (PAM), and pH value of the solution, were systematically studied. Experiments implied that polymer PAM played a key role in the formation of CdClOH sub‐nanocones. A possible formation mechanism of CdClOH sub‐nanocones was suggested based on nucleation‐etching process‐recrystallization in a mild aqueous solution. Furthermore, the as‐prepared CdClOH sub‐nanocones could be further transformed into CdS hollow sub‐nanocones by an anion‐exchange reaction.

Nanocubes of PbS with visible luminescence synthesized by sulfonated polymer as stabilizer and modifier at room-temperature

Well-defined PbS nanocubes have been synthesized at room temperature by a mild solution-based simple method in the presence of sulfonated polymer as both stabilizer and crystal growth modifier. The simple method avoids high temperature which is required in the preparation of cubic-shaped PbS nanocrystals by hydrothermal reaction. A growth mechanism of the PbS nanocubes in the mild solution was discussed. The as-prepared samples exhibit intense visible emission and weaker near-infrared emission. The samples can be readily dissolved by organic solvents to form stable colloids for further processing, assembly or applications.

Effect of O2-Plasma Treatment of Mo on the Crystal Growth Mode of Pentacene of Organic Thin-Film Transistors

We report the change in the crystallinity of pentacene film on -plasma-treated molybdenum (Mo) and the electrical properties of pentacene thin-film transistors using Mo as source–drain electrodes. The surface energy of the Mo film was increased with -plasma treatment. Synchrotron radiation photoemission spectroscopy results revealed that the valence band split from the metallic Fermi level as the surface of the Mo was treated with plasma. This provides evidence that the surface of the Mo film changed to Mo oxide . Grazing-angle incidence X-ray diffraction results showed that pentacene molecules on -plasma-treated Mo has well-aligned features in the vertical direction as well as in the lateral direction, leading to a high crystalline film growth. The growth mode of pentacene changed from a tilted bulklike structure to a thin-film phase type by the treatment. This change in the growth mode is attributed to the reduction in interaction energy between pentacene and Mo via the formation of oxide at the Mo/pentacene interface. Secondary electron emission spectra showed that the work function increased by 0.55 eV after -plasma treatment on the Mo surface. Thus, the Mo oxides lowered the potential barrier for the hole injection from Mo to pentacene, increasing the drain current of bottom-contact organic thin-film transistors.

Polymer‐Controlled Growth of CuO Nanodiscs in the Mild Aqueous Solution

AbstractCuO nanodiscs have been synthesized on a large scale by a facile solution‐based method using polymers as crystal growth modifiers. X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) were carried out to characterize the structures and morphologies of the obtained products. The effects of reaction temperature, concentrations of polyacrylamide (PAM) and reactants on the morphology and size of the product were studied. The results revealed that the CuO nanodisc had single‐crystal monoclinic structures, and grew along (002) and (110) planes. Experimental conditions had all influence on the shape and size of the final products, but polymer PAM played the key role in formation of the CuO nanodisc. A possible growth mechanism of the CuO nanostructures based on typical polymer‐crystal interactions in a mild aqueous solution was given. Polymer‐directed crystal growth may provide promising routes to rational synthesis of various ordered inorganic and inorganic‐organic hybrid materials with complex forms and structural specialization.

Reactive epitaxial growth of MnSi ultrathin films on Si(111) by Mn deposition

Manganese (Mn) adsorption on the $\text{Si}(111)\text{\ensuremath{-}}(7\ifmmode\times\else\texttimes\fi{}7)$ surface followed by annealing at a relatively low temperature of $250\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ has been studied by using scanning tunneling microscopy as well as low-energy electron diffraction and Auger-electron spectroscopy. The B20-type structure of a Mn monosilicide (MnSi) of epitaxial ultrathin films is formed with a $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})\text{R}30\ifmmode^\circ\else\textdegree\fi{}$ periodicity. Morphologies of the crystalline MnSi ultrathin films have been investigated for Mn coverage of 1.5, 3, and 5 monolayers (ML). We found a characteristic mode of crystal growth for compound formation in the solid-on-solid system. At each amount of the Mn deposition, structural features, morphology, and formation processes of the MnSi films can be explained by the mass balance between deposited Mn and usable Si atoms. We found that the epitaxial MnSi ultrathin films can be grown coherently on Si(111) at 3 ML of Mn deposition. At 5 ML, the supply of Si atoms from bulk to surface becomes significant, then many deep holes are formed and the surface morphology becomes rough. It is found that the codeposition of Mn and Si leads to the formation of anomalously smooth MnSi surfaces.

The use of iminodiacetic acid for low-temperature synthesis of aragonite crystal microrods: Correlation between aragonite crystal microrods and stereochemical effects

The particle size, morphology, crystallization, and growth of calcium carbonate have been widely studied in the presence of organics, biomacromolecules, and biopolymers. Calcium carbonate with regular surface-relief structures has been synthesized by templating methods in the absence of dual negatively charged organic additives. Although a number of attempts have been made, the large-scale synthesis of 90 wt.% aragonite microrods by a facile route has hitherto remained difficult to achieve at temperatures below 60 °C. By using iminodiacetic acid as a crystal growth modifier, aragonite precipitated calcium carbonate (PCC) in the form of single-crystal microrods has been successfully synthesized at lower temperatures. It has been shown that the crystallographic and morphological characteristics of aragonite PCC microrods synthesized in the presence of iminodiacetic acid at a lower temperature are the same as those of aragonite obtained at 75 °C without an organic additive. The stereochemical relationship between calcium ions and the arrangement around ions bound to the carboxyl groups of iminodiacetic acid is suggested as a potential factor in the oriented nucleation and selectivity for formation of aragonite PCC microrods. The morphology, size, and crystal structure have been characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD).

Dispersity and growth kinetics of K2SO4 crystals in drops of an evaporating solution

Growth of K2SO4 crystals is studied in solution drops that have different initial heights and evaporate in different times. The dependences of the crystal size on the crystal growth time are obtained. The following three crystal growth modes are detected: rapid crystal growth in a supersaturated solution, a stop in the growth as a result of complete removal of supersaturation, and slow growth at a quasi-equilibrium solution concentration. The dispersities of the crystals that are retained at the bottom of the drop after complete evaporation of the solvent are calculated. A linear relation between the crystal dispersity and the reciprocal crystal growth time is revealed. The dispersity of K2SO4 crystals and the dispersity of the solid-solution dendrites in aluminum alloys are found to exhibit the same character of their dependences on the reciprocal crystal growth time.

Effects of ammonium citrate additive on crystal morphology of aluminum phosphate ammonium taranakite

In this communication, we demonstrated the growth of aluminum phosphate ammonium taranakite (NH 4-AlPO 4) crystals from regular hexagonal form into the disk-like form could be controlled by ammonium citrate (AMC) as the effective crystal growth modifier at 90 °C. Prepared crystals were characterized by field emission scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of AMC's concentration on the crystal form and morphology of NH 4-AlPO 4 were studied. The results showed that the AMC's concentration is an important parameter to control the size and morphology of NH 4-AlPO 4 crystal. The formation mechanism of the special morphology of NH 4-AlPO 4 crystals was also analyzed.

Biomineralization process of calcium phosphate: Modulation of the poly-amino acid with different hydroxyl/carboxyl ratios

Organic species are thought to exert an important effect on the formation of the mineral materials by their electrostatic attraction with the cations of minerals. In this work, a series of polyaspartic acids with different hydroxylation degrees (PAsp- x%OH) have been used as crystal growth modifiers to direct the synthesis of calcium phosphate. The change of x in the PAsp- x%OH can precisely adjust its electrostatic interaction with calcium ions and, thereby, modulate the formation process and property of calcium phosphate, such as morphology, crystallinity, organic component content and calcium-to-phosphate ratio. Two competitive reactions are suggested in this system, that is, the combination of calcium ions to PAsp- x%OH and the precipitation of calcium hydrogen phosphate dihydrate. The trends of these two reactions are determined by variation of x in the PAsp- x%OH: lower value of x tends to involve the former, while the higher tends to latter. It has been found that the mineralization process involving PAsp-15%OH displayed a special point to counterbalance the two competitive reactions, leading to the longest induction time. These findings indicate that how an organic species controls the morphology and the formation dynamics of inorganic crystals in biomineralization by the slight modification of its molecular structure.

Diffusion-controlled and diffusionless crystal growth in liquid o-terphenyl near its glass transition temperature

o-terphenyl is one of the organic liquids in which a fast mode of crystal growth is activated near the glass transition temperature T(g) and continues deep in the glassy state. This growth mode, termed glass-crystal (GC), is not limited by molecular diffusion in the bulk liquid, in contrast to the diffusion-controlled growth at higher temperatures. The GC mode has been previously described as abruptly emerging near T(g) and having a constant growth rate at a fixed temperature, two features important for testing its various explanations. We report here that the GC mode already exists in the equilibrium liquid of o-terphenyl up to 1.15T(g) (T(g)=246 K) in the form of loose, fast-growing fibers and that its growth rate is constant at T(g)+2 K, but decreases by 30% in 10 h at T(g)-13 K, during which time the glass' fictive temperature decreases by 6 K. The slow down of GC growth becomes less noticeable over time so that fast growth is still observable after long annealing. The fiber growth, similar to the fully activated GC growth that yields compact spherulites, is also not limited by bulk diffusion. Crystal growth in the GC mode has a comparable activation energy as liquid desorption but a much faster rate, properties in common with polymorphic conversions. The time dependence of GC growth is not readily explained by the effect of physical aging on the thermodynamic driving force of crystallization, the liquid desorption, the primary structural relaxation, or a secondary relaxation. The secondary dielectric relaxation observed by dielectric spectroscopy in glassy o-terphenyl disappears too quickly for its molecular motions to be responsible for GC growth.

Polymer-controlled crystallization of dumbbell-like ZnO hollow architectures

Dumbbell-like ZnO hollow architectures have been achieved on a large scale by a facile solution-based method by using water-soluble polymer (poly(sodium 4-styrenesulfonate)) as crystal growth modifier. The as-prepared ZnO architectures were in fact assembled by numerous sheet-like particles with an average size of ~ 10 nm. Studies found that the existence of PSS played an important role in the formation of these unique ZnO microstructures. The possible formation mechanism has been discussed based on the experimental results and the function of organic molecules. The hollow ZnO architectures exhibit unique photoluminescence characteristics at room temperature, suggesting promising potential for optoelectronic applications.

Effect of symmetry of substrate surfaces on the orientation and growth mode of ZnO films

The growth behaviors of ZnO films prepared by laser molecular beam epitaxy (L-MBE) were investigated on the substrates with different symmetry. The growth mode, the out-of-plane and in-plane orientations of ZnO thin films have been estimated by in-situ reflected high-energy electron diffraction (RHEED) and ex-situ X-ray diffraction (XRD). ZnO films on amorphous glass substrates were polycrystalline with mixed (1 0 0) and preferred (0 0 1) crystal orientation. Single-domain ZnO films were arranged on (0 1 1)-, (1 1 1)-cubic perovskite and (0 0 1)-hexagonal substrates. On (0 0 1)-cubic perovskite surfaces, ZnO films contained poly-domain twined structure. The orientation difference of ZnO films could be attributed to the competition between the factors of the surface and interface influence including surface energy, strain energy and electrostatic energy. The crystal quality and growth mode were found to be dependent on not only the interface mismatch but also domain symmetry.

Synthesis of Cd(OH)2 with Doughnut Microstructure and Its Controlled Growth Mechanism

AbstractDoughnut‐like Cd(OH)2 microstructure was obtained by a facile solution‐based method using polymer polyacrylamide (PAM) as a crystal growth modifier. Hexagonal flake‐like Cd(OH)2 is the building‐block to assemble doughnut‐like microstructures. The block concaves from one side when PAM is present in the synthesis system. However, nano‐size Cd(OH)2 doughnuts with a hole in the middle part were formed if carboxyl‐functionalized polyacrylamide (PAM‐COOH) was used as a crystal growth modifier. A possible mechanism for the Cd(OH)2 microstructure formation based on typical oriented attachment process in the presence of polymer was discussed. Polymer‐directed crystal growth and mediated self‐assembly of nanocrystals may promise synthesis routes for variously ordered inorganic and inorganic‐organic hybrid materials with complex forms and special structures.

Biomimetic Synthesis of Tooth-Like Hydroxyapatite under Organic Polymer Monolayer

Based on the basic theory of molecular recognition , we design a organic molecules model to induce the crystallization of hydroxyapatite to synthesized tooth-like calcium phosphate/hydroxyapatite under a controllable way in vitro. The cross-linking of collagen on the dentin surface and extraneous collagen was optimized by varying the molar ratio of N,N-(3-dimethylaminopropyl)- N'-ethyl-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) at a constant EDC concentration. CaCl2 and Na3PO4-12H2O solutions were added after the crosslinking process. X-ray photoelectron spectroscopic (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis of organic protein monolayer for samples. The obtained composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) as well as energy dispersive X-ray (EDX). XPS and FTIR analysis showed the surface organic compositions in experimental group is higher than that of normal dentin and decalcified dentin surface. The results showed that the dentinal tubule were blocked by neonatal hydroxyapatite layer which has a continuous structure of columns crystal with size of 10-40nm. Furthermore, there were column crystal with parallel direction inside, similar to the crystal array in the top of enamel rod. This study showed that the specific organic molecule model can be used as a potential effective crystal growth modifier.

Hierarchically Nano-structured In<sub>2</sub>S<sub>3</sub> Hollow Microspheres Synthesized Using Amino Acids as Crystal Growth Modifiers

Hierarchically nano-structured In2S3 hollow microspheres were synthesized by a hydrothermal method and the hollowing effect was attributed to an Ostwald ripening process. Using different amino acids as crystal growth modifiers, In2S3 with different surface morphologies, such as raspberry-like, urchin-like, and flower-like hollow microspheres, were selectively fabricated. The shells of the microspheres were composed of nanosized particles or nanoflakes of In2S3.These results demonstrate that amino acids with different functional groups, such as -NH2, -COOH, and -SH, can induce the formation of different indium sulfide nanostructures. A blue shifted UV band in the UV-Vis spectrum as well as a strong emission at ca 385 nm and a weak emission at ca 364 nm in the photoluminescence (PL) spectrum of In2S3 hollow microspheres indicate strong quantum confinement because of the presence of nanocrystalline particles. Using different amino acids as crystal growth modifiers, microspheres with different surface morphologies were fabricated. These results demonstrate that amino acids with different functional groups can induce the formation of different indium sulfide nanostructures.