Showing papers on "Crystal growth published in 2007"

Carbon and Nitrogen Co-doped TiO2 with Enhanced Visible-Light Photocatalytic Activity

Abstract: To utilize visible light more efficiently in photocatalytic reactions, carbon-doped TiO2 (C−TiO2), nitrogen-doped TiO2 (N−TiO2), and carbon and nitrogen co-doped TiO2 (C−N−TiO2) nanoparticles with different nitrogen and carbon contents were prepared by a sol−gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV−vis spectroscopy. XRD results showed that the doping of C and N atoms could suppress the crystal growth of TiO2, and the effect of C doping was more pronounced than that of N doping. XPS, UV−vis spectroscopy, and lattice parameter analysis revealed that N atoms could incorporate into the lattice of anatase through substituting the sites of oxygen atoms, while most C atoms could form a mixed layer of deposited active carbon and complex carbonate species at the surface of TiO2 nanoparticles. The photocatalytic activities of obtained C−TiO2, N−TiO2, and C−N−TiO2 samples with different C and N contents were evalua...

Shape-Controlled Syntheses of Gold Nanoprisms and Nanorods Influenced by Specific Adsorption of Halide Ions

Abstract: This paper describes the effect of halide ions during the seed-mediated growth of gold nanoparticles employing cetyltrimethylammonium bromide (CTAB) as a cationic surfactant system. With the addition of a small amount of iodide ion (∼20 μM) in a growth solution, the major product of the gold nanostructures formed were notably changed into triangular nanoprisms in the presence of excessive bromide ion (∼0.1 M); otherwise, in its absence, nanorods with an aspect ratio of ∼11 were the main products. The major role of the iodide ion was in retarding the overall rate of crystal growth, and the iodide adsorption appeared to repress the crystal growth along Au(111) direction, resulting in Au(111)-faced triangular nanoprisms. When the counteranions of the surfactant were replaced with chloride ions, a novel nanostructure (i.e., nanorice) was manufactured, which demonstrates the effectiveness of the adsorption of halide ions. However, this finding is quite contrasted with the work of the Sastry group (J. Nanosci. ...

Synthesis of NaYF4 Nanocrystals with Predictable Phase and Shape

Abstract: In this Full Paper, a water/alcohol/oleic acid system was developed to prepare NaYF 4 nanocrystals with predictable size, shape and phase. The structural and kinetic factors that govern the phase and shape evolution of NaYF 4 nanocrystals have been carefully studied, and the influence of NaF to Y 3+ ratio, reaction time and temperature on the phase and shape evolution of the as-prepared NaYF 4 samples was systematically investigated and discussed. It was found that the NaF to Y 3+ ratio was responsible for the shape evolution while temperature and reaction time was the key for the phase control of the NaYF 4 nanocrystals. This study would be suggestive for the precisely controlled growth of inorganic nanocrystals, especially for those usually crystallizing in diverse crystal structures.

Trapping metal-organic framework nanocrystals: an in-situ time-resolved light scattering study on the crystal growth of MOF-5 in solution.

Abstract: The addition of p-perfluoro-ethylbenzoic acid as capping reagent yields stable size-selected MOF-5 colloids and suggests a general concept for controlled particle formation of carboxylic acid based MOFs in solution.

Mechanism of molecular beam epitaxy growth of GaN nanowires on Si(111)

Abstract: GaN nanowires have been grown without external catalyst on Si(111) substrates by plasma-assisted molecular beam epitaxy. Nanowire aspect ratios (length/diameter) of about 250 have been achieved. During the initial stage of the growth, there is a nucleation process in which the number of wires increases and the most probable nucleation diameter of about 10nm has been observed, which slowly increases with deposition time. For deposition time longer than the nucleation stage, the nanowire length as a function of diameter monotonically decreases. This phenomenon can be explained by adatom diffusion on the nanowire lateral surface towards the tip.

Additives and crystallization processes

Abstract: Additives and crystallization processes , Additives and crystallization processes , کتابخانه الکترونیک و دیجیتال - آذرسا

Secondary Nucleation and Growth of ZnO

Abstract: Recently we discovered that under certain conditions new crystal growth (branch) can be induced on specific crystalline planes of the same material. This is a new phenomenon and is in sharp contrast to typical nucleation and growth in which a crystal will simply grow larger in preferred directions depending on the surface energy of the specific crystalline planes. Based on our observation, we developed a sequential nucleation and growth technique offering the power to assemble complex hierarchical crystals step-by-step. However, the key questions of when and how the secondary nucleation takes place have not been answered. Here we systematically study secondary ZnO crystal growth using organic diamine additives with a range of chain lengths and concentration. We found that ZnO branches form for a narrow diamine concentration range with a critical lower and upper critical nucleation concentration limit, which increases by about a factor of 5 for each additional carbon in the diaminoalkane chain. Our results suggest that the narrow window for secondary growth is dictated by the solubility of the ZnO crystals, where the low critical nucleation concentration is determined by slight etching of the surface to produce new nucleation sites, and the upper critical concentration is determined by the supersaturation concentration. Kinetic measurements show that the induction time and growth rate increase with increasing diamine concentration and follow classical nucleation and growth theory. Observations of branch morphological evolution reveal the mechanisms guiding the tunable crystal size and morphology.

Synthesis of crystals with a programmable kinetic barrier to nucleation

Abstract: A central goal of chemistry is to fabricate supramolecular structures of defined function and composition In biology, control of supramolecular synthesis is often achieved through precise control over nucleation and growth processes: A seed molecule initiates growth of a structure, but this growth is kinetically inhibited in the seed's absence Here we show how such control can be systematically designed into self-assembling structures made of DNA tiles These structures, "zig-zag ribbons," are designed to have a fixed width but can grow arbitrarily long Under slightly supersaturated conditions, theory predicts that elongation is always favorable but that nucleation rates decrease exponentially with increasing width We confirm experimentally that although ribbons of different widths have similar thermodynamics, nucleation rates decrease for wider ribbons It is therefore possible to program the nucleation rate by choosing a ribbon width The presence of a seed molecule, a stabilized version of the presumed critical nucleus, removes the kinetic barrier to nucleation of a ribbon Thus, we demonstrate the ability to grow supramolecular structures from rationally designed seeds, while suppressing spurious nucleation Control over DNA tile nucleation allows for proper initiation of algorithmic crystal growth, which could lead to the high-yield synthesis of micrometer-scale structures with complex programmed features More generally, this work shows how a self-assembly subroutine can be initiated

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.

Abstract: 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 ...

Additives and Crystallization Processes: From Fundamentals to Applications

Abstract: Preface. 1 Complexes in Solutions. 1.1 Structure of Common Solvents. 1.2 Structure of Pure Aqueous Electrolyte Solutions. 1.2.1 Solvation of Electrolyte Ions in Solutions. 1.2.2 Concentrated and Saturated Electrolyte Solutions. 1.2.3 Formation of Aquo and Partially Aquo Complexes. 1.3 Structure of Aqueous Electrolyte Solutions Containing Additives. 1.4 Polyelectrolytes and Surfactants in Solutions. 1.5 Polydentate Ligands and Molecular Additives. 1.6 Crystal-Additive Interactions. References. 2 Three-Dimensional Nucleation and Metastable Zone Width. 2.1 Driving Force for Phase Transition. 2.2 Three-Dimensional Nucleation of Crystals. 2.2.1 Three-Dimensional Nucleation Rate. 2.2.2 Three-Dimensional Heterogeneous Nucleation. 2.3 Metastable Zone Width. 2.4 Nucleation and Transformation of Metastable Phases. 2.4.1 Crystallization of Metastable Phases. 2.4.2 Overall Crystallization. 2.5 Induction Period for Crystallization. 2.6 Effects of Additives. 2.6.1 Solubility. 2.6.2 Three-Dimensional Nucleation Rate. 2.6.3 Metastable Zone Width. References. 3 Kinetics and Mechanism of Crystal Growth: An Overview. 3.1 Crystal Growth as a Kinetic Process. 3.2 Types of Crystal-Medium Interfaces. 3.3 Roughening of Steps and Surfaces. 3.3.1 Thermodynamic Roughening and the Surface Entropy Factor. 3.3.2 Kinetic Roughening. 3.4 Growth Kinetics of Rough Faces. 3.5 Growth Kinetics of Perfect Smooth Faces. 3.6 Growth Kinetics of Imperfect Smooth Faces. 3.6.1 Surface Diffusion and Direct Integration Models. 3.6.2 Bulk Diffusion Models. 3.6.3 Growth by a Group of Cooperating Screw Dislocations. 3.6.4 Preferential Growth at Edge Dislocations. 3.7 Effect of Foreign Substances on Growth Kinetics. 3.7.1 Some General Considerations. 3.7.2 Growth Kinetics by Heterogeneous Two-Dimensional Nucleation. 3.8 Real Crystal Growth Mechanisms. 3.8.1 Structure of Interfacial Layer. 3.8.2 Sources of Growth Steps. 3.9 Techniques for Studying Growth Kinetics. References. 4 Effect of Impurities on Crystal Growth Kinetics. 4.1 Mobile and Immobile Impurities. 4.2 Surface Coverage and Adsorption Isotherms. 4.2.1 Adsorption Isotherms. 4.2.2 Changes in Surface Free Energy by Adsorption of Impurities. 4.3 Kinetic Models of Impurity Adsorption. 4.3.1 Earlier Models. 4.3.2 Velocity of Curved Steps. 4.3.3 Impurity Adsorption at Kinks in Steps: Kubota-Mullin Model. 4.3.4 Impurity Adsorption at Surface Terrace: Cabrera-Vermilyea Model. 4.3.5 Effectiveness Factor for Impurity Adsorption. 4.3.6 Adsorption of Two Competing Impurities. 4.4 Confrontation of Impurity Adsorption Mechanisms with Experimental Data. 4.5 Time-Dependent Impurity Adsorption. 4.6 Growth Kinetics in the Presence of Impurities. 4.6.1 Basic Kinetic Equations. 4.6.2 Time Dependence of Face Displacement. 4.6.3 Dependence of Kinetic Coefficient for Step Motion on Impurity Concentration. 4.7 Tapering of KDP-Type Crystals. 4.8 Growth-Promoting Effects of Impurities. 4.8.1 Decrease in Step Free Energy and Roughening of Steps. 4.8.2 Formation of Surface Macroclusters. 4.9 Impurity Adsorption on Rough Faces. 4.10 Formation of Two-Dimensional Adsorption Layer. 4.11 Interactions Between Additives and Crystal Interface. 4.11.1 Nature of Impurity-Crystal Interactions. 4.11.2 Chemical Aspects of Impurity-Crystal Interactions. 4.12 Tailor-Made Additives. References. 5 Dead Supersaturation Zone and Threshold Supersaturations for Growth. 5.1 Origin of Threshold Supersaturations for Growth. 5.1.1 Basic Kinetic Equations. 5.1.2 Three Different Distances Between Impurity Particles. 5.2 Determination of Threshold Supersaturations from v(sigma) and R(sigma) Data. 5.2.1 Relationship Between the Model Involving Cooperating Spirals and the Power-Law Approach. 5.2.2 Relationship Between the Power-Law Approach and an Empirical Expression with Corrected Supersaturation. 5.2.3 Determination of sigma. 5.3 Dependence of Threshold Supersaturations on Impurity Concentration: Basic Theoretical Equations and Linear Approximations. 5.4 Confrontation of Theoretical Equations with Experimental Data. 5.4.1 Impurity Adsorption at Kinks and Surface Terrace. 5.4.2 Threshold Supersaturations and Impurity Adsorption Isotherms. 5.5 Impurity Adsorption and Solution Supersaturation. 5.6 Dependence of Ratios sigmad/sigma and sigma/sigma on ci References. 6 Mineralization in Natural and Artificial Systems. 6.1 Biomineralization as a Process. 6.1.1 Structure and Composition of Biominerals. 6.1.2 Humans and Animals. 6.1.3 Plants. 6.1.4 Mollusk Shells and Avian Eggshells. 6.2 Pathological Mineralization. 6.3 Effect of Biologically Active Additives on Crystallization Processes. 6.3.1 Overall Precipitation Kinetics. 6.3.2 Overall Growth Kinetics. 6.3.3 Phases and Polymorphs of Crystallizing Calcium Salts. 6.3.4 Transformation of Metastable Phases. 6.4 Scale Formation and Salt Weathering. References. 7 Morphology and Size Distribution of Crystals. 7.1 Growth Morphology of Crystals. 7.1.1 General Concepts. 7.1.2 Effect of Additives on Surface Morphology. 7.1.3 Effect of Solvent on Crystal Morphology. 7.1.4 Growth Morphodroms. 7.2 Ostwald Ripening and Crystal Size Dispersion. 7.3 Crystal Size Distribution. 7.3.1 Population Balance Approach. 7.3.2 Balanced Nucleation-Growth Approach. 7.3.3 Approach Based on Law of Proportionate Effect. 7.3.4 Effect of Additives on Crystal Size Distribution. 7.4 Control of Shape and Size of Particles. 7.4.1 Growth-Directed Synthesis. 7.4.2 Template-Directed Synthesis. 7.5 Biological Tissue Engineering. References. 8 Additives and Crystallization Processes in Industries. 8.1 Pharmaceutical Industry. 8.1.1 Nucleation, Growth and Morphology of Drug Crystals. 8.1.2 Preparation and Size Distribution of Drug Particles. 8.2 Petroleum Industry. 8.2.1 Some Basic Concepts. 8.2.2 Crystallization Behavior of Linear Long-Chain n-Alkanes. 8.2.3 Biodiesels and their Crystallization Behavior. 8.3 Food Industry. 8.3.1 Some Basic Concepts. 8.3.2 Crystallization of Food Fats in the Bulk. 8.3.3 Crystallization of Polymorphs. 8.3.4 Crystallization of Fats and Oils in Emulsion Droplets. 8.3.5 Number of Nucleation Centers and Overall Crystallization in Emulsion Systems. References. 9 Incorporation of Impurities in Crystals. 9.1 Types of Impurity Incorporation and the Segregation Coefficient. 9.2 Equilibrium Segregation Coefficient. 9.2.1 Binary Mixture Approach. 9.2.2 Thermodynamic Approach. 9.2.3 Theoretical Predictions and their Comparison with Experimental Data on Segregation Coefficient. 9.3 Effective Segregation Coefficient. 9.3.1 Volume Diffusion Model. 9.3.2 Diffusional Relaxation Approach. 9.3.3 Statistical Selection Approach. 9.3.4 Surface Adsorption Approach. 9.4 Relationship Between Effective Segregation Coefficient and Face Growth Rate. 9.5 Threshold Supersaturation for Trapping of Impurities During Growth. 9.6 Effective Segregation Coefficient and Internal Stresses Caused by Impurities. References. List of Symbols. Subject Index. Author Index.

Shape‐Controlled Synthesis and Self‐Assembly of Hexagonal Covellite (CuS) Nanoplatelets

Abstract: Single-crystalline, hexagonal covellite (CuS) nanoplatelets were successfully synthesized through a facile, inexpensive, reproducible, and improved solvothermal process in toluene at 120 degrees C for 24 h with hexadecylamine as a capping agent and copper acetate and carbon disulfide as precursors. These nanoplatelets are about 26+/-1.5 nm in diameter and 8+/-1.2 nm thick, and have a tendency to self-assemble into pillarlike nanostructures with face-to-face stacks, raftlike nanostructures with side-by-side arrays, and stratiform nanostructures with layer-by-layer self-assembly. The crystal shape, morphology, and crystallographic orientation of the covellite obtained were investigated by means of XRD, TEM, and high-resolution TEM, and a potential self-assembly mechanism was proposed.

Microwave effect in the fast synthesis of microporous materials: which stage between nucleation and crystal growth is accelerated by microwave irradiation?

Abstract: Microporous materials, such as silicalite-1 and VSB-5 molecular sieves, have been synthesized by both microwave irradiation (MW) and conventional electric heating (CE). The accelerated syntheses by microwave irradiation can be quantitatively investigated by various heating modes conducted in two steps such as MW-MW, MW-CE, CE-MW, and CE-CE (in the order of nucleation-crystal growth). In the case of synthesis by MW-CE or CE-MW, the heating modes were changed for the second step just after the appearance of X-ray diffraction peaks in the first step. We have quantitatively demonstrated that the microwave irradiation accelerates not only the nucleation but also crystal growth. However, the contribution to decrease the synthesis time by microwave irradiation is larger in the nucleation stage than in the step of crystal growth. The crystal size increases in the order of MW-MW

Au-assisted molecular beam epitaxy of InAs nanowires: Growth and theoretical analysis

Abstract: The Au-assisted molecular beam epitaxial growth of InAs nanowires is discussed. In situ reflection high-energy electron diffraction observations of phase transitions of the catalyst particles indicate that they can be liquid below the eutectic point of the Au-In alloy. The temperature range where the catalyst can be liquid covers the range where we observed nanowire formation (380–430 °C). The variation of nanowire growth rate with temperature is investigated. Pure axial nanowire growth is observed at high temperature while mixed axial/lateral growth occurs at low temperature. The change of the InAs nanowire shape with growth duration is studied. It is shown that significant lateral growth of the lower part of the nanowire starts when its length exceeds a critical value, so that their shape presents a steplike profile along their axis. A theoretical model is proposed to explain the nanowire morphology as a result of the axial and lateral contributions of the nanowire growth.

Influence of ZrO2 on the crystallization and properties of lithium disilicate glass-ceramics derived from a multi-component system

Abstract: Lithium disilicate glass-ceramic in the Li2O–SiO2–Al2O3–K2O–P2O5 system has been investigated by incorporation of ZrO2. The influence of ZrO2 on phase formation, microstructure, biaxial flexural strength and translucency were determined. Investigations were carried out by means of differential scanning calorimetry, X-ray diffractometry and scanning electron microscopy. The mechanical strength was measured corresponding to dental norm ISO 6872 and the contrast ratio determined by BS 5612 method. Zirconia influences the crystallization by hampering crystal growth. With the increasing ZrO2 content, the crystals become smaller. By increasing the crystallization temperature the crystal growth could be improved. The translucency of the glass-ceramic is adjusted by adding ZrO2. A highly translucent glass-ceramic with a contrast ratio of approx. 0.4 with a high strength microstructure has been developed.

Size-selective Synthesis of Zinc Sulfide Hierarchical Structures and Their Photocatalytic Activity

Abstract: Hierarchical ZnS structures with different sizes have been successfully prepared by a facile one-step method. By modulating the experimental parameters, we were able to fabricate hierarchical zinc sulfide (wurtzite) assembled structures with average sizes of 30, 200, and 400 nm on a large scale. Systematic experiments were carried out to investigate the factors such as the amounts of the reagents (thiourea and sodium hydroxide), which have great influence on the morphologies and sizes of the products. In addition, studies of the photocatalytic properties by exposure to UV light irradiation demonstrated that the as-obtained ZnS structures show potential photocatalytic activity. Therefore, the preparation and properties studies of different ZnS structures will offer great opportunities to explore the dependence of a material's properties on the morphology and size and find many interesting applications in the optoelectronic devices.

Electrochemical processes of nucleation and growth of hydroxyapatite on titanium supported by real-time electrochemical atomic force microscopy.

Abstract: Recently, interest in electrochemical formation of hydroxyapatite has evolved. In this work, highly crystalline hydroxyapatite is electrodeposited on pure titanium and Ti-6Al-4V alloy. In situ and ex situ imaging, coupled with potentiostatic and potentiodynamic measurements, is conducted by means of electrochemical atomic force microscopy. This allows for a study of the nucleation and growth of hydroxyapatite as well as of its near-atomic structure. Electrodeposition of hydroxyapatite is shown to result from precipitation in solution, following two stages: (1) instantaneous nucleation, two-dimensional growth; (2) progressive nucleation, three-dimensional growth. Although some nucleation occurs already at -842 mV, potentials that are more negative than -1.26 V versus SCE are required for enhanced growth. Mass transport is found to have only secondary effect on the deposition process. The conclusions of this work have implications in optimization of coatings on implants as well as in enhancement of the understanding of bone mineralization in vivo.

From homogeneous to heterogeneous nucleation of chain molecules under nanoscopic cylindrical confinement.

Abstract: The crystallization of monodisperse linear polyethylene confined in nanoporous alumina is investigated with the calorimetric measurements. We observe a drastic change in crystallization behavior, specifically nucleation, with a decrease in the pore diameter. Crystallization in relatively larger pores with the diameters of 62 and 110 nm occurs at lower temperatures within a very narrow range, whereas crystallization in smaller pores with diameters of 15-48 nm occurs at a higher and broad range of temperatures. Nucleation and crystallization kinetics in nanopores is discussed based on classical nucleation theory as well as the Avrami theory.

Oriented Crystallisation on Supports and Anisotropic Mass Transport of the Metal‐Organic Framework Manganese Formate

Abstract: The oriented in situ crystallisation of microporous manganese(II) formate [Mn(HCO2)2] on different porous supports (e.g. porous alumina and graphite) has been investigated. The anisotropic growth of Mn(HCO2)2 was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The intracrystalline diffusion of methanol in Mn(HCO2)2 was studied by observation of the sorption kinetics by interference microscopy (IFM). It was found that untreated discs of porous alumina and graphite supports exhibit poor densities of Mn(HCO2)2 crystals per supported area. Even lower crystal densities are found for activated supports such as for alumina after basic treatment and for oxidized graphite supports. Improved results have been achieved by replacing formic acid by sodium formate in the synthesis route. Crystal growth on graphite gives results superior to those on alumina with respect to the crystal density as well as the relative orientation of the 1D channel network to the support surface. Methanol uptake from the vapour phase is similar at 25 and 40 °C and gives an adsorption capacity of about 95 mL g–1. The BET surface area was found to be 280 m2 g–1. IFM indicates that diffusion occurs only along one crystallographic axis, thus proving the presence of a 1D channel system. Diffusion coefficients of about 10–12 m2 s–1 for methanol in microporous Mn(HCO2)2 were found. These results can be used to prepare supported metal–organic framework (MOF) membranes for molecular sieving. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Effect of the cooling rate on the nucleation kinetics of poly(L-lactic acid) and its influence on morphology

Abstract: Although the crystallization kinetics of PLLA is slow enough to allow one to obtain amorphous samples by cooling from the melt at moderate rates, surprisingly, at the same time, the formation of crystallization nuclei is difficult to avoid. Their amount depends on the cooling rate from the melt: the higher the cooling rate, the lower the amount of available nuclei after reaching the glass state. Cooling at controlled rates of 5−300 °C/min was performed by making use of a relatively new high-speed calorimetry technology, high-performance DSC (HPer DSC). Subsequent isothermal cold crystallization of amorphous PLLA, at different temperatures distributed across the bell-shaped crystal growth curve, was shown to depend on the rate at which the glass state was attained, reflecting the number of nuclei formed. However, (only) after complete cold crystallization, the DSC heating curves and the resulting morphology measured by optical microscopy and AFM were shown to be independent of the previous cooling rate in...

Inhibiting Surface Crystallization of Amorphous Indomethacin by Nanocoating

Abstract: An amorphous solid (glass) may crystallize faster at the surface than through the bulk, making surface crystallization a mechanism of failure for amorphous pharmaceuticals and other materials. An ultrathin coating of gold or polyelectrolytes inhibited the surface crystallization of amorphous indomethacin (IMC), an anti-inflammatory drug and model organic glass. The gold coating (10 nm) was deposited by sputtering, and the polyelectrolyte coating (3−20 nm) was deposited by an electrostatic layer-by-layer assembly of cationic poly(dimethyldiallyl ammonium chloride) (PDDA) and anionic sodium poly(styrenesulfonate) (PSS) in aqueous solution. The coating also inhibited the growth of existing crystals. The inhibition was strong even with one layer of PDDA. The polyelectrolyte coating still permitted fast dissolution of amorphous IMC and improved its wetting and flow. The finding supports the view that the surface crystallization of amorphous IMC is enabled by the mobility of a thin layer of surface molecules, a...

A growth diagram for plasma-assisted molecular beam epitaxy of In-face InN

Abstract: We investigated the role of temperature and In∕N flux ratios to determine suitable growth windows for the plasma-assisted molecular beam epitaxy of In-face (0001) InN. Under vacuum, InN starts decomposing at 435°C as defined by the release of N2 from the InN crystal and a buildup of an In adlayer and liquid In droplets on the sample surface. At temperatures greater than 470°C, InN decomposition was characterized by a release of both In vapor and N2 in the absence of a significant accumulation of an In adlayer. No growth was observed at substrate temperatures above 500°C or at temperatures in which the decomposition rates were higher than the growth rates. A growth diagram was then constructed consisting of two growth regimes: the “In-droplet regime” characterized by step-flow growth and relatively flat surfaces and the “N-rich regime” characterized by rough, three-dimensional surfaces. The growth diagram can then be used to predict the surface structure of films grown at varying substrate temperatures and...

Solid state interconversions of coordination networks and hydrogen-bonded salts

Abstract: Thermal or chemical treatment of crystalline 4,4-bipyridinium salts of [MCl4]2- (M=Co, Zn, Fe, or Pt) leads to HCl loss and formation of coordination network solids [{MCl2(4,4-bipy)}n]. For M=Co, Zn, and Fe, these solids can also be prepared by mechanochemical means. Their exposure to HCl vapor or the mechanochemical reaction of metal dichlorides with [4,4-H2bipy]Cl2 gives [4,4-H2bipy]2+ salts of [CoCl4]2-, [ZnCl4]2-, and, for the first time, [FeCl4]2-.

Controlling the morphology of zinc oxide nanorods crystallized from aqueous solutions : The effect of crystal growth modifiers on aspect ratio

Abstract: The effect of growth modifiers on the morphology of zinc oxide (ZnO) nanorods crystallized from solution is characterized. During hydrolysis of zinc nitrate at pH = 7.6 and 75 °C, hexagonally prismatic ZnO crystals were grown in the presence of three growth modifiers: poly(diallyldimethylammonium chloride) (PDADMAC), sodium poly(styrene sulfonate) (PSS), and trisodium citrate. Using statistical analyses of scanning electron microscopy (SEM) images, crystal dimensions were quantified, and the median aspect ratio (ratio of prism length to width) was determined as a function of modifier concentration. In the absence of growth modifiers, the median crystal aspect ratio was 5.2. The aspect ratio was reduced to 4.7, 2.5, and 0.25 in the presence of, respectively, 67 nmol/L (nM) PDADMAC, 130 nM PSS, and 40 μmol/L (μM) citrate. These effects are explained in terms of both electrostatic and coordinative binding between growth modifier and crystal surface.

Isothermal growth, thickening, and melting of poly(ethylene oxide) single crystals in the bulk

Abstract: Characteristic features of isothermal growth, thickening, and melting behavior of melt grown single crystals of low molecular weight poly (ethylene oxide) fractions are presented and discussed in terms of their relevance to basic concepts of polymer crystal growth. Measurements of growth (G) and thickening rates of once folded chain crystals were extended (up to the melting point) into a temperature range where usually only extended chain crystals grow. Monolayer extended and folded chain crystals melt by lateral shrinkage, the rate of which (G−) depends not only on temperature, but also on thermal history. G− increases exponentially with the degree of superheating, and the value of the temperature coefficient d log G−/dT is proportional to the lamellar thickness. In the narrow temperature interval where transition from once folded to extended chain growth occurs, the crystal morphology displays some spectacular features. These may be accounted for in terms of the crystal habit and the rate of completion, g. of a molecular layer in the particular (hk0) prism face considered. Morphological analysis shows that g is of the same order of magnitude as G(hkO), leading to the conclusion that the growth of these PEO crystals is controlled by multiple surface nucleation rather than by deposition of a single surface nucleus.

A Polymorph Lost and Found: The High-Temperature Crystal Structure of Pentacene

Abstract: Reference LCR-ARTICLE-2007-009doi:10.1002/adma.200602072View record in Web of Science Record created on 2007-11-27, modified on 2017-05-12