Two-dimensional Crystal Growth Research Articles

Phase-field modeling of two-dimensional crystal growth with anisotropic diffusion

In the present article, we introduce a phase-field model for thin-film growth with anisotropic step energy, attachment kinetics, and diffusion, with second-order (thin-interface) corrections. We are mainly interested in the limit in which kinetic anisotropy dominates, and hence we study how the expected shape of a crystallite, which in the long-time limit is the kinetic Wulff shape, is modified by anisotropic diffusion. We present results that prove that anisotropic diffusion plays an important, counterintuitive role in the evolving crystal shape, and we add second-order corrections to the model that provide a significant increase in accuracy for small supersaturations. We also study the effect of different crystal symmetries and discuss the influence of the deposition rate.

The comparative kinetic analysis of the non-isothermal crystallization process of Eu3 + doped Zn2SiO4 powders prepared via polymer induced sol–gel method

The comparative kinetic analysis of the non-isothermal crystallization was performed for Eu3+ doped Zn2SiO4 samples, prepared by the polymer induced sol–gel procedure and thermally treated in the conventional furnace and in a microwave oven. This comparison is done using various thermal analysis techniques and is supported by SEM investigation. It was found that low values of Avrami constant (n), identified in the primary crystallization stage resulted from a not constant radial growth rate. One possible mechanism that could alter the linear crystal growth rate is a diffusion-controlled transition, with instantaneous nucleation mechanism. In the secondary crystallization stage, observed for both samples, it was found that the probability for two-dimensional crystal growth increases, especially at higher heating rates. It was found that the substitution of zinc ions by europium ions in Zn2SiO4 matrix can lead to some defects due to different radius and charges, which induces autocatalytic behavior of the tested systems. It was shown that the two-parameter Šesták–Berggren (SB) autocatalytic model best describes the non-isothermal crystallization of doped samples. It has been shown that SB model is adequate to describe the crystallization kinetics for the fine powder samples (crystallite size of 60–65nm).

Selection theory of free dendritic growth in a potential flow

The Kruskal-Segur approach to selection theory in diffusion-limited or Laplacian growth is extended via combination with the Zauderer decomposition scheme. This way nonlinear bulk equations become tractable. To demonstrate the method, we apply it to two-dimensional crystal growth in a potential flow. We omit the simplifying approximations used in a preliminary calculation for the same system [Fischaleck, Kassner, Europhys. Lett. 81, 54004 (2008)], thus exhibiting the capability of the method to extend mathematical rigor to more complex problems than hitherto accessible.

Well-posedness of a needle crystal growth problem with anisotropic surface tension

We study an initial value problem for two-dimensional needle crystal growth with anisotropic surface tension. The initial value problem is derived from the so called one-sided model based on complex variables method. We then obtain the existence and uniqueness of local solution in Sobolev spaces for the needle crystal problem with arbitrary initial interface. Furthermore, we obtain that, on average in time, the solution gains derivative of smoothness in spatial variable compared to the initial data. The continuous dependence on the initial data of the solution map is also established.

Two-dimensional crystal growth of thermally converted organic semiconductors at the surface of ionic liquid and high-mobility organic field-effect transistors

We report a novel solution-crystallization method to grow two-dimensional platelet-shaped single-crystals of well-known insoluble organic semiconductors via thermal conversion of their precursor molecules dissolved in ionic liquids (ILs). By optimizing conditions of the crystal growth regarding physical properties of ILs such as density and viscosity, we successfully and reproducibly obtained thin platelets of pentacene and dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) single-crystals, with which nearly the best performing field-effect transistors are constructed for the two compounds. The prompt and simple technique has opened the way to use practically insoluble organic semiconductor materials for high-performance printed electronics, which enables mass-producible and large-area organic circuitry devices.

Physical properties and crystallization behavior of ethylene-vinyl acetate rubber/polyamide/graphene oxide thermoplastic elastomer nanocomposites

Graphene oxide (GO) reinforced ethylene-vinyl acetate rubber/ternary polyamide copolymer (EVM/tPA) thermoplastic elastomer (TPE) was prepared via a dynamic vulcanization technique with the assistance of tetraethoxysilane (TEOS) for transesterification crosslinking reaction of EVM. The crosslinked EVM phase was dispersed in continuous tPA phase even at the component ratio of EVM/tPA 70/30 wt%. GO nanosheets were found to be distributed homogeneously in both EVM and tPA phases. The addition of GO up to 1.81 wt% not only enhanced the stress at 100% extension of the TPE, but also increased the dielectric permittivity of the TPE. In particular, the presence of GO nanosheets greatly affected the crystallization behavior of the tPA phase in the EVM/tPA (70/30) TPE that were demonstrated as the increased crystallization temperature, crystallization rate constant and activation energy, as well as a two-dimensional crystal growth mode of tPA. Therefore, the GO acts as a heterogeneous nucleating agent for tPA with nucleation activity α of 0.4–0.6, as well as reinforcement for the EVM/tPA TPE.

Crystal Growth Mechanisms and Morphological Control of the Prototypical Metal–Organic Framework MOF‐5 Revealed by Atomic Force Microscopy

Crystal growth of the metal-organic framework MOF-5 was studied by atomic force microscopy (AFM) for the first time. Growth under low supersaturation conditions was found to occur by a two-dimensional or spiral crystal growth mechanism. Observation of developing nuclei during the former reveals growth occurs through a process of nucleation and spreading of metastable and stable sub-layers revealing that MOFs may be considered as dense phase structures in terms of crystal growth, even though they contain sub-layers consisting of ordered framework and disordered non-framework components. These results also support the notion this may be a general mechanism of surface crystal growth at low supersaturation applicable to crystalline nanoporous materials. The crystal growth mechanism at the atomistic level was also seen to vary as a function of the growth solution Zn/H(2)bdc ratio producing square terraces with steps parallel to the <100> direction or rhombus-shaped terraces with steps parallel to the <110> direction when the Zn/H(2)bdc ratio was >1 or about 1, respectively. The change in relative growth rates can be explained in terms of changes in the solution species concentrations and their influence on growth at different terrace growth sites. These results were successfully applied to the growth of as-synthesized cube-shaped crystals to increase expression of the {111} faces and to grow octahedral crystals of suitable quality to image using AFM. This modulator-free route to control the crystal morphology of MOF-5 crystals should be applicable to a wide variety of MOFs to achieve the desired morphological control for performance enhancement in applications.

Influence of nanofiller dimensionality on the crystallization behavior of HDPE/carbon nanocomposites

The isothermal and nonisothermal crystallization behavior of high density polyethylene (HDPE) containing various zero, one, and two dimensional (0-D, 1-D, and 2-D) carbon nanofillers were investigated by means of differential scanning calorimetry. For a given temperature, the isothermal crystallization incubation time of HDPE became longer with the addition of lower dimensional carbon nanofillers, and the isothermal crystallization rate got slower. The values of Avrami and Tobin exponents indicated that the isothermal crystallization of HDPE followed two-dimensional crystal growth in the presence of 2-D and 1-D carbon nanofillers, while exhibited three-dimensional heterogeneous crystal growth in the presence of 0-D carbon nanofillers. Contrary to the isothermal study, the nonisothermal crystallization of HDPE was accelerated in the presence of lower dimensional nanofillers. The nonisothermal crystallization data were finally analyzed using Ozawa and Mo methods. It was observed that only Mo approach could successfully describe the nonisothermal crystallization process of HDPE and HDPE/carbon nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

TDNMR characterization of a model crystallizing surfactant system

Complex fluids with high concentrations of crystallizing fatty acids are important for consumer skin care products. These fluids exhibit solid-like elastic behavior at rest, but yield and flow under an applied strain. Such behavior is characteristic of isotropic, space-filling networks. The processing determines the microstructure of these systems, which in turn influences their macroscopic rheological properties. The kinetics of crystal growth in model system compositions, comprising (by weight) 9% sodium dodecyl sulfate, 3% cocamidopropyl betaine, and different specified amounts of palmitic acid in H2O or D2O, were studied by time domain nuclear magnetic resonance (TDNMR) and differential scanning calorimetry (DSC). The data were analyzed using the Avrami equation; both DSC and TDNMR gave consistent Avrami exponent values of approximately 1.5 for formulations with 11wt% and greater amounts palmitic acid content. The Avrami exponent is consistent with two-dimensional crystal growth limited both by diffusion and surface incorporation. The solids content at 25°C was found to be proportional to the concentration of palmitic acid level above its solubility limit of ca. 2wt%. TDNMR, combined with DSC, microscopy, and rheology provide valuable insights into the molecular structure and mechanism of crystallization in surfactant/fatty acid systems.

Abstract 3867: Dual blockade of HER2 in HER2-overexpressing tumor cells does not eliminate HER3 function completely: Clinical implications

Abstract There is mounting evidence that the most efficacious approach to treat HER2+ breast cancer is dual blockade with HER2 inhibitors such as the monoclonal antibody trastuzumab and the tyrosine kinase inhibitor lapatinib. We examined what effect dual blockade had on HER3 protein levels. The combination of lapatinib and trastuzumab treatment increased both cell-surface and total HER3 protein levels in BT474, SKBR3, and MDA453 cells. Treatment with the HER3 neutralizing antibody U3-1287 decreased HER3 levels starting at 1 h and continuing through 24 h in these cell lines. Moreover, adding U3-1287 to lapatinib and trastuzumab reversed the upregulation of cell surface and total HER3. Addition of the HER3 antibody to lapatinib and trastuzumab treatment improved the action of lapatinib and trastuzumab as assessed by the TUNEL apoptosis assay, three-dimensional matrigel growth and two-dimensional crystal violet growth assays. We next examined the effect of dual blockade of HER2 in combination with the HER3 antibody in cells with acquired resistance to trastuzumab. Treatment with U3-1287 blocked the upregulation of HER3 that followed therapy with lapatinib and trastuzumab. In mice bearing trastuzumab resistant xenografts, there was a reduction in tumor volume of mice treated with U3-1287 and trastuzumab compared to mice treated with single agent trastuzumab, U3-1287, or vehicle. We next hypothesized that inhibition of HER3 combined with dual HER2 blockade would result in decreased tumor recurrence in vivo. Mice bearing BT474 xenografts were treated with either lapatinib and trastuzumab (L+T) or lapatinib, trastuzumab and U3-1287 (L+T+U) for 3 weeks. After 3 weeks of treatment mice from both groups exhibited almost complete tumor regressions. At 7 weeks post-treatment 5 of 10 mice (50%) in the L+T group exhibited tumor re-growth (defined as a tumor larger than 200 mm3), whereas only 1 of 12 mice (8.3%) in the L+T+U group did so (p= 0.043, fisher's exact test). We are additionally performing studies in a transgenic mouse model with conditional ablation of HER3 to further examine if lapatinib and trastuzumab do not completely eliminate HER3 function. Finally we are comparing genetic inhibition of HER3 via stable inducible shRNA to pharmacological inhibition of HER3 to determine the most efficacious approach to inhibit HER3. In summary, a HER3 inhibitor prevents the upregulation of HER3 observed with lapatinib and trastuzumab treatment and sensitizes breast cancer cells to lapatinib and trastuzumab. Moreover, lapatinib and trastuzumab in combination with a HER3 inhibitor prevent tumor recurrence better than lapatinib and trastuzumab. These data suggest dual blockade of HER2 may only be partially effective in some instances due to maintenance of active HER3 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3867. doi:1538-7445.AM2012-3867

Phase Transitions in Prequenched Mesomorphic Isotactic Polypropylene during Heating and Annealing Processes As Revealed by Simultaneous Synchrotron SAXS and WAXD Technique

Time-resolved simultaneous synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) technique was used to investigate the phase transitions in prequenched mesomorphic isotactic polypropylene (iPP) samples during heating and annealing processes, respectively. For the heating process, it is shown that the mesomorphic-to-monoclinic phase transition is relatively faster for the mesomorphic iPP sample obtained with the high quenching rate than that with the low quenching rate. For the former, the stability of α-monoclinic crystals formed during heating is relatively higher. As for the annealing process, WAXD and SAXS data illustrate that the higher the annealing temperature (T(a)), the earlier the mesomorphic-to-monoclinic phase transition occurs. Namely, T(a) controls the phase transition rate. Both heating and annealing processes show that the increase of content of α-monoclinic crystal phase is mainly at the expense of the mesomorphic phase, with the content of amorphous phase almost invariable. The isothermal crystallization kinetics for the prequenched mesomorphic iPP sample was analyzed through the Avrami equation, revealing a two-dimensional crystal growth under the diffusion-limited mechanism.

Hydrothermal synthesis of brookite-type titanium dioxide with snowflake-like nanostructures using a water-soluble citratoperoxotitanate complex

Hydrothermal synthesis of brookite-type titanium dioxide was performed with excellent reproducibility using an aqueous NH 3 solution of a water-soluble citratoperoxotitanate (CPT) complex. X-ray diffraction confirmed that the brookite phase was formed by hydrothermal treatment of the CPT complex in NH 3 solution with a concentration of more than 6.5 wt%, whereas single phase anatase was obtained when distilled water without any additives was applied as the solvent. The aspect ratios of the obtained rod-like brookite particles increased from 5 up to 20 with an increase of the NH 3 concentration. Transmission electron microscopy and selected area electron diffraction measurements provided evidence that the growth of the brookite particles is along the c-axis. Hydrothermal treatment of the CPT complex at high NH 3 concentrations resulted in the formation of agglomerated brookite particles with unusual shapes, where many rod-like particles were branched around a somewhat longer central particle, and the side view of the agglomerated particles revealed two-dimensional crystal growth within a given restricted plane. The multi-needle agglomerate of particles was snowflake shaped. The reason for the formation of brookite with this unique morphology may be attributed to an intrinsic character of the CPT complex itself, although the mechanism is yet to be clarified.

Liquid−Liquid Biphasic Synthesis of Layered Zinc Hydroxides Intercalated with Long-Chain Carboxylate Ions and Their Conversion into ZnO Nanostructures

A method for synthesizing layered zinc hydroxide compounds in high yields is developed using an immiscible liquid-liquid system in one pot. Long-chain carboxylate ions such as heptanoate, decanoate, and dodecanoate were successfully intercalated between zinc hydroxide layers in one process starting from a xylene-water system. Typically, a xylene phase dissolving the respective carboxylic acids was allowed to stand in contact with an aqueous phase dissolving zinc nitrate hexahydrate and urea. During keeping the resultant biphasic system at 80 °C, urea was thermo-hydrolyzed to supply OH(-) in the aqueous phase while the carboxylic acids were continuously transferred from the xylene phase under the distribution law. The aqueous phase was then supersaturated, and a solid phase of layered basic zinc carboxylate was precipitated as films on glass substrates through heterogeneous nucleation and subsequent two-dimensional crystal growth. Crystal structures and morphology of the films were modulated by the kind of the carboxylic acids employed. The layered basic zinc carboxylate films could be converted to nanostructured, mesoporous ZnO films by heating at 450 °C in air. The relationship between the initial solution compositions and the final solid products was systematically examined to discuss reaction mechanisms in the biphasic systems.

Inducing order using nanolaminate templates

Abstract

Formation of Highly Thin, Electron-Transparent Gold Nanoplates from Nanoseeds in Ternary Mixtures of Cetyltrimethylammonium Bromide, Poly(vinyl pyrrolidone), and Poly(ethylene glycol)

A simple approach to grow highly thin and electron-transparent gold nanoplates with a micrometer range edge-length dimension is demonstrated. The thin nanoplates were obtained by realizing an effective two-dimensional (2D) crystal growth of the nanoseed in a ternary surfactant mixture of cetyltrimethylammonium bromide (CTAB), poly (vinyl pyrrolidone) (PVP), and poly (ethylene glycol) (PEG). By simply controlling the concentration ratio of these three surfactants in the growth solution, high yield triangular and hexagonal nanoplates with thicknesses as low as ca. < 5 nm and edge-length dimensions extended up to ca. 1 μm could be realized. It was found that PVP and PEG play a unique combinative function in the projection of effective 2D crystal growth of the nanoseed probably via effective selective adhesion on the nanocrystals plane. Owing to their special characteristics, the highly thin gold nanoplates should find extensive use in catalysis, nanoelectronics, and surface-enhanced Raman spectroscopy (SERS)...

Existence and uniqueness of solution in Sobolev space for an unsteady crystal growth problem with zero surface tension

We study an initial value problem for a two-dimensional dendritic crystal growth model with zero surface tension. If the initial data is in Sobolev space H 2 ( R ) , it is proved that an unique local solution exists in proper Sobolev space.

Formation of High-Yield Gold Nanoplates on the Surface: Effective Two-Dimensional Crystal Growth of Nanoseed in the Presence of Poly(vinylpyrrolidone) and Cetyltrimethylammonium Bromide

This paper reports a simple technique to grow high-yield gold nanoplates directly on the surface via an effective two-dimensional growth promotion of the attached nanoseeds in the presence of a binary surfactant mixture, namely, poly(vinylpyrrolidone) (PVP) and cetyltrimethylammonium bromide (CTAB). The gold nanoplates formation strongly depended on the concentration of PVP used in the solution, while the nanoplate size depended on the CTAB concentration. In a typical process with optimum PVP and CTAB concentrations, 60% of the nanocrystal product was nanoplates. Triangular nanoplates were found to be the major shape of the nanoplates with a yield of up to ca. 50%, while hexagonal or truncated-hexagonal and rounded-nanoplates shared up to ca. 30 and 20% of the nanoplates product, respectively. The nanoplates were characterized by a very thin structure with a thickness of less than 10 nm. The edge-length size of the nanoplates was found to be up to ca. 1 μm. At optimum growth conditions, ca. 70% of the sur...

Influence of nucleation agents on crystallization and machinability of mica glass–ceramics

Abstract Effects of ZrO 2 , La 2 O 3 , CeO 2 , Yb 2 O 3 and V 2 O 5 on the crystallization kinetics, microstructure and mechanical properties of mica glass–ceramics were investigated by the differential scanning calorimetry (DSC), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness tester. Results show that bulk crystallization can be obtained by introducing proper nucleation agents into the glass. Both Ozawa method and Kissinger method are suitable for analyzing the crystallization kinetics of mica glass–ceramic. The addition of nucleation agents has little influence on the value of n , keeping two-dimensional crystal growth mechanism. ZrO 2 and V 2 O 5 are best nucleation agents in mica system. The increase of crystallization temperature is helpful for the increase of aspect ratio, and the microstructure of the glass–ceramics becomes interconnected, which contributes the improvement of the machinability of the glass–ceramics. Microhardness ( H v ), cutting energy ( μ 1 ) and machinability parameter ( m ) can be used for estimating the machinability of mica glass–ceramics.

A study on the dimensionality of the crystal growth and the exponents of the power laws of the time-dependence for the nucleation frequency and for the crystal growth rate: Application to the non-isothermal crystallization of the Ag 0.16As 0.42Se 0.42 glassy alloy

A procedure has been developed to establish the thermal process type, to determine the dimensionality of the crystal growth and to evaluate the exponents of the power laws of the time-dependence both for the nucleation frequency and for the crystal growth rate in glass–crystal transformations under non-isothermal regime. To carry out the quoted procedure, it is established a linear relation between the logarithms of the heating rate and of the temperature corresponding to the maximum crystallization rate, which allows to obtain other linear relation between the logarithm of the quoted temperature and the reciprocal of this temperature. From the slope of the last relation, once the thermal process type has been determined by means of the comparison of the kinetic exponent values for the as-quenched and reheated samples, the dimensionality of the crystal growth is deduced. By comparing the theoretical values of the activation energy for one-, two- and three-dimensional crystal growth, obtained from the quoted slope, with the experimental value for this quantity, it is chosen the theoretical value nearest to the experimental one. Thus, the dimensionality of the crystal growth is determined. From the dimensionality and of the kinetic exponent values for the as-quenched and reheated samples, the exponents of the above-mentioned power laws have been evaluated. The procedure developed has been applied to the crystallization kinetics of the Ag 0.16As 0.42Se 0.42 glassy semiconductor, which presents two exothermic peaks. For the first one, the thermal process is a glass–crystal transformation with “site saturation” and two-dimensional crystal growth; whereas, for the last one, it is a process of continuous nucleation and three-dimensional crystal growth.

Influence of thermal treatment conditions on two-dimensional crystal growth of nanocrystal corundum abrasives

The effect of thermal treatment on mechanical property and microstructure evolution in two-dimension of nanocrystal corundum abrasives has been investigated. The abrasives with and without presence of bond were calcined at different thermal treatment temperatures. The results indicated that thermal treatment conditions had obvious influence on crystal size and mechanical strength of corundum abrasives. Crystal size increased with increasing of the calcining temperature, and crystal growth of sample with presence of bond was more remarkable than that without presence of bond. And it was found that 950 °C is the critical temperature of abnormal crystal growth of corundum abrasives in the heated treatment conditions. Beyond this critical temperature, crystal size evidently increased while strength and wear resistance of abrasive decreased. In this case, the degradation of the abrasive in microstructure and strength should be important considerations for the preparation of ceramic corundum abrasive grinding tool.