Showing papers on "Nucleation published in 2003"
TL;DR: In this article, a template-less and surfactant-free aqueous method is proposed to generate metal oxide thin films with controlled complexity. But the synthesis involves a templateless and a surfactent-free approach, which enables the generation of, at large-scale, low-cost, and moderate temperatures, advanced metal oxide particle-to-particle thin films.
Abstract: A novel approach to the rational fabrication of smart and functional metal oxide particulate thin films and coatings is demonstrated on the growth of ZnO nanowires and oriented nanorod arrays The synthesis involves a template-less and surfactant-free aqueous method, which enables the generation of, at large-scale, low-cost, and moderate temperatures, advanced metal oxide thin films with controlled complexity The strategy consists of monitoring of the nucleation, growth, and aging processes by means of chemical and electrostatic control of the interfacial free energy It enables the control of the size of nano-, meso-, and microcrystallites, their surface morphology, orientations onto various substrates, and crystal structure
2,619 citations
TL;DR: Comparison with previously reported membranes shows that these microstructurally optimized films have superior performance for the separation of organic mixtures with components that have small differences in size and shape, such as xylene isomers.
Abstract: A seeded growth method for the fabrication of high-permeance, high-separation-factor zeolite (siliceous ZSM-5, [Si 96 O 192 ]-MFI) membranes is reported. The method consists of growing the crystals of an oriented seed layer to a well-intergrown film by avoiding events that lead to a loss of preferred orientation, such as twin overgrowths and random nucleation. Organic polycations are used as zeolite crystal shape modifiers to enhance relative growth rates along the desirable out-of-plane direction. The polycrystalline films are thin (∼1 micrometer) with single grains extending along the film thickness and with large in-plane grain size (∼1 micrometer). The preferred orientation is such that straight channels with an open diameter of ∼5.5 angstroms run down the membrane thickness. Comparison with previously reported membranes shows that these microstructurally optimized films have superior performance for the separation of organic mixtures with components that have small differences in size and shape, such as xylene isomers.
959 citations
TL;DR: This work follows in real time the evolution of individual clusters, and compares their development with simulations incorporating the basic physics of electrodeposition during the early stages of growth, to analyse dynamic observations—recorded in situ using a novel transmission electron microscopy technique—of the nucleation and growth of nanoscale copper clusters during electro Deposition.
Abstract: Dynamic processes at the solid–liquid interface are of key importance across broad areas of science and technology. Electrochemical deposition of copper, for example, is used for metallization in integrated circuits, and a detailed understanding of nucleation, growth and coalescence is essential in optimizing the final microstructure. Our understanding of processes at the solid–vapour interface has advanced tremendously over the past decade due to the routine availability of real-time, high-resolution imaging techniques yielding data that can be compared quantitatively with theory1,2,3. However, the difficulty of studying the solid–liquid interface leaves our understanding of processes there less complete. Here we analyse dynamic observations—recorded in situ using a novel transmission electron microscopy technique—of the nucleation and growth of nanoscale copper clusters during electrodeposition. We follow in real time the evolution of individual clusters, and compare their development with simulations incorporating the basic physics of electrodeposition during the early stages of growth. The experimental technique developed here is applicable to a broad range of dynamic phenomena at the solid–liquid interface.
666 citations
TL;DR: In this paper, the basic ideas pertinent to modelling helium accumulation in metals are reviewed and possible effects of bubble formation on mechanical properties are briefly addressed: hardening and embrittlement, particularly at high temperature where intergranular fracture is induced by the transformation of bubbles to voids at grain boundaries.
658 citations
TL;DR: In this paper, the kinetics and microscopic mechanisms of laser melting and disintegration of thin Ni and Au films irradiated by a short, from 200 fs to 150 ps, laser pulse are investigated in a coupled atomistic-continuum computational model.
Abstract: The kinetics and microscopic mechanisms of laser melting and disintegration of thin Ni and Au films irradiated by a short, from 200 fs to 150 ps, laser pulse are investigated in a coupled atomistic-continuum computational model. The model provides a detailed atomic-level description of fast nonequilibrium processes of laser melting and film disintegration and, at the same time, ensures an adequate description of the laser light absorption by the conduction band electrons, the energy transfer to the lattice due to the electron-phonon coupling, and the fast electron heat conduction in metals. The interplay of two competing processes, the propagation of the liquid-crystal interfaces (melting fronts) from the external surfaces of the film and homogeneous nucleation and growth of liquid regions inside the crystal, is found to be responsible for melting of metal films irradiated by laser pulses at fluences close to the melting threshold. The relative contributions of the homogeneous and heterogeneous melting mechanisms are defined by the laser fluence, pulse duration, and the strength of the electron-phonon coupling. At high laser fluences, significantly exceeding the threshold for the melting onset, a collapse of the crystal structure overheated above the limit of crystal stability takes place simultaneously in the whole overheated region within \ensuremath{\sim}2 ps, skipping the intermediate liquid-crystal coexistence stage. Under conditions of the inertial stress confinement, realized in the case of short $\ensuremath{\tau}l~10\mathrm{ps}$ laser pulses and strong electron-phonon coupling (Ni films), the dynamics of the relaxation of the laser-induced pressure has a profound effect on the temperature distribution in the irradiated films as well as on both homogeneous and heterogeneous melting processes. Anisotropic lattice distortions and stress gradients associated with the relaxation of the laser-induced pressure destabilize the crystal lattice, reduce the overheating required for the initiation of homogeneous melting down to $T\ensuremath{\approx}{1.05T}_{m},$ and expand the range of pulse durations for which homogeneous melting is observed in 50 nm Ni films up to \ensuremath{\sim}150 ps. High tensile stresses generated in the middle of an irradiated film can also lead to the mechanical disintegration of the film.
634 citations
TL;DR: In this article, a unified view of nucleation in solutions is presented from a unified point of view, where the thermodynamics of the process is considered and expressions for the supersaturation, the nucleation work and the size of the nucleus in homogeneous or heterogeneous nucleation.
Abstract: Existing and new results in nucleation in solutions are outlined from a unified point of view. The thermodynamics of the process is considered and expressions are given for the supersaturation, the nucleation work and the size of the nucleus in homogeneous or heterogeneous nucleation. It is shown how the nucleation theorem can be used for a model-independent determination of the nucleus size from experimental data. The mechanism and kinetics of nucleation are also considered and formulae are presented for the supersaturation dependence of the monomer attachment frequency and the stationary rate of homogeneous or heterogeneous nucleation. General expressions for the induction time and the critical supersaturation ratio for crystallization are given. An approximate formula is derived for estimating the width of the metastable zone with the help of data for the solubility of the substance crystallized. Existing experimental data are used for verification of the validity of some of the presented theoretical dependences.
577 citations
TL;DR: In this paper, self-assembled cylindrical particles of wild type and recombinant tobacco mosaic virus (TMV) were used as organic templates for the controlled deposition and organization of Pt, Au, or Ag nanoparticles.
Abstract: Self-assembled cylindrical particles of wild type and recombinant tobacco mosaic virus (TMV) were used as organic templates for the controlled deposition and organization of Pt, Au, or Ag nanoparticles. Chemical reduction of [PtCl6]2- or [AuCl4]- complexes at acidic pH gave rise to the specific decoration of the external surface of wild-type TMV rods with metallic nanoparticles less than 10 nm in size. In contrast, photochemical reduction of Ag(I) salts at pH 7 resulted in nucleation and constrained growth of discrete Ag nanoparticles aligned within the 4 nm-wide internal channel. The number of encapsulated nanoparticles increased when Ag benzoate rather than Ag nitrate was used due to reduced supersaturation associated with the lower Ag/benzoate redox couple, which enhanced the surface-templating effect of the channel wall carboxylates compared with nucleation in solution. Similar experiments using a mutant TMV with reduced negative charge along the central cavity confirmed that glutamic and aspartate ac...
549 citations
TL;DR: Simultaneous measurements of the concentration and composition of tropospheric aerosol particles capable of initiating ice in cold (cirrus) clouds are reported, suggesting a predominant potential impact of these nuclei on cirrus formed by slow, large-scale lifting or small cooling rates, including subvisual cirrus.
Abstract: This article addresses the need for new data on indirect effects of natural and anthropogenic aerosol particles on atmospheric ice clouds. Simultaneous measurements of the concentration and composition of tropospheric aerosol particles capable of initiating ice in cold (cirrus) clouds are reported. Measurements support that cirrus formation occurs both by heterogeneous nucleation by insoluble particles and homogeneous (spontaneous) freezing of particles containing solutions. Heterogeneous ice nuclei concentrations in the cirrus regime depend on temperature, relative humidity, and the concentrations and physical and chemical properties of aerosol particles. The cirrus-active concentrations of heterogeneous nuclei measured in November over the western U.S. were <0.03 cm–3. Considering previous modeling studies, this result suggests a predominant potential impact of these nuclei on cirrus formed by slow, large-scale lifting or small cooling rates, including subvisual cirrus. The most common heterogeneous ice nuclei were identified as relatively pure mineral dusts and metallic particles, some of which may have origin through anthropogenic processes. Homogeneous freezing of large numbers of particles was detected above a critical relative humidity along with a simultaneous transition in nuclei composition toward that of the sulfate-dominated total aerosol population. The temperature and humidity conditions of the homogeneous nucleation transition were reasonably consistent with expectations based on previous theoretical and laboratory studies but were highly variable. The strong presence of certain organic pollutants was particularly noted to be associated with impedance of homogeneous freezing.
534 citations
TL;DR: The first direct experimental demonstration of Frank's complete hypothesis is presented, showing a correlation between the nucleation barrier and a growing icosahedral short-range order with decreasing temperature in a Ti39.5Zr 39.5Ni21 liquid.
Abstract: To explain the unusual stability of undercooled liquids against crystallization, Frank hypothesized that the local structures of undercooled liquids contain a significant degree of icosahedral short-range order, which is incompatible with long-range periodicity. We present here the first direct experimental demonstration of Frank's complete hypothesis, showing a correlation between the nucleation barrier and a growing icosahedral short-range order with decreasing temperature in a Ti39.5Zr39.5Ni21 liquid. A new experimental facility, BESL (Beamline Electrostatic Levitation), was developed to enable the synchrotron x-ray structural studies on deeply undercooled, reactive liquids.
529 citations
TL;DR: It is reported that dentin matrix protein 1 (DMP1), an acidic protein, can nucleate the formation of hydroxyapatite in vitro in a multistep process that begins by DMP1 binding calcium ions and initiating mineral deposition.
Abstract: Bones and teeth are biocomposites that require controlled mineral deposition during their self-assembly to form tissues with unique mechanical properties. Acidic extracellular matrix proteins play a pivotal role during biomineral formation. However, the mechanisms of protein-mediated mineral initiation are far from understood. Here we report that dentin matrix protein 1 (DMP1), an acidic protein, can nucleate the formation of hydroxyapatite in vitro in a multistep process that begins by DMP1 binding calcium ions and initiating mineral deposition. The nucleated amorphous calcium phosphate precipitates ripen and nanocrystals form. Subsequently, these expand and coalesce into microscale crystals elongated in the c-axis direction. Characterization of the functional domains in DMP1 demonstrated that intermolecular assembly of acidic clusters into a beta-sheet template was essential for the observed mineral nucleation. Protein-mediated initiation of nanocrystals, as discussed here, might provide a new methodology for constructing nanoscale composites by self-assembly of polypeptides with tailor-made peptide sequences.
485 citations
TL;DR: It was found that CoPt(3) nanocrystals nucleate and grow up to their final size at an early stage of the synthesis with no Ostwald ripening observed upon further heating, which allows the synthesis to be considered as a model system for the hot organometallic synthesis of metal nanoparticles.
Abstract: High quality CoPt(3) nanocrystals were synthesized via simultaneous reduction of platinum acetylacetonate and thermodecomposition of cobalt carbonyl in the presence of 1-adamantanecarboxylic acid and hexadecylamine as stabilizing agents. The high flexibility and reproducibility of the synthesis allows us to consider CoPt(3) nanocrystals as a model system for the hot organometallic synthesis of metal nanoparticles. Different experimental conditions (reaction temperature, concentration of stabilizing agents, ratio between cobalt and platinum precursors, etc.) have been investigated to reveal the processes governing the formation of the metal alloy nanocrystals. It was found that CoPt(3) nanocrystals nucleate and grow up to their final size at an early stage of the synthesis with no Ostwald ripening observed upon further heating. In this case, the nanocrystal size can be controlled only via proper balance between the rates for nucleation and for growth from the molecular precursors. Thus, the size of CoPt(3) nanocrystals can be precisely tuned from approximately 3 nm up to approximately 18 nm in a predictable and reproducible way. The mechanism of homogeneous nucleation, evolution of the nanocrystal ensemble in the absence of Ostwald ripening, nanocrystal faceting, and size-dependent magnetic properties are investigated and discussed on the example of CoPt(3) magnetic alloy nanocrystals. The developed approach was found to be applicable to other systems, e.g., FePt and CoPd(2) magnetic alloy nanocrystals.
TL;DR: Nucleation and expansion theories are presented along with quantitative data that support them and the effect of processing conditions and properties of the biopolymeric matrix on nucleation and Expansion are discussed.
Abstract: Expansion of biopolymer matrices is the basis for the production of a wide variety of cereal foods. A limited number of manufacturing processes provide practical solutions for the development of an impressive variety of expanded products, just by changing process variables. It is therefore essential that the mechanisms involved in expansion are well known and controlled. This paper summarizes the knowledge of nucleation and expansion in extruded and microwaved products available to date. The effect of processing conditions and properties of the biopolymeric matrix on nucleation and expansion are discussed. Moisture content enables the glassy polymeric matrix to turn into rubbery state at process temperatures, which allows superheated steam bubbles to form at nuclei and then expand, expansion being governed by the biaxial extensional viscosity of the matrix. Nucleation and expansion theories are presented along with quantitative data that support them.
TL;DR: Structural characterizations by transmission electron microscopy (TEM) and electron diffraction showed that nanowires of Au, Ag, and Cu are single-crystalline with a preferred [111] orientation, whereas Ni, Co, and Rh wires are poly Crystalline.
Abstract: Metallic nanowires (Au, Ag, Cu, Ni, Co, and Rh) with an average diameter of 40 nm and a length of 3−5 μm have been fabricated by electrodeposition in the pores of track-etched polycarbonate membranes. Structural characterizations by transmission electron microscopy (TEM) and electron diffraction showed that nanowires of Au, Ag, and Cu are single-crystalline with a preferred [111] orientation, whereas Ni, Co, and Rh wires are polycrystalline. Possible mechanisms responsible for nucleation and growth for single-crystal noble metals versus polycrystalline group VIII-B metals are discussed.
TL;DR: It is shown both experimentally and theoretically that a single oxygen vacancy can bind 3 Au atoms on average, and a new growth model for the TiO2(110) system involving vacancy-cluster complex diffusion is presented.
Abstract: Through an interplay between scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we show that bridging oxygen vacancies are the active nucleation sites for Au clusters on the rutile TiO2(110) surface. We find that a direct correlation exists between a decrease in density of vacancies and the amount of Au deposited. From the DFT calculations we find that the oxygen vacancy is indeed the strongest Au binding site. We show both experimentally and theoretically that a single oxygen vacancy can bind 3 Au atoms on average. In view of the presented results, a new growth model for the TiO2(110) system involving vacancy-cluster complex diffusion is presented.
TL;DR: In this paper, it was demonstrated that in a high-carbon steel where carbide precipitation is suppressed, bainite can be obtained by isothermal transformation at temperatures as low as 200°C.
Abstract: It is demonstrated that in a high-carbon steel where carbide precipitation is suppressed, bainite can be obtained by isothermal transformation at temperatures as low as 200°C. The time taken for nucleation at this temperature can be many days, but the transformation results in the growth of extremely thin platelets of bainite, so thin that the hardness of the resulting steel can be greater than 600 HV.
TL;DR: These findings indicate that, at typical upper troposphere and lower stratosphere conditions, particles are formed by this nucleation process and grow to measurable sizes with sufficient sun exposure and low preexisting aerosol surface area.
Abstract: Unexpectedly high concentrations of ultrafine particles were observed over a wide range of latitudes in the upper troposphere and lower stratosphere. Particle number concentrations and size distributions simulated by a numerical model of ion-induced nucleation, constrained by measured thermodynamic data and observed atmospheric key species, were consistent with the observations. These findings indicate that, at typical upper troposphere and lower stratosphere conditions, particles are formed by this nucleation process and grow to measurable sizes with sufficient sun exposure and low preexisting aerosol surface area. Ion-induced nucleation is thus a globally important source of aerosol particles, potentially affecting cloud formation and radiative transfer.
TL;DR: 29Si NMR, small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) are used to monitor the synthesis of silica nanoparticles from the base-catalyzed hydrolysis of TEOS in methanol and ethanol to find that after an induction period where there is a buildup of singly hydrolyzed monomer, the first nuclei are fractal and open in structure.
TL;DR: A significant reduction in the nucleation rate of the anatase TiO(2) with increasing pH is revealed, as is explained by the reduction of the concentration of a precursor complex, Ti(OH)(3)(+), and the adsorption of hydroxide ion onto the embryos of TiO (2).
TL;DR: In this paper, the delicate interplay between stereochemical control, monitoring at the sub-nanometer level, and an understanding of crystal nucleation is probed using tailor-made auxiliaries, which are either nucleation inhibitors or promoters.
Abstract: In this review, the delicate interplay between stereochemical control, monitoring at the subnanometer level, and an understanding of crystal nucleation is probed Control of crystal nucleation may be achieved employing tailor-made auxiliaries, which are either nucleation inhibitors or promoters The process may be monitored at an interface via grazing incidence X-ray diffraction (GIXD) By these means, we can glean experimental knowledge of crystal nucleation in various molecular systems A hypothesis was invoked that supersaturated solutions containing molecular clusters adopt various arrangements and shapes, some of which resemble the crystals into which they develop This hypothesis was taken advantage of for the design of tailored inhibitors in achieving kinetic resolution of enantiomers and induced precipitation of particular crystal polymorphs The control and behavior of polymorphic crystallization may be understood at the molecular level through the interplay between inhibitor, solvent, solute, cr
TL;DR: ZnO nanoparticles are synthesized by precipitation from zinc acetate in a series of n-alkanols from ethanol to 1-hexanol as a function of temperature and the rate constant for coarsening is determined by the solvent viscosity, surface energy, and the bulk solubility of ZnO in the solvent.
TL;DR: A review of the state-of-the-art of the understanding of cavity formation during stages I and II (primary and secondary) creep in polycrystalline metals and alloys, particularly at elevated temperatures, can be found in this article.
TL;DR: Using depth-sensitive hardness measurements, the homogenous nucleation of dislocations has been observed in dislocation-free single crystals as discussed by the authors, which is related to a sudden displacement jump in the force-displacement curve.
Abstract: Using advanced depth-sensitive hardness measurements, the homogenous nucleation of dislocations has been observed in dislocation-free single crystals This process is related to a sudden displacement jump in the force-displacement curve The mechanical stress for the set-in of this pop-in effect has been estimated with the Hertzian elastic contact theory Experimental results of dislocation loop nucleation show good agreement with the continuum theory of dislocations Electron microscopy provides a direct proof of dislocation nucleation during nanoindentation
TL;DR: In this article, the influence of Ti addition on the development of acicular ferrite microstructure during the γ/α transformation in C-Mn steels has been studied.
TL;DR: In this article, silica nanoparticle-filled poly(ethylene 2,6-naphthalate) composites were melt-blended to improve the mechanical and rheological properties of PEN.
IBM1
TL;DR: In this paper, growth behavior, structure, thermal stability and electrical properties of ultrathin hafnium oxide films deposited by atomic layer deposition using sequential exposures of HfCl4 and H2O at 300°C on a bare silicon surface or a thin thermally grown SiO2-based interlayer.
TL;DR: In this paper, temperature-programmed reduction was used to characterize precipitated iron oxide samples and two-stage reduction was observed: Fe2O3 was reduced to Fe3O4 and then reduced to metallic Fe.
TL;DR: In this article, the formation of recrystallization texture is explained by oriented nucleation, and the origin of nuclei with specific orientations is studied. But, the mechanism responsible for the formation is still disputed.
TL;DR: In this paper, a simulation study of the initial stages of indentation using the embedded atom method (EAM) is presented, and a comparison is made between atomistic simulations and continuum models for elastic deformation.
Abstract: Nanoindentation experiments have shown that microstructural inhomogeneities across the surface of gold thin films lead to position-dependent nanoindentation behavior [Phys. Rev. B (2002), to be submitted]. The rationale for such behavior was based on the availability of dislocation sources at the grain boundary for initiating plasticity. In order to verify or refute this theory, a computational approach has been pursued. Here, a simulation study of the initial stages of indentation using the embedded atom method (EAM) is presented. First, the principles of the EAM are given, and a comparison is made between atomistic simulations and continuum models for elastic deformation. Then, the mechanism of dislocation nucleation in single crystalline gold is analyzed, and the effects of elastic anisotropy are considered. Finally, a systematic study of the indentation response in the proximity of a high angle, high sigma (low symmetry) grain boundary is presented; indentation behavior is simulated for varying indenter positions relative to the boundary. The results indicate that high angle grain boundaries are a ready source of dislocations in indentation-induced deformation.
TL;DR: In this article, the phase behavior of the binary system consisting of the commercial nucleating and clarifying agent 1,3:2,4-bis(3,4)-dimethyldibenzylidene)sorbitol (DMDBS, Millad 3988) and isotactic polypropylene (i-PP) was investigated over the entire concentration range by means of differential scanning calorimetry (DSC), rheology, and optical microscopy.
Abstract: The phase behavior of the binary system consisting of the commercial nucleating and clarifying agent 1,3:2,4-bis(3,4-dimethyldibenzylidene)sorbitol (DMDBS, Millad 3988) and isotactic polypropylene (i-PP) was investigated over the entire concentration range by means of differential scanning calorimetry (DSC), rheology, and optical microscopy. Experimental phase diagrams were constructed from data obtained in melting and crystallization studies, and a simple binary monotectic is advanced. Distinct regimes in the phase diagram, which apparently dictate nucleation and clarification of i-PP by DMDBS, are discussed. A maximum increase in the crystallization temperature of i-PP due to the nucleating action of DMDBS was observed in compositions containing between 0.2 and 1 wt % of the latter. Liquid−liquid phase separation was observed at elevated temperatures for i-PP/DMDBS mixtures comprising more than 2 wt % of DMDBS. A study of the optical properties of the i-PP/DMDBS system revealed that values for haze and ...
TL;DR: In this paper, the morphology of the obtained intragranular microstructures has been found to depend on the steel composition, the prior austenite grain size, and the density of particles able to promote intra-granular nucleation.
Abstract: Acicular ferrite formation, promoted by the intragranular nucleation of ferrite plates, is well known to be beneficial for achieving a good combination of mechanical properties. However, the set of microstructures that can be obtained during the subsequent development of the transformation from the primary plates generated at particles can be quite complex and depends on a certain number of variables: steel composition, temperature range, prior austenite grain size, and particle density. In the present work, acicular ferrite microstructures have been produced by isothermal treatments in three different steels with different active particle types and densities. The morphology of the obtained intragranular microstructures has been found to depend on the steel composition, the prior austenite grain size, and the density of particles able to promote intragranular nucleation. Electron backscattered diffraction (EBSD) techniques have been used to define the microstructural unit controlling toughness in these types of microstructures.