Showing papers on "Nucleation published in 1994"
01 Jan 1994
TL;DR: Pulsed laser deposition of high-temperature superconducting thin films for active and passive device applications is discussed in this article, with a focus on the commercial scale-up of Pulsed Laser Deposition.
Abstract: Partial table of contents: History and Fundamentals of Pulsed Laser Deposition (J. Cheung). Diagnostics and Characteristics of Laser--Produced Plasmas (D. Geohegan). Particulates Generated by Pulsed Laser Ablation (L.--C. Chen). Angular Distribution of Ablated Material (K. Saenger). Film Nucleation and Film Growth in Pulsed Laser Deposition of Ceramics (J. Horwitz & J. Sprague). Processes Characteristics and Film Properties in Pulsed Laser Plasma Deposition (S. Metev). Commercial Scale--Up of Pulsed Laser Deposition (J. Greer). Pulsed Laser Deposition: Future Trends (T. Venkatesan). Comparison of Vacuum Deposition Techniques (G. Hubler). Pulsed Laser Deposition of High--Temperature Superconducting Thin Films for Active and Passive Device Applications (R. Muenchausen & X. Wu). Pulsed Laser Deposition of Metals (J. Kools). Appendix. References. Index.
3,228 citations
IBM1
TL;DR: It is shown that strained epitaxial layers can relax by two competing mechanisms; this work discusses how temperature, surfactants, or compositional grading change and so control the mode of relaxation.
Abstract: We show that strained epitaxial layers can relax by two competing mechanisms. At large misfit, the surface becomes rough, allowing easy nucleation of dislocations. However, strain-induced surface roughening is thermally activated, and the energy barrier increases very rapidly with decreasing misfit \ensuremath{\varepsilon}. Thus below some misfit ${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{c}}$, the strain relaxes by nucleation of dislocations at existing sources before the surface has time to roughen. Relaxation via surface roughening is technologically undesirable; we discuss how temperature, surfactants, or compositional grading change ${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{c}}$ and so control the mode of relaxation.
679 citations
TL;DR: In this paper, a pressure quench was employed to generate a microcellular core structure encased by a nonporous skin, which can be used to model the effects of saturation pressure, temperature, and time on the cell density of the porous materials.
Abstract: Supercritical carbon dioxide is known to swell and plasticize poly(methyl methacrylate), PMMA, dramatically. We have employed a pressure quench in a CO2-swollen PMMA sample to generate a microcellular core structure encased by a nonporous skin. Further, we have demonstrated that classical nucleation theory can be used to model the effects of saturation pressure, temperature, and time on the cell density of the porous materials, provided that the effects of the CO2-diluent on the surface tension of PMMA are adequately taken into account. This is because our system is in a homogeneous liquid state at our operating conditions because of the plasticization. Both model predictions and data indicate that cell density rises sharply at a saturation pressure of approximately 14 MPa (at 40°C), leveling out above 27 MPa. By contrast, the effect of temperature on cell density in the range 40°C to 80°C is minimal.
475 citations
TL;DR: It was shown that in both samples significant crystallization to the most stable polymorphic form occurred over several days when stored below Tg, and in some cases this process was preceded by the relaxation of one amorphous form to the other.
433 citations
TL;DR: In this article, the authors investigated the factors influencing particle size and found that high silica contents in conjunction with high alkalinities favor the synthesis of colloidal silicalite suspensions.
431 citations
TL;DR: In this article, the influence of the process parameters on the optical properties of TiO2 films, such as index of refraction, scattering of light, and absorption, is discussed.
388 citations
TL;DR: This experimental technique may be useful in the development of new types of optical sensors that respond to their environment by changing the reflectivity of patterned regions and for studying phenomena such as drop nucleation, contact angle hysteresis, and spontaneous dewetting and break-up of thin liquid films.
Abstract: Heterogeneous, patterned surfaces comprising well-defined hydrophobic and hydrophilic regions and having micrometer-scale periodicities were prepared by patterning the adsorption of ω-functionalized alkanethiolates in self-assembled monolayers (SAMs) on gold. Condensation of water on such surfaces resulted in drops that followed the patterns in the SAMs. These patterned condensation figures (CFs) acted as optical diffraction gratings for reflected (or transmitted) light from a helium-neon laser (wavelength of 632.8 nanometers). Under an atmosphere of constant relative humidity, the development of the condensation figure was monitored quantitatively, as the temperature of the surface was lowered, by following the change in intensity of a first-order diffraction spot. This experimental technique may be useful in the development of new types of optical sensors that respond to their environment by changing the reflectivity of patterned regions and for studying phenomena such as drop nucleation, contact angle hysteresis, and spontaneous dewetting and break-up of thin liquid films.
355 citations
TL;DR: In this paper, a general theorem that relates the variation of the work of formation of the critical nucleus with chemical potential and the size and composition of critical nuclei was proved. But the results applied to the smallest nuclei of a few molecules only.
Abstract: We prove a general theorem that relates the variation of the work of formation of the critical nucleus with chemical potential and the size and composition of the critical nucleus. Applications are made to multicomponent nucleation and to both isothermal and nonisothermal phase transformations. We show that the excess number of molecules and the excess entropy of the critical nucleus are thus accessible to experimental determination with the help of data for the dependence of the nucleation rate on supersaturation. The results derived do not rely on classical nucleation approximations and thus apply down to the smallest nuclei of a few molecules only.
342 citations
TL;DR: In this article, the authors review the experimental procedures used in FIM surface diffusion studies and discuss the results in relation to the atomistics of crystal and epitaxial growth processes.
342 citations
TL;DR: In this paper, measurements of aerosol size distributions (0.005 < r < 20 μm), cloud droplet spectra, SO2, O3, CN, and other supporting quantities were made in the cloud-topped and clear marine boundary layer (MBL) from an airship operating within about 50 km of the Oregon coast.
Abstract: Measurements of aerosol size distributions (0.005 < r < 20 μm), cloud droplet spectra, SO2, O3, CN, and other supporting quantities were made in the cloud-topped and clear marine boundary layer (MBL) from an airship operating within about 50 km of the Oregon coast. Comparison of size distribution of interstitial aerosol within the cloud with the size distribution below the cloud clearly indicates that the processing of the aerosol through (nonprecipitating) stratus can lead to increased mass of the subset of particles which had served as cloud condensation nuclei (CCN). This increase in mass in the CCN results in a distinct “cloud residue” mode in the size distribution measured below the cloud. In all cases the aerosol mass in the cloud residue mode greatly exceeded the mass in the interstitial mode, even though the number concentration of interstitial particles sometimes exceeded the CCN concentration. Evidence of new particle formation in clear air was also found on numerous occasions. Analyses of the data indicate that the growth of newly formed particles into the observed size range is consistent with gas phase oxidation of SO2 to sulfate and subsequent condensation on the aerosol. However, the exact nucleation process, whether by homogeneous nucleation, ion-assisted nucleation, or heterogeneous nucleation on precursor embryos, is still an open question.
340 citations
TL;DR: The nucleation and growth of two-dimensional islands during the submonolayer stage of epitaxial growth is studied with kinetic Monte Carlo simulations and mean-field rate equations and previous work on irreversible growth is extended to include relaxation of island shapes by edge diffusion.
Abstract: The nucleation and growth of two-dimensional islands during the submonolayer stage of epitaxial growth is studied with kinetic Monte Carlo simulations and mean-field rate equations. Previous work on irreversible growth is extended to include relaxation of island shapes by edge diffusion. Island morphologies range from ramified structures at low temperatures to compact, polygonal shapes at higher temperatures. Using a self-consistent calculation of the rate coefficients, [ital quantitative] agreement is obtained between the solution to coupled, mean-field rate equations and the simulation results for average quantities. The island size distribution function is described by a single universal scaling function.'' The average island size is the only important scale for determining island densities. It is shown that the general form of the scaling [ital ansatz] applies to wider range of coverages than anticipated previously. This scaling form is combined with the solution to the rate equations to explore explicitly the [ital D]/[ital F] dependence of the number density of islands ([ital D] is the surface diffusion coefficient and [ital F] is the deposition flux).
TL;DR: In this paper, the first measurement of bubble nucleation in hydrated rhyolitic melts in response to pressure release was reported, and the results demonstrate the importance of heterogeneous nucleation.
TL;DR: In this paper, the atomic processes taking place during deposition are described in terms of rate and diffusion equations; the concept of competitive capture is outlined, where adatoms are forced to choose between competing sinks.
TL;DR: In this article, a substrate is set in contact with particles of CaO-SiO2-based glass soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma for forming the apatite nuclei on the substrate.
Abstract: Dense and uniform layers of a biologically active carbonate-containing hydroxyapatite can be formed on various kinds of organic polymers by the following biomimetic method. First, a substrate is set in contact with particles of CaO–SiO2-based glass soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma for forming the apatite nuclei on the substrate. Second, the substrate is soaked in another solution highly supersaturated with respect to the apatite, e.g, with ion concentrations 1.5 times those of SBF (1.5SBF) for making the apatite nuclei grow on the substrate in situ. The induction period for the apatite nucleation, which is defined as the time of the first treatment required for forming enough of the apatite nuclei to make the continuous layer after the second treatment, was almost 24 h for most of the examined polymers. The adhesive strength of the formed apatite layer to the polymers was as high as 3 to 4 M Pa for poly(ethylene terephthalate), poly-ether sulfone, and poly (vinyl alcohol) hydrogel. This type of apatite–organic polymer composite is expected to be useful for repairing not only living hard tissues but also soft ones.
TL;DR: In this article, the effects of pyrolysis temperature, post-pyrolyisation thermal treatments, and excess lead addition on the growth and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated.
Abstract: The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350–450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.
TL;DR: In this paper, a new way to tailor the crystal chemistry of inorganic solids involves molecular recongnition between two-dimensional organic templates and embryonic inorganic aggregates.
Abstract: A new way to tailor the crystal chemistry of inorganic solids involves molecular recongnition between two‐dimensional organic templates and embryonic inorganic aggregates. Langmuir monolayers adopted as model surfaces offer opportunities for molecular engineering of the template. The Figure shows one example of oriented nucleation of vaterite under octadecylamine monolayers. (Figure Presented.) Copyright © 1994 Verlag GmbH & Co. KGaA, Weinheim
TL;DR: The crystallization of a model compound, sucrose, from the amorphous solid state has been studied non-isothermally using differential scanning calorimetry to determine crystallization temperature, Tc, and is othermally at 30°C by subjecting samples to 32.4% relative humidity and gravimetrically monitoring water vapor uptake and subsequent loss with time due to crystallization.
Abstract: The crystallization of a model compound, sucrose, from the amorphous solid state has been studied non-isothermally using differential scanning calorimetry to determine crystallization temperature, Tc, and isothermally at 30°C by subjecting samples to 32.4% relative humidity and gravimetrically monitoring water vapor uptake and subsequent loss with time due to crystallization. From the measurement of glass transition temperature, Tg, and melting temperature, Tm, for sucrose alone and in the presence of absorbed water it was possible to predict Tc and thus to directly relate the plasticizing effects of water to its tendency to promote crystallization. Colyo-philization of sucrose with lactose, trehalose, and raffinose, all having Tg values greater than that of sucrose, increased Tc significantly, even at levels as low as 1 – 10% w/w. In the isothermal studies the time required for crystallization to commence, due to the plasticizing effects of water, i.e., the induction time, assumed to be mostly affected by rates of nucleation, was greatly increased by the presence of the additives at these low levels, with raffinose producing a greater effect than lactose and trehalose. Similarly, these additives reduced the rate of water loss, i.e., the rate of crystal growth, but now no significant differences were noted between the three additives. The possible relationships of nucleation and crystal growth and the effects of additives on molecular mobility are discussed.
TL;DR: In this article, a theoretical analysis of the super lateral growth (SLG) phenomenon observed in the pulsed laser-induced solidification of amorphous thin Si films on SiO2 is presented.
Abstract: This letter reports on the experimental findings, and provides a theoretical description of the super lateral growth (SLG) phenomenon observed in the pulsed laser‐induced solidification of amorphous thin Si films on SiO2. Experimentally, we report and elaborate on the isolated single‐crystal disk structure that is observed at the upper threshold of the SLG regime; the structure is revealed as an important microstructural feature for understanding the phenomenon. A theoretical discussion of the SLG phenomenon is provided in terms of the key factors that are suggested by our model—the interface response function of the solid, the nucleation kinetics of the solid, and a highly transient lateral‐thermal profile near the solid‐melt interface. Our model and analysis point out the important inadequacies associated with the vertical solidification rate/temperature gradient model, which is currently being utilized to explain the excimer laser crystallization of thin Si films on SiO2.
TL;DR: In this paper, the energy required to thermally activate a stable, incipient dislocation into its unstable saddle-point configuration is directly calculated for loads less than that critical value.
Abstract: THE ACTIVATION energy for dislocation nucleation from a stressed crack tip is calculated within the Peierls framework, in which a periodic shear stress vs displacement relation is assumed to hold on a slip plane emanating from the crack tip. Previous results have revealed that the critical G (energy release rate corresponding to the “screened” crack tip stress field) for dislocation nucleation scales with y., (the unstable stacking energy), in an analysis which neglects any coupling between tension and shear along the slip plane. That analysis represents instantaneous nucleation and takes thermal effects into account only via the weak temperature dependence of the elastic constants. In this work, the energy required to thermally activate a stable, incipient dislocation into its unstable “saddle-point” configuration is directly calculated for loads less than that critical value. We do so only with the simplest case, for which the slip plane is a prolongation of the crack plane. A first calculation reported is 2D in nature, and hence reveals an activation energy per unit length. A more realistic scheme for thermal activation involves the emission of a dislocation loop, an inherently 3D phenomenon. Asymptotic calculations of the activation energy for loads close to the critical load are performed in 2D and in 3D. It is found that the 3D activation energy generally corresponds to the 2D activation energy per unit length multiplied by about 5 -10 Burgers vectors (but by as many as 17 very near to the critical loading). Implications for the emission of dislocations in copper. K-iron, and silicon at elevated temperature are discussed. The effects of thermal activation are very significant in lowering the load for emission. Also, the appropriate activation energy to correspond to molecular dynamics simulations of crack tips is discussed. Such simulations, as typically carried out with only a few atomic planes in a periodic repeat direction parallel to the crack tip. are shown to greatly exaggerate the (aheddy large) effects of temperature on dislocation nucleation. WE BUILD on recent advances in the modeling of dislocation nucleation at a crack tip
TL;DR: In this paper, the metastable region for hydrate nucleation is discussed and the driving force for hydrates is defined, and the induction period data for the various hyddrates from a total of 93 hydrate formation runs were modelled as a function of the nucleation driving force.
TL;DR: In this paper, the authors demonstrate that a highly organized composite material can be bio-fabricated on disks of glass, mica and MoS2 inserted between the mantle and shell of Haliotis rufescens (red abalone).
Abstract: THE study of biomineralization is inspiring new approaches to the controlled fabrication of synthetic materials such as nanoparticles, polymer–mineral composites and templated crystals1–3. Although this biomimetic approach is gaining momentum, the biological mechanisms involved in biomineralization remain relatively unexplored. One major reason for this is the difficulty of analysing biomineralization processes in their native dynamic state. Here we demonstrate that a highly organized composite material—a 'flat pearl'—can be biofabricated on disks of glass, mica and MoS2 inserted between the mantle and shell of Haliotis rufescens (red abalone). We show that the construction of this material is spatially and temporally regulated and proceeds through a developmental sequence that closely resembles that at the growth front of the natural shell. Recognition of the implanted inorganic surfaces by mantle cells apparently governs a switch, perhaps genetically controlled, from aragonite to calcite biomineralization. Once a partially oriented calcite—protein primer layer has been deposited, there is a switch back to the nucleation and assembly of columnar stacks of highly ordered aragonitic nacre. Thus the presence of an inorganic surface between the mantle and shell of the organism triggers a change in the nature of the mineral phase deposited.
TL;DR: In this paper, a unique nucleation mechanism that involves formation of HNO3/H20 solutions on the sulfate ice particles was proposed, resulting in the formation of a relatively small number of large particles.
Abstract: Mechanisms for the formation of Type I (nitric acid-based) polar stratospheric clouds (PSCs) are discussed. If the pre-existing sulfate aerosols are liquid prior to PSC formation, then nitric acid particles (Type Ib) form by HNO3 dissolution in aqueous H2SO4 solution droplets. This process does not require a nucleation step for the formation of HNO3 aerosols, so most pre-existing aerosols grow to become relatively small HNO3-containing particles. At significantly lower temperatures, the resulting supercooled solutions (Type Ib) may freeze to form HNO3 ice particles (Type Ia). If the pre-existing sulfate aerosols are initially solid before PSC formation, then HNO3 vapor can be deposited directly on the frozen sulfate particles. However, because an energy barrier to the condensation exists a nucleation mechanism is involved. Here, we suggest a unique nucleation mechanism that involves formation of HNO3/H20 solutions on the sulfate ice particles. These nucleation processes may be highly selective, resulting in the formation of relatively small number of large particles.
TL;DR: In this article, a model for the critical driving force at the M s temperature was developed and tested for the martensitic transformation in binary, ternary and multicomponent Fe-base alloys.
Abstract: Employing available experimental data for athermal f.c.c. → b.c.c. martensitic transformation in binary, ternary and multicomponent Fe-base alloys, a model is developed and tested for the critical driving force at the M s temperature. Incorporating the theory of solid solution hardening, we describe the composition dependence of the athermal frictional work for martensitic interface motion governing the kinetics of barrierless heterogeneous nucleation. The available data suggests that the composition dependence of the athermal frictional work is of the same form as that for slip deformation. We have evaluated the athermal strengths of 14 alloying elements Al, C, Co, Cr, Cu, Mn, Mo, N, Nb, Ni, Si, Ti, V and W from the experimental data. Except for Al, Ni and Co, the athermal strengths of the common substitutional alloying elements are similar in magnitude, while the interstitial solutes C and N exert a stronger influence. Previously proposed superposition laws are used to account for the presence of multiple solutes having different athermal strengths. With an improved assessment of the magnetic parameters of alloy systems, the model predicts M s temperatures within ±40 K for M s > 300 K where thermal contributions to the frictional work can be neglected.
TL;DR: An analysis of the island size and separation distributions of Fe islands, observed in the initial stages of growth in the homoepitaxy of Fe on Fe(001) whiskers, shows scaling properties recently predicted in nucleation and growth theories.
Abstract: An analysis of the island size and separation distributions of Fe islands, observed in the initial stages of growth in the homoepitaxy of Fe on Fe(001) whiskers, shows scaling properties recently predicted in nucleation and growth theories. A critical size of one atom, where islands greater than the critical size undergo irreversible nucleation, is supported by the measured scaling functions for the Fe on Fe system in the temperature range of 20--250 \ifmmode^\circ\else\textdegree\fi{}C.
TL;DR: In this article, the volume fraction of the reversed area of the D -E hysteresis loop of ferroelectrics is theoretically studied on the basis of the extended Avrami theory.
Abstract: The D - E hysteresis loop of ferroelectrics is theoretically studied on the basis of the extended Avrami theory. If the sideway velocity depends only on the instant value of the applied field, the volume fraction of the reversed area is expressed as q ( E )=1-exp (- f - d Φ( E )), where f and d are, respectively, the frequency of the applied field and the growth dimension of domains, and Φ is a function of E . This result is obtained irrespective of the waveform of the applied field and the field dependence of the sideway velocity, if the nucleation event is deterministic. For the stochastic nucleation due to thermal fluctuation, on the other hand, the above result is modified as q ( E )=1-exp (- f -( d +1) Φ( E )). The effect of the delay of wall motion is also discussed.
TL;DR: A new screening protocol is evaluated which employs less classical precipitating agents and a panel of more than 30 detergents are evaluated for their ability to prevent sample aggregation and influence crystal growth.
Abstract: Today the determination of successful crystallization conditions for a particular macromolecule remains a highly empirical process. Sparse-matrix and grid-screening procedures are rapid and economical means to determine preliminary crystallization conditions. During optimization the variable set (pH, precipitant type and precipitant concentration) utilized in these procedures is screened in an attempt to determine appropriate conditions for the nucleation and growth of single crystals suitable for X-ray diffraction analysis. Unfortunately, in many cases this strategy will not produce single crystals suitable for X-ray diffraction analysis. We have explored, in an empirical sense, other tools for use during optimization. First, a new screening protocol is evaluated which employs less classical precipitating agents. Second, a set of 24 electrostatic crosslinking agents are evaluated for their ability to promote crystallization. Third, a panel of more than 30 detergents are evaluated for their ability to prevent sample aggregation and influence crystal growth.
AeA1
TL;DR: In this paper, the authors derived a model which gives a full description of the form of current transients and a simple statement of factors controlling the stability of propagation of micropits, chiefly relating to their geometry, is obtained.
TL;DR: The phase diagram of microtubules is mapped as a function of temperature and tubulin concentration and a transition in the length dynamics of micro Tubules from bounded to unbounded growth is revealed.
Abstract: We map the phase diagram of microtubules as a function of temperature and tubulin concentration. We observe spontaneous and site-nucleated microtubule assembly. At temperatures and concentrations below the onset of spontaneous nucleation, we measure the steady-state proportion of occupied nucleation sites and the distribution of lengths of site-nucleated microtubules. Our observations reveal a transition in the length dynamics of microtubules from bounded to unbounded growth. This transition is also evident in the length dynamics of individual site-nucleated microtubules. The transition to spontaneous microtubule assembly completes the phase diagram. We measure the temperature and concentration dependence of the latent time for spontaneous nucleation of microtubules in the bulk.
TL;DR: In this article, the authors evaluated the depth to which metastable olivine (α) can survive in a subduction zone and the depth interval over which transformation to β- or γ-(Mg,Fe)2SiO4 occurs.
TL;DR: In this paper, a theoretical model for predicting the kinetics of ice crystallization inside cells during cryopreservation was developed, and applied to mouse oocytes, by coupling separate models of water transport across the cell membrane, ice nucleation, and crystal growth.
Abstract: A theoretical model for predicting the kinetics of ice crystallization inside cells during cryopreservation was developed, and applied to mouse oocytes, by coupling separate models of (1) water transport across the cell membrane, (2) ice nucleation, and (3) crystal growth. The instantaneous cell volume and cytosol composition during continuous cooling in the presence of glycerol were predicted using the water transport model. Classical nucleation theory was used to predict ice nucleation rates, and a nonisothermal diffusion‐limited crystal‐growth model was used to compute the resulting crystallization kinetics. The model requires knowledge of the nucleation rate parameters Ω and κ, as well as the viscosity η of a water‐NaCl‐glycerol solution as a function of both the composition and temperature of the solution. These dependences were estimated from data available in the literature. Cell‐specific biophysical parameters were obtained from previous studies on mouse oocytes. A sensitivity analysis showed that...