Late-stage Growth Research Articles

Dynamical renormalization group calculation of a two-phase sharp interface model.

The temporal evolution of an interface separating two phases is studied using renormalization group and scaling theory and exact calculation of a sharp interface model incorporating surface tension and kinetic undercooling. Under conditions favoring rapid solidification the characteristic length, R(t), varies as t(1/2) while the total surface area of the interface, S(t), varies as t((d-1)/2). This complements the results of Jasnow and Vinals who found R(t) approximately t in the quasistatic regime. The transition in exponents from R(t) approximately t to R(t) approximately t(1/2), as solidification proceeds from the quasistatic to the rapid solidification regime, suggests a complex evolution toward a self-similar late stage growth.

Application of the exchange Monte Carlo method to ordering dynamics

We have applied the exchange Monte Carlo method to the ordering dynamics of the three-state Potts model with conserved order parameter. Even for the deeply quenched case to low temperatures, we have observed a rapid domain growth; we have proved the efficiency of the exchange Monte Carlo method for the ordering process. The late-stage growth law has been found to be R(t) ~ t1/3 for the case of the conserved order parameter of a three-component system.

No coarsening in Pt(111) homoepitaxy

The absence of coarsening in late-stage growth, the evolution of the surface width, and mound shapes in homoepitaxy on Pt(111) around 440 K all agree well with predictions of one-dimensional deterministic growth models for large step-edge barriers. Initial coarsening, which is at variance with these models, is traced to an initially lower effective step-edge barrier that only gradually increases during growth.

Thin Nematic Films: Metastability And Spinodal Dewetting

We present new results about the stability of 5CB nematic films spun cast onto silicon wafers. We observe experimentally the dewetting of thin films while thick ones remain stable. We interpret this behavior as a competition between elasticity and van der Waals forces. At later stages, the experimentally observed dewetting instability leads to the formation of structures (islands) which grow and finally merge to form a film of uniform thickness. We show that the islands' characteristic size $L(t)$ scales as ${t}^{1/3}$ as expected from late stage growth theories.

Evolution of surface morphology during Fe/Si(111) and Fe/Si(001) heteroepitaxy

The evolution of Fe surface morphology during heteroepitaxial growth on Si(111) and Si(001) substrates was investigated using real-time synchrotron x-ray reflectivity measurements. The growth on the Si(111) surface was divided into the initial stage heteroepitaxial regime, the intermediate stage crossover regime, and the final-stage homoepitaxial regime. The evolution of the surface roughness in the late stage growth was described by the dynamic scaling exponent of $\ensuremath{\beta}\ensuremath{\sim}0.24$ consistent with reported values. On the Si(001) surface, an interlayer was formed prior to the growth of a nonepitaxial Fe layer. The roughness evolution of the Fe/Si(001) was described by $\ensuremath{\beta}\ensuremath{\sim}0.36.$

Effect of convective transport on droplet spinodal decomposition in fluids

The effect of convective transport on the late stage growth of droplets in the presence of sedimentation and shear flow is analyzed. The high Peclet number limit (UR/D)≫1 is considered, where U is the characteristic velocity, R is the radius of the droplet, and D is the diffusion coefficient. The growth of the droplet depends on the boundary condition for the fluid velocity at the droplet interface, and two types of boundary conditions are considered. For a rigid interface, which corresponds to the interface between a solid and a fluid, the tangential velocity is zero and the normal velocity is equal to the velocity of the surface. For a mobile interface, which corresponds to an interface between two fluids, the tangential and normal velocities are continuous. These results indicate that the scaling relations for the critical radius are Rc(t)∝t(1/2) for a sedimenting droplet with a rigid interface, Rc(t)∝t(2/3) for a sedimenting droplet with a mobile interface, Rc(t)∝t(3/7) for a droplet with a rigid interface in a simple shear flow, and Rc(t)∝t(1/2) for a droplet with a mobile interface in a simple shear flow. The rate of droplet growth is enhanced by a factor of Pe(1/3) for rigid interfaces and Pe(1/2) for mobile interfaces.

Involvement of a rhamnolipid-producing strain of Pseudomonas aeruginosa in the degradation of polycyclic aromatic hydrocarbons by a bacterial community.

A rhamnolipid-producing strain of Pseudomonas aeruginosa GL1 was isolated from a bacterial community growing on a mixture of polycyclic aromatic hydrocarbons (PAH) as sole carbon source. Strain GL1 did not grow on PAH but grew on known degradation metabolites of phenanthrene (O-phthalic acid) and of naphthalene (salicylic acid). In co-culture with a phenanthrene-degrading strain, Ps. aeruginosa GL1 accelerated the degradation of phenanthrene. Strain GL1 was resistant to toxic amphiphilic compounds such as cationic and anionic detergents. Rhamnolipid production took place in a late stage growth in cultures of strain GL1 on glycerol or n-hexadecane. It coincided with a substantial decrease in cell hydrophobicity and with morphological changes of the outer membrane as observed by transmission electronic microscopy. The rhamnolipids produced inhibited the growth of bacteria such as Rhodococcus erythropolis, Bacillus cereus and Ps. fluorescens. The overall results suggested an outer membrane origin for the rhamnolipids. They also indicate that the utilization of PAH metabolites by strain GL1 is important for the stability of the PAH-degrading community.

Effect of Morphometric Maturity and Size on Enzyme Activities and Nucleic Acid Ratios in the Snow Crab Chionoecetes Opilio

Indicators of metabolic capacity and the potential for protein synthesis in male snow crabs, Chionoecetes opilio, were measured to estimate how these factors are affected by morphometric maturity and body size. The metabolic capacity of muscle, as depicted by cytochrome C oxidase (CCO), citrate synthase (CS), and lactate dehydrogenase (LDH) activity, was greater in adults than in adolescents, while that of the digestive gland was not affected by maturity. These differences may reflect the different locomotory habits of adults and adolescents. Indicators of the potential for protein synthesis, the RNA:DNA and protein:RNA ratios, did not differ between adult and adolescent crabs, presumably because the animals were in late intermolt stage and flesh growth was already completed. The total mass of muscle, as estimated by the flesh content of the merus, and the total capacity of muscle CCO scaled isometrically with body mass, while that of CS scaled with an exponent <1. The mass of the digestive gland, as well as the total capacity of both mitochondrial enzymes in this organ, increased more slowly than body size. These results support the hypothesis that the negative allometry generally observed for aerobic metabolism may be caused by the decreasing size of the metabolically most active tissues with an increase of body mass. In contrast with the positive allometry of the anaerobic capacity of fast-swimming fish with body mass, we noted an isometric relationship between these two variables in the rather slow-moving C. opilio. This supports the hypothesis that an enhanced anaerobic capacity is necessary for the largest individuals of a fast-moving species in order to maintain their burst swimming speed despite the increased friction generated by increased speed and body size. The effects of body size on the aerobic capacity of vertebrates have been thoroughly investigated during the last two decades (reviewed by Robinson et al., 1983; SchmidtNielsen, 1984; Goolish, 1991). Far fewer allometric studies have been concerned with invertebrates, on the one hand, or with glycolytic capacity, on the other hand. Given the differences in locomotory strategies and dependency upon aerobic and anaerobic metabolism, the relationships between body size and metabolic capacities may differ between mammals, fish, and invertebrates. Growth not only leads to increases in body size, but may also be associated with changes in maturity, morphology, and behavior. For example, immature males of many crustacean species, including crabs and shrimps, undergo molt cycles until they reach the adult stage. Whether the molt leading to morphometrical maturity is terminal or not in majid male crabs is still subject to controversy (Hartnoll, 1963; Conan and Comeau, 1986; Dawe et al., 1991; Sainte-Marie and Hazel, 1992), although the general opinion favors the terminal molt hypothesis. Adult males have larger gonads as well as a higher chela height to carapace width ratio than adolescent males, and th y display mating behaviors more frequently (Donal son an Adams, 1989; Claxton, 1992; Cassier et al., 1997). Adult males of various crab species also migrate over longer distances than immature males (SainteMarie and Hazel, 1992; Hines et al., 1995). Maturity is thus likely to affect muscle metabolic capacities and should be considered in allometric studies. Whether an adjustment in enzyme activities with maturity or body size is strictly due to locomotory habits can be inferred by comparison with enzymatic responses in nonlocomotory tissues such as the digestive gland. To our knowledge, the effect of maturity on the relationship between metabolic capacity and body mass in invertebrates has not been investigated. The equation describing the relationship between metabolic rate (Y) and body mass (M) is Y = aMb, where a is a constant and b the scaling factor. Numerous studies have demonstrated that the oxygen consumption of a given endothermic species is proportional to the body mass to the power 0.67. Interspecifically, an exponent of 0.75 is often reported for ectothermic animals, although

Effect of hydrodynamic flow on kinetics of nematic-isotropic transition in liquid crystals

We investigate kinetics of nematic-isotropic transition by solving the hydrodynamic equations for the nematic 3 × 3 tensor order parameter Q αβ and the fluid velocity in two space dimension (x-y plane). Numerical results indicate that nematic directors tend to align parallel to the x-y plane when hydrodynamic flow is incorporated. Late stage growth exponents, φc for the correlation length and φdef for the number of topological defects, are not significantly altered by hydrodynamic flow. However, in contrast to the case without flow, the relation φdef = ‒2φc holds well, which may indicate the validity of dynamical scaling for the case with hydrodynamic flow.

Surface-Influenced Phase Separation in Organic Thin Films on Drying

Kinetics of phase separation at the air/polymer interface in a binary polymer mixture on evaporation of common solvent is studied. The lateral dimension of the highly anisotropic, pancake-like, minority phase increases with a growth exponent of 2 / 3 , identical to late-stage growth under (classical) thermal quench at interface. The wetting-layer formed at the surface is directly visualized using atomic force microscopy. In contrast to the thermal quench, during drying the kinetics depends on the initial condition (i.e., initial concentration, co) that is resealed to obtain a master curve.

Ordering of clusters during late-stage growth on surfaces

The size ordering and spatial ordering of metal clusters on semiconductor surfaces has been experimentally investigated for systems in the late stages of phase separation. Specific late stage cluster growth mechanisms were achieved by suitable experimental conditions, and include (i) Ostwald ripening, (ii) coalescence, and (iii) an ``intermediate'' regime where mass conservation is only marginally violated by a relatively small deposition rate during cluster growth. The size ordering and spatial ordering of clusters were quantified by the standard deviations of the cluster size distribution and the nearest-neighbor distribution, respectively. In the Ostwald ripening regime, the size distribution is less ordered (broader) and the spatial distribution is more ordered (narrower) than is predicted by the mean-field Lifshitz-Slyozov ripening theory. In the intermediate regime, a higher degree of size ordering is observed (when compared to Ostwald ripening), but little spatial ordering with a near random spatial distribution. Finally, in the coalescence regime little size ordering and no spatial ordering are observed. These results are described using a model of local ripening, a mechanism where the ripening of an individual cluster is dominated by its nearest neighbor rather than the global growth conditions.

Late stage cluster growth: spatial correlations and ordering on surfaces

The widely accepted models for late stage clustering, the Lifshitz-Slyozov-Wagner theory for Ostwald ripening and the self-similar Monte Carlo simulations by Family and Meakin for coalescence growth, are consistent with random spatial distributions of the clustered phase. Several detailed investigations have revealed that cluster-cluster interactions have to be further considered. Only one of these studies lead to predictions of spatial ordering when long-range repulsive forces were included. In this paper we investigate nearest neighbor cluster distance distributions for both late stage growth processes (coalescence for Ga on GaAs(0 0 1) and Ostwald ripening for Sn and In on Si(1 1 1)) and correlate the results with experimental and theoretical results for the cluster-cluster interaction in these systems. Non-random spatial distributions are found for ripening even at rather low areal cluster densities, indicating that (i) cluster-cluster interactions play a major role in the morphological evolution of ripening structures at much smaller areal fractions than previously assumed and (ii) the Gibbs-Thomson effect, in combination with a diffusion controlled exchange of matter between clusters, is sufficient as a driving force to obtain partially ordered structures.

The Dynamics of Thermal-Induced Phase Separation in PMMA Solutions

Small-angle light scattering and scanning electron microscopy (SEM) have been used to study morphology development in poly(methyl methacrylate) membranes formed by the thermal inversion method. Analysis of the early time behavior of the scattered intensity in terms of Cahn−Hilliard theory establishes spinodal decomposition as the mechanism of phase separation for the conditions studied. The intensity maximum position for late-stage growth follows a power law dependence with a time exponent of approximately one-third, which is consistent with diffusive coarsening mechanisms. Solutions quenched to regions of the phase diagram below the glass transition temperature show an immediate arrest in the location of the scattered intensity maximum, indicating a locking-in of the phase-separated structure. Domain sizes obtained from SEM measurements of annealed, quenched samples are shown to be consistent with light scattering measurements.

Phase separation in two-dimensional binary fluids: A molecular dynamics study.

We present results of molecular dynamics computer simulation experiments of phase separation in a two-dimensional model binary fluid. For critical quenches the tubularlike domain structure grows at late times according to a power law with an exponent 1/2 which later crosses over to 2/3. This latter result has recently been questioned by Ossadnik et al. [Phys. Rev. Lett. 72, 2498 (1994)], and we present further evidence that the fast exponent is indeed present in the dynamical growth. That these exponents are hydrodynamic in origin is demonstrated by performing runs where the velocity field is disturbed at regularly spaced intervals of time. The perturbation consists of resetting the velocities of the particles to those characteristic of a Boltzmann distribution, which destroys the hydrodynamic tail of the velocity autocorrelation function. The resulting exponent changes to that predicted by experiments using stochastic techniques (Monte Carlo), i.e., 1/3. Also, we present results of experiments for off-critical quenches. The late-stage growth exponent for not too off-critical concentrations is close to 1/3, but we observe a continuous transition from this exponent to that characteristic of a critical quench. \textcopyright{} 1996 The American Physical Society.

A seismic analysis of differential compaction in the Frasnian Duhamel reef, south-central Alberta

The Duhamel reef is an isolated Upper Devonian Leduc Formation limestone bioherm, situated immediately NNE of the Bashaw reef complex in south-central Alberta. Although Duhamel has a relatively small basal area (less than 12 km 2), this reef rises some 275 m above the platform facies. From seismic data we interpret that there is a raised peripheral reef rim that appears to be elevated about 25 m relative to the interior of the reef. Raised rims are considered to be diagenetic in origin and attributed to differential compaction within the reef complexes. Although late-stage accretionary growth about the periphery of the reef complex may have contributed to its development, we interpret the raised rim at Duhamel to be principally of secondary origin. This thesis is consistent with the incorporated seismic and well-top data. The facies within the reef rim have a lower seismic velocity than the facies within the structurally lower reef interior, consistent with the observation that the raised rim is generally more porous than the encircled and structurally lower lagoon and, therefore, constitute a preferred well-completion site. Optimal hydrocarbon recovery could be realized if all production wells were drilled into the raised reef rim. The Duhamel example shows that even relatively small Leduc reefs can exhibit raised rims and that these rims may be seismically visible. Before drilling, reflection seismic data should be acquired across similar reefs with a view to imaging and locating the complete raised rim, not simply its updip side, so that all parts of the rim can be tested by the drill.

Influence of modulated structures on ordering dynamics in CuAu

Using a microscopic model, we have studied the evolution of microstructure in a model metallic alloy. The Hamiltonian was derived from the effective medium theory of cohesion in metals (EMT): an approximation scheme for integrating out the electronic degrees of freedom and constructing an effective classical Hamiltonian. The alloy chosen for this study was CuAu which exhibits a sequence of first-order phase transitions: disordered → modulated → ordered. To describe the dynamics of ordering, a free energy functional was constructed from the EMT Hamiltonian and used in a Langevin equation. This study demonstrates the feasibility of predicting microstructure in alloys starting from a description based on the electronic structure of alloys. The simulations exhibit interesting features in late-stage growth which are attributed to the presence of the modulated phase as a metastable phase in the ordered regime.

Melt movement and the occlusion of porosity in crystallizing granitic systems

AbstractPorosity occlusion has been studied in a granodiorite rock from the Peruvian Coastal Batholith. The texture of the granodiorite is characteristic of Cordilleran I-type rocks, and the textural relations and modelled crystallization path within the quaternary An-Ab-Or-Qz system indicate alkali feldspar was the last major phase to start crystallizing. In thin section, alkali feldspar crystals occur both as large anhedral ‘plates’ containing numerous inclusions, and small interstitial cuneiform ‘pockets’. The alkali feldspar pockets are interpreted as late stage nucleation and growth of new crystals in pores that became isolated from the larger crystals during the latter stages of crystallization. Their geometry therefore mirrors that of the pores immediately after isolation.From the modal abundance of the interstitial pockets, and taking into account contemporaneous growth of the other major phases, it is suggested that crystallization in isolated pores involved solidification of the final 3–4% of liquid. Alkali feldspar growth on the rims of the large anhedral plates prior to pore isolation is evidence for the localised (mm-cm scale) diffusion of chemical species within the interconnected melt phase. However, Rayleigh number calculations indicate that the separation of melt from crystals by compositional convection is unlikely to have occurred during interstitial crystallization.

Studies on Palatability of Rice in Northern Kyushu. VII. Locational differences in palatability of rice and its related factors.

The palatability and physiochemical properties of milled rice produced on different types of soils and latitudes were studied in order to improve the culture technique to produce good eating quality rice. There was locational difference, we found that the differences in soil types had a great influence on palatability. No clear relationship between the altitude and palatability was found. The palatability of rice produced on Light-colored Andosols (LAN) was inferior to that of rice produced on other soil types: Fine-textured Yellow soils, Fine-textured Brown Lowland soils, Gravelly Gray Lowland soils. The protein content of rice produced on LAN was significantly higher than that of rice produced on other soil types. Protein content was significantly correlated with the palatability using rice grown in various locations. On the other hand, amylose content and amylographic characteristics were not related to palatability. The results lead to the conclusion that the main cause of the deterioration of palatability of rice grown in LAN was increases in protein content due to increases in nitrogen released from LAN during the late stage growth period of rice plant. Therefore, it is important to restrict the amount of nitrogen absorbed by rice plant i.e., improvement of the method of fertilizer application and soil improvement, in order to improve the eating quality of rice grown in LAN.

Synthetic Diamond Strength Enhancement Through High Pressure/High Temperature Annealing

ABSTRACTAnnealing of low inclusion, single crystals of synthetic Type I diamond at 1200–1700°C and 50–60kbar, was observed to increase average crystal compressive fracture strength by as much as 20%. The increase in strength is associated with the healing of lattice dislocations, coalescence of small (&lt; 400 nm) metal inclusions, and dissociation of aggregatenitrogen. Photoluminescence and FTIR spectroscopic data indicate H3 and “A”-type defect centers are unstable relative to NVx and “C”-type defect centers under the conditions of these experiments. Dissociation rate is greater in the (111) growth sector than in the (100). Changes in residual lattice strain of the samples could not be detected using Raman spectroscopy and optical microscopy. A model reaction of the type, 2V + N2V = NV2 + NV, in which N = nitrogen and V = vacancy (i.e., N2V = H3 center) is proposed which provides a qualitative thermodynamic understanding of the observations reported in this study consistent with previous results of other researchers. In addition, photoluminescence examination of smaller crystals produced from a quench of early stage non-equilibrium growth reveal a lower concentration of aggregate nitrogen than those quenched from late stage growth suggesting that nitrogen may aggregate via in situ annealing processes. Ultimately, understanding mechanisms to improve synthetic single crystal diamond strength will lead to improved tools which utilize such crystals (e.g., drill bits and saws for cutting stone and concrete) which constitute a market of ≈ $2b worldwide.

The formation mechanism of plate in beta Cu-Zn and Cu-Zn-Al alloys

The initial formation and the subsequent early and late stage growth of the α1 plates in Cu-Zn and Cu-Zn-AI alloys are studied by optical microscopy, transmission electron microscopy (TEM), and high-temperature TEMin situ. Single-phase α1 plates (initial α1 plates) can be obtained only at the early stage of isothermal transformation. Striations corresponding to stacking faults are observed during the nucleation of initial α1 plates. A strong and discontinuous strain-stress field exists in front of the tips of initial α1 plates and causes inducing nucleation and crossing growth. The displacement between stacking fault faces and the thickening along the direction of streaking contrast show that the growth of initial α1 plate has the nature of shear transformation, and the shear direction along the streaking contrast corresponds to stacking faults. The superledges at the broad faces of the α1 plates are also observed, but they move only along the direction of streaking contrast during plates thickening. The “overannealing” of initial α1 plates during longer transformation time results in the disappearing of stacking faults, and corresponding initial α1 plates are partially or completely “degenerated” into equilibrium α phase (here designated as late α1 (α) plates). The thickening kinetics of late α1 (α) plates seems to be compatible with the diffusional ledge mechanism, but the lateral movement of superledges along the broad faces of late α1 (α) plates is not observed. According to the facts mentioned previously, a possible atomic mechanism for the formation of the α1 plates is suggested.