Dependence Of Growth Kinetics Research Articles

Temperature Dependent Growth Kinetics of Pd Nanocrystals: Insights from Liquid Cell Transmission Electron Microscopy.

Quantifying the role of experimental parameters on the growth of metal nanocrystals is crucial when designing synthesis protocols that yield specific structures. Here, the effect of temperature on the growth kinetics of radiolytically-formed branched palladium (Pd) nanocrystals is investigated by tracking their evolution using liquid cell transmission electron microscopy (TEM) and applying a temperature-dependent radiolysis model. At early times, kinetics consistent with growth limited is measured by the surface reaction rate, and it is found that the growth rate increases with temperature. After a transition time, kinetics consistent with growth limited by Pd atom supply is measured, which depends on the diffusion rate of Pd ions and atoms and the formation rate of Pd atoms by reduction of Pd ions by hydrated electrons. Growth in this regime is not strongly temperature-dependent, which is attributed to a balance between changes in the reducing agent concentration and the Pd ion diffusion rate. The observations suggest that branched rough surfaces, generally attributed to diffusion-limited growth, can form under surface reaction-limited kinetics. It is further shown that the combination of liquid cell TEM and radiolysis calculations can help identify the processes that determine crystal growth, with prospects for strategies for control during the synthesis of complex nanocrystals.

Ordering kinetics and steady state of Malthusian flock

We study a collection of polar self-propelled particles or polar flock on a two dimensional substrate involving birth and death. Most of the previous studies of polar flock with birth and death have focused on the steady state characteristics of Malthusian flock. We emphasize on the significance of rate of birth and death on the kinetics as well as steady state of the system. Our system is modeled using coarse-grained hydrodynamic equations of motion for local density and velocity of the flock. Results are obtained for different birth and death rates by solving the hydrodynamic equations using numerical integration and linearized calculation about the broken symmetry state. The presence of finite birth and death rate affects the density field significantly, whereas the effect on velocity field is moderate. The early time growth of velocity field slows down in the presence of finite birth and death rate, whereas at late times it approaches the value of non-conserved growth kinetics for all birth and death rates. The density field shows the strong time dependent growth kinetics. The asymptotic growth law for density depends on the birth and death rates and shows a crossover from 5/6 for the immortal flock to 1/4 for large birth and death rates. In the steady state, the presence of birth and death rate leads to the suppression of speed of sound wave, velocity, and density fluctuations in the system.

Continuous Nucleation and Size Dependent Growth Kinetics of Indium Phosphide Nanocrystals

Aminophosphines derived from N,N′-disubstituted ethylenediamines (R–N(H)CH2CH2N(H)–R; R = ortho-tolyl, phenyl, benzyl, iso-propyl, and n-octyl) were used to adjust the kinetics of InP nanocrystal f...

Spectroscopic ellipsometer study of laser ablation wavelength dependent growth kinetics of Ag nanoislands: An insight to potential plasmonic applications

Effect of inhomogeneous particle-size distribution on the effective LSPR peak position and broadening of the optical spectra of metal nanoislands thin films has been examined using Modified-Yamaguchi’s model (MYM). Effective dielectric constants (ɛ1, ɛ2) of the pulsed laser deposited metallic nanoislands thin films has been extracted using Spectroscopic Ellipsometer (SE) to provide an insight of laser ablation wavelength dependent growth kinetic of the films. Simultaneous fitting of polarized spectra along with psi and delta parameters strengthens the applicability of applied set of oscillators. Origin of negligible film roughness in ellipsometric results has been attributed to the plasmonic averaging of the spectra. Effective polarizability and the phase difference between transmitted and scattered wave have been calculated using ɛ1 and ɛ2. Present study shows the way of selecting laser ablation wavelength to deposit Ag nanoislands thin films as per the requirement of sensors and photovoltaic solar cells. A practical use of SE has been reported unlike previous studies which are limited to the measurement of dielectric constants only.

Sputtering temperature dependent growth kinetics and CO2 sensing properties of ZnO deposited over porous silicon

We report the growth kinetics and sensing properties of ZnO deposited over macro-porous silicon substrates at 400 and 600 °C using magnetron-sputtering technique. Scanning electron microscopy was employed to investigate the morphology and the particle size of the ZnO nanoparticles (NPs). The grain growth kinetics was analyzed with the help of the phenomenological equation rn=k0texp(−Q/RT) finding an activation energy Q = 13.92 kJ/mol. The grain growth exponent (n = 2.85) for the growth at 400 °C corresponds to an Ostwald ripening process, while the growth at 600 °C is described by n = 1.66 implying a higher growth rate attributed to a high surface diffusion of add-atoms contributing to the formation of larger grains. The sensing response of the complete structure has been tested at different temperatures. The highest sensitivity, S ∼10, was obtained at a sensor temperature of 300 °C on the ZnO NPs sputtered on to the porous silicon substrate at 400 °C. The high response is attributed to the infiltration, uniform and homogenous distribution of the ZnO NPs into the pores. ZnO NPs sputtered at 400 °C are found to be smaller than those grown at 600 °C, exhibiting a larger surface-area/volume ratio and hence increasing the oxygen adsorption resulting in an enhanced CO2 sensitivity.

Hydrogen and thiosulfate limits for growth of a thermophilic, autotrophic Desulfurobacterium species from a deep-sea hydrothermal vent.

Hydrothermal fluids (341°C and 19°C) were collected < 1 m apart from a black smoker chimney and a tubeworm mound on the Boardwalk edifice at the Endeavour Segment in the northeastern Pacific Ocean to study anaerobic microbial growth in hydrothermal mineral deposits. Geochemical modelling of mixed vent fluid and seawater suggests the mixture was anoxic above 55°C and that low H2 concentrations (79 μmol kg(-1) in end-member hydrothermal fluid) limit anaerobic hydrogenotrophic growth above this temperature. A thermophilic, hydrogenotrophic sulfur reducer, Desulfurobacterium strain HR11, was isolated from the 19°C fluid raising questions about its H2 -dependent growth kinetics. Strain HR11 grew at 40-77°C (Topt 72-75°C), pH 5-8.5 (pHopt 6-7) and 1-5% (wt vol(-1) ) NaCl (NaClopt 3-4%). The highest growth rates occurred when S2 O3 (2-) and S° were reduced to H2 S. Modest growth occurred by NO3 (-) reduction. Monod constants for its growth were Ks of 30 μM for H2 and Ks of 20 μM for S2 O3 (2-) with a μmax of 2.0 h(-1) . The minimum H2 and S2 O3 (2-) concentrations for growth were 3 μM and 5 μM respectively. Possible sources of S2 O3 (2-) and S° are from abiotic dissolved sulfide and pyrite oxidation by O2 .

In-situ observations of nanoscale effects in germanium nanowire growth with ternary eutectic alloys.

Vapour-liquid-solid (VLS) techniques are popular routes for the scalable synthesis of semiconductor nanowires. In this article, in-situ electron microscopy is used to correlate the equilibrium content of ternary (Au0.75 Ag0.25 -Ge and Au0.65 Ag0.35 -Ge) metastable alloys with the kinetics, thermodynamics and diameter of Ge nanowires grown via a VLS mechanism. The shape and geometry of the heterogeneous interfaces between the liquid eutectic and solid Ge nanowires varies as a function of nanowire diameter and eutectic alloy composition. The behaviour of the faceted heterogeneous liquid-solid interface correlates with the growth kinetics of the nanowires, where the main growth facet at the solid nanowire-liquid catalyst drop contact line lengthens for faster nanowire growth kinetics. Pronounced diameter dependent growth kinetics, as inferred from liquid-solid interfacial behaviour, is apparent for the synthesised nanowires. Direct in-situ microscopy observations facilitates the comparison between the nanowire growth behaviour from ternary (Au-Ag-Ge) and binary (Au-Ge) eutectic systems.

Applicability of the Arrhenius model for ammonia oxidizing bacteria subjected to temperature time gradients

The aim of this work is to identify the range of applicability of Arrhenius type temperature dependence for Ammonia Oxidizing Bacteria (AOB) subjected to temperature time gradients through continuous titrimetric tests. An innovative online differential titrimetric technique was used to continuously monitor the maximum biologic ammonia oxidation rate of the biomass selected in a pilot scale membrane bioreactor, as a function of temperature time gradients. The monitoring technique is based on the measurement of alkalinity and hydrogen peroxide consumption rates in two parallel reactors operated in nonlimiting substrate conditions for AOB; both reactors were continuously fed with mixed liquor and in one of them AOB were inhibited with allylthiourea. The effects of temperature decrease rates in the range 1 to 4°C·h−1 were evaluated by controlling the titrimetric reactor in the temperature range 10°C-20°C. The dependence of growth kinetics on temperature time gradients and the range of applicability of Arrhenius model for temperature dependency of AOB growth kinetics were assessed. The Arrhenius model was found to be accurate only with temperature gradients lower than 2°C·h−1. The estimated Arrhenius coefficients (θ) were shown to increase from 1.07 to 1.6 when the temperature decrease rate reached 4°C·h−1.

A computational investigation of attrition-enhanced chiral symmetry breaking in conglomerate crystals

Attrition-enhanced chiral symmetry breaking in crystals, also known as Viedma ripening, is a remarkable phenomenon from a variety of perspectives. By providing a direct route to solid-phase homochirality in a controllable manner, it is of inherent interest to those who study chiral symmetry-breaking/amplification mechanisms. When applied to intrinsically chiral molecules, Viedma ripening may have implications for the origin of biological homochirality, as well as applications in chiral drug resolution. Despite an abundance of research, the mechanistic details underlying this phenomenon have not been unambiguously elucidated. We employ a Monte Carlo algorithm to study this driven system, in order to gain further insights into the mechanisms capable of reproducing key experimental signatures. We provide a comprehensive numerical investigation of how the model parameters (attrition rate, liquid-phase racemization kinetics, and the relative rates of growth and dissolution kinetics) impact the system's overall behavior. It is shown that size-dependent crystal solubility alone is insufficient to reproduce most of the experimental signatures of Viedma ripening, and that some form of a solid-phase chiral feedback mechanism must be invoked in order to reproduce experimentally observed behavior. In this work, such feedback mechanisms can take the form of agglomeration, or of artificial modification of the size dependent growth kinetics.

Spectral UV losses in 355 nm pulsed laser delivery system at low temperatures

For a delivery system using high OH polyimide coated all-silica multimode fibers the photo degradation and recovery were investigated for 355nm pulsed laser radiation at a cryogenic temperature of 77K (liquid nitrogen) and at room temperature, as reference. For comparison, UV-induced fiber losses generated during light transportation of a deuterium lamp were measured. For these quite different light sources the efficiency of defect generation including UV-induced optical absorption at 214nm and at 265nm is significantly different at both temperatures used in these studies. At 77K, the UV-induced optical loss at 214nm is significantly reduced, while the same loss at 265nm is increased, for the tested high OH fibers. In addition, the values of both losses are rapidly changed when the fiber is warmed up from 77K to room temperature. The observed temperature dependent growth kinetics of UV-induced absorption at 214nm is considered to be explained by at least two different mechanisms of defect generation.

Size selected growth of nanodots: analytical prediction for the selected size

In size selected growth of metal and semiconductor nanodots the selected mean size is frequently larger than the size corresponding to the minimum of free energy of dots. This “overshooting” effect is studied here using a reaction kinetic model with size dependent growth kinetics in adatom processes and thermodynamical free energy difference of nanodots. We calculate analytical prediction for the selected mean size of the dots using stationary state approximation. It is shown, that the overshooting depends on the skewness of the Gaussian size distribution.

Catalyst and its diameter dependent growth kinetics of CVD grown GaN nanowires

GaN nanowires were grown using chemical vapor deposition with controlled aspect ratio. The catalyst and catalyst-diameter dependent growth kinetics is investigated in detail. We first discuss gold catalyst diameter dependent growth kinetics and subsequently compare with nickel and palladium catalyst. For different diameters of gold catalyst there was hardly any variation in the length of the nanowires but for other catalysts with different diameter a strong length variation of the nanowires was observed. We calculated the critical diameter dependence on adatoms pressure inside the reactor and inside the catalytic particle. This gives an increasing trend in critical diameter as per the order gold, nickel and palladium for the current set of experimental conditions. Based on the critical diameter, with gold and nickel catalyst the nanowire growth was understood to be governed by limited surface diffusion of adatoms and by Gibbs–Thomson effect for the palladium catalyst.

Lycopene Production Using Blakeslea trispora in the Presence of 2-Methyl Imidazole: Yield, Selectivity, and Safety Aspects

The potential role of 2-methyl imidazole in improving lycopene production by Blakeslea trispora with regards to yield, selectivity, and safety aspects was investigated in batch culture. Optimization of the bioprocess conditions in terms of (a) (+) and (-) strain ratio in the inoculum, (b) initial crude soybean oil (CSO) addition level, and (c) the amount of 2-methyl imidazole was based on response surface methodology to achieve maximum lycopene production. The dependence of growth kinetics, lycopene yield, and selectivity of the bioprocess on the above factors was clear. 2-Methyl imidazole at 50 mg/L was found equally active in terms of lycopene cyclase inhibition with that at 200 or 100 mg/L; in all cases, lycopene accounted for 94% of the total carotenoids. The highest yield was observed at a 50 mg/L level of addition (24 mg/g of biomass dry weight,) in a substrate supplemented with CSO (48 g/L of culture medium) and inoculated with 1(+)/7(-) strain ratio.

The Kinetics of Calcite Growth: Interpreting Chemical Affinity-Based Rate Laws Through the Lens of Direct Observation

ABSTRACTChemical affinity-based rate laws are used across the geochemical and materials communities to quantify mineral/material corrosion and growth kinetics. These rate expressions are founded in assumptions regarding reaction mechanism with little evidence for surface processes. Using Atomic Force Microscopy (AFM), this study demonstrates the dependence of growth kinetics upon the structures of dislocation sources. In situ observations show that the dominant mode of growth occurs by hillock development initiated at complex sources. Derivations of surface process-based rate expressions show a complex dependence of rate on chemical affinity. This dependence is approximated by second order affinity-based rate laws only under the special conditions that 1) growth proceeds by development of single sourced spirals and 2) growth occurs at very near equilibrium conditions where spiral formation is the only operative mechanism. This suggests that growth experiments that measure temporal changes in solution chemistry yield a composite rate that arises from the contributions of the different hillock types. Hence, chemical affinity-based rate laws do not generally give meaningful interpretations of growth mechanism. By combining direct observations with macroscopic methods that monitor temporal changes in solution chemistry, rate laws with greater predictive capabilities may be possible.

Nutrient control of estuarine macroalgae:growth strategy and the balance between nitrogen requirements and uptake

The ability to sustain growth at low availability of nltrogen (N) was examined in 6 species of macroalgae with different growth strategies by compdrlng substrate dependent growth kinetics. The N rcqulred to support optimal growth and the N uptake kinetics of 2 slow-growing algae. Fucus r~esiculosus and Codium fragilc, and 4 fast-growing specles, Chnetolnorpha I jn~~rn, Cladophora serica, Cerarn~um rubrum and Ulva lactuca, were experimentally determ~ned In summer when the algae were N limited. The N required to support maximum growth vaned 16-fold among specles, w ~ t h fdst-gro\ving algae having the highest N demands. The high N requirements of ephemeral algae were caused by up to 13-fold h ~ g h e r growth ratps and 2to 3-fold higher N content at maximum growth. Also, the fastgrowing specles took up ammonium and nitrate 4 to 6 times faster per u n ~ t of biomass than slo\v-growing speclcs at both low and high substrate concentrations, but the ratios of maxlinum Pi uptake to requirements were larger among the slow-growing algae. Thus, the fast-growing specles tended to requlre relatively higher external concrntrations of inorganic N to saturate the11 growth Under N limited conditions, all 6 macroalgae were able to explo~t pulses of high concentrations of ammonium by taking up ammonium a t transiently enhanced rates (i.e. surge uptake). Uptake was, however, only marginally enhanced at low, and naturally occurring, concentrations of ammonium, suggesting that surge uptake is of minor ecological importance. Our results show that large, slow-growing macroalgae may be better able to meet their N requirements at low N availability than fast-growing species. This is consistent with the common observation that nutrient-poor coastal areas are dominated by slowgrowing macroalgae rather than ephemeral species, although ephemeral species have higher N uptake capacities.

Influence of orientation dependent growth kinetics on the performance of InGaAsP buried crescent lasers

The growth reproducibility of the separate optical confinement buried crescent laser has been studied in the wavelength region of 1.3&amp;lt;λ≤1.62 μm. The performance and yield of λ=1.55 μm lasers were found to be impaired by the competition between the (100) and (111) growth habits leading to the perturbed growth of the active layer. These results are discussed in terms of the crystallographic direction dependence of the liquid-solid distribution coefficient.