Search results for "Nucleation"

Nucleation in Supersaturated Vapors

2009

Solidification kinetics of hard-sphere colloidal suspensions

2007

We investigate the solidification dynamics of hard-sphere colloidal suspensions applying simultaneously small-angle and Bragg light scattering. These experiments allow a consistent picture of nucleation and crystal growth on the level of large-scale density fluctuations and of density fluctuations on the level of individual crystallites. We observe a temporally almost constant nucleation rate after an induction time that decreases with supersaturation. The classical expectation for the nucleation rate density as a function of supersaturation is in accordance with our data. We investigate the validity of the Wilson—Frenkel growth law for hard-sphere systems, which also fits our data satisfac…

Quantitative description of C-60 diffusion on an insulating surface

2010

The diffusion of ${\text{C}}_{60}$ molecules on large, atomically flat terraces of the ${\text{CaF}}_{2}(111)$ surface is studied under ultrahigh vacuum conditions at various substrate temperatures below room temperature. The weak molecule-substrate interaction on this insulating surface makes a direct observation of hopping events difficult. Therefore, to determine a quantitative value of the diffusion barrier, we employ the so-called onset method. This method is based on the analysis of spatial properties of islands created by nucleation of diffusing ${\text{C}}_{60}$ molecules, as measured by noncontact atomic force microscopy. We first determine the critical cluster size to be ${i}^{\en…

Global Synchronization via Homogeneous Nucleation in Oscillating Surface Reactions

1999

The mechanism leading to globally synchronized oscillations in the $\mathrm{CO}+{\mathrm{O}}_{2}/\mathrm{Pt}\left(110\right)$ reaction system is investigated by means of Monte Carlo simulations. The model considers the reconstruction of the surface via phase border propagation and spontaneous phase nucleation. The reason for global oscillations turns out to be the spontaneous phase nucleation. This nucleation, which is modeled as a weak noise process, results in a random creation of dynamic defects and leads to global synchronization via stochastic resonance. The mechanism of global coupling via the gas phase, as it is proposed to date, does not occur.

Supersaturation and Crystal Nucleation in Confined Geometries

1998

Surface aggregation as a necessary condition for interfacially induced crystal nucleation is studied with a surface forces apparatus (SFA).1-3 As a model system, we use the chloride salt of the rod...

The role of surface diffusion in the growth mechanism of III-nitride nanowires and nanotubes.

2021

Abstract The spontaneous growth of GaN nanowires (NWs) in absence of catalyst is controlled by the Ga flux impinging both directly on the top and on the side walls and diffusing to the top. The presence of diffusion barriers on the top surface and at the frontier between the top and the sidewalls, however, causes an inhomogeneous distribution of Ga adatoms at the NW top surface resulting in a GaN accumulation in its periphery. The increased nucleation rate in the periphery promotes the spontaneous formation of superlattices in InGaN and AlGaN NWs. In the case of AlN NWs, the presence of Mg can enhance the otherwise short Al diffusion length along the sidewalls inducing the formation of AlN …

Estimation of Nucleation Barriers from Simulations of Crystal Nuclei Surrounded by Fluid in Equilibrium

2016

Nucleation rates for homogeneous nucleation are commonly estimated in terms of an Arrhenius law involving the nucleation barrier, written in terms of a competition of the contribution in surface free energy of the nucleus and the free energy gain proportional to the nucleus volume. For crystal nuclei this “classical nucleation theory” is hampered by the problem that the nucleus in general is non spherical, since the interfacial excess free energy depends on the orientation of the interface relative to the crystal axes. This problem can be avoided by analyzing the equilibrium of a crystal nucleus surrounded by fluid in a small simulation box in thermal equilibrium. Estimating the fluid press…

Determination of cluster binding energies on metal surfaces by statistics

2000

Abstract Two simple formulae to determine binding energies of two-dimensional clusters on surfaces in thermal equilibrium are derived. One requires measurement of monomer and cluster populations and of the surface temperature. The cluster dissociation rate is derived and related to the atom hopping rate, allowing the theory to be extended to adatom populations that are not in chemical equilibrium. The result gives a recipe for determining dissociation energies that requires measurements of only two rates at a single temperature.

Simulation of fluid-solid coexistence in finite volumes: A method to study the properties of wall-attached crystalline nuclei

2012

The Asakura-Oosawa model for colloid-polymer mixtures is studied by Monte Carlo simulations at densities inside the two-phase coexistence region of fluid and solid. Choosing a geometry where the system is confined between two flat walls, and a wall-colloid potential that leads to incomplete wetting of the crystal at the wall, conditions can be created where a single nanoscopic wall-attached crystalline cluster coexists with fluid in the remainder of the simulation box. Following related ideas that have been useful to study heterogeneous nucleation of liquid droplets at the vapor-liquid coexistence, we estimate the contact angles from observations of the crystalline clusters in thermal equil…

Simulation of binary fluids exposed to selectively adsorbing walls: a method to estimate contact angles and line tensions

2011

For an understanding of interfacial phenomena of fluids on the nanoscale a detailed knowledge of the excess free energies of fluids due to walls is required, as well as of the interfacial tension between coexisting fluid phases. A description of simulation approaches to solve this task is given for a suitable model binary (A + B) fluid. Sampling the order parameter distribution of the system without walls, the curvature dependent and flat interfacial tensions of coexisting ‘bulk’ phases is extracted. In a thin film geometry, the difference in wall free energies is found via a new thermodynamic integration method. Thus the contact angle θ of macroscopic droplets is estimated from Young's equ…