Search results for "Nucleation"
showing 10 items of 364 documents
Investigation of Finite-Size Effects in the Determination of Interfacial Tensions
2014
The interfacial tension between coexisting phases of a material is an important parameter in the description of many phenomena such as crystallization, and even today its accurate measurement remains difficult. We have studied logarithmic finite-size corrections in the determination of the interfacial tension with large scale Monte Carlo simulations, and have identified several novel contributions which not only depend on the ensemble, but also on the type of the applied boundary conditions. We present results for the Lennard-Jones system and the Ising model, as well as for hard spheres, which are particularly challenging. In the future, these findings will contribute to the understanding a…
Superfluid density in metastable 3He4He mixtures
1990
Abstract We havestudied superfluld 3He4He mixtures quenched into nonequilibrium states inside the miscibility gap by means of second sound . From the results for the second sound velocity we conclude that the superfluid density in the metastable state is well described by extrapolation from equilibrium values. The boundary of the metastable region, where nucleation processes set in rapidly, is reflected in a sharp increase of the second sound attenuation.
Magnetic Direct-Write Skyrmion Nanolithography
2020
Magnetic skyrmions are stable spin textures with quasi-particle behavior and attract significant interest in fundamental and applied physics. The metastability of magnetic skyrmions at zero magnetic field is particularly important to enable, for instance, a skyrmion racetrack memory. Here, the results of the nucleation of stable skyrmions and formation of ordered skyrmion lattices by magnetic force microscopy in (Pt/CoFeSiB/W)n multilayers, exploiting the additive effect of the interfacial Dzyaloshinskii-Moriya interaction, are presented. The appropriate conditions under which skyrmion lattices are confined with a dense two-dimensional liquid phase are identified. A crucial parameter to con…
How Do Droplets Depend on the System Size? Droplet Condensation and Nucleation in Small Simulation Cells
2003
Using large scale grandcanonical Monte Carlo simulations in junction with a multicanonical reweighting scheme we investigate the liquid-vapor transition of a Lennard—Jones fluid. Particular attention is focused on the free energy of droplets and the transition between different system configurations as the system tunnels between the vapor and the liquid state as a function of system size. The results highlight the finite size dependence of droplet properties in the canonical ensemble and free energy barriers along the path from the vapor to the liquid in the grandcanonical ensemble.
Mechanisms for the Decay of Unstable and Metastable Phases: Spinodal Decomposition, Nucleation and Late-Stage Coarsening
1989
The basic concepts on the kinetics of phase separation in alloys are introduced, and the current status of the theory is briefly reviewed. Particular emphasis is given to questions such as the conditions under which the linearized theory of spinodal decomposition is valid, the significance of spinodal curves, the possible description of coarsening in terms of power laws and structure-factor scaling, and non-equilibrium percolation phenomena.
Heterogeneous nucleation at a wall near a wetting transition: a Monte Carlo test of the classical theory
2009
While for a slightly supersaturated vapor the free energy barrier ΔF(hom)(*), which needs to be overcome in a homogeneous nucleation event, may be extremely large, nucleation is typically much easier at the walls of the container in which the vapor is located. While no nucleation barrier exists if the walls are wet, for incomplete wetting of the walls, described via a nonzero contact angle Θ, classical theory predicts that nucleation happens through sphere-cap-shaped droplets attracted to the wall, and their formation energy is ΔF(het)(*) = ΔF(hom)(*)f(Θ), with f(Θ) = (1-cosΘ)(2)(2+cosΘ)/4. This prediction is tested through simulations for the simple cubic lattice gas model with nearest-nei…
Frustration of structural fluctuations upon equilibration of shear melts
2002
Abstract We report on the formation of amorphous solids from aquaeous suspensions of charged colloidal spheres. Comprehensive light scattering and microscopic studies show that in these systems the nucleation rate density continuously increases to very high values. At the highest particle densities of 47.5 μm −3 (packing fraction Φ =0.146) an amorphous state is observed of only short range order, finite static shear modulus and frozen long time dynamics. This state is composed of a piling of––as we propose pre-critical––nuclei. Differences from the Hard Sphere case are discussed in some detail. There the arrest of density fluctuations is observed and described by Mode Coupling scenarios. In…
Protofibril formation of amyloid beta-protein at low pH via a non-cooperative elongation mechanism.
2005
Deposition of the amyloid beta-protein (Abeta) in senile or diffuse plaques is a distinctive feature of Alzheimer's disease. The role of Abeta aggregates in the etiology of the disease is still controversial. The formation of linear aggregates, known as amyloid fibrils, has been proposed as the onset and the cause of pathological deposition. Yet, recent findings suggest that a more crucial role is played by prefibrillar oligomeric assemblies of Abeta that are highly toxic in the extracellular environment. In the present work, the mechanism of protofibril formation is studied at pH 3.1, starting from a solution of oligomeric precursors. By combining static light scattering and photon correla…
Enhanced crystal stability in a binary mixture of charged colloidal spheres.
2009
We report on the phase behavior of a binary charged sphere mixture of size ratio $\ensuremath{\Gamma}=0.68$ and charge ratio $\ensuremath{\Lambda}\ensuremath{\approx}1$ as a function of composition $p$ and number density $n$. For $p=0.1--0.3$ we observe freezing at densities well below the freezing densities of the pure components. At all compositions our data indicate the formation of substitutional alloy crystals of body centered cubic structure. No indications for compound formation were observed. Rather, our findings point at the first observation of an upper azeotrope. Measurements of the crystallization kinetics reveal a combined density and composition dependence of growth velocities…
Classical growth of hard-sphere colloidal crystals.
1995
The classical theory of nucleation and growth of crystals is examined for concentrated suspensions of hard-sphere colloidal particles. The work of Russel is modified, extended, and evaluated, explicitly. Specifically, the Wilson-Frenkel growth law is modified to include the Gibbs-Thomson effect and is evaluated numerically. The results demonstrate that there is a critical nucleus radius below which crystal nuclei will not grow. A kinetic coefficient determines the maximum growth velocity possible. For large values of this coefficient, quenches to densities above the melting density show interface limited growth with the crystal radius increasing linearly with time. For quenches into the coe…