Free Energy Of Critical Nucleus Research Articles

Line-tension-induced scenario of heterogeneous nucleation on a spherical substrate and in a spherical cavity.

Line-tension-induced scenario of heterogeneous nucleation is studied for a lens-shaped nucleus with a finite contact angle nucleated on a spherical substrate and on the bottom of the wall of a spherical cavity. The effect of line tension on the free energy of a critical nucleus can be separated from the usual volume term. By comparing the free energy of a lens-shaped critical nucleus of a finite contact angle with that of a spherical nucleus, we find that a spherical nucleus may have a lower free energy than a lens-shaped nucleus when the line tension is positive and large, which is similar to the drying transition predicted by Widom [B. Widom, J. Phys. Chem. 99, 2803 (1995)]. Then, the homogeneous nucleation rather than the heterogeneous nucleation will be favorable. Similarly, the free energy of a lens-shaped nucleus becomes negative when the line tension is negative and large. Then, the barrier-less nucleation with no thermal activation called athermal nucleation will be realized.

A Nanothermodynamic Analysis of Cubic Boron Nitride Nucleation upon Chemical Vapor Deposition

AbstractBased on a boron nitride thermodynamic equilibrium phase diagram, a nanothermodynamic analysis was proposed, with respect to the effect of nanometer‐size‐induced additional pressure on the Gibbs' free energy of critical nuclei and the phase transition of hexagonal boron nitride (h‐BN) to cubic boron nitride (c‐BN), to elucidate nucleation of c‐BN during chemical vapor deposition (CVD). Notably, the analysis showed that the effect of surface tension induced by the nanometer‐size curvature of critical nuclei could drive the metastable phase region of c‐BN nucleation into the stable phase region of the boron nitride phase diagram; consequently, c‐BN nucleation would occur prior to h‐BN nucleation in the competing growth of c‐BN and h‐BN upon CVD.

Nucleation stability of diamond nanowires inside carbon nanotubes: A thermodynamic approach

Aiming at synthesis diamond nanowires, a simple thermodynamic approach was performed with respect to the effect of nanosize-induced additional pressure on the Gibbs free energy of critical nuclei to elucidate diamond nucleation inside carbon nanotubes upon chemical vapor deposition, based on the carbon thermodynamic equilibrium phase diagram. Notably, these analysis showed that the diamond nucleation would be preferable inside a carbon nanotube due to the effect of surface tension induced by the nanosize curvature of the carbon nanotube and diamond critical nuclei, compared with diamond nucleation on the flat surface of a silicon substrate. Meanwhile, the metastable phase region of diamond nucleation would be driven into a new stable phase region in the carbon thermodynamic equilibrium phase diagram by the effect of nanosize-induced additional pressure. Eventually, we predicted that carbon nanotubes would be an effective path to grow diamond nanowires by chemical vapor deposition.

Particle ordering at the initial stage of colloidal crystallization: implication for non-classical dynamic behavior

The particle ordering dynamics of polystyrene colloids were studied using low-angle laser light scattering and Brownian dynamics (BD) simulation. The polystyrene particles were prepared in the highly deionized water and crystalline states were realized after shear melting due to vigorous circulation of fluids. The radius of gyration of crystalline clusters was evaluated by the laser light scattering and showed the rapid increase of cluster size similar to percolation dynamics with increasing crystalline fraction. The following dynamics were confirmed by BD simulation. The ordered domains were formed under the repulsive potential of latex particles and extended to all over the sample within a relatively short time. The domains were connected as in percolation transitions at a critical threshold. This means that the critical clusters are not compact as in the final crystal but form a rather loose structure in the nucleation stage of colloidal crystallization. The consistent results between experiments and simulation indicate a new ordering dynamics from metastable liquid, which is quite different from the standard nucleation minimizing the free energy of critical nucleus.

Wetting dynamics. On the decay of metastable states near a first-order wetting transition

For a system with a first-order wetting transition we discuss the decay of metastable wetting layers by nucleation. The assumption of detailed balance implies that some essential properties of the decay process follow from statics alone. E.g., the lifetime of the metastable states is predominantly determined by the excess free energy of critical nuclei. The latter are either droplets on a microscopic layer or dents in a macroscopic layer on the wall of the system. We discuss the form and the excess free energy of the critical nuclei in various regions of the phase diagram.

Nucleation processes in the charge density wave state of 2H-TaSe2

The authors examine the free energy barrier associated with critical nuclei in the homogeneous nucleation of discommensurations at the commensurate-incommensurate transition in the charge density wave state of 2H-TaSe2. The various terms entering the free energy of critical nuclei are estimated within a Landau theory. The parameters in the Landau theory are deduced, as well as possible, from experiment. The energy barrier that results is reasonable, also somewhat too high to account for the homogeneous nucleation rate observed by electron microscopy. The reduction of the energy barrier due to internal strains associated with the orthorhombic domain structure is estimated.