Solid single-crystal films

Abstract

An evolution partial differential equation for the surface of a non-wetting single-crystal film
in an attractive substrate potential is derived and used to study
the dynamics of a pinhole for the varying initial depth of a pinhole and the strengths of the potential and
the surface energy anisotropy.
The results of the simulations demonstrate how
the corresponding parameters
may lead to complete or partial dewetting of the film.
Anisotropy of the surface energy, through faceting of the pinhole walls, is found
to most drastically affect the time to film rupture. In particular, the similations
support the conjecture that the strong anisotropy is capable of the complete suppression of dewetting
even when the attractive substrate potential is strong.

Abstract

The surface evolution model based on geometric partial differential equation
is used to numerically study the kinetics of dewetting and dynamic morphologies for the
localized pinhole defect in the surface of the ultrathin solid film with the strongly anisotropic
surface energy. Depending on parameters such as the initial depth and width of the pinole,
the strength of the attractive substrate potential and the strength of the surface energy anisotropy,
the pinhole may either extend to the substrate and thus rupture the film, or evolve to the quasiequilibrium
shape while the rest of the film surface undergoes phase separation into a hill-and-valley structure
followed by coarsening. Overhanging (non-graph) morphologies are possible for deep, narrow (slit-like) pinholes.

Abstract

We compare dewetting characteristics of a thin nonwetting solid film in the absence of stress, for two models of a wetting potential: the exponential and the algebraic. The exponential model is a one-parameter (r) model, and the algebraic model is a two-parameter (r,m) model, where r is the ratio of the characteristic wetting length to the height of the unperturbed film, and m is the exponent of h (film height) in a smooth function that interpolates the system's surface energy above and below the film-substrate interface at z=0. The exponential model gives monotonically decreasing (with h) wetting chemical potential, while this dependence is monotonic only for the m=1 case of the algebraic model. Linear stability analysis of the planar equilibrium surface is performed. Simulations of the surface dynamics in the strongly nonlinear regime (large deviations from the planar equilibrium) and for large surface energy anisotropies demonstrate that for any m the film is less prone to dewetting when it is governed by the algebraic model. Quasiequilibrium states similar to the one found in the exponential model (M. Khenner, Phys. Rev. B 77, 245445 (2008)) exist in the algebraic model as well, and the film morphologies are similar.

Publications:
1. Dewetting of an ultrathin solid film on a lattice-matched or amorphous substrate, Phys. Rev. B 77, 165414 (2008)
2. Morphologies and kinetics of a dewetting ultrathin solid film, Phys. Rev. B 77, 245445 (2008)
3. Comparative study of a solid film dewetting in an attractive substrate potentials with the exponential and the algebraic decay, accepted
Sample surface morphologies (see [2]):



Liquid films

Abstract

Dynamics of a thin dewetting liquid film on a vertically oscillating substrate is considered. We assume
moderate vibration frequency and large (compared to the mean film thickness) vibration amplitude. Using the
lubrication approximation and the averaging method, we formulate the coupled sets of equations governing the
pulsatile and the averaged fluid flows in the film, and then derive the nonlinear amplitude equation for the
averaged film thickness. We show that there exists a window in the frequency-amplitude domain where the
parametric and shear-flow instabilities of the pulsatile flow do not emerge. As a consequence, in this window
the averaged description is reasonable and the amplitude equation holds. The linear and nonlinear analyses of
the amplitude equation and the numerical computations show that such vibration stabilizes the film against
dewetting and rupture.

Publications:
1. Enhanced stability of a dewetting thin liquid film in a single-frequency vibration field, Phys. Rev. E 77, 036320 (2008)