Search

Dewetting is a well-known degradation mechanism for thin films at elevated temperatures. It is driven by surface energy minimization and occurs while the film is solid. The dewetting process is characterized by the formation of holes, retracting edges, and the formation of thickened rims on retracting edges. In anisotropic single-crystal thin films, holes are initially faceted. It is often observed that the corners of the holes retract faster than the edges of the hole, leading to dendritic or star-shaped holes. This so-called "corner instability" is one of the defining morphological characteristics of the dewetting process, and an understanding of this instability may lead to new film patterning techniques. In this work, we present a study of the growth of natural and patterned initially square holes in single-crystal Ni thin films on MgO substrates. A characteristic structure near the corners of the holes was observed, and a model for the growth of faceted holes was developed based on these observations. Despite its simplicity, the model reproduces the observed phenomenology and is in quantitative agreement with experiments. The model reveals that the corner instability arises from a redistribution of mass to create a new hole perimeter, which can only be created at the corner. The consequence is that the corner reaches a steady-state constant retraction rate while mass accumulation at the rims causes their retraction rate to continuously decrease. [ABSTRACT FROM AUTHOR]

This paper reviews the fundamental concepts and the terminology of wetting. In particular, it focuses on high temperature wetting phenomena of primary interest to materials scientists. We have chosen to split this review into two sections: one related to macroscopic (continuum) definitions and the other to a microscopic (or atomistic) approach, where the role of chemistry and structure of interfaces and free surfaces on wetting phenomena are addressed. A great deal of attention has been placed on thermodynamics. This allows clarification of many important features, including the state of equilibrium between phases, the kinetics of equilibration, triple lines, hysteresis, adsorption (segregation) and the concept of complexions, intergranular films, prewetting, bulk phase transitions versus 'interface transitions', liquid versus solid wetting, and wetting versus dewetting. [ABSTRACT FROM AUTHOR]

Existing methods to rapidly compute interface-energy minimizing shapes with anisotropy are collected and clarified, and new methods are introduced. A description of freely available, platform-independent software for the computation and display of equilibrium geometries is provided. The software relies on a new computational method to rapidly find equilibrium geometries. It also features a graphical user interface and includes the 32 crystallographic point groups to simplify inputting interfacial energies and their associated orientations. When a particle is completely enclosed within a single interface (isolated), the software computes and provides visualization for Wulff shapes. When a particle is enclosed by two interfaces, such as a particle at a grain boundary, the software minimizes their collective interfacial energy; if one of the interfaces is planar, the computation reproduces the Winterbottom construction. When both interfaces are deformable, the software provides a new tool for calculating the particle shape and the distortions of boundaries that are attached to it, even for highly anisotropic interfaces. The properties of particles bounded by two deformable interfaces are discussed, and applications of the software are illustrated. In some cases, the software can be used as a method to infer values of relative interfacial energies from a microscopic observation. [ABSTRACT FROM AUTHOR]

Abstract: The identification of triple lines as one of a hierarchy of defects is presented. There are several distinct cases of triple junctions, and these are sorted into classes. Viewpoints about open questions and directions for future research are offered, including: (1) the effect of induced order on the structure and energy of a triple line; (2) considerations of interfacial (complexion) transitions; (3) suggestions of methods for the direct measurement of triple line energy; (4) observations of the possibility of triple line anisotropy. [Copyright &y& Elsevier]

Examines the approaches to modeling surface-diffusion-controlled pore shape morphology evolution. Factors influencing rate of pore shape evolution; Effect of the equilibrium Wulff shape on the features of evolution; Importance of surface structure in pore evolution; Dominance of surface diffusion in the alumina diffusional process.

Abstract: Recent observations of nanoscale surficial amorphous films in Bi2O3-doped ZnO are briefly reviewed. The experimental results are modeled with two approaches. A pressure-balance model with the volumetric free energy being the dominant temperature-dependent interaction extended from Clarke''s intergranular films model is proposed and numerically evaluated. This quantitative model predicts thicknesses versus temperature behavior for subeutectic films consistent with experimental results. Alternatively, the sequence of adsorption and wetting events as a function of temperature and composition is interpreted as a case of combined surface prewetting and premelting in a two-component system with a bulk eutectic reaction as a generalization of Cahn''s critical point wetting model. In this second approach that better represents the through-thickness gradients, diffuse-interface formulation is proposed and analyzed for assessing surficial film stability as well as associated drying and complete wetting transitions. The observation made for Bi2O3 on ZnO can be represented by one of the possible surface prewetting/premelting phase diagrams. [Copyright &y& Elsevier]