title: Phase transitions in thin films with competing surface fields and gradients.
abstract: As a generic model for phase equilibria under confinement in a thin-film geometry in the presence of a gradient in the field conjugate to the order parameter, an Ising-lattice gas system is studied by both Monte Carlo simulations and a phenomenological theory. Choosing an L×L×D geometry with L≫D and periodic boundary conditions in the x,y directions, we place competing surface fields on the two L×L surfaces. In addition, a field gradient g is present in the z direction across the film, in competition with the surface fields. At temperatures T exceeding the critical temperature of the interface localization-delocalization transition, one finds a phase coexistence between oppositely oriented domains, aligned parallel to the surface fields and separated by an interface in the center of the film, for small enough g. For a weak gradient, a second-order transition to a monodomain state occurs, but it becomes first order if g exceeds a tricritical threshold. For sufficiently large gradients, another domain state becomes stabilized with domains oriented antiparallel to the surface fields.
authors.affiliation: Center for Simulational Physics, Department of Physics and Astronomy, The University of Georgia, Athens, Georgia 30602-2451, USA.
authors.forename: Lijun
authors.initials: L
authors.lastname: Pang
authors.forename: D P
authors.initials: DP
authors.lastname: Landau
authors.forename: K
authors.initials: K
authors.lastname: Binder