DM - GISC - Artículos de Revistashttp://hdl.handle.net/10016/58612019-10-23T07:02:17Z2019-10-23T07:02:17ZThe local structure factor near an interface; beyond extended capillary-wave modelsParry, A.ORascón, CarlosEvans, R.http://hdl.handle.net/10016/290632019-10-23T00:02:51Z2016-06-22T00:00:00ZThe local structure factor near an interface; beyond extended capillary-wave models
Parry, A.O; Rascón, Carlos; Evans, R.
We investigate the local structure factor S (z;q) at a free liquid-gas interface in systems with short-ranged intermolecular forces and determine the corrections to the leading-order, capillary-wave-like, Goldstone mode divergence of S(z;q) known to occur for parallel (i.e. measured along the interface) wavevectors q -> 0. We show from explicit solution of the inhomogeneous Ornstein-Zernike equation that for distances z far from the interface, where the profile decays exponentially, S (z;q) splits unambiguously into bulk and interfacial contributions. On each side of the interface, the interfacial contributions can be characterised by distinct liquid and gas wavevector dependent surface tensions, sigma(l)(q) and sigma(g)(q), which are determined solely by the bulk two-body and three-body direct correlation functions.
2016-06-22T00:00:00ZPair correlation functions and the wavevector-dependent surface tension in a simple density functional treatment of the liquid-vapour interfaceParry, A.ORascón, CarlosWillis, G.Evans, Rhttp://hdl.handle.net/10016/290622019-10-23T00:02:50Z2014-09-03T00:00:00ZPair correlation functions and the wavevector-dependent surface tension in a simple density functional treatment of the liquid-vapour interface
Parry, A.O; Rascón, Carlos; Willis, G.; Evans, R
We study the density-density correlation function G(r, r') in the interfacial region of a fluid (or Ising-like magnet) with short-ranged interactions using square gradient density functional theory. Adopting a simple double parabola approximation for the bulk free-energy density, we first show that the parallel Fourier transform G(z, z'; q) and local structure factor S(z; q) separate into bulk and excess contributions. We attempt to account for both contributions by deriving an interfacial Hamiltonian, characterised by a wavevector dependent surface tension sigma(q), and then reconstructing density correlations from correlations in the interface position. We show that the standard crossing criterion identification of the interface, as a surface of fixed density (or magnetization), does not explain the separation of G(z, z'; q) and the form of the excess contribution. We propose an alternative definition of the interface position based on the properties of correlations between points that 'float' with the surface and show that this describes the full q and z dependence of the excess contributions to both G and S. However, neither the 'crossing-criterion' nor the new 'floating interface' definition of sigma(q) are quantities directly measurable from the total structure factor S tot(q) which contains additional q dependence arising from the non-local relation between fluctuations in the interfacial position and local density. Since it is the total structure factor that is measured experimentally or in simulations, our results have repercussions for earlier attempts to extract and interpret sigma(q).
2014-09-03T00:00:00ZConcurrent segregation and erosion effects in medium-energy iron beam patterning of silicon surfacesRedondo-Cubero, AndresLorenz, K.Palomares, F. J.Muñoz Castellanos, ÁngelCastro Ponce, MarioGarcía Muñoz, JavierCuerno, RodolfoVazquez Burgos, Luishttp://hdl.handle.net/10016/290342019-10-17T00:02:38Z2018-06-12T00:00:00ZConcurrent segregation and erosion effects in medium-energy iron beam patterning of silicon surfaces
Redondo-Cubero, Andres; Lorenz, K.; Palomares, F. J.; Muñoz Castellanos, Ángel; Castro Ponce, Mario; García Muñoz, Javier; Cuerno, Rodolfo; Vazquez Burgos, Luis
We have bombarded crystalline silicon targets with a 40 keV Fe+ ion beam at different incidence angles. The resulting surfaces have been characterized by atomic force, current-sensing and magnetic force microscopies, scanning electron microscopy, and x-ray photoelectron spectroscopy. We have found that there is a threshold angle smaller than 40 degrees for the formation of ripple patterns, which is definitely lower than those frequently reported for noble gas ion beams. We compare our observations with estimates of the value of the critical angle and of additional basic properties of the patterning process, which are based on a continuum model whose parameters are obtained from binary collision simulations. We have further studied experimentally the ripple structures and measured how the surface slopes change with the ion incidence angle. We explore in particular detail the fluence dependence of the pattern for an incidence angle value (40 degrees) close to the threshold. Initially, rimmed holes appear randomly scattered on the surface, which evolve into large, bug-like structures. Further increasing the ion fluence induces a smooth, rippled background morphology. By means of microscopy techniques, a correlation between the morphology of these structures and their metal content can be unambiguously established.
This paper is part of: Special Issue on Surfaces Patterned by Ion Sputtering
2018-06-12T00:00:00ZDynamics of thin fluid films controlled by thermal fluctuationsNesic, SvetozarCuerno, RodolfoMoro, EstebanKondic, L.http://hdl.handle.net/10016/290312019-10-17T00:02:39Z2015-03-01T00:00:00ZDynamics of thin fluid films controlled by thermal fluctuations
Nesic, Svetozar; Cuerno, Rodolfo; Moro, Esteban; Kondic, L.
We consider the influence of thermal fluctuations on the dynamics of thin fluid films in two regimes. Working within the stochastic lubrication approximation, we generalize the results on (stochastic) similarity solutions [B. Davidovitch, et al., Phys. Rev. Lett. 95, 244505 (2005)] that focused on surface tension dominated regime, to gravity-driven relaxation. In particular, we verify numerically the validity of the results in gravity-dominated regime, and find that fluctuations enhance spreading, as in surface tension dominated regime, even in the presence of a faster deterministic relaxation. Considering further the novel case of fluid droplet spreading driven by surface tension and van der Waals forces, our simulations show that the presence of noise affects the value of droplet contact angle.
Part of the following topical collections: IMA7 – Interfacial Fluid Dynamics and Processes
2015-03-01T00:00:00Z