Control morphology of nanostructures with electric field

Abstract

We showed that the morphology of nanostructures on a dielectric substrate may be tuned by electric field. The collective action of surface energy, interface energy between nanostructures and the substrate, and electrostatic energy defines a thermodynamic force that drives surface diffusion. The evolution is characterized by a quick adjustment of the dihedral angle at the triple junction, followed by an extrusion of a thin layer from the edges, and subsequent significant overall morphology change through long range mass transport. A high voltage can induce instability of the extrusion, causing the formation of a pattern of tiny islands.The ability of designing and constructing useful devices with engineered properties and features at the nanometer length scale promises to have a dramatic impact on the future. Controlled surface morphology of nanostructure is critical for the applications. Electric field is an excellent driving force to control structures on length scales difficult to manipulate in other manner. It is easy to apply and the electrostatic interactions are strong and long range. Electric field has been used to move, separate and assemble micro/nanoparticles, 1,2 trap nanospheres, 3 and align nanowires. 4 It has also been used on continuum fluidic media to change the morphology such as inducing surface features in polymer melts. 5 Recent studies showed that the wetting angles of liquid droplets on a dielectric substrate can be tuned by an applied electric field. This electrowetting approach has become a promising mechanism for many applications, such as next generation optical systems with camera lens of variable focal lengths achieved by applying designed electric fields. 6 While these systems have demonstrated morphological changes of continuum liquids, we expect electric field can also be used to control the morphology of solids like stress field. 7,8 The effect may be negligible in larger scale bodies, but is important in nanostructures due to high mobility and small dimension comparable to the diffusion length. For instance, the action of electric fields has been shown to have significant effects on the surface morphological stability of solids, including the current-induced stabilization of stressed solid surfaces. 9,10 In this letter we aim to illuminate the dynamic shape evolution process of conductive nanostructures under electric field.Several features distinguish the morphological evolution of solid nanostructures from the typical electrowetting phenomenon. The latter involves putting a liquid droplet on the surface of a thin dielectric substrate with a conductive plate beneath it. Electric field is applied to the conductive droplet and the substrate. Equilibrium configuration is of major interest in electrowetting process due to the fluidic media and kinetics of viscous flow. However, the evolution process through surface diffusion and various transitional morphologies are important in solid structures. The droplet size for electrowetting applications ranges from a few millimeters to hundre...

A review of conduction phenomena in Li-ion batteries

“…This reduces the mathematical difficulties associated with applying the boundary conditions at the interfaces. The phase field method has been extensively applied to the modeling of microstructure evolution such as grain growth [149], interaction of nanoparticles with lipid layers [150], and control morphology of nanostructures within an electric field [151]. In electrochemistry, the phase field method has been used to explore the equilibrium structure and kinetics of an electric field between two phases consisting of charged components [152,153].…”

Plasma nanoscience: from nano-solids in plasmas to nano-plasmas in solids

“…Fourth, the plasma sheath electric field (which is normal to the surface away from it and has a horizontal component upon approaching the nanostructures/nanofeatures) can be used to tune the NS morphology and arraying. Indeed, the interplay between the surface energy, energy of the substrate-nanostructure interface, and the electrostatic energy determine a driving force for mass relocation through surface diffusion [55].…”

“…in turn includes contributions from the chemical energy of phase separation G phs , electrostatic energy G el , energy of the nanoparticle-gas interface G g int , and the energy of the nanoparticle-substrate interface G s int [55]. The latter may include surface stress-related contributions, which can also be modified by the plasma-specific effects (e.g., ion impact).…”