Casimir quantum levitation tuned by means of material properties and geometries

Abstract

The Casimir force between two surfaces is attractive in most cases. Although stable suspension of nano-objects has been achieved, the sophisticated geometries make them difficult to be merged with well-established thin film processes. We find that by introducing thin film surface coating on porous substrates, a repulsive to attractive force transition is achieved when the separations are increased in planar geometries, resulting in a stable suspension of two surfaces near the force transition separation. Both the magnitude of the force and the transition distance can be flexibly tailored though modifying the properties of the considered materials, that is, thin film thickness, doping concentration, and porosity. This stable suspension can be used to design new nanodevices with ultralow friction. Moreover, it might be convenient to merge this thin film coating approach with micro-and nanofabrication processes in the future. If the distance of two neutral objects is very close (typically nanoscale), the Casimir force, which arises from quantum fluctuations, becomes dominant and increases rapidly as the distance decreases. The force is generally attractive in configurations with vacuum separated dielectrics or metallic objects. By properly choosing the materials, such as magnetic compounds [1], fluid-separated dielectrics [2], or topological insulators [3], the force can, however, turn out to be repulsive. Although the fundamental theory of Casimir force has been well studied, tuning this force for potential technology applications is still in its infancy and has recently attracted considerable attention. As microelectromechanical systems [4,5] evolve into nanoelectromechanical systems, the attractive Casimir stiction phenomenon becomes important and has to be faced. On the other hand, such phenomena may also be of significant interest when designing new nanodevices, such as the Casimir anharmonic oscillator [6,7] or the ultrasensitive sensor [8]. Several interesting works have appeared regarding the use of repulsive Casimir force to achieve stable levitation of nano-objects, such as cylinder in cylinder [9], sphere on surface [10], or rotated hockey pucks [11]. Most of them are, however, achieved in sophisticated geometries that are difficult to fabricate using well-established micro-and nanofabrication technologies. In this work, we demonstrate by means of multilayer modeling that the Casimir induced quantum levitation can be achieved in traditional planar geometry containing nanosheets. Moreover, this configuration could be further extended to thin film cladding on a mesoporous substrate without destroying the quantum levitation. Remarkably, both the magnitude of the force and the levitation distance are tunable through modifying the properties of the involved materials, that is, the thickness of the film, the doping concentration, and the porosity.In this Rapid Communication we consider a configuration of four layers, labeled as m, j , s, and l. The retarded Casimir force acting on layer j per unit area include...

Increased porosity turns desorption to adsorption for gas bubbles near water-SiO2interface

“…We can still infer that by inducing more pores, a transition from desorption to adsorption of bubbles is predicted near a porous SiO 2 in water. This is in line with the work of Lifshitz et al and others [3][4][5][6][7][8], which predicts changes in attraction to repulsion depending on the dielectric functions in the three-layer system. Gas bubbles that could include CO 2 molecules may bind by physisorption to a porous SiO 2 surface.…”

“…A well-known aspect of the Casimir-Lifshitz force is that, according to theory, it can also be repulsive [3][4][5][6]. It has been speculated that this effect could allow quantum levitation of nanoscale devices [6][7][8]. It was demonstrated by Phan and Viet [9], and by Boström et al [10], that the force may change sign as the separation is increased.…”

The influence of Lifshitz forces and gas on premelting of ice within porous materials

“…We observe that the dielectric function of water [1], ice [1], silica [14] and gold [37] can be found as parameterised dielectric functions in the literature. Together with the Lifshitz theory in multilayer systems, described in many papers ( see for instance previous works [6,31,32,[46][47][48]), this makes our main results straightforward to reproduce. The dielectric functions for ice and water have in the past also been used in a study as approximate dielectric functions for water in different phases, at other temperatures and pressures, in a study of van der Waals (vdW) interactions involving methane gas hydrates (i.e.…”

“…The details for calculations of this kind of geometries were outlined recently by Dou et al. [6,32] The Lifshitz pressure is given by the negative of the derivative of the Lifshitz energy with respect to the water film thickness. In the present work, we cal- [14].…”

Critical and near-critical phase behavior and interplay between the thermodynamic Casimir and van der Waals forces in a confined nonpolar fluid medium with competing surface and substrate potentials

“…Very recently in Ref. [164] the authors suggested controlled quantum Casimir levitation caused by the introduction of thin film surface coating on a porous planar substrates both immersed in a suitable fluid. More specifically, they have shown that the Casimir force between Teflon and cassiterite (SnO 2 ) nanosheet immersed in cyclodecane is attractive at large separations but repulsive at small separations, resulting in a stable equilibrium distance where the total force is zero.…”