Contact angle influence on the pull-in voltage of microswitches in the presence of capillary and quantum vacuum effects

Capillary condensation between the electrodes of microswitches influences the effective pull-in voltage in a manner that depends on the contact angle of the capillary meniscus and the presence of plate surface roughness. Indeed, surface roughening is shown to have a stronger influence on the pull-in potential for relatively small contact angles with respect to that of a flat surface when capillary condensation takes place. For long wavelength roughness ratios w/ξ«1 with w the rms roughness amplitude and ξ the in-plane correlation length, the pull-in voltage increases with increasing theoretical contact angle θ0 for flat surfaces. With decreasing correlation length ξ (increasing roughness), the pull-in potential decreases faster for smaller contact angles θ0 In addition, with decreasing roughness exponent H (0<H<1), which characterizes short wavelength roughness fluctuation at short length scales (<ξ), the pull-in potential shows a steeper decrease with decreasing correlation length ξ. Finally, with increasing relative humidity, the sensitivity of the pull-in voltage at small correlation lengths attenuates significantly with increasing contact angle θ0.

Allan variance of frequency fluctuations due to momentum exchange and thermomechanical noises

We investigate the Allan variance of nanoresonators with random rough surfaces under the simultaneous influence of thermomechanical and momentum exchange noises. Random roughness is observed in various surface engineering processes, and it is characterized by the roughness amplitude w, the lateral correlation length ξ, and the roughness exponent 0<H<1. The roughness influence becomes significant for measurement time τA so that ωoτA~1, with ωo the fundamental resonance frequency. The Allan variance increases significantly with increasing roughness (decreasing H and/or increasing ratio w/ξ) if the quality factor due to gas collisions is smaller than the intrinsic quality factor associated with thermomechanical noise.

Frequency shift of a quartz crystal oscillator bounded by a self-affine fractal rough surface in contact with a liquid

An investigation of the coupling of shear oscillations of a quartz crystal resonator bounded by a self-affine rough surface with dumped waves in a liquid is performed. Calculation of the roughness effect is achieved in terms of a correlation model for self-affine fractal rough surfaces with analytic form of the associated roughness spectrum G(k)∝(1+ak^2ξ^2)^–1–H

Self-affine case for the roughness effect on the frictional force in boundary lubrication

We comment on the analytic expressions earlier obtained for the case where the wall roughness is described by self-affine structure for the frictional forces in confining geometry systems

Slope-Slope Correlations for Self-Affine Rough Surfaces

The slope-slope correlation function N(r) is investigated for self-affine rough surfaces. Calculations of N(r) are performed in terms of analytic phenomenological height-height correlation functions, which however compare well to real data. It is found that N(r) behaves as: N(r)∝r^2(H-1) for 0 « r « ξ, N(r) &lt; 0 for r &gt; ξ and N(r)→0- for r→+∞. The parameters ξ and H (0 &lt; H &lt; 1) are respectively the in-plene roughness correlation length, and the roughness exponent. Moreover, connection of the results to model predictions describing stable and unstable growth is attempted

Chaotic behavior in Casimir oscillators: A case study for phase change materials

Casimir forces between material surfaces at close proximity of less than 200 nm can lead to increased chaotic behavior of actuating devices depending on the strength of the Casimir interaction. We investigate these phenomena for phase change materials in torsional oscillators, where the amorphous to crystalline phase transitions lead to transitions between high and low Casimir force and torque states respectively, without material compositions. For a conservative system bifurcation curve and Poincare maps analysis show the absence of chaotic behavior but with the crystalline phase (high force/torque state) favoring more unstable behavior and stiction. However, for a non-conservative system chaotic behavior can occur introducing significant risk for stiction, which is again more pronounced for the crystalline phase. The latter illustrates the more general scenario that stronger Casimir forces and torques increase the possibility for chaotic behavior. The latter is making impossible to predict whether stiction or stable actuation will occur on a long term basis, and it is setting limitations in the design of micro/nano devices operating at short range nanoscale separations.Comment: 30 pages, 13 figure

Applications of Casimir forces:Nanoscale actuation and adhesion

Here, we discuss possible applications of the Casimir forces in micro- and nanosystems. The main part of this paper is devoted to actuation with quantum fluctuations and to the relative contribution of van der Waals and Casimir interactions to adhesion. Switching between the amorphous and crystalline states of phase change materials could generate force contrast sufficient for actuation, though for practical applications, the influence of protective capping layers and volume compression have to be better understood. Resilience against the pull-in instability is also a critical point defined by the material choice, dissipation in the system, and roughness of the surfaces. The adhesion induced by the Casimir forces is omnipresent, and it can play a pivotal role in unwanted stiction demanding deeper understanding. The open problems are the distance upon contact and the relative area of the real contact since both of them control the adhesion. An experiment designed to answer these questions is briefly discussed

Polarity-dependent reversible resistance switching in Ge–Sb–Te phase-change thin films

In this paper, we demonstrate reversible resistance switching in a capacitorlike cell using a Ge–Sb–Te film that does not rely on amorphous-crystalline phase change. The polarity of the applied electric field switches the cell resistance between lower- and higher-resistance states, as was observed in current-voltage characteristics. Moreover, voltage pulses less than 1.25 V showed this switching within time scales of microseconds with more than 40% contrast between the resistance states. The latter are found to be nonvolatile for months. The switching could also be achieved at nanoscales with atomic force microscopy with a better resistance contrast of three orders of magnitude.

Nonlinear actuation of casimir oscillators toward chaos:Comparison of topological insulators and metals

In the current study, we explore the sensitivity of the actuation dynamics of electrome-chanical systems on novel materials, e.g., Bi2Se3, which is a well-known 3D Topological Insulator (TI), and compare their response to metallic conductors, e.g., Au, that are currently used in devices. Bifurcation and phase portraits analysis in conservative systems suggest that the strong difference between the conduction states of Bi2Se3 and Au yields sufficiently weaker Casimir force to enhance stable operation. Furthermore, for nonconservative driven systems, the Melnikov function and Poincare portrait analysis probed the occurrence of chaotic behavior leading to increased risk for stiction. It was found that the presence of the TI enhanced stable operation against chaotic behavior over a significantly wider range of operation conditions in comparison to typical metallic conductors. Therefore, the use of TIs can allow sufficient surface conductance to apply electrostatic compensation of residual contact potentials and, at the same time, to yield sufficiently weak Casimir forces favoring long-term stable actuation dynamics against chaotic behavior