Large amplitude flexural vibrations have been excited in single layer silicon-on-insulator micromechanical cantilever beams in ambient air environment. Our driving approach relies on a single co-planar electrode located symmetrically around the actuated grounded cantilever. Electrostatic forces are created via tailored asymmetries in the fringing fields of deformed mechanical states during their electric actuation, with strong restoring forces acting in a direction opposite to the deflection. This results in an effective increase in the structure stiffness in its elastic regime. The devices had been fabricated using deep reactive ion etching based process and their responses were characterized in a laser Doppler vibrometer under ambient conditions. Harmonic voltages applied to the electrode result in the periodic modulation of the effective stiffness and lead to strong parametric excitation of the structure. As opposed to close gap actuators, where high-amplitude drives are severely limited by pull-in instabilities, squeezed gas damping, and stiction, our resonators exhibit very large vibration amplitudes (up to 8 in terms of the amplitude to thickness ratio in the strong parametric regime), with no apparent damage, via the application of highly tunable distributed forces. A reduced order model, based on the Galerkin decomposition, captures the main dynamical features of the system, and is consistent with the observed beam characteristics.

We demonstrate that silicon-polymer composite microbridges provide a robust means of water vapor detection at ambient pressure. Volumetric changes in the reactive polymer alter the tension in a doubly clamped structure leading to large and rapid changes in the resonance frequency. We demonstrate stress-based sensing of water vapor in ambient pressure nitrogen using doubly clamped buckled beams coated with a hygroscopic polymer. We show stress sensitivity of around 20 kPa ͑ϳ170 ppb of water vapor͒ and subsecond response time for coated microbridges.

Ce and Bi comodified iron garnet (Ce2.2Bi0.8Fe5O12) thin films for magneto-optic applications were epitaxially grown on a (111)-oriented Gd3Ga5O12 substrate by pulsed laser deposition. We found that epitaxial film quality could be achieved under a low-pressure Ar atmosphere. Surprisingly, our 1 μm thick epitaxial films showed a record Faraday rotation as high as 0.55 deg/μm, a value strongly dependent on the concentration of Bi3+ ions.

We experimentally study the nonlinear scattering by local photonic structures embedded in continuous Kerr media and demonstrate nonlinear trapping in guiding structures and resonant transmission in antiguiding structures. An intuitive physical picture is presented and verified in simulations.

We describe sensing of chemical vapors from the atmosphere using critically buckled polycrystalline silicon doubly clamped mechanical resonators coated on one side with polymethyl methacrylate (PMMA). Our method of sensing is based on stress-induced resonance frequency shifts through volumetric swelling of the 60 nm thick PMMA layer resulting in altered tension in the beams. The stress change produces shifts in the resonance frequency as large as 150% of the baseline frequency. In order to maximize the sensitivity, we tailor residual stress of the polycrystalline silicon resonators to slightly exceed the critical buckling stress. We incorporate a relatively large gap between the bridge and a substrate to provide optical readout and minimize squeezed film effects. We show that the larger gap results in substantial improvements of the quality factor and frequency stability of our resonators under ambient pressure and temperature conditions compared to previous implementations. These lead to resonance frequency shift per concentration change of ethanol vapors of ∼360 Hz/ppm with a response time of a few seconds measured in our gas delivery and readout system.