CPM Seminar

Dissipation in Micro/Nanomechanical Resonators

Srikar Vengallatore

Department of Mechanical Engineering
McGill University

Micro/nanomechanical resonators are the building blocks of entirely new classes of systems for sensing (force-detected magnetic resonance imaging; mass spectroscopy; probe microscopy; medical diagnostics), ultra-low power signal processing, vibration energy harvesting, and fundamental studies at the intriguing boundary between classical and quantum physics. All these applications share one essential requirement: minimize dissipation by structural damping and increase the quality factor (Q) of resonance. In this talk, I will describe our efforts to probe the mechanisms of dissipation in micro/nanomechanical resonators. The first part will focus on progress towards the long-standing goal of predictive modeling and rational design of damping. Under certain conditions, and for a small and special class of materials, it is possible to machine microresonators that can vibrate with very low dissipation approaching the ultimate thermodynamically-mandated limits of damping. This limit is set by the mechanism of thermoelastic damping. Models for thermoelastic damping and experiments with single-crystal silicon microresonators will be presented.

The second part of the seminar will focus on dissipation in ultrathin nanocrystalline films of common metals. These materials are widely used as coatings on micro/nanomechanical resonators to enhance electrical conductivity, optical reflectivity, and surface chemistry. Unfortunately, they also degrade the performance by causing a disproportionate increase in dissipation. In these films, damping is dominated by internal friction caused by the irreversible motion of crystallographic defects. As a first step towards scale-dependent process-structure-dissipation correlations, we have measured the effects of frequency, thickness, and grain size on internal friction in nanocrystalline aluminum films. The details of these measurements, and the contribution of grain-boundary sliding to internal friction in aluminum films, will be discussed.