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Nano-electromechanical systems for mass detection

Mechanical nanoresonators are miniaturised planks clamped at both ends whose vibration patterns change when tiny masses 'fall' on them. Scientists exploited nanoresonators in novel device configurations with exciting results.
Nano-electromechanical systems for mass detection
Tuning forks are a type of mechanical resonator, a device that vibrates at specific frequencies. Mechanical resonators or oscillators have been used for over a century in computer clocks, watches and virtually all types of musical instruments.

Small things have become really big in the last 50 years, and resonators are no exception. Nanoresonators have captured the attention of scientists for their use in detection of very small masses. Nanoresonators clamped at both ends and induced to vibrate can detect a small mass placed on it due to altered vibration patterns. The smaller the mass of the resonator, the higher the sensitivity.

Scientists initiated the EU-funded project 'Array of coupled nanoresonators' (ACRES) to investigate the possibilities afforded by coupling or connecting two or more nanoresonators together. Collective non-linear interactions in arrays of coupled mechanical resonators could provide novel functionalities or enhanced resolution of detection.

Researchers discovered that a number of factors currently limit the application of coupled systems in nano-electromechanical systems (NEMS). Perhaps the most important is the inaccuracy associated with fabrication equipment. The smaller the pieces to be machined, the more magnified are the resulting inaccuracies, requiring compensatory mechanisms such as stronger coupling or active tuning.

ACRES scientists therefore focused on NEMS based on piezoelectric actuation (inducing a movement by applying a small voltage) and piezometallic detection (detecting the resonator motion through a change in resistivity of a metal loop). They developed a highly sensitive integrated NEMS transduction technique. This method used the strain in thin layers of metal to develop the smallest-to-date NEMS-based frequency sources at room temperature. Along the way, numerous important observations led to scientific publications.

Project outcomes highlighted current limitations to increasingly sensitive mass detection via coupled mechanical nanoresonators. Scientists then developed NEMS devices from piezoelectric materials with groundbreaking results.

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