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Elastic strain engineering for ultralow mechanical dissipation

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Science  18 May 2018:
Vol. 360, Issue 6390, pp. 764-768
DOI: 10.1126/science.aar6939

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Better performance under stress

Engineering stress or strain into materials can improve their performance. Adding mechanical stress to silicon chips, for instance, produces transistors with enhanced electron mobility. Ghadimi et al. explore the possibility of enhancing the vibrational properties of a micromechanical oscillator by engineering stress within the structure (see the Perspective by Eichler). By careful design of the micromechanical oscillator, and by building in associated stresses, exceptional vibrational properties can be produced. Such enhanced oscillators could be used as exquisite force sensors.

Science, this issue p. 764; see also p. 706

Abstract

Extreme stresses can be produced in nanoscale structures; this feature has been used to realize enhanced materials properties, such as the high mobility of silicon in modern transistors. We show how nanoscale stress can be used to realize exceptionally low mechanical dissipation when combined with “soft-clamping”—a form of phononic engineering. Specifically, using a nonuniform phononic crystal pattern, we colocalize the strain and flexural motion of a free-standing silicon nitride nanobeam. Ringdown measurements at room temperature reveal string-like vibrational modes with quality (Q) factors as high as 800 million and Q × frequency exceeding 1015 hertz. These results illustrate a promising route for engineering ultracoherent nanomechanical devices.

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