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Séminaire MCBT

Mardi 28 mars à 11h00,
Salle Louis Weil, E424

Orateur : Pierre VERLOT
"Optomechanics and Electromechanics with Low-Dimensions Mechanical Systems"

Abstract

Nanomechanical systems have considerably developed over the past 15 years, enabling significant advance both in fundamental and applied Science. The reasons of such success are essentially twofold : On the one hand, the ultra-low mass of these devices intrinsically protects their mechanical motion against the detrimental effects of decoherence, such as thermal noise. On the other hand, the solid-state nature of these systems makes them available for long-term averaged measurements, resulting in a substantial extension of their sensing potential.

At present, low-dimension materials such as carbon nanotubes and graphene have become routinely available for possible nanomechanical sensing applications. However, the extremely reduced size of these systems also appears as their Achilles’ heel. First, their detection is extremely challenging and generally relatively inefficient. Moreover, their typically large motion amplitudes are associated with increased nonlinear dynamical behaviours. Last, the increased sensitivity of low-dimension nanomechanical systems is generally not limited to selective interactions. This makes the interpretation of the motion output very challenging and restricts their use to specifically designed, isolated environments. Therefore, the actual gain of reducing the size of nanomechanical resonator below the 100-nanometre scale has so far remained an open question.

Here we will review our recent efforts to detect and characterize the dynamics of a variety of low-dimension nanomechanical resonators. We have developed two novel, ultra-sensitive detection techniques. The first scheme is based on coupling a focused electron beam to nanomechanical objects, enabling sensitive motion detection through the current fluctuations of scattered secondary electrons. The second method relies on detecting the photons scattered by a nanoparticle previously attached on the nanomechanical device. With these two schemes, we are able to achieve ultra-sensitive detection of thermally driven nanomechanical devices with masses ranging in the 10 attograms to 1 picogram range. We will present the analysis of the observed noise-driven dynamics, including measurement induced backaction on semi-conducting nanowires and carbon nanotube resonators, nonlinear mode coupling in carbon-based nanotube hybrid resonators, and frequency noise in both carbon nanotube and suspended graphene resonators. We will finally draw the perspectives of our work, notably with on-going applications in near-field microscopy and bio-sensing.

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