"Nanoelectromechanical systems (NEMS) are very promising for sensing purposes, information technology, or exploration of quantum mechanics in extended bodies. A decisive parameter for any oscillator is the quality factor, Q, determining how much energy the system dissipates during one oscillation period. A high Q signifies large oscillator amplitudes and a sharp resonance. Although NEMS resonators display quality factors up to 10^6, their amplitudes are typically in the pm range or below, which makes the conversion into a readable electrical signal extremely challenging.
Traditionally, the mechanical motion is immediately translated into an electrical signal, which is then amplified with high gain. Such electrical amplification creates an additional noise floor that limits the signal resolution even at cryogenic temperatures. To overcome this limit, we propose two stategies in order to enhance a mechanical signal before its conversion into an electrical current: parametric amplification (PA) and self-sustained oscillations (SSO).
PA describes the augmentation of the amplitude of an oscillator by a periodic modulation of the spring constant. In other fields of physics and engineering, PA has already been studied and implemented, but suspended carbon nanotubes (CNT) and graphene strips appear especially promising since the spring constant of these oscillators can be tuned over a broad range by a backgate voltage.
SSO describes in our context the creation of a high amplitude mechanical oscillation using a d.c. biased electron current as power source. These oscillations are expected to produce very sharp resonances with a high effective Q. Suspended CNT resonators are excellent candidates for SSO due to the strong coupling between the mechanical and charge degrees of freedom.
Once successfully developed, we intend to use both PA and SSO in mass sensing experiments with CNT resonators, aiming at a sensitivity of the mass of a single nucleus, 1 yg."
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