MACNEMS

Mechanical Amplification in Carbon-based NanoElectroMechanical Systems

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 Obiettivo del progetto (Objective)

'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.'

Introduzione (Teaser)

Detecting a mass equivalent to that of a single proton is now possible for the first time. To achieve this, European scientists used exceptionally light mechanical resonators made from single carbon nanotubes.

Descrizione progetto (Article)

EU-supported researchers have achieved groundbreaking developments in the context of the project 'Mechanical amplification in carbon-based nanoelectromechanical systems' (MACNEMS). They exploited nanoresonators made from carbon-based nanostructures, nanotubes and graphene sheets.

These miniature systems have low masses, exhibit relatively large displacements with small forces (low spring constants) and/or have high resonant frequencies. As such, they have attracted great interest as sensors for extremely small masses or forces.

However, an inherent challenge to detection of the mechanical signal is the very small oscillation amplitude of nanotube and graphene resonators. If the mechanical signal is transduced to an electrical one and then amplified with conventional methods, the noise is amplified together with the signal.

MACNEMS scientists produced exciting results by applying parametric amplification (PA) in which oscillation amplitude is enhanced through modification of the spring constant to enhance the mechanical signal (without amplifying the noise) prior to conversion into an electrical current.

Researchers achieved the first-ever demonstration of PA with nanotube resonators, including a 10-fold increase in mechanical amplitude. Surprisingly, it was limited by non-linear damping not usually seen in nanoresonators made of semiconductors or metals. Based on this finding, the partners used very small driving forces to achieve record quality factors of 100 000 with a graphene resonator and were able to reach a mass sensitivity corresponding to the mass of a proton with mechanical resonators made from carbon nanotubes.

Additional experiments are ongoing, already demonstrating exceptional force sensitivity. MACNEMS scientists have made important progress in the use of mechanical amplification techniques, demonstrating PA and mass sensing with a resolution on the scale of a single proton. Insight gained from the experiments will be of great significance to the development of novel nanoelectromechanical systems (NEMS) and devices employing nanoresonators.