Nanoresonators for high-sensitivity mass detection
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.
