Résumé
Carbon nanotubes as nanomechanical resonators are very promising systems due to their small size and mass as well as their stiffness that grant them great sensitivity as a sensor. As a result, ample research [1][2] is oriented towards these devices in order to understand the sources of noise and reach better sensitivities. In this work, we are interested in the mass-sensing applications and will analyze their mechanics, both in the linear and nonlinear regimes. The treatment of nonlinearities is particularly challenging because there is no unique solution to the equation of motion. In addition, even if we do not perceive its characteristic bi-stability at room temperature, we still enter the nonlinear regime where the well-known models are no longer accurate. However, it is not easy to distinguish between the two regimes, since the linear model is only an approximation of the nonlinear model for small drives. The benefit of the nonlinear regime is that the received signal is stronger.There are several parameters to take into account (drive power, temperature,...), we studied some that affect the sensitivity to understand which are relevant for our system. We obtained a record-breaking sensitivity of 2x10⁻²⁵ g.We usually work at room temperature and cannot observe bi-stability, but we observed bi-stability when the temperature is lowered, which is in agreement with the theory that a small Q prevents hysteresis from appearing. With this in mind, it is interesting to have a low Q system at room temperature, as a sharper resonator would introduce additional noise due to bi-stability. We have therefore found a compromise between a large damping [3], which blocks hysteresis, and a sharp resonance, which gives precision.We achieved a record-breaking sensitivity at room temperature of 0.2 yg which is promising for future applications, given that the previous record sensitivity was reached in a cryostat [4].[1] K. L. Ekinci, M. L. Roukes. Nanoelectromechanical systems. Review of Scientific Instruments, (2005). https://doi.org/10.1063/1.1927327.[2] De Bonis, Sergio & Urgell, Carles & Yang, Wei & Samanta, C. & Noury, Adrien & Vergara-Cruz, J. & Dong, Quan & Jin, Yong & Bachtold, A.. (2018). Ultrasensitive Displacement Noise Measurement of Carbon Nanotube Mechanical Resonators. Nano Letters. 18. 10.1021/acs.nanolett.8b02437.[3] Swapan K. Roy et al. ,Improving mechanical sensor performance through larger damping.Science360,eaar5220(2018).DOI:10.1126/science.aar5220[4] Chaste, J., Eichler, A., Moser, J. et al. A nanomechanical mass sensor with yoctogram resolution. Nature Nanotech 7, 301–304 (2012). https://doi.org/10.1038/nnano.2012.42