Mass sensing of adsorbed molecules in sub-picogram sample with ultrathin silicon resonator

Ultrathin single-crystalline silicon cantilevers with a thickness of 170 nm as a resonating sensor are applied to mass sensing. The hydrogen storage capacity of a small amount of carbon nanotubes (CNTs), which were mounted on an ultrathin resonator by a manipulator, is measured from the resonant frequency change. The resonator is annealed in ultrahigh vacuum to clean the surface and increase the quality factor, and exposed to oxygen gas to oxidize the surface for long-term stability. The resonator can be electrostatically actuated, and the vibration is measured by a laser Doppler vibrometer in ultrahigh vacuum. The mass of the CNTs is determined by the difference of resonant frequencies before and after mounting the CNTs, and the hydrogen storage capacity is determined from the frequency change after exposure to high-pressure hydrogen as well. The obtained hydrogen storage capacitance is 1.6%–6.0%. The available mass resolution and the achieved stability of the resonance of the 170-nm-thick resonator are below ${10}^{\text{−18}}$ g and 5 Hz/days, respectively.