Capacitive Spring Softening in Single-Walled Carbon Nanotube Nanoelectromechanical Resonators

We report the capacitive spring softening effect observed in single-walled carbon nanotube (SWNT) nanoelectromechanical (NEM) resonators. The nanotube resonators adopt a dual-gate configuration with both bottom gate and end gat capable of tuning the resonance frequency through capacitive coupling. Interestingly, downward resonance frequency shifting is observed with increasing end-gate voltage, which can be attributed to the capacitive softening of the spring constant. Furthermore, in vibrational modes exhibit a much stronger spring softening effect than out modes. Our dual-gate design should enable the differentiation between these two types of vibrational modes and open up the new possibility for nonlinear operation resonators.