Mechanical stress relaxation in adhesively clamped carbon nanotube resonators

We report a detailed experimental investigation of the adhesive clamping instability in CNT nanoresonators fabricated on silicon wafers with palladium electrodes and suspended CNT channels. The nanotube is clamped down onto the palladium electrodes adhesively by van der Waals forces and operates in the string regime. We observe a decrease in the nanotube tension when the device is operated in large amplitude regime. This mechanical stress relaxation, or decrease in internal stress of the nanotube, was observed as a frequency downshift resulting from weak clamping behavior between the nanotube and the underlying palladium surface. Frequency downshifts from 97.5 MHz to 39 MHz with 60 % stress relaxation and from 72.7 MHz to 60.5 MHz (17 % relaxation) were observed for two devices. Q-factors show no change due to decrease in internal stress. Our temperature measurements in the range of 298-420 K suggest that Q-factors might arise from the interplay between adhesive clamping associated dissipation mechanisms and spectral broadening due to thermal fluctuations.