Few-hundred GHz Carbon Nanotube NEMS

We study 23 to 30 nm long suspended single-wall carbon nanotube quantum dots and observe both their stretching and bending vibrational modes. We use low-temperature DC electron transport to excite and measure the tubes' bending mode by making use of a positive feedback mechanism between their vibrations and the tunneling electrons. In these nano-electro-mechanical-systems (NEMS), we measure fundamental bending frequencies $f_{bend}\approx$ 75 - 280 GHz, and extract quality factors $Q \sim 10^{6}$. The NEMS' frequencies can be tuned by a factor of two with tension induced by mechanical breakjunctions actuated by an electrostatic force, or tension from bent suspended electrodes.