High frequency torsional-mode nanomechanical resonators enabled by very thin nanocrystalline diamond diaphragms

• Torsional resonators based on 50–100 nm thick nanocrystalline diamond
• Multimode resonances (up to ~ 10MHz) via ultrasensitive laser interferometry
• Two supporting tethers as small as 90 nm × 50 nm fabricated by focused ion beam
• Young's modulus of 977 GPa for nanocrystalline diamond extracted from resonance
• Characterization of the diamond film properties by using Raman spectroscopy

We report an experimental demonstration of high-frequency (HF) torsional-mode nanomechanical resonators based on nanocrystalline diamond films as thin as 50 nm. Devices axially supported by pairs of tethers as small as 90 nm × 50 nm in cross section are fabricated from suspended diaphragms by using focused ion beam (FIB), showing multi-mode resonances with frequencies (fres) into the HF band (up to ~ 10 MHz, while most existing sensitive torsional devices are at kHz or low-MHz), and quality (Q) factors exceeding 1800 at room temperature in moderate vacuum (~ 20 mTorr). This fabrication process evades the conventional electron-beam lithography and etching steps that are destructive for very thin diaphragms. From the torsional and flexural modes of device resonances, we calculate Young's modulus (EY) to be as high as 977 GPa, which is almost comparable to the known value of 1220GPa for single-crystal diamond.