Nanomechanical resonators are increasingly becoming of interest across a range of applied and fundamental physics applications. Within many of these, the retention of bulk diamond's high Young's modulus, coupled with the compatibility with standard substrate materials, makes nanocrystalline diamond (NCD) particularly well suited for fabricating high-frequency devices. As device dimensions shrink in pursuit of ever-higher frequencies, however, dissipation from sources such as clamping and surface loss often becomes increasingly significant. To address this, a series of doubly clamped beams and clamping-loss-suppressing free-free resonator geometries were fabricated from both as-grown and chemically mechanically polished NCD. At 12 K, the free-free geometries curtailed the pronounced length-dependent loss seen in doubly clamped beams, reducing dissipation by up to 8.8× and achieving Q factors of the order of 10,000 from ~40 MHz to ~100 MHz. Minor differences in dissipation between devices fabricated from the as-grown and polished stock, meanwhile, suggest that surface-related loss is likely a minor contributor to dissipation at this temperature, contrasting with trends in alternative material counterparts. As such, the combination of NCD's apparent low surface-related loss and the loss-scaling suppression offered by free-free geometries provides a promising route to minimising dissipation in high-frequency nanomechanical resonators.
Thomas et al. (Tue,) studied this question.