Diamond nanoelectromechanical resonators: dissipation and superconductivity

Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.Nanoelectromechanical systems (NEMS) have become a viable commercial technology and are becoming more and more prevalent in research applications. Through miniaturization, the mechanical response to external sources becomes ever more sensitive. This transduction, coupled to an electrical readout circuit, results in unprecedented sensitivity. This thesis examines dissipation in diamond NEMS resonators in the MHz to GHz range. NCD (Nano-crystalline diamond) has extraordinary properties that make it an intriguing material to study. To begin with, the mechanical hardness allows for a boost in resonance frequency, but beyond that, boron-doped diamond also shows extraordinary electrical behavior. Although scaling benefits speed and sensitivity, dissipation increases dramatically with miniaturization, negating some of the gains in sensitivity. The dissipative mechanisms at play in the MHz range are identified at high temperatures. It is found that extrinsic dissipation mechanisms, mainly circuit and clamping losses, can limit the quality factor (inverse of the dissipation). Furthermore, due to the high surface-to-volume ratio of NEMS, surface defects become significant at the nano-scale. For the first time, quantum dissipation due to assisted phonon tunneling of two level systems is observed in diamond NEMS resonators at millikelvin temperatures. Through scaling, it is shown that the low temperature behavior is universal for a broad range of MHz resonators, including silicon and gallium arsenide, as well as graphene and carbon-nanotubes. Beyond the mechanical response, the superconducting properties of highly boron-doped diamond (BDD) are studied. It is found that the critical temperature of 3.3 K for the thin-film is maintained at the nann-scale. The high critical field, on the order of;) T for thin-films, is strongly suppressed, already at the micro-scale. The zero resistance state is compromised with fields as low as 0.1 T for submicron wide constrictions. It is known that the superconducting state will couple to the strain field. Here, the piezoresistive detection technique is developed for BDD structures in the MHz range at room as well as cryogenic temperatures. This serves as a framework for future studies of strain-superconductivity coupling.2031-01-0