title: Understanding the effects of surface chemistry on Q: mechanical energy dissipation in alkyl-terminated (C1-C18) micromechanical silicon resonators.
abstract: The rate of mechanical energy dissipation in 300-nm-thick, megahertz-range micromechanical silicon resonators is sensitive to single monolayer changes in surface chemistry. Resonators terminated with a single monolayer of methyl groups have significantly higher quality factors (Q's), and thus lower mechanical energy dissipation, than comparable resonators terminated with either long-chain alkyl monolayers (C2H2n+1, n = 2-18) or monolayers of hydrogen atoms. This effect cannot be attributed to mechanical energy dissipation within the alkyl monolayer, as a 9-fold increase in alkyl chain length does not lead to an observable increase in dissipation. Similarly, this effect is not correlated with the chemical structure of the silicon-monolayer interface (e.g., the density of Si-H vs Si-C bonds.) Instead, the chemical trends in resonator quality and stability are consistent with a dissipation mechanism involving the coupling of long-range strain fields to localized, electronically active defects in the monolayer coatings.
authors.affiliation: Department of Chemistry, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Henry
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Debodhonyaa
authors.initials: D
authors.lastname: Sengupta
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Hines