Understanding the effects of surface chemistry on Q: mechanical energy dissipation in alkyl-terminated (C1-C18) micromechanical silicon resonators |
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Authors: | Henry Joshua A Wang Yu Sengupta Debodhonyaa Hines Melissa A |
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Institution: | Department of Chemistry, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA. |
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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. |
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