Effect of Surface Chemistry on Mechanical Energy Dissipation: Silicon Oxidation Does Not Inherently Decrease the Quality Factor

Abstract

The rate of energy dissipation in megahertz-range micromechanical silicon resonators is unaffected by the controlled oxidation of one-half monolayer of surface sites, thereby proving that silicon oxidation does not inherently decrease the quality factor (Q). Homogeneously mono-oxidized surfaces were prepared by the controlled reaction of dodecyl aldehyde with H-terminated silicon surfaces to form dodecoxy-terminated surfaces (C12H25O−Si). The existence of an approximately half monolayer of Si−O−R species (the maximum allowed by steric constraints) was confirmed by infrared spectroscopy. As a control, dodecyl-terminated surfaces (C12H25−Si) were prepared by the reaction of 1-dodecene with H-terminated surfaces. Infrared spectroscopy showed that the density and ordering of the alkyl chains on the dodecoxy- and dodecyl-terminated surfaces were nearly identical, and no subsurface oxidation was detected on either surface. Dodecoxy- and dodecyl-terminated resonators displayed similar quality factors both immediately after functionalization and after extended exposure to vacuum and H2O-saturated air. Although the dodecoxy-terminated resonators appeared to adsorb more mass (as evidenced by frequency shifts), the increased adsorption did not have a deleterious effect on resonator quality. The relatively high qualities of mono-oxidized resonators stand in stark contrast to the low qualities displayed by resonators terminated with native or chemical oxides. This result suggests that oxide defect species may play a role in mechanical energy dissipation at surfaces.