Nanowires vibrating at resonance in a gas can serve as sensitive detectors of mass (< 10−18 grams), of use to molecular diagnosis of disease. They can also serve as sensitive detectors of damping force in an ambient gas environment. The Q-factor of resonance spectra, quantifies the sharpness of the peak and is a measure of the ratio of inertial to dissipative (damping) forces. Q-factor data enable quantification of the gas damping force in different regimes of rarefied gas dynamics. Measurements were made with silicon and rhodium nanowires of comparable size, in pure dry nitrogen, with pressure increasing from high vacuum (10−10 atm) to one atmospheric pressure. The data show that, for the silicon nanowires, the Q-factor begins to decrease from its high-vacuum value at a lower pressure and reaches a lower minimum value at one atmosphere, compared to the rhodium nanowires. We show that nanowire structural properties, namely the elastic modulus and intrinsic damping, are responsible for these differing sensitivities to a similar gas damping force range. The results show an important coupling of fluid and structural interaction for rarefied gas dynamics at nanoscale. For practical sensing applications in an ambient gas, this coupling indicates that silicon nanowires are better suited for gas damping force sensing, while rhodium nanowires would fare better as mass sensors for molecular diagnosis.

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