  We studied the frequency and quality factor of mechanical plasmonic
nanoresonators as a function of temperature, ranging from ambient to 4 K. Our
investigation focused on individual gold nanorods and nanodisks of various
sizes. We observed that oscillation frequencies increase linearly as
temperature decreases until saturation is reached at cryogenic temperatures.
This behavior is explained by the temperature dependence of the elastic
modulus, with a Debye temperature compatible with reported bulk values for
gold. To describe the behavior of the quality factor, we developed a model
considering the nanostructures as anelastic solids, identifying a dissipation
peak around 150 K due to a thermally activated process, likely of the
Niblett-Wilks mechanism type. Importantly, our findings suggest that external
dissipation factors are more critical to improving quality factors than
internal friction, which can be increased by modifying the nanoresonator's
environment. Our results enable the design of structures with high vibration
frequencies and quality factors by effectively controlling external losses.
