  A large measured 2D diffusion coefficient of gold nanoclusters on graphite
has been known experimentally and theoretically for about a decade. When
subjected to a lateral force, these clusters should slide with an amount of
friction that could be measured. We examine the hypothetical possibility to
measure by Quartz Crystal Microbalance (QCM) the phononic sliding friction of
gold clusters in the size range around 250 atoms on a graphite substrate
between 300 and 600 K. Assuming the validity of Einstein's relations of
ordinary Brownian motion and making use of the experimentally available
activated behavior of the diffusion coefficients, we can predict the sliding
friction and slip times as a function of temperature. It is found that a
prototypical deposited gold cluster could yield slip times in the standard
measurable size of 10^(-9) sec for temperatures around 450-500 K, or 200 C.
Since gold nanoclusters may also melt around these temperatures, QCM would
offer the additional chance to observe this phenomenon through a frictional
change.
