  We aim to illuminate how the microscopic properties of a metal surface map to
its electric-field noise characteristics. In our system, prolonged heat
treatments of a metal film can induce a rise in the magnitude of the
electric-field noise generated by the surface of that film. We refer to this
heat-induced rise in noise magnitude as a thermal transformation. The
underlying physics of this thermal transformation process is explored through a
series of heating, milling, and electron treatments performed on a single
surface ion trap. Between these treatments, $^{40}$Ca$^+$ ions trapped 70
$\mu$m above the surface of the metal are used as detectors to monitor the
electric-field noise at frequencies close to 1 MHz. An Auger spectrometer is
used to track changes in the composition of the contaminated metal surface.
With these tools we investigate contaminant deposition, chemical reactions, and
atomic restructuring as possible drivers of thermal transformations. The data
suggest that the observed thermal transformations can be explained by atomic
restructuring at the trap surface. We hypothesize that a rise in local atomic
order increases surface electric-field noise in this system.
