  The electronic Seebeck response in a conductor involves the energy-dependent
mean free path of the charge carriers and is affected by crystal structure,
scattering from boundaries and defects, and strain. Previous
photothermoelectric (PTE) studies have suggested that the thermoelectric
properties of polycrystalline metal nanowires are related to grain structure,
though direct evidence linking crystal microstructure to the PTE response is
difficult to elucidate. Here, we show that room temperature scanning PTE
measurements are sensitive probes that can detect subtle changes in the local
Seebeck coefficient of gold tied to the underlying defects and strain that
mediate crystal deformation. This connection is revealed through a combination
of scanning PTE and electron microscopy measurements of single crystal and
bicrystal gold microscale devices. Unexpectedly, the photovoltage maps strongly
correlate with gradually varying crystallographic misorientations detected by
electron backscatter diffraction. The effects of individual grain boundaries
and differing grain orientations on the PTE signal are minimal. This scanning
PTE technique shows promise for identifying minor structural distortions in
nanoscale materials and devices.
