  Nanoscale structuring holds promise to improve thermoelectric properties of
materials for energy conversion and photodetection. We report a study of the
spatial distribution of the photothermoelectric voltage in thin-film nanowire
devices fabricated from single metal. A focused laser beam is used to locally
heat the metal nanostructure via a combination of direct absorption and
excitation of a plasmon resonance in Au devices. As seen previously, in
nanowires shorter than the spot size of the laser, we observe a thermoelectric
voltage distribution that is consistent with the local Seebeck coefficient
being spatially dependent on the width of the nanostructure. In longer
structures, we observe extreme variability of the net thermoelectric voltage as
the laser spot is scanned along the length of the nanowire. The sign and
magnitude of the thermoelectric voltage is sensitive to the structural defects,
metal grain structure, and surface passivation of the nanowire. This finding
opens the possibility of improved local control of the thermoelectric
properties at the nanoscale.
