Photothermoelectric detection of local strain variations in gold single-crystal and bicrystal stripes

Nanoscale manipulation of the thermoelectric effect has recently been used in photodetection and energy conversion applications. In metals, the electronic Seebeck coefficient depends on the energy-dependent electrical conductivity. At the nanoscale, single metal thermocouples are created by modifying the conductivity via nanostructuring, changing the energy-dependent mean free path of the charge carriers. Here, we present scanning photothermoelectric measurements of gold single crystal devices and compare the photovoltages with electron back-scatter diffraction measurements, which provide insight on the local strain variation in the device. The good correlation between these measurements show that photovoltage measurements are sensitive to local variation in strain. Finite-element modeling suggests that these results are consistent with long-scale gradients in the Seebeck coefficient, which yield reasonable estimates of local strain. Extending these measurements to devices with individual grain boundaries demonstrate that local strain has a larger effect than simple changes in crystallographic orientation. These measurements show that residual strain gradients in nanostructures can dominate thermoelectric response.