Detection of Trace Impurity Gradients in Noble Metals by the Photothermoelectric Effect

Abstract

Trace impurity concentrations in noble metals can have profound effects on chemical and physical properties, yet detecting these impurity concentrations remains a challenge using typical spectroscopic characterization tools and specialized techniques such as secondary ion mass spectrometry. In this work, we demonstrate that the photothermoelectric effect can be leveraged to detect low-concentration platinum gradients in wire-shaped gold nanostructures with high sensitivity. The photothermoelectric voltage measurements show significant contributions from platinum impurities to the bulk Seebeck coefficient of gold at length scales that agree with theoretical platinum diffusion lengths. Using finite element modeling, the Seebeck distribution is calculated for the gold− platinum system, showing that even a 0.01% variation in platinum concentration along a 1 μm length of gold wire can contribute significantly to the local Seebeck coefficient. These measurements indicate that the photothermoelectric effect can be a highly sensitive tool for detecting low-level impurity concentrations in host metals in a wire geometry.