Investigation on the homogeneity of pulsed electrochemically deposited thermoelectric films with synchrotron μ-XRF, μ-XRD and μ-XANES

Abstract

Thermoelectric materials are able to generate a voltage and current, when subjected to a gradient of temperature. A cost and time efficient production of thermoelectric units is the goal for future miniaturized thermoelectric generators based on thin films up to 200 μm. A comprehensive analysis of chemical and physical properties is a crucial part of the developments. One of the key parameters for the materials' physical properties is the Seebeck coefficient (S = ΔU/ΔT), which is the generated voltage for a given temperature difference. To determine the origin of a variation of S, which is found for thermoelectric materials, such as Bi2Te3 and Sb2Te3 an investigation on their stoichiometric and structural homogeneity is presented. Nondestructiveness and a mesoscopic spatial resolution are the key parameters which allow for repetitive analyses. The samples are electrochemical deposits of 10 μm thickness on Si wafers. Micro-X-ray fluorescence (μ-XRF) and micro-X-ray diffraction analysis (μ-XRD) with 15 μm spot size are performed simultaneously with focused synchrotron X-ray radiation at 30 keV. Additionally micro-X-ray absorption near edge structure (μ-XANES) measurements are performed. No inhomogeneity is detectable for samples prepared under optimized, pulsed potential conditions. Instead an indication of a correlation between the thermopower (S) variations and sample thickness variations is found.