CORRELATING THERMOELECTRIC PROPERTIES TO NANO STRUCTURES BY ADVANCED STEM/TEM TECHNIQUES

Abstract

Thermoelectrics enable direct heat-to-electricity transformation, but their performance has so far been restricted by the ambiguous understanding of the nanoscale atomic structure and its effect on carrier and phonon transport. Thanks to the recent development of aberration-corrected scanning transmission electron microscopy (STEM), the atomic structure of all nanoscale defects can now be imaged. Preliminary works link these defects to lattice thermal conductivity but they are rarely linked with carrier mobility. In this thesis, we develop an understanding of the relationship between the nanostructure and the properties of thermoelectric materials, for example, the effect of subtle strain fields on lattice thermal conductivity and the effect of interface on electrical mobility, through the utilization of the versatile techniques of STEM and transmission electron microscopy (TEM). The employed methods comprise geometric phase analysis, nano-beam diffraction, atomic resolution energy dispersive Spectroscopy, differential phase contrast, and electron holography.