Year: 2017
Type: article
Abstract: Materials with low thermal conductivity are key to achieving high thermoelectric performance [1], which in turn can enable technologies that directly and efficiently convert heat to electrical energy and vice versa. In recent breakthrough developments in the field of thermoelectrics, it has been shown that heterogeneous composite materials with multiple phases on the nano- and microscales can achieve very high dimensionless figures of merit (ZT) [2]. Therefore, it is of high interest in understanding the thermal conductivity not only of the composite materials, but also of its individual component phases. To date, thermal conductivity of thermoelectric materials is typically measured at the macroscopic scale [3,4]. Effective methods to measure local thermal conductivity with high spatial resolution are not available. Such information is crucial to further guide the effective material development that could lower their thermal conductivities. Nasr Esfahani et al. reported a powerful method to directly investigate local thermal conductivity using scanning thermal microscopy combined with finite element simulations [5], as schematically shown in Fig. 1. By using a thermal probe with a micro-fabricated heater that also serves as a temperature sensor, they demonstrated that the resistance change of the probe upon touching the sample can be quantitatively correlated with the sample's local thermal conductivity. The effects of thermal conduction, radiation, convection and contact resistance have been carefully addressed by finite element simulations. Using such a technique, Nasr Esfahani et al. successfully measured the local thermal conductivity of a three-phase filled skutterudite, resolved their variation at the phase interface and obtained the thermal image in one-to-one correspondence with the microstructural phase compositions. Crosstalk with topography, a common issue in scanning thermal microscopy, is not observed. Atomic force microscope (AFM) and scanning thermal microscopy (SThM) schematics with thermal conductivity, topography and back-scattered electron (BSE) mappings, respectively, from top to bottom. Image courtesy of E. Nasr Esfahani, University of Washington. This method reported by Nasr Esfahani et al. is a valuable advancement in thermoelectric materials characterization and, if it can be widely adopted, it will add to the toolbox of characterization techniques used in searching for ever-higher-performance thermoelectric materials. It seems promising as a means to accurately measure thermal conductivity for nanostructuring interfaces, nano-wires and 2D thermoelectric systems.
Source: National Science Review
DOI: 10.1093/nsr/nwx092
Authors: Li-Dong Zhao, Mercouri G Kanatzidis
Institutions: Beihang University, Northwestern University
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $2,000
OpenAlex ID: W2743224495