Engineering and Probing Phonons and Thermal Transport

University of Basel

The recently growing research field called “Nanophononics” deals with the investigation and control of vibrations in solids at the nanoscale. Phonon engineering leads to a controlled modification of phonon dispersion, phonon interactions, and transport. However, engineering and probing phonons and phonon transport at the nanoscale is a non-trivial problem.
In this talk, we discuss how phononic properties and thermal transport can be engineered and measured in nanowires and the challenges and progresses in the measurement of the thermal conductivity of nanostructures and low dimensional systems. The concept of phonon engineering in nanowires is exploited in GaAs/GaP superlattice nanowires. We experimentally show that a controlled design of the nanowires’ phononic properties can be decided à la carte by tuning the superlattice period. 
We also investigated thermal rectification in semiconducting gallium arsenide nanowires with an abrupt change in diameter, also called telescopic nanowires. We measured rectification values ranging from 2 to 7% at a range of ambient temperatures, with rectification values increasing for larger temperature gradients. The direction of rectification and its dependence on temperature gradient is con-firmed by ab-initio calculations using the acoustic mismatch model, taking into account the contribution from interfacial thermal resistance.
Finally, Raman thermometry is used to probe the temperature profile in nanostructures upon application of a thermal gradient, enabling the differentiation between different thermal transport regimes.