Speaker: Ryan A. Duncan, Massachusetts Institute of Technology (Keith Nelson Group)
Program Description:
Time-resolved laser-based techniques are excellent for investigating the thermal transport properties of materials at micron/nanometer length scales. In particular, transient thermal grating (TTG) techniques are well-suited for studying the dependence of the thermal transport dynamics on an experimentally imposed length scale in the form of the grating period of the excitation spatial profile. In this talk I will discuss micro- and nanoscale phonon-mediated thermal transport in non-metallic crystals and the deviations from the Fourier law that emerge at these length scales due to the interplay between the experimental/structural limiting dimensions and the phonon mean-free-paths (MFPs). I will highlight recent work utilizing TTG techniques to study deviations from the Fourier law in semiconductor nanostructures and semiconductor alloys at the microscale, as well as the emergence of the hydrodynamic thermal transport regime and the observation of so-called “second sound”—i.e., the wavelike transport of heat—in graphite at exceptionally high temperatures (~100 K). Finally, I will discuss recent advances in extending TTG techniques to the extreme-ultraviolet (EUV) spectral range at the FERMI EUV free-electron laser of the Elettra Synchrotron Facility, and present the results of TTG measurements at grating periods in the range of 10s-100s of nanometers using these recently developed capabilities.
