Abstract Spatially resolved vibrational mapping of nanostructures is indispensable to the development and understanding of thermal nanodevices 1 , modulation of thermal transport 2 and novel nanostructured thermoelectric materials 3–5 . Through the engineering of complex structures, such as alloys, nanostructures and superlattice interfaces, one can significantly alter the propagation of phonons and suppress material thermal conductivity while maintaining electrical conductivity 2 . There have been no correlative experiments that spatially track the modulation of phonon properties in and around nanostructures due to spatial resolution limitations of conventional optical phonon detection techniques. Here we demonstrate two-dimensional spatial mapping of phonons in a single silicon–germanium (SiGe) quantum dot (QD) using monochromated electron energy loss spectroscopy in the transmission electron microscope. Tracking the variation of the Si optical mode in and around the QD, we observe the nanoscale modification of the composition-induced red shift. We observe non-equilibrium phonons that only exist near the interface and, furthermore, develop a novel technique to differentially map phonon momenta, providing direct evidence that the interplay between diffuse and specular reflection largely depends on the detailed atomistic structure: a major advancement in the field. Our work unveils the non-equilibrium phonon dynamics at nanoscale interfaces and can be used to study actual nanodevices and aid in the understanding of heat dissipation near nanoscale hotspots, which is crucial for future high-performance nanoelectronics.
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Nanoscale thermal interface rectification in the quantum regime
To enable the on-demand control of heat flow for sustainable energy solutions, we have been longing for functional thermal components at the nanoscale, in analogue to electronic diodes and transistors. Understanding and discovering fundamental mechanisms that drive thermal rectification are critical to advancing this field. Different mechanisms have been proposed for thermal rectification effects in the classical regime. Using anharmonic atomistic Green's function, we discovered a thermal rectification phenomenon in the quantum regime for nanometer-thick three-dimensional solid interfaces. We found that the anharmonic phonon scatterings across the interface act on the temperature-dependent phonon populations on both sides of the interface, generating the necessary nonlinearity to achieve thermal rectification. This intrinsic thermal interface rectification is a universal phenomenon that can be observed and engineered for nanoscale interfaces.
more » « less- NSF-PAR ID:
- 10440263
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Applied Physics Letters
- Volume:
- 122
- Issue:
- 12
- ISSN:
- 0003-6951
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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