Nanoscale Energy Transport and Phonon Engineering. A Review

Nanoscale energy transport and phonon engineering have become central topics in modern thermal science due to the breakdown of classical heat conduction models at reduced dimensions. In nanoscale systems, energy transport is governed by ballistic and quasi-ballistic phonon dynamics rather than purely diffusive Fourier behavior, necessitating advanced theoretical frameworks such as the Boltzmann transport equation, molecular dynamics, and density functional theory. This review provides a comprehensive overview of phonon-mediated heat transport, emphasizing scattering mechanisms, mean free path effects, and interface-driven thermal resistance. It highlights recent advances in phonon engineering strategies, including nanostructuring, alloying, phononic crystals, and low-dimensional materials, for controlling thermal conductivity. Experimental techniques such as time-domain thermoreflectance and Raman spectroscopy are discussed alongside computational and data-driven approaches. Applications in thermoelectrics, nanoelectronics, and energy systems are explored, demonstrating the importance of thermal control at the atomic scale. Finally, key challenges and future directions in nanoscale thermal management are outlined