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1. Prominent phonon transmission across aperiodic superlattice through coherent mode-conversion

   https://doi.org/10.1063/5.0220824  

   Maranets, Theodore; Wang, Yan (July 2024, Applied Physics Letters)

   In both particle and wave descriptions of phonons, the dense, aperiodically arranged interfaces in aperiodic superlattices are expected to strongly attenuate thermal transport due to phonon-interface scattering or broken long-range coherence. However, non-trivial thermal conductivity is still observed in these structures. In this study, we reveal that incoherent modes propagating in the aperiodic superlattice can be converted, through interference, into coherent modes defined by an approximate dispersion relation. This conversion leads to high transmission across the aperiodic superlattice structure, which contains hundreds of interfaces, ultimately resulting in non-trivial thermal conductivity. Such incoherent-to-coherent mode-conversion behavior is extensively observed in periodic superlattices. This work suggests an effective strategy to manipulate the phonon dispersion relation through layer patterning or material choice, enabling precise control of phonon transmission across aperiodic superlattices. 

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2. Role of interface mixing on coherent heat conduction in periodic and aperiodic superlattices

   https://doi.org/10.1088/1361-648X/adf36b  

   Maranets, Theodore; Doe, Evan; Wang, Yan (August 2025, Journal of Physics: Condensed Matter)

   Abstract Superlattices (SLs) can induce phonon coherence through the periodic layering of two or more materials, enabling tailored thermal transport properties. While most theoretical studies assume atomically sharp, perfect interfaces, real SLs often feature atomic interdiffusion spanning approximately a single atomic layer or more. Such interface mixing can significantly influence phonon coherence and transport behavior. In this study, we employ atomistic wave-packet simulations to systematically investigate the effects of interface mixing on coherent heat conduction. Our analysis identifies two competing mechanisms that govern phonon transport across mixed interfaces: (1) interface mixing disrupts coherent mode-conversion effects arising from the interface arrangement. (2) The disorder enhances the potential for interference events, generating additional coherent phonon transport pathways. The second mechanism enhances the transmission of Bragg-reflected modes in periodic SLs and most phonons in aperiodic SLs, which otherwise lack coherent mode-conversion in perfect structures. Conversely, the first mechanism dominates in periodic SLs for non-Bragg-reflected modes, where transmission is already high due to substantial mode-conversion. These findings provide insights into the interplay between interface imperfections and phonon coherence. 

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3. Thermal Transport Across Intra-Molecular Junctions Between Boron Nitride Nanotubes and Sheets

   https://doi.org/10.1115/IMECE2025-168138  

   Ellison, Josh; Park, Jungkyu (November 2025, American Society of Mechanical Engineers)

   Abstract In this research, we investigate the effect of mechanical strain on thermal transport in interfacial thermal resistance in pillared hexagonal boron nitride sheet (hBNNS) structures using molecular dynamics simulations. More specifically, Reverse nonequilibrium molecular dynamics (RNEMD) is used together with Tersoff force field. The results show that the interfacial thermal resistance across boron nitride nanotube (BNNT)-hBNNS is minimal when compared to typical interfacial thermal resistances found in traditional materials. Interfacial thermal resistance values become lowered when the pillar heights are longer. This indicates that the thermal transport in pillared hBNNS structures is still ballistic and phonon mode conversion through the junctions is very efficient. When the structure is strained, interfacial thermal resistance increases. This can be attributed to the deformed junctions with stretched interatomic bonds. Although the direction of the phonon transport becomes less radical while being deformed, the altered lattice structure by strain impacts the phonon mode conversion across the junction more negatively, resulting in increased interfacial thermal resistance. The largest increase in interfacial thermal resistance was observed for the case with the longest interplanar spacing because the longest interplanar spacing allowed for the largest deformation in the pillared hBNNS structure without fracutre. 

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4. Acoustic and optical phonon frequencies and acoustic phonon velocities in Si-doped AlN thin films

   https://doi.org/10.1063/5.0233163  

   Wright, Dylan; Mudiyanselage, Dinusha Herath; Guzman, Erick; Fu, Xuke; Teeter, Jordan; Da, Bingcheng; Kargar, Fariborz; Fu, Houqiang; Balandin, Alexander A (September 2024, Applied Physics Letters)

   We report the results of the study of the acoustic and optical phonons in Si-doped AlN thin films grown by metal–organic chemical vapor deposition on sapphire substrates. The Brillouin–Mandelstam and Raman light scattering spectroscopies were used to measure the acoustic and optical phonon frequencies close to the Brillouin zone center. The optical phonon frequencies reveal non-monotonic changes, reflective of the variations in the thin film strain and dislocation densities with the addition of Si dopant atoms. The acoustic phonon velocity decreases monotonically with increasing Si dopant concentration, reducing by ∼300 m/s at the doping level of 3 × 1019 cm−3. The knowledge of the acoustic phonon velocities can be used for the optimization of the ultra-wide bandgap semiconductor heterostructures and for minimizing the thermal boundary resistance of high-power devices. 

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5. Lattice thermal conductivity of embedded nanoparticle composites: the role of particle size distribution

   https://doi.org/10.1088/1361-6528/ad06d6  

   Maranets, Theodore; Cui, Haoran; Wang, Yan (November 2023, Nanotechnology)

   Abstract Nanoparticles embedded within a crystalline solid serve as impurity phonon scattering centers that reduce lattice thermal conductivity, a desirable result for thermoelectric applications. Most studies of thermal transport in nanoparticle-laden composite materials have assumed the nanoparticles to possess a single size. If there is a distribution of nanoparticle sizes, how is thermal conductivity affected? Moreover, is there a best nanoparticle size distribution to minimize thermal conductivity? In this work, we study the thermal conductivity of nanoparticle-laden composites through a molecular dynamics approach which naturally captures phonon scattering processes more rigorously than previously used analytical theories. From thermal transport simulations of a systematic variety of nanoparticle configurations, we empirically formulate how nanoparticle size distribution, particle number density, and volume fraction affect the lattice thermal conductivity. We find at volume fractions below 10%, the particle number density is by far the most impactful factor on thermal conductivity and at fractions above 10%, the effect of the size distribution and number density is minimal compared to the volume fraction. In fact, upon comparisons of configurations with the same particle number density and volume fractions, the lattice thermal conductivity of a single nanoparticle size can be lower than that of a size distribution which contradicts intuitions that a single size would attenuate phonon transport less than a spectrum of sizes. The random alloy, which can be considered as a single size configuration of maximum particle number density where the nanoparticle size is equal to the lattice constant, is the most performant in thermal conductivity reduction at volume fractions below 10%. We conclude that nanoparticle size distribution only plays a minor role in affecting lattice thermal conductivity with the particle number density and volume fraction being the more significant factors that should be considered in fabrication of nanoparticle-laden composites for potential improved thermoelectric performance. 

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