Tuning phonon transmission via single-atom substituents

Thermal transport plays a crucial role in many modern electronic, photonic and energy conversion devices. Recent work has provided fundamental insights into the effects of nanostructuring on heat transport. However, the atomic-scale control of phonon transport has barely been explored. Here we present systematic studies of thermal transport in molecular junctions at 77 K, enabled by high-resolution cryogenic-compatible calorimetric scanning probes developed in this work. Our experiments provide direct evidence that atomistic changes to molecular junctions, implemented by substituting an individual hydrogen atom by a halogen atom (-F, -Cl, -Br, -I), tune the thermal conductance of the junctions by a factor of two. Our detailed first-principles modelling elucidates how the interaction between the vibrational eigenmodes of molecular junctions is modified by atomic substituents, resulting in both suppression of resonances and creation of antiresonances in the phonon transmission function. Further, the advances reported here and insights from this work inform how thermal transport in molecular materials can be probed and controlled.