Phonon softening and significant thermal conductivity drop induced by tailoring interlayer interactions in Nb-doped rhombohedral MoS2

The differences in stacking configurations result in rhombohedral transition metal dichalcogenides (3R-TMDs), compared to their hexagonal counterparts, exhibiting stronger interlayer interactions, sliding ferroelectricity, and bulk piezophotovoltaic effects. However, the effects of doping on interlayer interactions and phonon transport in 3R-TMDs have not been fully explored. In this study, we demonstrate Nb doping in 3R-MoS₂ effectively modulates interlayer interactions and causes a significant decrease in thermal conductivity. The increased carrier concentration induced by doping enhances screening, leading to the softening and deceleration of optical phonons. Additionally, doping modulates the interlayer interactions, causing changes in the phonon vibrational modes. This results in an avoided crossing between optical and acoustic phonons, further reducing the group velocity of acoustic phonons. Combined with the reduction in phonon mean free path due to point defect scattering, this ultimately leads to a 56 % decrease in the lattice thermal conductivity of 3R-MoS₂. This study deepens our understanding of the relationship between phonon dispersion and interlayer interactions in 3R-TMDs, providing valuable insights for the design of thermal management materials.