Significant reduction of thermal conductivity in monolayer MoSe2 through fractional-layer engineering

Controlling phonon-mediated heat transport in two-dimensional (2D) materials through intrinsic and disorder-free mechanisms remains a fundamental challenge. Here, we demonstrate that fractional-layer engineering provides a general route to intrinsically suppress thermal conductivity in 2D materials. Using first-principles calculations combined with the Boltzmann transport equation, thermal conductivity of monolayer MoSe2 and fractional-layer MoSe was investigated. Specifically, fractional-layer reconstruction leads to an almost twofold reduction in thermal conductivity. Phonon analysis shows that thermal conductivity suppression is dominated by strongly enhanced four-phonon scattering of acoustic phonons, with splitting processes playing the leading role. Additionally, fractional-layer engineering drives a sign reversal and a pronounced enhancement of the Grüneisen parameter for the out-of-plane acoustic mode, indicating strengthened phonon anharmonicity. Our results identify fractional-layer engineering as a broadly applicable strategy for intrinsic phonon and thermal-transport regulation in 2D materials.