Mediating coherent acoustic phonon oscillation of a 2D semiconductor/3D dielectric heterostructure by interfacial engineering

Abstract

Coherent acoustic phonon (CAP) oscillation of a 2D layered semiconductor/3D dielectric heterostructure generated by femtosecond laser pulse excitation can realize ultrafast photoacoustic conversion by emitting picosecond acoustic (PA) pulse; however, the photoacoustic conversion efficiency suffers from interfacial phonon scattering of simultaneously laser-induced lattice heat. Here, taking advantage of graphene’s high thermal conductivity and large acoustic impedance, we demonstrate that phonon scattering can be markedly mediated in a MoS₂/graphene/glass heterostructure via femtosecond laser pump–probe measurements. The equilibrium temperatures of the MoS₂ lattice have been cooled down by about 45%. As a benefit, both the lifetime of CAP oscillations and the pump pulse-picosecond acoustic pulse energy conversion efficiency have been enhanced by a factor of about 2. Our results offer insights into CAP and PA pulse manipulations via interfacial engineering that are fundamentally important for ultrafast photoacoustics based on 2D layered semiconductors.