Thickness-dependent ultrafast hot carrier and phonon dynamics of PtSe2 films measured with femtosecond transient optical spectroscopy

Abstract We systematically investigate the ultrafast hot carrier and phonon dynamics of PtSe 2 with various van der Waals (vdW) layer numbers using femtosecond transient optical spectroscopy. The hot carrier dynamics of PtSe 2 is found to be strongly dependent on its thickness. For semiconducting PtSe 2 films (≤4 vdW layers), electron–phonon coupling, interlayer charge transfer and nonradiative recombination of electrons and holes contribute to the hot carrier decay, while electron–phonon coupling dominates the carrier decay in metallic PtSe 2 films (with > 4 vdW layers). The PtSe 2 films with 2 vdW layers show the most pronounced interlayer charge transfer decay process and are thus most suitable for photoelectric sensors and energy harvesting devices. The phonon dynamics of PtSe 2 is also thickness dependent; its LB mode phonon frequency decreases as the number of vdW layers increases, as a result of the thickness-dependent dielectric screening of the long-range Coulomb interaction.