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 PtSe2 with various van der Waals (vdW) layer numbers using femtosecond transient optical spectroscopy. The hot carrier dynamics of PtSe2 is found to be strongly dependent on its thickness. For semiconducting PtSe2 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 PtSe2 films (with vdW layers). The PtSe2 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 PtSe2 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.