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Free keywords:
Bandgap renormalization, Time-and angle-resolved photoemission spectroscopy, Transition metal dichalcogenides, Ultrafast carrier dynamics, Conduction bands, Dynamics, Electronic structure, Gold compounds, Gold metallography, Graphene, Layered semiconductors, Molybdenum compounds, Photoelectron spectroscopy, Silver metallography, Transition metals, Tungsten compounds, Angle resolved photoemission spectroscopy, Charge carrier dynamics, Quasiparticle spectrum, Semiconducting transition, Transient conduction, Transient electronics, Transition metal dichalcogenides, Ultrafast carrier dynamics, Substrates
Abstract:
The quasiparticle spectra of atomically thin semiconducting transition metal dichalcogenides (TMDCs) and their response to an ultrafast optical excitation critically depend on interactions with the underlying substrate. Here, we present a comparative time- and angle-resolved photoemission spectroscopy (TR-ARPES) study of the transient electronic structure and ultrafast carrier dynamics in the single- and bilayer TMDCs MoS2 and WS2 on three different substrates: Au(111), Ag(111) and graphene/SiC. The photoexcited quasiparticle bandgaps are observed to vary over the range of 1.9–2.5 eV between our systems. The transient conduction band signals decay on a sub-50 fs timescale on the metals, signifying an efficient removal of photoinduced carriers into the bulk metallic states. On graphene, we instead observe a fast timescale on the order of 170 fs, followed by a slow dynamics for the conduction band decay in MoS2. These timescales are explained by Auger recombination involving MoS2 and in-gap defect states. In bilayer TMDCs on metals we observe a complex redistribution of excited holes along the valence band that is substantially affected by interactions with the continuum of bulk metallic states. © 2021 The Author(s)
