Journal
JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA
Volume 250, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.elspec.2021.147093
Keywords
Time-and angle-resolved photoemission spectroscopy; Transition metal dichalcogenides; Ultrafast carrier dynamics; Bandgap renormalization
Categories
Funding
- VILLUM FONDEN, Denmark [15375]
- Centre of Excellence for Dirac Materials, Denmark [11744]
- Danish Council for Independent Research, Natural Sciences, Denmark under the Sapere Aude program [DFF-9064-00057B, DFF-6108-00409]
- STFC
- International Max Planck Research School for Chemistry and Physics of Quantum Materials (IMPRS-CPQM)
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In this study, the transient electronic structure and ultrafast carrier dynamics of single- and bilayer TMDCs MoS2 and WS2 on different substrates were investigated using time- and angle-resolved photoemission spectroscopy. The variation of photoexcited quasiparticle bandgaps and the efficient removal of carriers into bulk metallic states were observed. Complex dynamics of excited holes along the valence band in bilayer TMDCs on metals were attributed to interactions with bulk metallic states.
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.
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