Journal
ACS APPLIED NANO MATERIALS
Volume 5, Issue 10, Pages 15557-15562Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsanm.2c03517
Keywords
terahertz near-field spectroscopy; terahertz conductivity; electron-phonon coupling; tungsten disulfide; transition metal dichalcogenide; density functional theory
Funding
- Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) [Vici 680-47-628]
- ITN 4PHOTON Marie Sklodowska Curie grant [721394]
- NWO START-UP grant [740.018.009]
- Center for Molecular Quantum Transduction (CMQT), an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0021314]
- Marie Curie Actions (MSCA) [721394] Funding Source: Marie Curie Actions (MSCA)
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By using THz near-field spectroscopy, time-resolved THz measurements were conducted on a single nanolayered crystal. This technique allows for the investigation of the relation between carrier dynamics and phonon transport in nanolayered crystals.
Time-resolved terahertz (THz) spectroscopy is a powerful technique for the determination of charge transport properties in photoexcited semiconductors. However, the relatively long wavelengths of THz radiation and the diffraction limit imposed by optical imaging systems reduce the applicability of THz spectroscopy to large samples with dimensions in the millimeter to centimeter range. Exploiting THz near-field spectroscopy, we present the first time-resolved THz measurements on a single exfoliated 2D nanolayered crystal of a transition metal dichalcogenide (WS2). The high spatial resolution of THz near-field spectroscopy enables mapping of the sheet conductance for an increasing number of atomic layers. The single-crystalline structure of the nanolayered crystal allows for the direct observation of low-energy phonon modes, which are present in all thicknesses, coupling with free carriers. Density functional theory calculations show that the phonon mode corresponds to the breathing mode between atomic layers in the weakly bonded van der Waals layers, which can be strongly influenced by substrate-induced strain. The non-invasive and high-resolution mapping technique of carrier dynamics in nanolayered crystals by time-resolved THz time domain spectroscopy enables possibilities for the investigation of the relation between phonons and charge transport in nanoscale semiconductors for applications in two-dimensional nanodevices.
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