Dresden 2026 – scientific programme
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O: Fachverband Oberflächenphysik
O 43: Scanning probe microscopy: light matter interaction at atomic scales – Poster
O 43.6: Poster
Tuesday, March 10, 2026, 14:00–16:00, P2
Investigation of atomic defects in quasi-freestanding MoS2 with THz-STM — •Caroline Firschke, Junyoung Sim, Vibhuti N. Rai, Paul Wiechers, Florian Faaber, Christian Lotze, and Katharina J. Franke — Freie Universität Berlin, Germany
Transition metal dichalcogenides (TMDCs) are an interesting class of materials due to their 2D-like nature and unique band structures. These materials tend to host different types of defects, heavily influencing their optoelectronic properties. THz-driven scanning tunneling microscopy is a unique technique to investigate the nature of these defects on atomic scales with ultrafast time resolution (1).
Here, we grow monolayers of MoS2 on Au(111) via chemical vapor deposition, which host quasi-freestanding monolayers of MoS2 with a band gap of around 2.7 eV, the so called "pits" (2). We find structural defects in these pits, which are decoupled from the metal substrate, and show sharp positive ion resonances in the band gap.
These sharp non-linearities of the I-V curve provide favorable conditions for their investigation via THz pulses. We find that these defects show sharp resonances in the light-wave-driven scanning tunneling spectroscopy, which vary depending on the THz field strength, DC bias voltage and tip-sample distance. The THz response of these resonances cannot be modeled with a simple convolution of THz pulses with the static I-V of the junction, suggesting a modulation of the charge state of the defects on ultrafast timescales.
(1) T. L. Cocker et. al. Nature Photon 7, 620-625 (2013)
(2) N. Krane et. al. Nano Letters 2016 16 (8), 5163-5168
Keywords: THz-STM; THz-STS; TMDC; light matter interaction; CVD