Exploring the nonlinear optical properties of colloidal WS2 nanosheets

Markus Fröhlich^a, Yang Zhao^b, Tim Parker^b, Felix Schneider^b, Onno Strolka^a^,^c, Marco Kögel^d, Alfred J. Meixner^a, Jannik Meyer^d^,^e, Jannika Lauth^a^,^c, Dai Zhang^b

^aInstitute of Physical and Theoretical Chemistry, Eberhard Karls University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany

^bCenter for Light-Matter-Interaction, Sensors, and Analytics (LISA+), Eberhard Karls University of Tübingen, Auf der Morgenstelle 15, 72076 Tübingen, Germany

^cLeibniz University of Hannover, Cluster of Excellence PhoenixD (Photonics, Optics and Engineering – Innovation Across Disciplines), Welfengarten 1a, D-30167, Hannover, Germany

^dNMI Natural and Medical Sciences Institute at the University of TÜbingen, Markwiesenstraße 55, D-72770 Reutlingen, Germany

^eUniversity of TÜbingen, Institute of Applied Physics, Auf der Morgenstelle 10, D-72076 Tu¨bingen, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Fall 2024 Conference (MATSUSFall24)

#NANOFUN - Functional Nanomaterials: from materials to applications.

Lausanne, Switzerland, 2024 November 12th - 15th

Organizers: Emmanuel Lhuillier and Shalini Singh

Oral, Markus Fröhlich, presentation 248
DOI: https://doi.org/10.29363/nanoge.matsusfall.2024.248
Publication date: 28th August 2024

Transition metal dichalcogenides (TMDCs) are highly researched photonic two-dimensional (2D) semiconductors. Among other members of the TMDC group, WS₂ shows remarkably high nonlinear susceptibility owing to its lack of inversion symmetry.^[1] This effect is observed for all odd-numbered WS₂ layers but is especially strong in monolayers and can be further increased by strain,^[2] while defective crystal structures lead to inversion symmetry breaking of even-layered WS₂.^[3]
The ability of TMDCs to yield stable monolayers with rich exciton physics^[4] inspired the wet-chemical synthesis of MoS₂^[5,6,7] and WS₂^[6,8] as well as their respective Mo1-xWxS2 alloys^[9] and heavier chalcogenides (Se ^[10] and Te). With the scalable bottom-up approach, predominantly atomically thin^[9] nanosheets (NSs) with controlled crystal phase-^[5,6], size^[5]- and composition^[9] are obtained and can be readily processed in solution or after precipitation. Comprehensive characterization via HR-TEM, Raman spectroscopy, and steady-state absorption spectroscopy confirms the synthesis of primarily monolayered semiconducting NSs with a narrow lateral size distribution (5-25 nm).

Here, we investigate the non-linear optical response of colloidal WS₂ with a femtosecond-laser-pulsed confocal mirror microscope. Our study includes one- and two-photon photoluminescence and efficient second harmonic generation (SHG) of colloidal WS₂ monolayers. The power-dependent SHG intensities from the colloidal WS₂ monolayers show steeper slopes than the commercially available CVD-grown WS₂ flakes, indicating a higher non-linear susceptibility for colloidal WS₂.
These results highlight the exceptionally high non-linear response in colloidal WS₂, underscoring the potential of colloidally synthesized WS₂ as functional 2D semiconductors.

References:

[1] Wang, Y.; Xiao, J.; Yang, S.; Wang, Y.; Zhang, x. Second harmonic generation spectroscopy on two-dimensional materials. Opt. Mater. Express. 2019, 9,1136-1149.

[2] Khan, A.R.; Liu, B.; Lü, T.; Zhang, L.; Sharma, A.; Zhu, Y.; Ma, W.; Lu, Y. Direct Measurement of Folding Angle and Strain Vector in Atomically Thin WS2 Using Second-Harmonic Generation. ACS Nano. 2020 14 (11), 15806-15815.

[3] Liu, J.; Lo, T.W.; Sun, J.; Yip,C.T.; Lam, C.H.; Lei, D.Y. A comprehensive comparison study on the vibrational and optical properties of CVD-grown and mechanically exfoliated few-layered WS2. J. Mater. Chem. C. 2017, 5, 11239-11245.

[4] Chhowalla, M.; Shin, H.; Eda, G.; Li, L.-J.; Loh, K.P.; Zhang, H.The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nature Chem. 2013, 5, 263–275.

[5] Niebur, A.; Söll, A.; Haizmann, P.; Strolka, O.; Rudolph, D.; Tran, K.; Renz, F.; Frauendorf, A.; Hübner, J.; Scheele, M.; Lauth, J. Untangling the intertwined: metallic to semiconducting phase transition of colloidal MoS2 nanoplatelets and nanosheets. Nanoscale, 2023,15, 5679-5688.

[6] Kapuria, N.; Patil, N.N.; Sankaran, A.; Laffir, F.; Geaney, H.; Magner, E.; Scanlon, M.; Ryan, K.M.; Singh, S. Engineering polymorphs in colloidal metal dichalcogenides: precursor-mediated phase control, molecular insights into crystallisation kinetics and promising electrochemical activity. J. Mater. Chem. A, 2023, 11, 11341-11353.

[7] Schiettecatte, P.; Singh, S.; Zhou, P.; Hens, Z. The Dynamic Interaction of Surfactants with Colloidal Molybdenum Disulfide Nanosheets Calls for Thermodynamic Stabilization by Solvents. Langmuir. 2023, 39, (18), 6568-6579.

[8] Frauendorf, A.P.; Niebur, A.; Harms, L.; Shree, S.; Urbaszek, B.; Oestreich, M.; Hübner, J.; Lauth, J. Room Temperature Micro-Photoluminescence Studies of Colloidal WS2 Nanosheets. J. Phys. Chem. C. 2021, 125, (34), 18841-18848.

[9] Fröhlich, M.; Kögel, M.; Hiller, J.; Kahlmeyer, L.; Meixner, A.J.; Scheele, M.; Meyer, J.C.; Lauth, J. Colloidal 2D Mo1−xWxS2 nanosheets: an atomic- to ensemble-level spectroscopic study. Phys. Chem. Chem. Phys., 2024,26, 13271-13278.

[10] Zhou, P.; Schiettecatte, P.; Vandichel, M.; Rousaki, A.; Vandenabeele, P.; Hens, Z.; Singh, S. Synthesis of Colloidal WSe2 Nanocrystals: Polymorphism Control by Precursor-Ligand Chemistry. Cryst. Growth Des. 2021, 21 (3), 1451-1460.

Acknowledgements:

This work was financially supported by the Chinese Scholarship Council (CSC) and the German Research Foundation projects ZH 279/13-1.

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