SEMINAR LMGP - May 3, 2022 - Petros ABI YOUNES

Petros ABI YOUNES

PhD student,
¹UGA, CNRS, Grenoble INP, LMGP, Grenoble, France; ²UGA, CEA, LETI, Grenoble, France

Metal Dichalcogenides (MDs) have recently emerged as a class of exceptional materials with many potential applications and are receiving great attention. Among them lamellar Titanium disulfide (TiS₂) is the lightest and cheapest member of the Transition MDs(TMDs) family,^[1] with 1T-TiS₂ crystallographic structure. Its electrical properties allow to use it in many fields of applications (optics, thermoelectrics and batteries).^[2–5]

However, the lack of scalable fabrication methods of continuous ultra-thin films on developed surfaces, at moderate temperature, stems a sizeable bottleneck for the full deployment of these materials. Beside the conventional Atomic Layer Deposition (ALD) process, which suffers from limitations, an innovative 2-step process comprising Molecular Layer Deposition (MLD) and thermal annealing has been developed to achieve atomically-thin synthesis of 2D TMDs MoS₂ and WS₂.^[6,7] interestingly, the process does not use the highly toxic H₂S molecule. By using this approach we have succeeded to synthesize continuous and textured TiS2 thin films on thermal SiO₂ ^[8]. An intermediate amorphous polymer (Ti-thiolate) is deposited by MLD at low temperature (T_sub = 50°C) upon a reaction between the metal precursor (TDMAT = Ti(NMe₂)₄) and organic sulfide molecule (1,2-ethanedithiol). Then, the amorphous thin film undergoes a thermal annealing under hydrogenated argon flow.

Both the MLD and thermal annealing were monitored by in situ synchrotron radiation techniques, including x-ray fluorescence (XRF), x-ray reflectivity (XRR) and x-ray absorption fine structure (XAFS), at SIRIUS beamline (SOLEIL, St Aubin), and in situ ellipsometry. Main results will be presented. Importantly, both the sulfur K and Ti K fluorescence line intensities could be recorded simultaneously, allowing us to monitor simultaneously the S and Ti contents throughout the whole process and from the very early stage of the Ti-thiolate deposition. The repetitive self-limiting growth behavior during the MLD step could be demonstrated. Upon thermal annealing the Ti-thiolate thin film transforms into lamellar TiS₂ monolayers parallel to the substrate surface as observed by Raman spectroscopy, transmission electron microscopy (TEM) and x-ray linear dichroism at the Ti K-edge. Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS) and lab-scale Hard XPS (HAXPES) show stoichiometric TiS₂ in the presence of carbon.

References

[1] X. Xu, W. Liu, Y. Kim, J. Cho, Nano Today 2014, 9, 604.

[2] L. Zhang, D. Sun, J. Kang, H. T. Wang, S. H. Hsieh, W. F. Pong, H. A. Bechtel, J. Feng, L. W. Wang, E. J. Cairns, J. Guo, Nano Lett. 2018, 18, 4506.

[3] A. Stoliaroff, C. Latouche, S. Jobic, Phys. Rev. B 2019, 99, 1.

[4] X. Zhu, S. Chen, M. Zhang, L. Chen, Q. Wu, J. Zhao, Q. Jiang, Z. Zheng, H. Zhang, Photonics Res. 2018, 6, C44.

[5] R. Z. Zhang, C. L. Wan, Y. F. Wang, K. Koumoto, Phys. Chem. Chem. Phys. 2012, 14, 15641.

[6] S. Cadot, O. Renault, M. Frégnaux, D. Rouchon, E. Nolot, K. Szeto, C. Thieuleux, L. Veyre, H. Okuno, F. Martin, E. A. Quadrelli, Nanoscale 2017, 9, 538.

[7] S. Cadot, O. Renault, D. Rouchon, D. Mariolle, E. Nolot, C. Thieuleux, L. Veyre, H. Okuno, F. Martin, E. A. Quadrelli, J. Vac. Sci. Technol. A Vacuum, Surfaces, Film. 2017, 35, 061502.