Van der Waals Epitaxy of Weyl-Semimetal Td-WTe2

• Published in: ACS applied materials & interfaces 2024-04, Vol.16 (16), p.20878-20885
• Main Authors: Llopez, Alexandre, Leroy, Frédéric, Tagne-Kaegom, Calvin, Croes, Boris, Michon, Adrien, Mastropasqua, Chiara, Al Khalfioui, Mohamed, Curiotto, Stefano, Müller, Pierre, Saùl, Andrés, Kierren, Bertrand, Kremer, Geoffroy, Fèvre, Patrick Le, Bertran, François, Fagot-Revurat, Yannick, Cheynis, Fabien
• Format: Article
• Language: English
• Subjects: Condensed Matter; Materials Science; Physics
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.4c00676

Epitaxial growth of WTe2 offers significant advantages, including the production of high-quality films, possible long-range in-plane ordering, and precise control over layer thicknesses. However, the mean island size of WTe2 grown by molecular beam epitaxy (MBE) in the literature is only a few tens of nanometers, which is not suitable for the implementation of devices at large lateral scales. Here we report the growth of Td -WTe2 ultrathin films by MBE on monolayer (ML) graphene, reaching a mean flake size of ≃110 nm, which is, on overage, more than three times larger than previous results. WTe2 films thicker than 5 nm have been successfully synthesized and exhibit the expected Td phase atomic structure. We rationalize the epitaxial growth of Td-WTe2 and propose a simple model to estimate the mean flake size as a function of growth parameters that can be applied to other transition metal dichalcogenides (TMDCs). Based on nucleation theory and the Kolmogorov-Johnson-Meh-Avrami (KJMA) equation, our analytical model supports experimental data showing a critical coverage of 0.13 ML above which WTe2 nucleation becomes negligible. The quality of monolayer WTe2 films is demonstrated by electronic band structure analysis using angle-resolved photoemission spectroscopy (ARPES), which is in agreement with first-principles calculations performed on free-standing WTe2 and previous reports. We found electron pockets at the Fermi level, indicating a n-type doping of WTe2 with an electron density of n = 2.0 ± 0.5 × 1012 cm-2 for each electron pocket.