| AVS 62nd International Symposium & Exhibition | |
| 2D Materials Focus Topic | Thursday Sessions |
| Session 2D+EM+MG+NS+SE+SM+SS+TF-ThM |
| Session: | Emergent 2D Materials |
| Presenter: | Ming-Wei Chen, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland |
| Authors: | M.W. Chen, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland M.B. Whitwick, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland O. Lopez-Sanchez, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland D. Dumcenco, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland A. Kis, Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland |
| Correspondent: | Click to Email |
Two-dimensional transition metal dichalcogenides (TMDs) have attracted widespread attention recently, and the focus is specifically on ultrathin layers due to the strong spin-orbit coupling and direct band-gap transition of single-layers. The unique properties of various TMDs also enable the possibilities for future optoelectronic applications. However, the synthesis of TMDs with uniform large-area and high-quality still remains challenging. While chemical vapour deposition has been demonstrated as a promising technique, the complexity of chemical precursors and the lacking of in-situ observation technique strongly hinder the progress.
Here, We propose to use ultra-high vacuum molecular beam epitaxy (MBE) to grow MoSe2 ultrathin layers, down to single-layer in a controllable way. Epitaxial MoSe2 layers were successfully grown on different crystalline substrates via van der Waals epitaxy mechanism, benefited from the weak interlayer interaction and the lacking of dangling bonds. Reflection high energy electron diffraction (RHEED) was used to in-situ monitor the initial growth stage and revealed a clear transition of the streaks, demonstrating the formation of MoSe2 layer. Sharp streaks were obtained in the growth end, with the streak spacing corresponding to MoSe2 lattice constant, and no significant strain effect was observed. In order to demonstrate the validity of van der Waals epitaxy, different crystalline substrates with lattice mismatch up to 30 % have been tested. The epitaxial layers showed a smooth and uniform surface in atomic force microscopy, and the quality was further confirmed in Raman spectrum and transmission electron microscopy. Furthermore, photoluminescence of the single-layer MoSe2 showing a sharp peak of ~1.58 eV at room temperature demonstrates the direct band-gap feature and indicates the potentials of photovoltaic applications. In the end, the growth of two-dimensional van der Waals heterostructures has also been addressed and the results pave way for heterostructure studies.
In summary, molecular beam epitaxy has been proved to be a reliable route to grow large-area and high-crystalline transition metal chalcogenides, and is promising to facilitate the integration of other two-dimensional materials in the future.