Dr. Ryotaro Sakakibara is a researcher in the 2D Semiconductor Group at MANA in NIMS since 2025. He received his Ph.D. from Nagoya University in 2024 and subsequently worked as a postdoctoral researcher at Tokyo Metropolitan University before joining NIMS. His research focuses on the growth and structural control of two-dimensional (2D) materials such as graphene and transition metal dichalcogenides, as well as their atomic-scale characterization using transmission electron microscopy (TEM). At NIMS, he is engaged in developing 2D materials and exploring their device applications toward next-generation electronics.

Semiconducting transition-metal dichalcogenides (TMDs), such as MoS₂ and WSe₂, are promising channel materials for highly scaled field-effect transistors (FETs). However, integrating suitable electrode materials with these atomically thin semiconductors remains a major challenge for their practical application.[1] In this context, metallic TMDs such as VSe₂[2] and NbSe₂[3] are attractive electrode materials because they can form well-defined interfaces with semiconducting TMDs. Area-selective epitaxial growth of metallic TMDs would therefore be highly desirable for device integration. In this study, we demonstrate epitaxial growth of NbSe₂ on WSe₂ via solid-phase selenization of lithographically patterned Nb films.

Multilayer WSe₂ was first grown by chemical vapor deposition, followed by deposition of a Nb thin film by RF magnetron sputtering. The Nb film was subsequently converted into NbSe₂ by annealing in a Se atmosphere. Cross-sectional scanning transmission electron microscopy (STEM) revealed a uniform NbSe₂/WSe₂ heterostructure with a clear epitaxial relationship (Fig. 1). Notably, NbSe₂ was laterally connected to the edges of WSe₂ at the interface. Furthermore, lithographic patterning of the Nb film before selenization enabled area-selective formation of NbSe₂ electrodes contacting the WSe₂ channel. FETs using these electrodes exhibited p-type operation. These results highlight solid-phase epitaxy as a promising route for integrating metallic TMD electrodes with semiconducting TMD channels.

1. S. Das, et al., Nat. Rev. Electr. Eng. 3, 421 (2026) DOI: 10.1038/s44287-026-00297-4
2. R. Wu, et al., Nat. Electron. 5, 497 (2022) DOI: 10.1038/s41928-022-00800-3
3. H. Choi, et al., Nano Lett. 26, 5307 (2026) DOI: 10.1021/acs.nanolett.6c00871