Publications by Yulin Chen


Electronic Structure, Surface Doping, and Optical Response in Epitaxial WSe2 Thin Films.

Nano letters 16 (2016) 2485-2491

Y Zhang, MM Ugeda, C Jin, S-F Shi, AJ Bradley, A Martín-Recio, H Ryu, J Kim, S Tang, Y Kim, B Zhou, C Hwang, Y Chen, F Wang, MF Crommie, Z Hussain, Z-X Shen, S-K Mo

High quality WSe2 films have been grown on bilayer graphene (BLG) with layer-by-layer control of thickness using molecular beam epitaxy. The combination of angle-resolved photoemission, scanning tunneling microscopy/spectroscopy, and optical absorption measurements reveal the atomic and electronic structures evolution and optical response of WSe2/BLG. We observe that a bilayer of WSe2 is a direct bandgap semiconductor, when integrated in a BLG-based heterostructure, thus shifting the direct-indirect band gap crossover to trilayer WSe2. In the monolayer limit, WSe2 shows a spin-splitting of 475 meV in the valence band at the K point, the largest value observed among all the MX2 (M = Mo, W; X = S, Se) materials. The exciton binding energy of monolayer-WSe2/BLG is found to be 0.21 eV, a value that is orders of magnitude larger than that of conventional three-dimensional semiconductors, yet small as compared to other two-dimensional transition metal dichalcogennides (TMDCs) semiconductors. Finally, our finding regarding the overall modification of the electronic structure by an alkali metal surface electron doping opens a route to further control the electronic properties of TMDCs.


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