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Spin splitting and strain in epitaxial monolayer WSe2 on graphene

DOI: 10.1103/PhysRevB.101.165103 DOI Help

Authors: H. Nakamura (Max Planck Institute for Solid State Research) , A. Mohammed (Max Planck Institute for Solid State Research) , Ph. Rosenzweig (Max Planck Institute for Solid State Research) , K. Matsuda (Max Planck Institute for Solid State Research; Nagoya University) , K. Nowakowski (Max Planck Institute for Solid State Research; University of Twente) , K. Küster (Max Planck Institute for Solid State Research) , P. Wochner (Max Planck Institute for Solid State Research) , S. Ibrahimkutty (Max Planck Institute for Solid State Research) , U. Wedig (Max Planck Institute for Solid State Research) , H. Hussain (Diamond Light Source) , J. Rawle (Diamond Light Source) , C. Nicklin (Diamond Light Source) , B. Stuhlhofer (Max Planck Institute for Solid State Research) , G. Cristiani (Max Planck Institute for Solid State Research) , G. Logvenov (Max Planck Institute for Solid State Research) , H. Takagi (Max Planck Institute for Solid State Research; University of Tokyo; University of Stuttgart) , U. Starke (Max Planck Institute for Solid State Research)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 101

State: Published (Approved)
Published: April 2020
Diamond Proposal Number(s): 18887

Open Access Open Access

Abstract: We present the electronic and structural properties of monolayer WSe 2 grown by pulsed-laser deposition on monolayer graphene (MLG) on SiC. The spin splitting in the WSe 2 valence band at ¯¯¯ K was Δ SO = 0.469 ± 0.008 eV, as determined by angle-resolved photoemission spectroscopy. Synchrotron-based grazing-incidence in-plane x-ray diffraction (XRD) revealed the in-plane lattice constant of monolayer WSe 2 to be a WSe 2 = 3.2757 ± 0.0008 Å. This indicates a lattice compression of − 0.19 % relative to bulk WSe 2 . By using the experimentally determined graphene lattice constant ( a MLG = 2.4575 ± 0.0007 Å), we found that a 3 × 3 unit cell of the slightly compressed WSe 2 is perfectly commensurate with a 4 × 4 graphene lattice with a mismatch below 0.03%, which could explain why the monolayer WSe 2 is compressed on MLG. From XRD and first-principles calculations, we conclude that the observed size of strain will affect Δ SO only on the order of a few meV. In addition, angle-resolved, ultraviolet, and x-ray photoelectron spectroscopies shed light on the band alignment between WSe 2 and MLG/SiC and indicate electron transfer from graphene to the WSe 2 monolayer. As further revealed by atomic force microscopy, the WSe 2 island size depends on the number of carbon layers on top of the SiC substrate. This suggests that the epitaxy of WSe 2 favors the weak van der Waals interactions with graphene, while it is perturbed by the influence of the SiC substrate and its carbon buffer layer.

Journal Keywords: Electronic structure; Spin-orbit coupling; Spintronics; Transition-metal dichalcogenide; Angle-resolved photoemission spectroscopy; First-principles calculations; Grazing incidence X-ray diffraction

Subject Areas: Materials, Physics


Instruments: I07-Surface & interface diffraction

Documents:
PhysRevB.101.165103.pdf