[Paper Review] Epitaxial Growth and Electronic Properties of QuasiFreeStanding Rhombohedral WSe2 Bilayers on Cubic W110

Niels Chapuis, Meryem Bouaziz+7 more|arXiv (Cornell University)|Mar 5, 2026

2D Materials and Applications0 citations

TL;DR

Demonstrates epitaxial growth of rhombohedral 3R-WSe2 bilayers on cubic W(110) via selenium passivation, yielding quasi free-standing bilayers with indirect-gap electronic structure and significant spin-orbit splitting, analyzed by ARPES and DFT.

ABSTRACT

Rhombohedral-stacked transition metal dichalcogenides (TMDs) break inversion symmetry between adjacent layers, giving rise to an intrinsic out-of-plane ferroelectric polarization.Controlling the formation of this stacking polytype is therefore essential for harnessing ferroelectric effects in two-dimensional materials. In this work, we demonstrate the epitaxial growth of rhombohedral bilayer tungsten diselenide (3R-WSe2) on a cubic W(110) single crystal by molecular beam epitaxy. We show that selenium passivation of the substrate is key to enable a quasi van der Waals epitaxy effectively suppressing strong interfacial bonding and promoting the growth of quasi free standing bilayer films. The 3R stacking order is confirmed through a combination of Raman spectroscopy and high-resolution angle-resolved photoemission spectroscopy (ARPES), supported by density functional theory (DFT) calculations. ARPES and DFT reveal an indirect-gap electronic structure with the valence-band maximum at the Gamma point, as well as a pronounced spin orbit driven splitting of 520 +- 20 meV at the K point. Analysis of the measured dispersions yields hole effective masses of 0.46 +- 0.04 me and 0.75 +- 0.06 me for the upper and lower valence bands at K point, respectively. These results establish a robust route for synthesizing quasi free standing 3R-WSe2 and provide a platform for exploring the electronic, optical, and ferroelectric functionalities that emerge from inversion symmetry breaking in layered TMDs. Our findings further highlight the potential of cubic substrates for deterministic fabrication of rhombohedral TMD heterostructures and ferroelectric devices at the nanoscale.

Motivation & Objective

• Demonstrate epitaxial growth of rhombohedral WSe2 bilayers on a cubic W(110) substrate.
• Show that selenium passivation enables quasi van der Waals epitaxy and suppresses strong interfacial bonding.
• Confirm stacking order and investigate electronic structure and ferroelectric-related properties via spectroscopy and theory.

Proposed method

• Use molecular beam epitaxy to grow 3R-WSe2 bilayers on W(110).
• Apply selenium passivation to promote quasi van der Waals epitaxy and reduce interfacial bonding.
• Characterize stacking with Raman spectroscopy and high-resolution ARPES, supported by DFT calculations.
• Extract electronic structure features such as indirect gap with VBM at Gamma and spin-orbit splitting at K from ARPES and compare with DFT.

Experimental results

Research questions

• RQ1 Can rhombohedral 3R-WSe2 bilayers be epitaxially grown on cubic W(110) substrates?
• RQ2 Does selenium passivation enable quasi free-standing bilayer growth by suppressing interfacial bonding?
• RQ3 What is the stacking order and the electronic structure (gap, VBM, SOC splitting) of the grown bilayers?

Key findings

• 3R-WSe2 bilayers can be epitaxially grown on W(110) using selenium passivation.
• The growth yields quasi free-standing bilayers with rhombohedral stacking confirmed by Raman and ARPES and supported by DFT.
• The electronic structure is indirect-gap with the valence-band maximum at Gamma.
• A pronounced spin-orbit driven splitting of 520 ± 20 meV is observed at the K point.
• Hole effective masses are 0.46 ± 0.04 and 0.75 ± 0.06 for the upper and lower valence bands at K, respectively.