Deterministic direct growth of WS₂ on CVD graphene arrays

Abstract

The combination of the exciting properties of graphene with those of monolayer tungsten disulfide (WS2) makes this heterostack of great interest for electronic, optoelectronic and spintronic applications. The scalable synthesis of graphene/WS2 heterostructures on technologically attractive substrates like SiO2 would greatly facilitate the implementation of novel two-dimensional (2D) devices. In this work, we report the direct growth of monolayer WS2 via chemical vapor deposition (CVD) on single-crystal graphene arrays on SiO2. Remarkably, spectroscopic and microscopic characterization reveals that WS2 grows only on top of the graphene crystals so that the vertical heterostack is selectively obtained in a bottom-up fashion.Spectroscopic characterization indicates that, after WS2 synthesis, graphene undergoes compressive strain and hole doping. Tailored experiments show that such hole doping is caused by the modification of the SiO2 stoichiometry at the graphene/SiO2 interface during the WS2 growth. Electrical transport measurements reveal that the heterostructure behaves like an electron-blocking layer at large positive gate voltage, which makes it a suitable candidate for the development of unipolar optoelectronic components.

Edge Defects Promoted Oxidation of Monolayer WS2 Synthesized on Epitaxial Graphene

“…The presence of oxygen in the as grown sample can be due to unreacted WO 3 residuals. 39 With an increase in the aging time, the sulfur peak completely vanishes; meanwhile the oxygen peak increases in intensity revealing that an oxidation of WS 2 MLs has occurred.…”

“…Figure d shows EDS spectra at different aging steps: the as-grown WS 2 MLs spectrum (red line) presents two large peaks, due to silicon and carbon (related to the SiC substrate), and two faint peaks related to the oxygen Kα (0.525 keV) and to the sulfur Kα (2.309 keV). The presence of oxygen in the as grown sample can be due to unreacted WO 3 residuals . With an increase in the aging time, the sulfur peak completely vanishes; meanwhile the oxygen peak increases in intensity revealing that an oxidation of WS 2 MLs has occurred.…”

Interlayer Energy Transfer and Photoluminescence Quenching in MoSe2/Graphene van der Waals Heterostructures for Optoelectronic Devices

“…Thus, photoinduced electron doping from MoSe 2 to graphene via interlayer coupling is negligible. 17,30,31 Interestingly, the fwhm of the 2D peak is broader in the GM region (37 cm −1 ) than in the graphene-only region (32 cm −1 ; Figure S4d), indicating that the contact with the smaller MoSe 2 domains caused the change in the local strain of graphene, which induced perturbation of the intervalley phonon scattering. 32 Figure 3d shows the PL mapping image obtained at the band-edge emission of MoSe 2 upon 532 nm excitation.…”

Synthesis and characterization of WS2/graphene/SiC van der Waals heterostructures via WO3−x thin film sulfurization

“…5 with the spectrum of epitaxial graphene before WS 2 synthesis presented in the top right. The 532 nm excitation used to acquire the spectrum is in resonance with the B exciton of WS 2 which produces a series of combination modes in addition the in-plane and out-of-plane vibrational modes 43 , 50 – 52 . The A 1g (G) peak at 419 cm −1 corresponds to an out-of-plane vibration of S atoms in the S-W-S stack.…”