Observation of Strong Interlayer Couplings in WS2/MoS2 Heterostructures via Low-Frequency Raman Spectroscopy

Abstract

Van der Waals (vdW) heterostructures based on two-dimensional (2D) transition metal dichalcogenides (TMDCs), particularly WS2/MoS2 heterostructures with type-II band alignments, are considered as ideal candidates for future functional optoelectronic applications owing to their efficient exciton dissociation and fast charge transfers. These physical properties of vdW heterostructures are mainly influenced by the interlayer coupling occurring at the interface. However, a comprehensive understanding of the interlayer coupling in vdW heterostructures is still lacking. Here, we present a detailed analysis of the low-frequency (LF) Raman modes, which are sensitive to interlayer coupling, in bilayers of MoS2, WS2, and WS2/MoS2 heterostructures directly grown using chemical vapor deposition to avoid undesirable interfacial contamination and stacking mismatch effects between the monolayers. We clearly observe two distinguishable LF Raman modes, the interlayer in-plane shear and out-of-plane layer-breathing modes, which are dependent on the twisting angles and interface quality between the monolayers, in all the 2D bilayered structures, including the vdW heterostructure. In contrast, LF modes are not observed in the MoS2 and WS2 monolayers. These results indicate that our directly grown 2D bilayered TMDCs with a favorable stacking configuration and high-quality interface can induce strong interlayer couplings, leading to LF Raman modes.

Observation of the photovoltaic effect in a van der Waals heterostructure

“…According to the procedure reported in previous work, multilayer WS 2 and MoS 2 flakes were mechanically exfoliated on SiO 2 /Si (270 nm) substrates and transferred to form vdWSs by the dry method with polymer stamps. 15 Raman spectra obtained with 532 nm excitation show the E 1 2g and A 1g peaks of WS 2 and MoS 2 , located at 354 cm −1 ,421.5 cm −1 and 384 cm −1 , 408.5 cm −1 respectively, 16 consistent with the multilayer structure (see ESI, Fig. S1 †).…”

Carrier Transport Properties in Few-Layer WS0.3Se1.7/(WOx)WS0.3Se1.7 Lateral p+–n Junctions Using a Metal–Oxide–Semiconductor Field-Effect Transistor (MOSFET) Structure

“…Additionally, XPS analysis indicated that the few-layer WS x , after selenization at 600 °C for 2400 s, showed an almost stoichiometric composition of WS 0.3 Se 1.7 (Figure S1), while the Stokes and anti-Stokes Raman spectra indicated 5–6 (few-layer) stacked layers for both WS 0.3 Se 1.7 and WS 2 (Figures S2 and S3). − In addition, the XRD pattern of WS 0.3 Se 1.7 shows peaks at 14.20° and 61.82° in agreement with the (002) and (112) diffraction planes with narrow full width at half-maximum (FWHM ∼ 0.2°) for the WSe 2 and WS 2 , respectively, whereas the hexagonal structure film formation indicated by the appeared peak of (002) (Figure S4). Figure b shows the schematic of the FET device structure and PL map image of the plasma-jet exposed area between the S/D electrodes (with a jet spot area of ∼8.0 μm 2 ).…”

Transition metal dichalcogenide electrodes with interface engineering for high-performance hybrid supercapacitors

“…Two major bands of A 1g and E 2g are observed that are traditionally observed in WS 2 . 38 Fig. 2a represent the SEM image of NF sputtered with pure WS 2 .…”