Interfacial Interactions in van der Waals Heterostructures of MoS₂ and Graphene

Abstract

Interfacial coupling between neighboring layers of van der Waals heterostructures (vdWHs), formed by vertically stacking more than two types of two-dimensional materials (2DMs), greatly affects their physical properties and device performance. Although high-resolution cross-sectional scanning tunneling electron microscopy can directly image the atomically sharp interfaces in the vdWHs, the interfacial coupling and lattice dynamics of vdWHs formed by two different types of 2DMs, such as semimetal and semiconductor, are not clear so far. Here, we report the ultralow-frequency Raman spectroscopy investigation on interfacial couplings in the vdWHs formed by graphene and MoS flakes. Because of the significant interfacial layer-breathing couplings between MoS and graphene flakes, a series of layer-breathing modes with frequencies dependent on their layer numbers are observed in the vdWHs, which can be described by the linear chain model. It is found that the interfacial layer-breathing force constant between MoS and graphene, α(I) = 60 × 10 N/m, is comparable with the layer-breathing force constant of multilayer MoS and graphene. The results suggest that the interfacial layer-breathing couplings in the vdWHs formed by MoS and graphene flakes are not sensitive to their stacking order and twist angle between the two constituents. Our results demonstrate that the interfacial interlayer coupling in vdWHs formed by two-dimensional semimetals and semiconductors can lead to new lattice vibration modes, which not only can be used to measure the interfacial interactions in vdWHs but also is beneficial to fundamentally understand the properties of vdWHs for further engineering the vdWHs-based electronic and photonic devices.

The influence of two-dimensional organic adlayer thickness on the ultralow frequency Raman spectra of transition metal dichalcogenide nanosheets

“…When the thickness of acetone adlayer was 0.5 nm, it could be comparable to that of monolayer graphene and might induce red shift of ULF breathing mode. When MoS 2 nanosheet was put on few-layer graphene (2L-5L), coexistence of red and blue shift of ULF breathing mode was also observed [47]. Meanwhile, coexistence of red and blue shift of ULF breathing mode was also observed in our results, implying the organic adlayers play similar role in affecting the ULF breathing modes of MoS 2 nanosheets to those of graphene layers.…”

“…The red shift of ULF breathing mode in MoS 2 nanosheet was also observed in heterostructures of MoS 2 and graphene [47], which was attributed to the interfacial interaction between MoS 2 and graphene. As previously reported, organic molecules such as THF and cyclohexane can form crystal-like adlayers in the confined space between graphene and mica substrate [24].…”

“…Theoretical simulation indicated that THF adlayer still exhibited solid-like behavior as the thickness increased [28]. Our previous report showed that even monolayer graphene can induce red shift of ULF breathing mode in MoS 2 nanosheet [47]. After being incubated in acetone environment for a certain time, the intercalated acetone adlayer can be considered as substrate for MoS 2 instead of the beneath SiO 2 substrate.…”

Decoupling the Interaction between Wet‐Transferred MoS2 and Graphite Substrate by an Interfacial Water Layer

“…According to the published references, the vacancy defects can induce an n‐doping effect to MoS 2 , while the adsorbed water molecules can weaken the n‐doping effect . The enhanced n‐doping effect in dry‐transferred MoS 2 is also evidenced by the apparent downshift of the A 1g peak in the Raman spectra (Figure g), which is also sensitive to electron doping . Briefly, the water monolayer trapped at the interface of wet‐transferred MoS 2 /HOPG acts as an insulating layer for tuning the dielectric environment of interface and the electronic property or bandgap of the MoS 2 overlayer.…”

Enhanced Lithium Storage Performance of Liquid‐Phase Exfoliated Graphene Supported WS2 Heterojunctions

“…A high concentraton of LEGr in NMP faciliates the construction of new LEGr@WS 2 heterojunctions by a one‐pot mirowave‐assisted solvothermal method. Due to the existence of the van der Waals interfacial interaction between WS 2 and LEGr,, the LEGr layer not only serves as a substrate to grow WS 2 but also serves as a mini‐current collector for the rapid transport of electrons in the anode. The mass loading of WS 2 on LEGr is optimized by the variation in the sulfur and WCl 6 concentrations.…”