Phonon modes and photonic excitation transitions of MoS2 induced by top-deposited graphene revealed by Raman spectroscopy and photoluminescence

Abstract

Although the MoS2/graphene 2D stack achieved a lot of attention in recent research on 2D semiconductor devices, the interface interaction between perfect MoS2 and graphene and its effects on the electronic properties are rarely studied. Here, we report our recent studies on Raman spectroscopy and photoluminescence of the MoS2/graphene heterostructure. A nearly perfect interface between these two materials was achieved with a dry transfer and forming gas annealing. Raman spectroscopy of the heterostructure shows that the strong interface interaction leads to blue-shifts of Raman modes in MoS2 and graphene. Moreover, indicated by the photoluminescene of the heterostructure, the photon excitation and electronic dynamics of MoS2 are significantly influenced by the additional graphene layer on top. Our results reveal that the interface of heterostructures plays an important role in determining the physical properties, and it is better to view the heterostructure as a newly emerging material rather than a simple physical combination of the two materials.

Synthesis, Characterization, and Typical Application of Nitrogen‐Doped MoS2 Nanosheets Based on Pulsed Laser Ablation in Liquid Nitrogen

“…[58] The Δ values of 18.4, 21.6, 23.4, and 25.5 cm À1 are characterized for monolayer, bilayer, trilayer, and bulk MoS 2 , respectively. [59] Here, the Raman data of N-doped MoS 2 and undoped MoS 2 attest to the evidence of trilayer and bilayer NSs according to Δ ¼ 23.4 cm À1 and Δ ¼ 21.1 cm À1 , respectively, in agreement with previous articles. [19,59,60] The discrepancy in the Raman mode frequencies attributes to the local thickness variations.…”

Exciton landscape in van der Waals heterostructures

“…The relative intensity of the two predicted phonon sidebands favoring the lower one agrees well with the experimental observation. An indirect dark exciton has also been observed in MoS 2 -MoS 2 [23,49] and WSe 2 -WSe 2 [26,49] located about 300 meV and 200 meV below the bright exciton, respectively -in a very good agreement with our results summarized in Table I. Similar observations have been made also for WS 2 -WS 2 including a peak roughly 200 meV below the K-K exciton [25].…”

“…1. Previous studies on interlayer excitons have been conducted, focusing mostly on their optical signatures [22][23][24][25][26]. However, the crucial question about the spectral position and ordering of bright and dark exciton states is still debated.…”

A Steep-Slope MoS2/Graphene Dirac-Source Field-Effect Transistor with a Large Drive Current

“…The frequency difference between the two modes is ∼24 cm −1 , indicating that it is a trilayer MoS 2 . 29,30 Figure 2c is the TEM image and the detailed EDS elemental map of the source region of the device where Gr is located above the MoS 2 channel, and the Gr/MoS 2 heterostructure is sandwiched between the top hBN encapsulating layer and the bottom hBN gate dielectric. As shown in the TEM image, the top and bottom hBN have a similar thickness of around 5 nm, and MoS 2 and Gr are trilayer and monolayer, respectively.…”

“…Meanwhile, the intensity ratio of 2D to G peak is ∼2.46 and the 2D band shows a single Lorentzian curve with a full width at half-maximum of ∼28.27 cm –1 , which indicates that it is a monolayer Gr. , The MoS 2 exhibits the E 2g 1 peak at ∼383.1 cm –1 and A 1g peak at ∼407.1 cm –1 . The frequency difference between the two modes is ∼24 cm –1 , indicating that it is a trilayer MoS 2 . , Figure c is the TEM image and the detailed EDS elemental map of the source region of the device where Gr is located above the MoS 2 channel, and the Gr/MoS 2 heterostructure is sandwiched between the top hBN encapsulating layer and the bottom hBN gate dielectric. As shown in the TEM image, the top and bottom hBN have a similar thickness of around 5 nm, and MoS 2 and Gr are trilayer and monolayer, respectively.…”