Revealing unique energy level alignment at graphene/MoS₂ 2-dimensional layered junction using in situ ambient pressure x-ray photoelectron spectroscopy

Abstract

The chemical/electronic structures of a 2-dimensional (2D) molybdenum disulfide (MoS2) monolayer were characterized using ambient pressure x-ray photoelectron spectroscopy (APXPS) under various gas environments. APXPS results captured the binding energy shifts for the MoS2 chemical states that represent the electronic-structure of the 2D MoS2 monolayer in a real gas environment. The effect of the presence of a 2D graphene (Gr) layer on the properties of the 2D MoS2 layer was simultaneously characterized. When coating a Gr layer on the MoS2 layer, electron injection from MoS2 to Gr occurs due to the Schottky barrier at the interface. As a result, the Gr layer and MoS2 layer attain relatively more n-type and p-type characteristics, respectively, compared to when they exist separately. The hole-injection barrier, formed between the MoS2 layer and the SiO2 substrate, is lower by about 0.3 eV in the Gr/MoS2/SiO2 structure compared to that in the MoS2/SiO2 structure. This gap in the energy level alignments is stable so that there is no change in Ar, N2, O2, and CO2 environments. Taken together, our results not only present an appropriate methodology for fabricating 2D material-based device components, but also suggest the need for consideration of the charge transfer at the MoS2/Gr junction when applied to a practical device.

Effect of temperature on the first excited state splitting energy of the impurity magneto acoustic polaron in monolayer graphene

“…However, most researchs on graphene have focused on batteries [6,7], sensors [8,9], energy storage [10][11][12], and transport characteristics [13][14][15][16]. Among the characteristics that require further research, the electron phonon coupling [17][18][19] and energy level characteristics [20][21][22][23][24] are the most critical research directions, because it determines the ultimate limit of any electronic device [25] and the optical properties of the material [26][27][28]. Actually,, due to the nonpolar nature of graphene, the electron phonon coupling via the acoustic phonon is more important than that of electron optical phonon coupling, which is usually used for the investigations of energy level characteristics [29,30].…”