Inter-Layer Coupling Induced Valence Band Edge Shift in Mono- to Few-Layer MoS2

Abstract

Recent progress in the synthesis of monolayer MoS2, a two-dimensional direct band-gap semiconductor, is paving new pathways toward atomically thin electronics. Despite the large amount of literature, fundamental gaps remain in understanding electronic properties at the nanoscale. Here, we report a study of highly crystalline islands of MoS2 grown via a refined chemical vapor deposition synthesis technique. Using high resolution scanning tunneling microscopy and spectroscopy (STM/STS), photoemission electron microscopy/spectroscopy (PEEM) and μ-ARPES we investigate the electronic properties of MoS2 as a function of the number of layers at the nanoscale and show in-depth how the band gap is affected by a shift of the valence band edge as a function of the layer number. Green’s function based electronic structure calculations were carried out in order to shed light on the mechanism underlying the observed bandgap reduction with increasing thickness, and the role of the interfacial Sulphur atoms is clarified. Our study, which gives new insight into the variation of electronic properties of MoS2 films with thickness bears directly on junction properties of MoS2, and thus impacts electronics application of MoS2.

Electronic properties of atomically thin MoS2 layers grown by physical vapour deposition: band structure and energy level alignment at layer/substrate interfaces

“…42 The ML doping is likely to be ascribed to the high density of S vacancies, as evidenced in our XPS analysis (see Fig. 2).…”

Evolution of Metastable Defects and Its Effect on the Electronic Properties of MoS2 Films

“…Previous experiments on defects and their impact on electronic structure of monolayer MoS 2 were carried out primarily by scanning tunneling microscopy and spectroscopy and photoluminescence spectroscopy 20 – 22 . Changes of surface structure and tunneling spectra was observed at edges and grain boundaries with presence of mid-gap electronic states 23 , 24 .…”

“…Changes of surface structure and tunneling spectra was observed at edges and grain boundaries with presence of mid-gap electronic states 23 , 24 . This led to observation of both p-type and n-type doping with varying contact resistance in molybdenite and synthetic MoS 2 12 , 15 , 16 , 19 , 22 . Strong interactions with the substrate could also induce local spatial modulation of the density of states via local strain or local charge accumulation 25 .…”

Bidirectional heterostructures consisting of graphene and lateral MoS2/WS2 composites: a first-principles study

“…This is in good agreement with previous studies. 20,25,54 As a result, the electric properties of (MoS 2 ) X /(WS 2 ) 4ÀX monolayer with high W concentration become not stable under the electric eld and present different trend.…”

“…), are promising candidates for electronic devices because they have a direct band gap, high carrier mobility, high on/off current ratios, and unique exaction properties. 2,6,12,[16][17][18][19][20][21][22][23][24] Vertical heterostructures composed of a pristine TMDs monolayer and graphene have been the subject of extensive investigation. 2,10,[12][13][14][15][16]19,[25][26][27][28] Lateral heterostructures have been fabricated within TMD monolayers (MoS 2 /WS 2 , WS 2 /WSe 2 , MoSe 2 /WSe 2 , etc.)…”