Abstract
Photoluminescence measurements in mono- and bilayer-MoS2 on SiO2 were undertaken to determine the thermal effect of the MoS2/SiO2 interface on the optical bandgap. The energy and intensity of the photoluminescence from monolayer MoS2 were lower and weaker than those from bilayer MoS2 at low temperatures, whilst the opposite was true at high temperatures above 200 K. Density functional theory calculations suggest that the observed optical bandgap crossover is caused by a weaker substrate coupling to the bilayer than to the monolayer.
Highlights
The discovery of unique transport properties of graphene prepared by mechanical exfoliation has spurred many new research activities for future electronic devices because of graphene’s intriguing energy band structure and high carrier mobility[1,2,3]
Note that when MoS2 layers lie on a substrate, each layer undergoes a different strain between the substrate and the MoS2 layers because the first layer of MoS2 is in direct contact with the substrate, whilst the other layers interact weakly due to van der Waals bonding between the MoS2 layers, which can affect the optical transition between the 1L-MoS2 and the other layers
Correspondence and requests for materials should be addressed to R.A.T. or H.I. or G.L. www.nature.com/scientificreports/
Summary
The discovery of unique transport properties of graphene prepared by mechanical exfoliation has spurred many new research activities for future electronic devices because of graphene’s intriguing energy band structure and high carrier mobility[1,2,3]. MoS2 can provide both indirect and direct bandgap transitions depending on the layer thickness[4,5,6]. A monolayer (1 L) of MoS2 (1L-MoS2) is a direct gap semiconductor with a band gap of 1.8~1.9 eV at the K-points of the 2D hexagonal Brillouin zone, whereas bulk MoS2 is an indirect semiconductor with a band gap of ~1.2 eV4–6. These findings have boosted the development of 2D materials for high-performance flexible electronic and optoelectronic devices[7,8]. In order to explain this phenomenon, density functional theory (DFT) calculations are performed taking into account the thermal expansion at the MoS2/SiO2 interface
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