Indirect Band Gap in Scrolled MoS2 Monolayers
Jeonghyeon Na, Changyeon Park, Chang Hoi Lee, Won Ryeol Choi, Soo Ho Choi, Jae‐Ung Lee, Woochul Yang, Hyeonsik Cheong, E. E. B. Campbell, Sung Ho Jhang
Abstract
MoS2 nanoscrolls that have inner core radii of ∼250 nm are generated from MoS2 monolayers, and the optical and transport band gaps of the nanoscrolls are investigated. Photoluminescence spectroscopy reveals that a MoS2 monolayer, originally a direct gap semiconductor (∼1.85 eV (optical)), changes into an indirect gap semiconductor (∼1.6 eV) upon scrolling. The size of the indirect gap for the MoS2 nanoscroll is larger than that of a MoS2 bilayer (∼1.54 eV), implying a weaker interlayer interaction between concentric layers of the MoS2 nanoscroll compared to Bernal-stacked MoS2 few-layers. Transport measurements on MoS2 nanoscrolls incorporated into ambipolar ionic-liquid-gated transistors yielded a band gap of ∼1.9 eV. The difference between the transport and optical gaps indicates an exciton binding energy of 0.3 eV for the MoS2 nanoscrolls. The rolling up of 2D atomic layers into nanoscrolls introduces a new type of quasi-1D nanostructure and provides another way to modify the band gap of 2D materials.