ABSTRACT
Two-dimensional (2D) heterostructures are more than a sum of the parent 2D materials, but are also a product of the interlayer coupling, which can induce new properties. In this paper, we present a method to tune the interlayer coupling in Bi2Se3/MoS2 2D heterostructures by regulating the oxygen presence in the atmosphere, while applying laser or thermal energy. Our data suggest that the interlayer coupling is tuned through the diffusive intercalation and deintercalation of oxygen molecules. When one layer of Bi2Se3 is grown on monolayer MoS2, an influential interlayer coupling is formed, which quenches the signature photoluminescence (PL) peaks. However, thermally treating in the presence of oxygen disrupts the interlayer coupling, facilitating the emergence of the MoS2 PL peak. Our density functional theory calculations predict that intercalated oxygen increases the interlayer separation â¼17%, disrupting the interlayer coupling and inducing the layers to behave more electronically independent. The interlayer coupling can then be restored by thermally treating in N2 or Ar, where the peaks will requench. Hence, this is an interesting oxygen-induced switching between "non-radiative" and "radiative" exciton recombination. This switching can also be accomplished locally, controllably, and reversibly using a low-power focused laser, while changing the environment from pure N2 to air. This allows for the interlayer coupling to be precisely manipulated with submicron spatial resolution, facilitating site-programmable 2D light-emitting pixels whose emission intensity could be precisely varied by a factor exceeding 200×. Our results show that these atomically thin 2D heterostructures may be excellent candidates for oxygen sensing.
ABSTRACT
Fiber-type composition and several stereological parameters of the levator ani (pubocaudal) muscle were evaluated in five nulliparous and five multiparous beagles using myosin ATPase-histochemistry and systematically selected muscle cross-sections. With respect to the narrow canine pelvic cavity, this study was also undertaken to determine whether vaginal birth of at least seven litters causes similar neuromuscular changes in the canine levator ani (pubocaudal) muscle analoguous to those seen in the pelvic floor muscles of women after vaginal delivery. The canine pubocaudal muscle is comprised of approximately equal amounts of slow twitch type I and fast twitch type II (IIA, IIS) fibers. The muscles of both the nulliparous and multiparous beagles did not display any signs indicative of denervation or myopathology. The multiparous dogs exhibited significantly increased mean absolute muscle (1720 mm(3)) and total fiber-type I volumes (850 mm(3)) as well as relevantly increased mean diameter of type I fibers (72.0 microm) when compared with the nulliparous group. The canine levator ani (pubocaudal) muscle is not pathologically affected by vaginal deliveries and seems to adapt to numerous successive pregnancies and births through fiber-type I hypertrophy.
