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Monolayer molybdenum disulphide (MoS 2 ) has attracted much attention, due to its attractive properties, such as two-dimensional properties, direct bandgap, valley-selective circular dichroism, and valley Hall effect. However, some of its fundamental physical parameters, e.g. refractive index, have not been studied in detail because of measurement difficulties. In this work, we have synthesized highly crystalline monolayer MoS 2 on SiO 2 /Si substrates via chemical vapor deposition (CVD) method and devised a method to measure their optical contrast spectra. Using these contrast spectra, we extracted the complex refractive index spectrum of monolayer MoS 2 in the wavelength range of 400 nm to 750 nm. We have analyzed the pronounced difference between the obtained complex refractive index spectrum and that of bulk MoS 2 . The method presented here is effective for two-dimensional materials of small size. Furthermore, we have calculated the color contour plots of the contrast as a function of both SiO 2 thickness and incident light wavelength for monolayer MoS 2 using the obtained refractive index spectrum. These plots are useful for both fundamental study and device application.

Bipolar magnetic perturbations along the normal to the local magnetopause associated with field magnitude enhancements are signatures of typical flux transfer events (T‐FTEs) and are interpreted as evidence of encounters with magnetic flux ropes with strong core fields. If the field magnitude dips at the center of the signature, we identify the event as a crater FTE (C‐FTE). In the multiple‐spacecraft data of the Time History of Events and Macroscale Interactions During Substorms (THEMIS) between 1 May and 31 October 2007, we have identified 622 FTEs of which only 23 manifested C‐FTE signatures. We analyze a C‐FTE (30 July 2007) that evolved into a T‐FTE and compare its properties with those of a T‐FTE (May 20, 2007). For all 23 C‐FTEs and 35 confirmed T‐FTEs, we compare solar wind conditions and internal plasma and field properties. The similarity of solar wind properties for events in the two classes suggests that differences in their structures are not related to the solar wind conditions. Systematic differences in internal peak fields (BC‐FTE < BMagnetosphere < BT‐FTE) and averaged number densities (NT‐FTE < 0.5 × NMagnetosheath < NC‐FTE) between the two groups are consistent with the evolution of C‐FTEs into T‐FTEs. We propose that parallel flows inside C‐FTEs deplete the internal ion densities and reduce the thermal pressures as the central field magnitude increases to maintain pressure balance.

Engineering the substrate of 2D transition metal dichalcogenides can couple the quasiparticle interaction between the 2D material and substrate, providing an additional route to realize conceptual quantum phenomena and novel device functionalities, such as realization of a 12-time increased valley spitting in single-layer WSe through the interfacial magnetic exchange field from a ferromagnetic EuS substrate, and band-to-band tunnel field-effect transistors with a subthreshold swing below 60 mV dec at room temperature based on bilayer n-MoS and heavily doped p-germanium, etc. Here, it is demonstrated that epitaxially grown single-layer MoS on a lattice-matched GaN substrate, possessing a type-I band alignment, exhibits strong substrate-induced interactions. The phonons in GaN quickly dissipate the energy of photogenerated carriers through electron-phonon interaction, resulting in a short exciton lifetime in the MoS /GaN heterostructure. This interaction enables an enhanced valley helicity at room temperature (0.33 ± 0.05) observed in both steady-state and time-resolved circularly polarized photoluminescence measurements. The findings highlight the importance of substrate engineering for modulating the intrinsic valley carriers in ultrathin 2D materials and potentially open new paths for valleytronics and valley-optoelectronic device applications.

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Charge density of the VBM (green) and CBM (blue) for armchair MoS2–WS2 heterostructures, indicating the spontaneous separation of photo-generated electrons and holes, which could strongly enhance the photocatalytic activity due to suppression of the electron–hole recombination.

Data from the two-spacecraft Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun mission to the Moon have been exploited to characterize the lunar wake with unprecedented fidelity. The differences between measurements made by a spacecraft in the solar wind very near the Moon and concurrent measurements made by a second spacecraft in the near lunar wake are small but systematic. They enabled us to establish the perturbations of plasma density, temperature, thermal, magnetic and total pressure, field, and flow downstream of the Moon to distances of 12 lunar radii (R M ). The wake disturbances are initiated immediately behind the Moon by the diamagnetic currents at the lunar terminator. Rarefaction waves propagate outward at fast MHD wave velocities. Beyond~6.5 R M , all plasma and field parameters are poorly structured which suggests the presence of instabilities excited by counter-streaming particles. Inward flowing plasma accelerated through pressure gradient force and ambipolar electric field compresses the magnetic field and leads to continuous increase in magnitude of magnetic perturbations. Besides the downstream distance, the field perturbation magnitude is also a function of the solar wind ion beta and the angle between the solar wind and the interplanetary magnetic field (IMF). Both ion and electron temperatures increase as a consequence of an energy dispersion effect, whose explanation requires fully kinetic models. Downstream of the Moon, the IMF field lines are observed to bulge toward the Moon, which is unexpected and may be caused by a plasma pressure gradient force or/and the pickup of heavy charged dust grains behind the Moon.