Interface engineering is a key strategy to deal with the two-dimensional (2D)/three-dimensional (3D) hybrid heterostructure, since the properties of this atomic-layer-thick 2D material can easily be impacted by the substrate environment. In this work, the structural, electronic, and optical properties of the 2D/3D heterostructure of monolayer MoS on wurtzite GaN surface without and with nitridation interfacial layer are systematically investigated by first-principles calculation and experimental analysis. The nitridation interfacial layer can be introduced into the 2D/3D heterostructure by remote N plasma treatment to GaN sample surface prior to stacking monolayer MoS on top. The calculation results reveal that the 2D/3D integrated heterostructure is energetically favorable with a negative formation energy. Both interfaces demonstrate indirect band gap, which is a benefit for longer lifetime of the photoexcited carriers. Meanwhile, the conduction band edge and valence band edge of the MoS side increases after nitridation treatment. The modification to band alignment is then verified by X-ray photoelectron spectroscopy measurement on MoS/GaN heterostructures constructed by a modified wet-transfer technique, which indicates that the MoS/GaN heterostructure without nitridation shows a type-II alignment with a conduction band offset (CBO) of only 0.07 eV. However, by the deployment of interface nitridation, the band edges of MoS move upward for ∼0.5 eV as a result of the nitridized substrate property. The significantly increased CBO could lead to better electron accumulation capability at the GaN side. The nitridized 2D/3D heterostructure with effective interface treatment exhibits a clean band gap and substantial optical absorption ability and could be potentially used as practical photocatalyst for hydrogen generation by water splitting using solar energy.

Linear magneto-resistance is observed in high magnetic field in topological insulator Bi 2 Se 3 films. As revealed by tilted magnetic field measurement, this linear magneto-resistance is associated with the gapless topological surface states and of quantum origin. In the ultra-thin limit, the inter-surface tunneling induced surface state gap opening quenches the linear magneto-resistance. Instead, weak negative magneto-resistance is observed in high magnetic fields in ultra-thin films.

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A linear magnetoresistance (LMR) with strong temperature dependence and peculiar non-symmetry with respect to the applied magnetic field is observed in high-index (221) Bi 2 Se 3 films. Different from the LMR observed in the previous studies which emphasize the role of gapless linear energy dispersion, this LMR is of disorder origin and possibly arises from the electron surface accumulation layer of the film. Besides, an abnormal negative magneto-resistance that shows a non-monotonic temperature dependence and persists even at high temperatures and in strong magnetic fields is also observed. V

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The threshold voltage (VT) instability of metal‐insulator‐semiconductor high electron mobility transistors (MIS‐HEMTs) is investigated. In the enhancement‐mode AlGaN/GaN MIS‐HEMT fabricated by fluorine plasma implantation technique featuring Al2O3 gate dielectric, a hysteresis of 0.6 V in transfer characteristics is observed by quasi‐static I ‐V (current‐voltage) measurement, in which the gate bias is swept at a low rate (0.7 V/s). Pulsed transfer characteristics measurement, however, unveils much larger hysteresis under the same gate voltage swing. The VT‐instability is attributed to the traps located at the dielectric/III‐nitride interface as well as in the bulk of gate dielectric. It is proposed that pulsed measurement can count for the effect of fast traps (shallow traps) while the quasi‐static measurement can only reflect slow traps (deep traps), and is more accurate for VT‐instability evaluation. In addition, the existence of bulk traps is implied by a slow time‐dependent shift of VT under large gate bias. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The metal nanoparticle size and shape impact the plasmonic enhancement of Raman and photoluminescence (PL) spectra of monolayer and few-layer MoS2 decorated with them. The plasmonic enhancement is investigated for Ag nanotriangles (NTs or nanoprisms) of different sizes in comparison to Ag nanospheres (NSs) at room temperature. After the decoration with Ag NTs, the intensity of both Raman modes of MoS2 increases up to 6.8 times. The μ-PL spectra of bare MoS2 show the presence of the A and B exciton bands as well as of a weak trion component. After covering the flakes with 50 nm Ag NTs, the highest integrated PL enhancement factors are 2.9 and 2.1 under 532 and 405 nm excitations, respectively. The revealed shape effect is that Ag NTs provide much stronger Raman and exciton emission enhancement than Ag NSs, which is due to the generation of plasmonic hot spots near the sharp edges and tips of NTs. Another mechanism of enhancement is the plasmonic coupling between the neighboring Ag NTs that causes the generation of hot spots in the gap between NTs. The revealed size effect is a decrease of Raman and PL enhancement with an increase in size of Ag NTs or NSs, which is due to an increase in radiative damping of plasmon oscillation occurring with an increase in nanoparticle size. The important feature is a strong enhancement of the A– trion component after decorating MoS2 with Ag nanoparticles. The phenomenon may be explained by the surface-plasmon-mediated generation of hot electrons in Ag nanostructures, which then inject to MoS2 flakes. This work gives new fundamental insights into the physical mechanisms of light–matter coupling in hybrid two-dimensional (2D) semiconductor/plasmonic nanoparticle structures, which are highly promising for next-generation optoelectronic and nanophotonic devices.

Harvesting solar energy for artificial photosynthesis is an emerging field in alternative energy research. In this work, the photocatalytic properties of InX(X=S, Se)/transition-metal disulfides (MoS2 and WS2) van der Waals...