Junmin Xu

Construction of MoS2/Si nanowire array heterojunction for ultrahigh-sensitivity gas sensor

Few-layer MoS2 thin films were synthesized by a two-step thermal decomposition process. In addition, MoS2/Si nanowire array (SiNWA) heterojunctions exhibiting excellent gas sensing properties were constructed and investigated. Further analysis reveals that such MoS2/SiNWA heterojunction devices are highly sensitive to nitric oxide (NO) gas under reverse voltages at room temperature (RT). The gas sensor demonstrated a minimum detection limit of 10 ppb, which represents the lowest value obtained for MoS2-based sensors, as well as an ultrahigh response of 3518% (50 ppm NO, ∼50% RH), with good repeatability and selectivity of the MoS2/SiNWA heterojunction. The sensing mechanisms were also discussed. The performance of the MoS2/SiNWA heterojunction gas sensors is superior to previous results, revealing that they have great potential in applications relating to highly sensitive gas sensors.

High-performance self-powered deep ultraviolet photodetector based on MoS2/GaN p–n heterojunction

High-performances deep-ultraviolet (DUV) photodetectors (PDs) are highly desired due to their great importance in numerous fields. In this study, self-powered MoS2/GaN p–n heterojunction PDs were constructed, which exhibited high sensitivity to DUV light illumination and pronounced photovoltaic behaviours. Photoresponse analysis revealed a high responsivity of 187 mA W−1, a high specific detectivity of 2.34 × 1013 Jones, a high linear dynamic range of 97.3 dB and fast response speeds of 46.4/114.1 μs (5 kHz) under a DUV light of 265 nm at zero bias voltage without an external power supply. Moreover, the MoS2/GaN p–n heterojunction PD could operate with excellent stability and repeatability in a wide frequency range over 10 kHz. The high performance could be attributed to the enhancment by the built-in electric field in the heterojunction. It is expected that such high-performance self-powered DUV PDs will have great potential applications in the future.

Polarized emission effect realized in CH3NH3PbI3 perovskite nanocrystals

In this study, we present a detailed investigation of the optical properties of organic–inorganic hybrid perovskite CH3NH3PbI3 nanocrystals (NCs). Temperature-dependent steady-state and time-resolved photoluminescence (PL) measurements were employed to understand the optical transition mechanisms and carrier recombination dynamics of CH3NH3PbI3 NCs. X-ray diffraction results showed a structural phase transition from the tetragonal to orthorhombic phase states during a cooling process although the PL results at low temperature revealed no signs of orthorhombic phase related emission. We analyzed in detail the possible reasons from three perspectives. In addition to the exciton related emission, two trap-mediated exciton emissions appear at low temperatures of 180 and 100 K because of the smaller binding energies of trapped excitons than that of free excitons. The corresponding exciton binding energy, optical phonon energy, and temperature sensitivity coefficient of the bandgap for CH3NH3PbI3 NCs were extracted from the experimental data. More importantly, we demonstrated the linearly polarized emission from the as-synthesized CH3NH3PbI3 NCs, and a linear polarization degree of 0.28 was obtained. It is reasonably believed that our obtained results open up possibilities for the development of new generation displays by using novel perovskite NCs with a high polarization property.