An optoelectronic diode based on a p–n junction is one of the most fundamental device building blocks with extensive applications. Compared with graphene, layered transition-metal dichalcogenides demonstrate promising applications in novel valley-electronics and opto-electronics. Here we reported the fabrication and optoelectronic properties of a single multilayer MoS₂ sheet. Our results indicate that the thin MoS₂ shows a linear transport property while thick MoS₂ shows diode characteristics with well-defined current rectification behavior. We assign that the rectification behavior is due to the formation of a p–n junction in the single multilayer MoS₂ piece. The intrinsic defects in MoS₂ can change the conduction polarity, such as: sulfur vacancies contribute to the n-type behavior while sulfur interstitials and molybdenum vacancies contribute to the p-type conduction. The variation of intrinsic defects and stoichiometry is obvious over the micrometer range in thick MoS₂. The fabricated MoS₂ transistors were assessed under bias and gate voltage modulation when exposed to red, green and UV light under vacuum. The multilayer MoS₂ shows dominant p-type behavior under dark conditions while its shows dominant n-type conduction under light illumination. In addition, this MoS₂ phototransistor shows an evident photovoltaic effect. The open-circuit voltage (V_oc) and short-circuit current (I_sc) are observed to be −0.48 V and 494 nA under red illumination. These results demonstrate the potential application of a single multilayer MoS₂ sheet in optoelectronics, such as light-emitting diodes (LEDs), field-effect photovoltaic cells and photodetectors.

Eight-dimensional (8D) transition-state wave packet simulations have been performed on two latest potential energy surfaces (PES), the Zhou-Fu-Wang-Collins-Zhang (ZFWCZ) PES [Y. Zhou, B. Fu, C. Wang, M. A. Collins, and D. H. Zhang, J. Chem. Phys. 134, 064323 (2011)] and the Xu-Chen-Zhang (XCZ)-neural networks (NN) PES [X. Xu, J. Chen, and D. H. Zhang, Chin. J. Chem. Phys. 27, 373 (2014)]. Reaction rate constants for both the H+CH₄ reaction and the H₂+CH₃ reaction are calculated. Simulations of the H+CH₄ reaction based on the XCZ-NN PES show that the ZFWCZ PES predicts rate constants with reasonable high accuracy for low temperatures while leads to slightly lower results for high temperatures, in line with the distribution of interpolation error associated with the ZFWCZ PES. The 8D H+CH₄ rate constants derived on the ZFWCZ PES compare well with full-dimensional 12D results based on the equivalent m-ZFWCZ PES, with a maximum relative difference of no more than 20%. Additionally, very good agreement is shown by comparing the 8D XCZ-NN rate constants with the 12D results obtained on the ZFWCZ-WM PES, after considering the difference in static barrier height between these two PESs. The reaction rate constants calculated for the H₂+CH₃ reaction are found to be in good consistency with experimental observations.