Optical identification of interlayer coupling of graphene/MoS_(2) van der Waals heterostructures

The interlayer coupling in van der Waals(vdW)heterostructures(vdWHs)is at the frontier of the fundamental research,underlying many optical behaviors.The graphene/MoS_(2) vdWHs provide an ideal platform to reveal the good interfacial coupling between graphene and MoS_(2) constituents.Here,three groups of graphene/MoS_(2) vdWHs were prepared by transferring 1–3 layers of graphene onto monolayer MoS_(2).The interlayer coupling within graphene/MoS_(2) vdWHs were characterized and analyzed by Raman spectroscopy,photoluminescence(PL)spectroscopy and optical contrast(OC)spectroscopy.The upshift of the A_(1g) peak of MoS_(2) and the upshift of the D and 2D peaks of SLG show that the electrons move from MoS_(2) to graphene accompanied by the dielectric shielding effect on graphene.The weakened PL intensities and the slight red shift of A peak prove that the electrons move from MoS_(2) to graphene meanwhile the recombination of hole and electron pairs is blocked in vdWHs.Our results deepen the understanding of the interlayer coupling of graphene/MoS_(2) vdWHs and therefore provide guidelines for the practical design and application of optoelectronic devices based on graphene/MoS_(2) vdWHs.

Structural, Optical, and Ferroelectric Behaviors of Cu_(1-x)Li_xO(0≤x≤0.09) Nanostructures

We report structural, optical, and ferroelectric behaviors of lithium-doped copper oxide （CU1-xLixO with x = 0.0, 0.05, 0.07, and 0.09） nanostructures synthesized by hydrothermal method. The XRD pattern indicates the pure phase formation of CuO without any impurity, and the crystallite size is found to be increases for x = 0-0.07 and decreases for x = 0.09. FESEM analysis shows that the average size of Cul xLixO nanostructures increases with the increasing the Li-doping concentrations up to 7% and then decreases for 9% Li doping concentration. Moreover, Raman and photoluminescence spectrum also confirm the phase formation of CuO. A significant reduction in optical band gap is observed up to x = 0.07, and then band gap increases for x ~ 0.09 due to segregation of the impurities on the surface or grain boundaries, which may suppress the grain growth and results the enhancement in optical band gap. Moreover, a weak ferroelectricity is observed in CuO nanostructures for pure and 9% Li doping through polarization versus electric field （P- E）.