| Duing to unique physical properties,the two-dimensional?2D?transition metal compound materials have been widely used in the fields of the field effect transistors,light detectors,photovoltaic cells and so on.They also have become a research hotspot in condensed matter physics.This paper mainly introduces a typical example among these materials-molybdenum disulfide?MoS2?,it is composed of a single or multi atom model which has similar structure with the 2D layered graphene.Compared with the non-semiconductor material of graphene which has a zero band gap structure,the band gap of the semiconducting 2D Mo S2 can be controlled,leading to a broad application prospects in the field of optoelectronic devices.In this paper,we mainly studied the preparation of low-dimensional Mo S2 with three morphologies and Mo S2/Mo O2 mixed layers with two morphologies.Meanwhile,the morphology,structure and optical properties of the samples were characterized using the optical microscopy,atomic force microscopy,scanning electron microscopy,X-ray photoelectron spectroscopy,Raman spectra and photoluminescence spectra,.The MoS2 films with the morphologies of triangular shape,flower-shaped and dendrite shape were prepared by chemical vapor deposition and adjusting the sulfur concentration in the reaction process.Measurement results indicate that triangular Mo S2 flakes are single crystalline films with monolayer or few layers,the flower-shaped are polycrystalline structure with obvious boundary.Raman peak of Mo S2 with dendrite shape is consistent with that of the bulk Mo S2,and obvious photoluminescence peak was not observed.Thus,the concentration of sulfur in the process of chemical vapor deposition has a decisive influence on the morphology of Mo S2.we have synthesized the samples with the morphologies of rectangular and hexagonal by controlling the temperature of the substrates.X ray photoelectron spectroscopy,scanning electron microscopy,energy dispersive spectrum and Raman spectrum have been used to characterize the MoS2/Mo O2 mixed layers.But the results showed that when the value of the Raman peaks spacing increased,that is,the increase of the number of MoS2 layers,the change of the Photoluminescence wavelength of the mixed layers structure was not observed.We speculated that the interaction in the interface of the special mixed layers is the reason for the phenomenon.A further study is needed for detailed reasons.Meanwhile,we discussed the formation mechanism for these two kinds of morphologies.Through the methods of micro-mechanical cleavage,the single-layer Mo S2 have been prepared and verified by the photoluminescence spectra.Based on the theory of Fresnel's law,we investigated the contrast of single layer Mo S2 on Si O2/Si,Si and Mn Ga/GaAs in three kinds of different substrates at a given wavelength,respectively,and obtained the optimal thickness of the substrate corresponding to the best contrast,which has provided a theoretical guidance for our later experiments.Meanwhile,the layer number of samples obtained by this method is consistent with the results of photoluminescence spectrum,it shows that the contrast spectroscopy provides a rapid,convenient and non-destructive method to determine the thickness of samples. |
PDF Full Text Request