Research On Preparation Of MoS₂ And Its Functional Devices

Molybdenum disulfide?MoS₂?is a kind of two-dimensional layered semiconductor material with graphene-like structure,and it has a natural turning band-gap.Owning to the quantum confinement effect,the single-layer MoS₂ exhibits many unique electronic and optical properties which is different from bulk materials.MoS₂ has been widely used in the fields of optics and electronics,and attracted much attention from the researchers.In this paper,the controllable preparation and application of MoS₂ materials are studied,the main contents are as follows:Different layers of MoS₂ were prepared by micromechanical stripping and characterized by optical microscopy and Raman spectroscopy.The size of the single layer MoS2 products are small,mostly from a few microns to tens of microns.High-purity MoS2nanosheets had been synthesized by thermal sulfuration method.The phase and morphology of the samples were characterized by X-ray diffraction,Raman spectrometer,scanning electron microscope and energy dispersive spectrometer,which were used to analyse the effects of reaction temperature on the MoS₂ nanosheets.The results show that the higher temperature is,the quality and dispersion of the MoS₂ is better,and the size tends to be larger.Layerd MoS₂ was prepared by CVD and its lays and crystal quality were characterized by optical microscopy,atomic force microscopy,Rama spectroscopy.The results showed that the products of MoS2 are single-layer and its size range from tens to hundreds of microns.The effects of substrate pretreatment,substrate placement,preparation temperature and time on the MoS₂ products were analyzed.It was found that the corrosion of the substrate by HF could increase the nucleation density of MoS₂,and the inclined substrate was favorable for the homogenization growth of MoS₂,and the growth temperature at 750?and time at 15 minutes were suitable.In this paper,the sensor based on MoS₂ nanosheets was prepared,and its photosensitivity and gas sensing properties were studied.It was found that the nanosheets was more sensitive to the green light than to the red,and the detection limit was 10 mW.High sensitivity and fast response/recovery time were observed in MoS₂ nanosheets device to methanol and ethanol.Gas molecules can form a strong adsorption on the MoS₂ surface and provide electrons to MoS₂,which leads to the Fermi level close to the conduction band and increases the carrier concentration,so that the conductivity of materials increases.Single-layer MoS₂ based on back gate field effect transistors was fabricated by photolithography and metal evaporation process.The electrode materials were Al and Au respectively,and the transistor characteristics were measured by semiconduct parameter.The effects of Al and Au electrodes on the performances of transistor were analyzed.Two kinds of metal-semiconductor contact types were found:Al-MoS₂ was schottky contact and Au-MoS₂ was ohmic contact.The total resistance of FETs were 10⁸ and 10⁶;the migration rates were 0.04 0.04 cm²/VS and 1.02 cm²/VS;on-off current ratio were 10³,which correspond to Al and Au electrodes FET respectively.The results indicate that Au is more suitable to be used as the contact electrode of MoS₂ based on devices compared with Al metal.