Experimental Study On The Thermal Conductivity Of Graphene And Its Heterostructure

Graphene is one of the most representative two-dimensional materials.It has super-high thermal conductivity,extremely high Young's modulus,super strength,high specific surface area,and excellent electrical conductivity.These excellent properties make it a promising material for thermal management devices,flexible electronics,and energy storage.However,in the production and application of devices,due to the influence of processing and working environment,graphene devices may produce strains and defects,which may seriously damage the structure of the device and affect the function realization and life of the device.Besides,the band gap of graphene is zero,which limits its application in semiconductors.Molybdenum disulfide has an electronic band gap covering the visible area,so the van der Waals heterostructure composed of single-layer graphene and molybdenum disulfide expands the application range of graphene.It is also important to study the thermal conductivity of heterostructure.Therefore,in this paper,the thermal conductivity of graphene and its heterostructure is experimentally studied,and the effects of temperature,thickness,and strain on the thermal conductivity of graphene and heterostructure are mainly analyzed.The main research contents of this thesis are summarized as follows:The monolayer graphene and molybdenum disulfide are prepared by mechanical exfoliation of highly oriented pyrolytic graphite and molybdenum disulfide crystals.The samples in the experiment were characterized by optical microscope,Raman spectroscopy,scanning electron microscopy,and atomic force microscopy.Besides,the transfer methods of graphene and heterostructure were improved,and the samples after transfer were characterized.The enhance transfer method was verified to improve the success rate of the sample transfer.A series of tests were performed on the thermal conductivity of graphene based on the photothermal Raman method.The effects of temperature and thickness on the thermal conductivity of graphene are briefly studied.The results show that the thermal conductivity of graphene decreases with increasing temperature and thickness.The effect of strain on the thermal conductivity of graphene is firstly studied through experiments.Experimental results demonstrate that,at 0.12%to 0.27%strains,the in-plane thermal conductivity of monolayer graphene is sensitive to the applied biaxial strains.Experimental results from different pore sizes indicate that tensile strain will reduce the thermal conductivity of graphene.The effect of temperature on the Raman spectrum of graphene/Mo S₂ heterostructure was studied by using a PRT-8A polarized melting point heating platform,and the temperature coefficient of the Raman spectra of heterostructure was measured.The thermal conductivity of graphene/Mo S₂ heterostructure and the influence of temperature on it were studied using the photothermal Raman method.The thermal conductivity obtained from the heterostructure2D characteristic peak is 28%lower at 350K compared to the single-layer graphene;the thermal conductivity obtained from the E¹_2g peak is increased by 56%and 16%,compared to that of the single-layer molybdenum disulfide at 350K and 500K,respectively.This study confirms the previous theoretical prediction that the thermal conductivity of monolayer graphene can be modified by temperature,thickness,and tensile strains.It also confirms that the heterostructure can retain the excellent thermal conductivity of its components.This work can provide experimental data and design basis on the future design of optothermal and electrothermal devices.