Preparation And Raman Study Of Black Phosphorus In Thin Layer

As a new two-dimensional semiconductor material,black phosphorus（BP）is considered to have great potential applications in optoelectronic devices due to its direct band gap,anisotropy and carrier mobility.However,only thin-layer BP can play a role in optoelectronic devices.Therefore,this paper mainly focuses on the preparation of thin-layer black phosphorus and the use of Raman spectroscopy to explore the intrinsic characteristics and application performance of BP,as a reference for its further research and application in the future.The first part of this paper focuses on the preparation of high-quality and large-scale thin-layer BP by mechanical stripping method and studies its related properties.By analyzing the polarization curves under the condition of parallel polarization and vertical polarization,it is clear that the phase delay caused by birefringence occurs in both incident and scattered light during the Raman scattering of low symmetry crystal.To modify the classical Raman selection rule by considering birefringence effect,the anomalous angle dependent polarized Raman scattering of A_g mode in BP crystal is explained.Secondly,we have also used variable temperature Raman spectroscopy to study the interfacial thermal conductivity of BP.In the temperature range of 83K-513K,for the 3.2nm BP thin-layer samples,the temperature coefficientsχvalues of A_g¹,B_2g and A_g² modes are-0.0136 cm^-1/K,-0.0227 cm^-1/K and-0.0224 cm^-1/K,respectively.Meanwhile,χobtained by fitting other BP samples with different thicknesses is analyzed.We also analyze the differences between the temperature coefficient in this study and the related reference,which paves the way for further research on the thermomechanical applications of flexible BP nano devices.Finally,we use thin layer BP as an enhanced substrate to study its surface enhanced Raman scattering（SERS）performance.Using dye crystal violet（CV）and methylene blue（MB）as probe molecules,it was found that the Raman signal of CV and MB was enhanced obviously.The detection limit of CV can reach 10^-6（mol/L）,and the enhancement factor of CV molecule with concentration of10^-6 mol/L is 1.2×10².The enhancement mechanism is mainly due to the chemical enhancement contribution of charge transfer between substrate and molecule.In the second part of the work,we mainly explore the preparation of thin layer BP by liquid phase stripping method,hoping to be able to large-scale and efficient preparation and expand its application range.First of all,we selected six commonly used solvents and analyzed the stripping effect by TEM.It was found that DMF,DMSO and NMP of non-proton and polar solvents had better stripping effect on BP.In order to further improve the preparation efficiency,we also used the electrochemical intercalation stripping method for more efficient preparation,and explored the anode intercalation method and the cathode intercalation method,respectively.The results show that both of the two intercalation methods can obtain the stripped BP thin layer,but considering that BP as anode may involve the oxidation of BP,while in the cathode intercalation method,the solution of DMSO electrolyte with TBA⁺makes the BP interface covered by dissolved residual organic matter,which can avoid the oxidation degradation caused by contact with water and oxygen,and ensure the quality and stability of BP.Therefore,we think that the electrochemical cathode intercalation method is a feasible method with high efficiency and large-scale preparation.In conclusion,this work explored the preparation method of thin-layer BP,and systematically studied the anisotropy,interfacial thermal conductivity and SERS performance of BP by Raman spectroscopy,which laid a foundation for the large-scale preparation of thin-layer BP and its application in the fields of optoelectronic devices and flexible sensors.