Single-Molecule Nanomechanical Properties Of Sulfur-Selenium Glass

Sulfur-selenium glass is widely used as optoelectronic materials and rechargeable battery materials,and great progress has been made in the study of its macroscopic properties.However,there is still little research on the microscopic conformation of chain molecules in sulfur-selenium glass,and the microstructure has a very significant influence on the properties of substances,so it is very necessary to study its molecular conformation.In this thesis,the single-chain structures of sulfur-selenium glass with different molar ratios have been studied by atomic force microscopy-based single-molecule force spectroscopy and quantum mechanical calculations.First,three kinds of molar ratios of sulfur-selenium glass（S₁Se₁,S₁Se₃,S₃Se₁）were synthesized according to the literature.Raman spectroscopy and electrochemistry analysis were used to characterize their macroscopic properties.Then,the single-chain mechanical properties of three kinds of sulfur-selenium glass were investigated in the nonpolar organic solvent-nonane,and their corresponding intrinsic elastic properties were obtained.Finally,quantum mechanical calculations were performed to calculate the theoretical elasticities of these three kinds of glass.By using a single-molecule theoretical model as the“bridge”,the calculated results were compared with the experimental normalized curves to determine the single-chain conformation of sulfur-selenium molecules in nonane.Based on the above discussion,this thesis mainly draws the following conclusions:（1）There are chain-like molecules in the synthesized sulfur-selenium glasses.According to the data obtained from the single-molecule force spectroscopy experiment,the length distribution of the single-molecule chain varies from tens to hundreds of nanometers;The force-extension curves obtained from the same sample can be superimposed well after normalization,indicating that the single-chain intrinsic elasticity of this sulfur-selenium glass is obtained.（2）This thesis investigates the theoretical elasticity of each glass chain molecular model（the four-atom planar zigzag conformation,the four-atom helical conformation,and the repeating unit model of the eight-atom planar zigzag conformation）using quantum mechanical ab initio calculations,and compares the results with the worm-like chain model.Then,the calculated fitting force-extension curves of the three ratios of S-Se glass molecular models were obtained.Comparing the theoretical calculation results with the experimental normalization curves,it is known that among the three kinds of glass inorganic chain molecules,the fitting curve of the planar four-atom zigzag conformation can well coincide with the experimental curve,and the other two models do not coincide with the experimental results;（3）The average deviation between the four-atom plane zigzag conformation fitting curves and the experimentally normalized force-extension curves of the three kinds of sulfur-selenium glass have been calculated,respectively.The optimal persistence lengths（l_p）of S₁Se₁,S₁Se₃,and S₃Se₁ are estimated to be 0.295,0.330,and 0.270 nm.They are all larger than the bond lengths of S-S bond,S-Se bond and Se-Se bond,which indicates that the chain-like molecules of the three glasses may be rigid molecules.