Computer Simulation Of Ge-As-Se Glass Structure At Different Temperature Across The Glass Transition

With the rapid development of the information era,computer simulation has already emerged in the fields of aerospace,military,medical,etc.,and is commonly used in new material design,properties analysis and prediction.Ge-As-Se material has attracted wide attention due to its extremely wide infrared transmission region and low phonon energy,excellent nonlinear quality factor and ultra-fast nonlinear response time.However,Ge-As-Se amorphous materials have suffered several structural problems such as structural relaxation,which deteriorate the performance of the chalcogenide-based optical/electrical devices and thus limits their commercial values.Therefore,the accurate description and characterization of Ge-As-Se material structure is very significant.Traditional experimental methods can provide some useful methods and means to recognize Ge-As-Se materials,however,there are still some limitations to get a full understanding the structure information of Ge-As-Se materials.And the complete process before and after the glass transition of Ge-As-Se materials can be fully characterized and understand the structure and properties of Ge-As-Se materials.In this thesis,we start from with neutron diffraction experimental data,and then use the Reverse Monte Carlo combined with the Molecular Dynamics simulation method to characterize and describe the structural information before and after Ge-As-Se glass transition,and briefly discuss the reasons for structural changes.Computational simulation of the experimental data has been demonstrated to be a useful tool to understand the glass structure.The specific research content and the results obtained are as follows.?1?We fabricated the glass and film samples of Ge₃As₂₄Se₇₃?Ge_11.5As₂₄Se_64.5?Ge₂₀As₂₄Se₅₆ by melt-quench and radio-frequency sputtering methods,respectively.The prepared Ge-As-Se samples are tested by traditional experimental methods and means,and the structures are qualitatively analyzed and characterized.The Ge-As-Se film samples are within the tolerance of the error and meet the target components in our research.The maximum transmission rate of Ge-As-Se film samples are all exceed 60%;The optical band gap of Ge-As-Se films are:0.52 eV,0.49 eV,0.46 eV.The optical band gaps are decreased as Ge content increases.There is no obvious crystallization in Ge-As-Se glass,it says that the quality of our glass samples are good;We compare the Raman spectroscopy between glass and film samples,it can conclude that the structure of Ge-As-Se film and glass are the same.?2?The structural changes of Ge-As-Se materials in the whole process before and after glass transition are studied.The structural information of Ge-As-Se materials was comprehensively and completely understood by the mechanism of structural change before and after the glass transition.Using neutron diffraction data,the changes in the structure of Ge-As-Se glass materials as a function of temperature were investigated.It can be seen intuitively that the structural factor S?Q?of neutron diffraction changes slowly,and it is speculated that it may be the change of local structures.Ge₃As₂₄Se₇₃ glass change in the same direction as the temperature change;It is not obvious for Ge_11.5As₂₄Se_64.5 glass as the temperature change;For Ge₂₀As₂₄Se₅₆6 glass,the structure is stable when the temperature is in glass transition and below.?3?We introduce two simulation methods:reverse Monte Carlo combined with experimental data and molecular dynamics simulation.We attempt to describe and characterize the structure of Ge-As-Se materials from microscopic scales such as atom bonding and bond angle distribution,and briefly explore the causes of structural changes.There happens a medium range order?MRO?in Ge₃As₂₄Se₇₃ glass before and after the glass transition,which is ascribed to homopolar As-As bonds;It is not sensitive to temperature changes for Ge_11.5As₂₄Se_64.5 glass a.The structure of Ge₂₀As₂₄Se₅₆ glass is stable within glass transition temperatures and below.In the end,we summarize the simulation work and make an outlook for the deficiencies,such as,we can take the repeated atoms on the boundary into consideration in our system segmentation program and optimize the segmentation process,make the segmentation result more reasonable;We can compare some more results of different temperature to get a more accurately description of the structural change before and after the glass transition.