| Due to the dominating role played by the charged particles in the field of radiation damage in materials,the accurate modeling of transporting and damage generation of charged particles in solids can profoundly benefit the research of radiation damage.As the two kinds of charged particles used most widely in damage research,ions and electron are carefully treated in the study of this dissertation.The most important achievement of the study is the DEEPER(damage creation and particle transport in matter)code system,which can be used to model both transporting and damage generation of ions and electrons by applying Monte Carlo method and reliable theoretic models.The study was also extended to the displacement cross section of low-dimensional carbon nano structures,the validation and verification of applying back-scattering electron in SEM to characterize the voids in materials,the fast calculation of damage in thin samples radiated by electrons and the multi-scale modeling of evolution of the defects induced by various kinds of charged particles in pure iron samples.The theoretical basics of this dissertation are the damage theory of radiation and the models describing the interaction between charged particles and materials.The damage theory of radiation in materials,based on the concepts of PKA(Primary knock-on atom)and DPA(displacement per atom),has shown great power in calibrating the radiation experiments,making damage equivalent induced by different types of particles and multi-scale modeling of damage accumulation and evolution.In the dissertation,we summarized the process of damage generation,collected the data of displacement energy of commonly-used solid materials and developed the method of correcting the primary defects information produced by MC code which is to be used as input of multi-scale modeling.The modeling of the interaction between charged particles and solids is based on the BCA(binary collision assumption),where the interaction was divided into inelastic process and elastic process which were treated separately.The inelastic interaction for both ions and electrons was simplified as continuous energy loss,which was described by fitting electronic stopping power(ionization and excitation)formula coming from experimental data for ions and by corrected Bethe formula(ionization and excitation)and radiation stopping power(bremmstrahlung radiation)for electrons.Elastic process(the direct collision between charged particles and atoms in the field of Coulomb force),which is the origin of damage generation,was described by fitting expression derived from geometric relationship in CM(center of mass)system for ions and by screened Mott scattering cross section together with the relativistic energy transfer expression.All the theoretical models mentioned above were implemented with C++ language after careful evaluation and used in DEEPER code.Using the damage theory of radiation and Mott cross section model,the displacement cross section of low-dimensional Carbon nano structures under electron radiation,including the graphene and nano-tube,was studied.The displacement energy at different direction which was obtained by MD(molecular dynamics)simulation carried out by LAMMPS,the differential cross section coming from Mott model and the energy transfer at specific direction calculated using relativistic energy transfer formula were used to calculate the average displacement cross section of graphene and nano-tube.The vibration of carbon atoms were described by Debye model and used to make temperature correction of displacement cross section.The results shown good agreement with previous study and we made improvement in the calculation of thresh energy of electron beam,the displacement cross section at high temperature and the dependence of displacement cross section on the diameter of nano-tube.The characterization of void is basic for the research of radiation swelling and usually carried out by TEM,which can achieve sub nano-meter resolution in a limited area observed and will fail for large area with non-uniformly distributed voids.A new approach using the back scattering electrons of SEM to characterize the voids in experimental research was provided and we studied the mechanism,imaging process and optimization of this technique using Monte Carlo simulation.The results were compared with the latest experimental investigation and we got both the validation and limitation of this technique,which will benefit the research of radiation swelling in non uniform materials.The damage induced by electrons in thin samples like TEM sample may change the micro-structure of samples,especially the structures formed by defects,when the sample radiated by electron beam during observation.Using the NRT model,Mott cross section and multi-scattering correction,we calculated the average damage generation in thin samples bombarded by numerous electrons and worked out a set of fitting formula,which can be used to calculate the damage in experimental study conveniently,by applying various reduced parameters.The validation of the formula was confirmed by the Monte Carlo simulation with DEEPER code and damage calculation using displacement cross section presented by previous study.This work provided a practical method of estimating the damage generation in electron radiation.We also payed efforts in multi-scale modeling of defects produced by various types of charged particles in pure iron by combining the MC(DEEPER code)and KMC(MMonca)method and established the dynamic parameter system of defects evolution. |
