Study Of The Irradiation Effect Of Alloys And Quartzs By Simulations Of Rutherford Backscattering Spectrometry In Channelling Conditions

The irradiation effect of crystal materials is one of intensive focus in the nuclear en-ergy,semiconductor industry,microelectronics industry and aerospace and other fields.Ion-induced cascades occurred in the magnitude of pico-seconds.The cascade evo-lution processes can not be directly observed by the current experimental technology.Nowadays,the development of computer technology,however,allows us to simulate the cascade evolution,which would greatly facilitated our understanding on the micro-scopic mechanism of radiation damage effects.Rutherford backscattering spectrometry in a channeling direction(RBS/C)is a very powerful means to study the ion-induced damage of material surfaces in_～μm depth.This technology has been widely used to characterize the damage in crystalline materials induced by ion irradiation.However,since the damage structures are often very com-plex,it is in many case difficult to analyze what is the actual defect structure underlying the RBS/C signals.The present work based on the computer simulation,utilizing the binary collision approximation,developed a code which can simulate the RBS/C spectrum from ar-bitrary defected crystals.Through combing the molecular dynamics,we proposed a method to simulated the RBS/C spectrum without any fitting parameters.We applied this method into concentrated solution alloys and quartzs to study the mechanism of irradiation damage.This work consisted of three parts:In the first part,we developed a code based on binary collision approximation for simulating the RBS/C from an arbitrarily defected crystals and named the code by RBSADEC(Rutherford backscattering spectrometry in Arbitrary Defected Crystals).The code reads in the damaged structure from an separated file,where a set of three-dimensional atom coordinates are listed.This makes RBSADEC can be easily com-bined with other atomic level simulation methods,e.g.,Molecular Dynamics,Monte Carlo,Kinetic Monte Carlo and so on.RBSADEC can be used to(I)simulate the range of ions in materials with any structures;(II)simulate the BBS/C from arbitrary defected crystals.We used this code to study the contribution of different types of defects,includ-ing point defects and extended defects,to the RBS/C signals.The results showed that the RBS/C is more sensitive to the extended defects than the point defects.Moreover the results reveal that the extended defects leads to RBS/C signals mainly due to the inter-action of dechannelled ions with material atoms,but not the interaction of channelling ions with defected atoms.Through the comparison of the experimental and simulation results,we explained the reason why large RBS/C yields are obtained in the Ni samples with a relatively low level of damage visible in high-resolution scanning transmission electron microscopy(STEM)image.In the second part,we used the molecular dynamic method to simulate the irradi-ation damage in the concentrated solid solution alloy(CSAs)NiFe and NiCoCr.Due to the size of molecular dynamics simulation box(_～tens of nm)is much smaller than interest depth of RBS/C technique,we formed a depth-dependent damaged structure corresponding to the experimental nuclear deposited energy profile and simulated the RBS/C spectra from the damage structures by RBSADEC.The simulation results agree well with the experimental results.In this study,we(I)combined the molecular dy-namics method with the binary collision approximation code RBSADEC developing a method to simulate the RBS/C spectra without any fitting parameters.This method was referred to as“MD-BCA”method in the remainder of this dissertation;(II)confirmed that CSAs shown better anti-radiation properties than pure metal Ni from the simula-tion point of view;(III)even the time scale of molecular dynamics simulation is much smaller than the experiment,the simulated RBS/C spectra of irradiated Ni and concen-trated solid solution alloys(CSAs,NiFe and NiCoCr),however,show a good agreement with the experimental results.The good agreement indicates the damage evolution un-der damage overlap conditions in Ni and CSAs at room temperature is dominated by defect recombination and migration induced by irradiation rather than activated ther-mally.Finally,we used the molecular dynamics method to simulate the amorphization of quartz induced by 50 keV Na ion irradiation.Then,the RBS/C spectra from the sam-ples with different irradiation fluence were simulated by the“MD-BCA”method,and a variety of other analytical methods,such as angular structure factor analysis,Wigner-Seitz analysis,coordination analysis and ring analysis were used to analyze the damaged structures under different irradiation dose.The simulated RBS/C spectra were in good agreement with the experimental results.From the comparison of simulated and exper-imental RBS/C spectra,following conclusions are drawn:(I)the surface of quartz is an effective sink for irradiation induced damage;(II)the annealing effect would lead to a small reduction of the damage produced by the ion irradiation.Through other analy-sis results and the comparison with the RBS/C results,we derived:(III)the threshold energy for amorphization of quartz is almost independent on the recoil energies,which indicates that the threshold energy for amorphization of quartz does not depend on the types of irradiation ions and their incident energies(at low energy region).(IV)the re-sults show that the atomic-level structure of the sample keeps,however,evolving much after the RBS signal has saturated,until up to a dose of about 5 eV/atom.The con-tinued evolution of the structures makes the definition of what is,on atomic level,an amorphized quartz ambiguous.In summary,we combined molecular dynamic methods and binary collision ap-proximation proposing a new methods to simulate the RBS/C spectra from arbitrary defected crystals without any fitting parameters.This method makes the RBS/C tech-nique can be used as a method to reveal the mechanisms how the damage builds up.We succeed to apply this method to study the ion-irradiation damage in the quartz and alloys and revealed the micro-mechanism of ion-irradiation damage processes.