Track Damage And Physical Property Evolution Of Single Crystal Induced By The Mechanism Of Intense Electronic Energy Loss Under Ion Irradiation

Basic research is the precursor and cornerstone of science and technology development,and the solution of related major basic scientific problems is often the key to the generation of new technologies and breakthroughs.Ion beam technology can realize the non-equilibrium phase transition process of nanostructures,lattice orientation,precise doping and fine structure control,etc.It is one of the international research directions that can achieve rapid breakthroughs in the near future in the study of energy-carrying particle-matter interactions,and it is also a research field that has the potential to rapidly form new technologies and realize industrialization.This study focuses on the fundamental scientific problem of microscopic damage formation,macroscopic property evolution and corresponding physical mechanism of structural and functional crystals under complex irradiation environment,and carries out characteristic research work based on the basic interaction process between charged particles and solid materials.The research results obtained through the combination of experiments,calculations and theories mainly include the following.The generation and evolution characteristics of nuclear track damage induced by the strong electronic energy loss process of high-energy ion irradiation are influenced by the cation radius of the material and complex thermodynamics parameters,as well as by the ion velocity and other effects.The present study systematically discusses the spatial and temporal evolution of microscopic damage in structural and functional crystals under the effect of strong electron excitation by ion irradiation,and elucidates the decisive role of single crystal cation radius and thermodynamic parameters in the formation and recrystallization of traces,which lead to different microscopic fine structures of stable nuclear traces in materials.Corresponding to the concept of dpa used to describe the ionization damage,the concepts of atomic energy threshold and lattice temperature threshold are proposed to describe the formation of nuclear track damage,and the quantitative relationship between it and track morphology is established to solve the scientific problem that a single electronic energy loss parameter cannot fully describe the track damage.Relative to the electronic energy loss threshold which depends on the ion velocity parameter,the relationship between atomic energy and lattice temperature threshold would be more basic and universal for clarifying irradiation-induced track damage behavior.For example,the quantitative relationship between track damage morphology and deposition energy of LiNbO3 crystal in the range of 2.6 keV nm-1～13.2 keV nm-1 electronic energy loss at the ion velocity of 0.09 MeV amu-1～6.17 MeV amu-1 can be described as follows.When the atomic deposition energy is lower than 0.48 eV atom-1(the corresponding atomic temperature is lower than 1553 K),no defect damage occurs.When the atomic deposition energy is 0.48 eV atom-1～0.53 eV atom-1,isolated spherical defects with a diameter of 3.0 nm are gradually produced.When atomic energy deposition ranges from 0.53 eV atom-1 to 0.67 eV atom-1(corresponding atomic temperature ranges from 1843 K to 2649 K),the isolated spherical defects gradually evolve into discontinuous tracks with diameters of 5.0 nm.Finally,when the atomic deposition energy exceeds 0.67 eV atom-1(the corresponding atomic temperature exceeds 2649 K),the discontinuous track evolves into a continuous track with uniform morphology,and the corresponding track diameter exceeds 5.0 nm.With the further increase of the deposition energy,a larger track diameter would be generated.The dominant effects of deposition energy and lattice temperature on the formation and evolution of track damage were revealed.In KTaO3 and SrTiO3 single crystals,the isolated spherical defect of disorder,the fine structure of discontinuous and continuous ion track composed of amorphous cores and disordered shells,and defined the formation of the disordered region(KTaO3:0.75 eV atom-1,3410 K;SrTiO3:0.6 eV atom-1,2363 K)and amorphous region formation(KTaO3:1.71 eV atom-1,7967 K;SrTiO3:1.81 eV atom-1.6493 K)are explored,and then the formation process and mechanism of the concentric core-shell track structure and the resulting thermal annealing effects are described.In Y3Al5O12 and Gd3Ga5O12 garnet crystals,the key parameters such as cationic radius and thermodynamics played a decisive role in track formation and recrystallization effect,and the corresponding damage formation threshold(Y3Al5O12:1.48 eV atom-1,5817 K,Gd3Ga5O12:0.95 eV atom-1,2985 K)and amorphous threshold(Gd3Ga5O22:2.35 eV atom-1,8613 K)was determined.By attributing the track response characteristics induced by the interaction between different ion velocities and electronic energy losses to a single parameter,atomic energy,or lattice temperature,the research groups in the irradiation field can obtain the results under different irradiation environments(ion energy,ion velocity,electronic energy loss,etc.)introduced by particle accelerators in different energy regions.Massive research data obtained from nuclear tracks and radiation annealing directions can be integrated and compared,to scientifically explain the internal mechanism of relevant radiation effects,and improve the predictability of damage formation and evolution of structural and functional materials under complex irradiation environments.Various micro and nanostructures(isolated spherical defects.discontinuous and continuous tracks.track core-shell structures)are finely prepared by utilizing the advantages of precise control of irradiation energy and ion mass deposition at the nanometer scale,and physical properties(energy band,fluorescence,photoelectric,etc.)of irradiation microzones are regulated.It provides research ideas and technical support for the cross-fusion of irradiation and ultrafiltration separation,salt difference power generation,energy storage,and other multidisciplinary frontier fields.Taking the nanoscale track structure as an example,the continuous track damage with a cross-section radius of several nanometers and a length of hundreds of microns,and the internal damage area is partially disordered or amorphous,which can regulate the optical band gap of materials and improve the photoconductivity of irradiated materials.In this paper,the cationic radius and thermodynamic parameters of single garnet crystals(Y3Al5O12 and Gd3Ga5O12)play a decisive role in track formation and recrystallization behavior,which makes stable nuclear tracks present different microscopic fine structures.At the same time,under the same irradiation conditions(645.0 MeV Xe35+),it is further explored that the bandgap of Y3Al5O12 crystal induced by irradiation can be regulated in the range of 5.88 eV～6.75 eV,and bandgap of Gd3Ga5O12 crystal can be regulated in the range of 4.83 eV～5.41 eV.The bandgap of ZnO crystal is regulated in the range of 2.66 eV～3.25 eV,while KTaO3 and SrTiO3 bandgaps are reduced to a slight extent.In terms of optical and electrical properties,such as optical absorption and fluorescence emission,it is confirmed that the internal defect state can be used as the absorption center to improve the absorbance inside the crystal.After irradiation,the intensity of the F-color center related to defects in Y3Al5O12,a series of absorption peaks in Gd3Ga5O12,and the overall absorption broadband of KTaO3 and SrTiO3 crystals increases slightly.Fluorescence enhancement in the visible region is achieved in Y3Al5O12 and Gd3Ga5O12,and green light(511 nm,2.42 eV;535 nm,2.31 eV)enhancement,red light generation(686 nm,1.81 eV),internal defects induced the internal rectifier phenomenon of ZnO crystal,and KTaO3 crystal from the insulator to the weak current phenomenon,which effectively improved the photoconductance properties of the two materials.This research work constructs an intrinsic correlation between irradiation parameters and spectroscopic properties and provides basic theoretical models and experimental data for understanding the spectroscopic properties of materials under extreme and complex irradiation conditions,as well as research ideas and technical solutions for cross-fertilization with multiple disciplines.Materials in complex irradiation environments would be subjected to ion action within a wide energy range.At this time,the nuclear energy loss process in the low-energy ion irradiation process and the electronic energy loss process in the high-energy ion irradiation process are no longer independent of each other.Based on the action mechanism of nuclear and electronic energy loss and the theory of solid defects,the evolution characteristics of thermal conductivity and electron-phonon coupling coefficient(g)in the damaged zone induced by nuclear energy and their effects on the thermal spike response intensity induced by electronic energy loss are discussed.The research on these problems is of great significance for clarifying the complex damage and property evolution behavior of materials under a real irradiation environment.In this research,the inelastic thermal spike model model was used to analyze the spatiotemporal evolution of energy and temperature of LiTaO3 predamaged by Si3+ ion irradiation.Compared with the pristine LiTaO3,the defect clusters in Au+ irradiation samples caused electron and phonon scattering,which reduced the thermal conductivity(Ke and Ka)and the mean free path(λ)of the electron system.As a result,due to the electron-phonon coupling coefficient(g)increases,the energy deposited into the lattice along the ion path increases from 0.68 eV atom-1 to 1.07 eV atom-1,and the corresponding atomic temperature increases from 2400 K to 3860 K.Compared with Au+irradiation alone,the track continuity of the sample pre-damaged by Si3+ irradiation increases significantly,meaning that a synergistic effect between nuclear and electronic energy loss promotes the thermal spike response of LiTaO3 crystals.Helium is an inert element that is insoluble in the material matrix.When helium is introduced into the material,it has a strong tendency to diffusion,aggregation,and precipitation in the solid due to its small atomic volume,low diffusion and activation energy in the lattice.When the concentration of helium reaches a certain threshold,certain accumulations in the matrix,grain boundary,and defect of the material are formed.It can achieve accurate control of the local refractive index,provide relevant data on refractive index evolution induced by in-plane and out-of-plane expansion,and promote the development of applications,such as effective optical modulation in optoelectronic devices of’cystal materials.In parallel,severe volume expansion,lattice distortion anisotropy,and other micro-zone changes caused by irradiation would reduce the strength and elongation of grain boundaries to a large extent,thus inducing the evolution of mechanical properties of materials.In this paper,0.6 McV H+ and 2.4 MeV He2+ are used to irradiate SrTiO3 crystal separately and successively.Compared with the crystal surface direction(in-plane),the refractive index reduction is more obvious along the direction perpendicular to the crystal surface(out-ofplane).which reflects the anisotropy of lattice expansion induced by irradiation and the difference of refractive index distribution.In SrTiO3 crystals irradiated by H+ and He2+individually and successively,the mechanical hardness increment increases successively,which reflects the promoting effect of the internal hvdrogen and helium behavior on the hardening level of the material.For LiNbO3 and LiTaO3 crystals,the local refractive index of the material can be accurately regulated based on radiation damage,and relevant data of inplane and out-of-plane refractive index evolution induced by lattice expansion can be provided.