[en] Ion range is one of the most important considerations in describing ion-solid interactions. When an energetic ion penetrates a solid, it undergoes electronic and nuclear stopping in the target. In the beginning of the slowing-down process at high energies, the ion is slowed down mainly by electronic stopping, and it moves almost in a straight path. As the ion energy decreases, the probability of collisions with nuclei increases and the nuclear stopping finally dominates the slowing-down process. During the collision processes, target atoms (target recoils), which receive significant recoiling energies from the ion, will be removed from their lattice positions and produce a cascade of further collisions in the target.

[en] The stopping powers for O, Al, Cr, Mn, Co and Cu in a self-supported SiC film have been measured in transmission geometry over a continuous range of energies using a time of flight elastic recoil detection analysis (ToF-ERDA) system. These stopping data, along with the stopping data in Si and C obtained previously using the same ions and measurement technique, are used to assess the validity of the Bragg additivity rule for stopping powers in SiC over a range of ions and energies. Within the experimental uncertainties (4%), the results indicate that Bragg's rule is valid in SiC for the ion species and energy region studied. The measured stopping powers in C, Si and SiC are also compared with the stopping power predictions of the two most recent versions of the SRIM (Stopping and Range of Ions in Matter) codes. While both versions of SRIM show varying degrees of agreement with the measured stopping data, there are significant deviations of the SRIM predictions for some ions and energy regions

[en] The stopping of ions in solids is due to the energy loss as a result of the resistance to ion passage of the electronic and ionic nuclei in the material. When an ion penetrates a solid, it experiences a number of collisions. Energetic charged particles interact with both electrons and atoms in materials. Kinetic energy transfers to atoms can result in displacement of atoms from their original sites; thereby forming atomic-scale defects in the structure. Energy transfers to the target electrons (either bound or free) produces electron-hole pairs that can result in charging of pre-existing defects, localized electronic excitations, rupture of covalent and ionic bonds, enhanced defect and atomic diffusion, increased free energy, changes in phase transformation dynamics, as well as formation of atomic-scale defects. Such atomic collisions and ionization processes can modify the physical and chemical behavior of nanomaterials. This box will discuss irradiation-induced defect, address nanostructure engineering and radiation effects in nanomaterials, as well as the scientific challenges of ion-solid interactions.

[en] The computer code, Stopping and Range of Ions in Matter (SRIM), is widely used to describe energetic processes of ion-solid interactions; its predictive power relies on the accuracy of energy loss/transfer and collision processes being considered. While the SRIM code is commonly applied in radiation effects research to predict damage production and in the semiconductor industry to estimate ion range and dopant concentration profiles, two challenges exist that affect its use: (1) inconsistency in estimations of atomic displacements between full-cascade and quick (modified Kinchin–Pease) options and (2) overestimation of electronic stopping power for slow heavy ions in light targets (e.g., Be and Si) or in compound targets containing light elements (e.g., C, N and O in carbides, nitrides and oxides). Based on a literature review and our experimental investigations, we discuss the underlying reasons for the discrepancies, clarify the physical limitations of the SRIM predictions, and, more importantly, provide recommendations to address the two challenges.

[en] A new technical and analysis approach based on using time-of-flight (ToF) to determine energy loss has been developed and used to improve the precision of measuring heavy-ion electronic stopping powers from a continuous energy spectrum of particles provided by a typical elastic recoil detection analysis geometry. The particle energies entering and exiting the stopping foil are determined using ToF spectrometry data, with and without the stopping foil. The Si detector is only used to tag identical energies and screen out the extraneous components from the spectrum. This approach, which is applicable to continuous energy measurements, eliminates the well-known calibration problem of Si detectors associated with heavy ions that is shown to lead to a clear deviation in the measured stopping power. Consequently, the stopping powers and the energy dependence are determined with higher precision. In this study, the stopping powers of a number of heavy ions (3≥atomic number≤53) in amorphous C, Al and Au have been determined with an absolute uncertainty of less than 2.5%. In some energy regimes, data are provided for the first time. In other energy ranges, the present data exhibit good agreement with most existing data. SRIM stopping power values show a reasonable agreement with experimental data in most cases; however, some deviations from the measured values, up to 15%, are observed around stopping maximum

[en] Determination of electronic stopping powers using Time of Flight (ToF) spectrometry have been demonstrated by measuring energy loss of He, O, and Al particles based on a ToF Elastic Recoil Detection Analysis (ERDA) set-up. In transmission geometry, the energy loss of the particles in self-supported stopping foils of C, Si and SiC is measured over a continuous range of energies using the ToF spectrometer. This study emphasizes the difference of the stopping power determination with and without dependence on the Si detector calibration over a wide energy range. By calibrating the Si detector for each channel over the measured energy region, the improved approach eliminates much of the error associated with pulsed height defects and measurement uncertainties of less than 4% are achieved. Stopping powers from this study are compared with limited experimental data from the literature and SRIM (The Stopping and Range of Ions in Matter) 2000 and 2003 predictions. In general, the predicted values are in reasonable agreement with the experimental data, and an improved accuracy of SRIM 2003 over SRIM 2000 can be observed in some cases. Furthermore, Braggs rule is valid in SiC for O and Al over the energy region studied

[en] Energetic ions interact with materials by collisions with the nuclei and electrons of the atoms that make up the material. In these collisions energy and momentum is transferred from the projectile particle which is a moving atom or ion, to the target particles (atomic nucleus or electron). Each collision leads to a slowing down of the moving projectile and also a deflection of the trajectory which gives rise to the term scattering which is often used synonymously to describe the energy transfer process. In this chapter, we introduce from an experimental viewpoint the underlying theory for interaction of ions for analysis and modification of nanometer scale materials. A more detailed theoretical overview of the topic can be found in the recent monographs by Sigmund. Detailed derivations of the formulae introduced will not be given here but can be found in standard texts that are indicated by references. The treatment here starts by considering an individual scattering event. The results are then used to consider the effects on the primary ion in the limit where a large number of collisions take place. Subsequently, the primary effects are considered in nanometer materials which approach the thin-medium limit where the primary particles encounter only limited number of scattering centers. Finally, the dissipation of the energy deposited by the primary projectiles in secondary processes such as cascades of displaced atoms and electrons will be considered in the thick and thin medium limits. This approach was chosen because it builds upon the standard concepts in ion-matter interactions that are well know and have been widely used in experimental measurements of the stopping force and applications such as Rutherford backscattering spectrometry (RBS), ion beam modification of materials etc.

[en] Response of materials to single radiation events is fundamental to research and many technological applications that involve energetic particles. Ion-solid interactions lead to energy loss of ions, production of electron-hole pairs, and light emission from excitation-induced luminescence. Employing a unique time-of-flight system, material response to single ion irradiation has been utilized to measure electronic energy loss, and to evaluate materials performance for radiation detection. Measurements of electronic energy loss of single ions in a thin ZrO2 foil over a continuous energy range exhibit good agreement with SRIM predictions for He and Be ions. For O and F ions, slight over- and under-estimation of SRIM prediction is evident at energies around 250 (near the stopping maximum) and above 800 keV/nucleon, respectively. For a Si semiconductor detector, its response to single ion irradiation shows that pulse height defect is clear for elements heavier than Si, and nonlinear energy response is significant for all elements at energies below ∼ 150 keV/nucleon. For a single crystal CsI:Tl scintillator, the response to H ion events is used to determine relative light yield and absolute energy resolution over a wide energy region, where energy resolution of ∼ 5.3% is achieved at 2 MeV.

[en] Recent demands for new radiation detector materials with improved γ-ray detection performance at room temperature have prompted research efforts on both accelerated material discovery and efficient techniques that can be used to identify material properties relevant to detector performance. New material discovery has been limited due to the difficulties of large crystal growth to completely absorb γ-energies; whereas high-quality thin films or small crystals of candidate materials can be readily produced by various modern growth techniques. In this work, an ion-scintillator technique is demonstrated that can be applied to study scintillation properties of thin films and small crystals. The scintillation response of a benchmark scintillator, europium-doped calcium fluoride (CaF2:Eu), to energetic proton and helium ions is studied using the ion-scintillator approach based on a time of flight (TOF) telescope. Excellent energy resolution and fast response of the TOF telescope allow quantitative measurement of light yield, nonlinearity and energy resolution over an energy range from a few tens to a few thousands of keV

[en] Disorder accumulation and amorphization in 6H-SiC single crystals irradiated with 2.0 MeV Au²⁺ ions at temperatures ranging from 150 to 550 K have been investigated systematically based on 0.94 MeV D⁺ channeling analyses along the <0001> axis. Physical models have been applied to fit the experimental data and to interpret the temperature dependence of the disordering processes. Results show that defect-stimulated amorphization in Au²⁺-irradiated 6H-SiC dominates the disordering processes at temperatures below 500 K, while formation of clusters becomes predominant above 500 K. Two distinctive dynamic recovery stages are observed over the temperature range from 150 to 550 K, resulting from the coupled processes of close-pair recombination and interstitial migration and annihilation on both sublattices. These two stages overlap very well with the previously observed thermal recovery stages. Based on the model fits, the critical temperature for amorphization in 6H-SiC under the Au²⁺ ion irradiation conditions corresponds to 501 ± 10 K