0000000000213259
AUTHOR
Sachiko T. Nakagawa
Box 5: Surface Crystallography Terminology
The crystalline nature of the surface differs from the bulk because atoms on the surface experience a different force field due to unterminated bonds, oxidation by adatoms etc. [1]. Free energy minimisation leads to reconstruction of the surface layer from the bulk by formation of dimers and displacement of atoms from their normal sites.
A predictive model for the electronic stopping force for molecular dynamic simulation (I)
Abstract We have examined a predictive model for the electronic stopping force (dE/dx)e to be used in the classical molecular dynamic (MD) simulation. The essential term (dE/dx)proton of (dE/dx)e is based on the Lindhard–Winther theory, while the effective charge follows the Brandt–Kitagawa model. The (dE/dx)proton term is expressed by the electron local density ρ(r) defined by the Muffin-tin model and the Hartree–Fock–Slater approximation. This model had been proposed to explain the impact-parameter dependence of (dE/dx)e for channeling ions passing through a semiconductor. Here the energy dependence of the averaged 〈dE/dx〉e after thin-film transmission was examined, where the electron–pho…
Ordering effects in extreme high-resolution depth profiling with MeV ion beams
Abstract The continuing development of depth profiling with MeV ion beam methods with depth resolutions in the nanometre, and even sub-nanometre, regime implies the resolved depth become comparable with the interatomic spacing. To investigate how short-range ordering influences depth profiles at these resolutions, we have employed a mathematical modelling approach. The radial, g ( r ) and depth distribution, g ( z ) functions were calculated for (1 0 0) surface, random and amorphous Si structures at 300 K produced using molecular dynamics simulations with the EDIP quasi-empirical potential. The results showed that short-range ordering lead to reduction of the scattering yield below the deep…
Crystallographic analysis of extended defects in diamond-type crystals
Abstract To investigate irradiation-induced Si amorphization during its initial stages, we have performed a classical molecular-dynamics (MD) calculation for the case of self-irradiation by 5 keV ions at a low temperature of 100 K. We examined the geometry of self-interstitial atom (SIA) clusters using the pixel mapping (PM) method, on the output data of MD calculations. Perfect crystalline silicon (c-Si) is amorphized by self-irradiation, and we observe that many SIA are produced. During sequential self-irradiation, the most frequently observed species were isolated SIA, i.e. I1 (monomer). The fractions of SIA clusters decreased as I2 (dimer), I3 (trimer), and I4 (tetramer) clusters, respe…
Detection of planar defects caused by ion irradiation in Si using molecular dynamics
We have analyzed the evolution of defects caused by self-irradiation of crystalline silicon. A classical molecular dynamics simulation was followed by defect analysis using the Pixel Mapping (PM) method. The PM identified {311} planar defects and long-chain structures of the so-called interstitial chains following low energy (1 keV) ion impact. The areal density obtained from simulation of self-interstitial atoms was about two thirds of that of experiments reported in the literature [Jpn. J. Appl. Phys. 30 (1991) L639], while the atomic configuration on respective planes agreed exactly.
Low-energy primary knock on atom damage distributions near MeV proton beams focused to nanometre dimensions
Abstract In this preliminary study, the spatial extent of the defects introduced in Si by a normally incident 1 MeV H + nanobeam was investigated using a hybrid approach. First, the standard SRIM code was employed to calculate the angular and energy distributions of Primary Knock-on Atoms (PKA) using the Binary Collision Approximation (BCA). The long mean free path and the kinematics of scattering in a screened Coulomb potential resulted in an anisotropic PKA distribution that was mainly directed perpendicular to the primary ion trajectories. The PKA energy E dependence was close to 1/ E n with 1.5 n The results revealed that the low energy PKA’s resulted in localised damaged regions with …