Channeling maps for Si ions in Si : Assessing the binary collision approximation

Simulations based on the binary collision approximation (BCA) are in principle less accurate than molecular dynamics (MD) simulations. In this work, we present a comprehensive comparison between BCA and MD for Si ions impinging on a (001)-Si surface by comparing "channeling maps", i.e., projected ranges of the ions as a function of incidence direction in a representative part of the angular space. We find quantitative differences to develop as the energy decreases below similar to 100 eV, but find qualitative agreement down to similar to 10 eV. Moreover, the quality of the BCA channeling maps depends on the implementation of the BCA, which is explained in terms of double-hits and missed collisions.Peer reviewe

An Efficient Molecular Dynamics Scheme for the Calculation of Dopant Profiles due to Ion Implantation

We present a highly efficient molecular dynamics scheme for calculating the concentration depth profile of dopants in ion irradiated materials. The scheme incorporates several methods for reducing the computational overhead, plus a rare event algorithm that allows statistically reliable results to be obtained over a range of several orders of magnitude in the dopant concentration. We give examples of using this scheme for calculating concentration profiles of dopants in crystalline silicon. Here we can predict the experimental profile over five orders of magnitude for both channeling and non-channeling implants at energies up to 100s of keV. The scheme has advantages over binary collision approximation (BCA) simulations, in that it does not rely on a large set of empirically fitted parameters. Although our scheme has a greater computational overhead than the BCA, it is far superior in the low ion energy regime, where the BCA scheme becomes invalid.Comment: 17 pages, 21 figures, 2 tables. See: http://bifrost.lanl.gov/~reed

On the missing single collision peak in low energy heavy ion scattering

We present experimental and simulation data on the oblique angle scattering of heavy Sn ions at 14 keV energy from a Mo surface. The simulations are performed with the binary collision approximation codes TRIM, TRIDYN, TRI3DYN, SDTrimSP, and IMSIL. Additional simulations were performed in the molecular dynamics framework with LAMMPS. Our key finding is the absence of an expected peak in the experimental energy spectrum of backscattered Sn ions associated with the pure single collision regime. In sharp contrast to this, however, all simulation codes we applied do show a prominent single collision signature both in the energy spectrum and in the angular scatter pattern. We discuss the possible origin of this important discrepancy and show in the process, that widely used binary collision approximation codes may contain hidden parameters important to know and to understand.</p

Early-Age-Related Changes in Proteostasis Augment Immunopathogenesis of Sepsis and Acute Lung Injury

adult) mechanisms that augment immunopathogenesis of sepsis and acute lung injury. model to standardize the efficacy of salubrinal (inhibitor of eIF2α de-phosphorylation) in controlling the accumulation of ubiquitinated proteins and the NFκB levels. Finally, we evaluated the therapeutic efficacy of salubrinal to correct proteostasis-imbalance in the adult mice based on its ability to control CLP induced IL-6 secretion or recruitment of pro-inflammatory cells.Our data demonstrate the critical role of early-age-related proteostasis-imbalance as a novel mechanism that augments the NFκB mediated inflammation in sepsis and ALI. Moreover, our data suggest the therapeutic efficacy of salubrinal in restraining NFκB mediated inflammation in the adult or older subjects

Dependence of ion channeling on relative atomic number in compounds

Ion channeling is a well-known radiation effect, important for understanding the passage of energetic ions and recoils in all crystalline materials. Recently we developed molecular dynamics and theory-based approaches to calculate ion channeling systematically over all crystal directions, providing ion `channeling maps' that easily show in which directions channeling is expected [Nordlund {\it et al.}, Phys. Rev. B. 94, 214109 (2016)]. As an extension of this work, which only considered pure elements, we consider here ion channeling in compounds. To obtain a comprehensive understanding of the effect of varying atom sizes on ion channeling, we compare compounds with pure elements of the same crystal structure, where the atomic number (nuclear charge) of the element is the average of that of the ions in the compound. The results show that the channeling effects in the compounds are very similar to the corresponding pure element, except if there is a really large ($\gtrsim 10$) ratio of atomic numbers. The reasons to this are discussed in terms of channeling theory.Peer reviewe