Anomalous Positive Ion Formation in Negative Ion Collisions with HOPG

Abstract

Charge transfer on graphite, a typical substrate and one of the fusion first wall materials, is of great importance in the plasma–wall interaction, thin-film growth, and surface catalysis. We present an experimental study of 8.5–22.5 keV energy carbon, oxygen, and fluorine negative ions scattering from a highly oriented pyrolytic graphite (HOPG) surface at a scattering angle of 8°. It is found that the positive ion fraction decreases monotonically with the increase of both incident velocity and angle. In particular, these dependences are very different from those presented in previous studies. A molecular dynamics simulation reveals that, around the critical condition for planar surface channeling, a number of projectiles may penetrate into the subsurface and become energetic atoms when they emerge from the surface. Hence, an exponential scaling related to the penetration probability has been proposed to well describe the velocity and angle dependences of positive ion fractions.

Olfactory Ensheathing Cell-Conditioned Medium Reverts Aβ25–35-Induced Oxidative Damage in SH-SY5Y Cells by Modulating the Mitochondria-Mediated Apoptotic Pathway

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“…128 OECs produce growth factors, nerve growth factor 129 (NGF), brain-derived neurotrophic factor (BDNF), glial 130 cell-derived neurotrophic factor (GDNF), and ciliary neu-131 rotrophic factor (CNTF), cell adhesion molecules, and 132 extracellular matrix proteins that are beneficial for axonal 133 regeneration (Woodhall et al 2001;Pellitteri et al 2009;134 Pastrana et al 2006). Olfactory ensheathing cell-condi-135 tioned medium (OECCM) reverts SH-SY5Y damage 136 induced by 6 hydroxydopamine (6OHDA) (Shukla et al 137 2014) and astrocyte damage induced by H 2 O 2 (Jinbo et al 138 2013;Liu et al 2013). Furthermore, OECCM increased 139 oligodendroglial and neuronal differentiation of neural 140 progenitor cells (Carvalho et al 2014) and human mes-141 enchymal stem cells (Zeng et al 2013) (Yang et al 2016), Ab [25][26][27][28][29][30][31][32][33][34][35] 179 (Sangon Biotech, Shanghai, China) was dissolved in ster-180 ilized, double-distilled, water at a concentration of 1 mM 181 and incubated in a capped vial at 37°C for 7 days to form 182 an aggregated form.…”

Unexpected Negative-Ion Conversion in Grazing Scattering of Negative Ions on HOPG

“…Except He ions and Li ions, 26−31 to date, few studies have been conducted on HOPG using heavy ions with dozens of keV energies. 32,33 In the previous study, we measured the positive-ion fraction as a function of incident velocity and angle for negative-ion scattering on HOPG. 33 Similar to proton scattering, we observe both negative and positive ions in the experiment.…”

“…32,33 In the previous study, we measured the positive-ion fraction as a function of incident velocity and angle for negative-ion scattering on HOPG. 33 Similar to proton scattering, we observe both negative and positive ions in the experiment. Whether the positive-ion production channel can hinder the complete conversion of neutral atoms to negative ions at short distances along the outgoing trajectory?…”

“…In order to answer this question, we further experimentally study the negative-ion formation on HOPG using the same projectiles and scattering conditions as in the previous study. 33 In this work, we mainly discuss here the negative-ion formation and the influence of the positive-ion production channel on it. Indeed, the angular dependence of the negative-ion fraction observed in this experiment is quite different from that observed in other experiments.…”