Sputtering and reflection processes from amorphous lithium surfaces by low-energy impacts of H and D atoms and D2 molecules

Processes at lithium-hydride/deuteride surfaces upon low energy impact of H/D

“…The TRIM.SP data [36] for the D+a:Li system, are also shown in Figure 3B. These data are almost a factor of two larger than our data for the D+a:LiD system though these show reasonable agreement with our data for the D+a:Li system [10]. One can draw the following conclusions from the above discussion: 1) The reflection probabilities in the considered impact energy range are significantly bigger from the a:Li surface than from a: LiH and a:LiD surfaces at low angles of incidence; and 2) Concerning isotope effects, reflection for the D+a:LiD system is, for most impact energies, 2-3 times smaller than for the H+a:LiH system.…”

“…We prepared crystalline (FCC, lattice constant 4.007Å) and amorphous LiH slabs with dimensions of 4.9 × 4.9 × 10.6 nm 3 consisting of 14,730 Li and 14,499 H atoms with an average mass density of 0.762 g/cm 3 , which is within 3% of the commonly reported LiH crystal density [28] of 0.78 g/cm 3 (Figure 1). The crystal structure was geometry optimized to minimize its energy, and the amorphization of LiH was achieved by subjecting the FCC LiH crystal to a repeated heating and cooling regime, as described in [10]. The periodic boundary conditions were removed from the z-direction (Figure 1), and the system was further equilibrated at 300 K to allow the relaxation of the surface atoms.…”

“…The maximal standard error (MSE) [29], which is shown as an error bar in the probability graphs (Section 3), was calculated as p/√n. A more detailed discussion of such computational methodology can be found elsewhere [10,11,20].…”

“…Understanding Li-based plasmamaterial interaction (PMI) is of particular importance for the Lithium Tokamak eXperiment-β (LTX-β), whose low recycling regime is enabled by Li-coated plasma-facing surfaces [2,8]. Although most of the plasma-facing wall in LTX-β is coated with Li, the surface is rapidly saturated by H bombardment in the presence of plasma, up to a Li:H ratio of 1:1 [9], implying that knowledge of the effects of H and D irradiation on pristine Li (amorphous and crystalline) [10,11] is not enough to reveal the properties of a complex material formed by accumulation of H or D in pure Li. In fact, wall surfaces and target surfaces in experiments might be even more complex than LiH due to additional reactions of Li and LiH with water in the background residual gases [6], resulting in a mixture of LiH, Li 2 O, and LiOH.…”

“…Namely, the low electronegativity of lithium (0.98) in comparison to hydrogen (2.2) [13,14] implies some ionic character (30%) in addition to the strong covalent character of Li-H bonding, creating a polarization environment for the impact hydrogen atoms and their consequential partial charging. As discussed in [10,11], this long-term polarization effect can be considered in CMD by the Electronegativity Equalization Method (EEM) [15,16], in combination with reactive bond-order (BO) potentials (ReaxFF [17,18]), implemented in the Large Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code [19]. Interestingly, the applications of ReaxFF combined with EEM [20-22] have shown good agreement with results of quantum-classical molecular dynamics [23] using tightbinding DFT [24][25][26], as well as with experimental results [27].…”