Ab Initio Simulation of Swift Heavy Ion-Driven Damage on Nanoscale Thermal Transport in ZnO

Swift heavy ion (SHI) irradiation of non-metallic materials is a promising approach to engineering their thermal transport properties at the nanometer scale. SHI damage can be imparted into host semiconducting and insulating solid lattices in the form of cylindrical ion tracks or near-surface point defects¹. However, there is a lack of clear understanding of the effect of SHI damage on nanoscale thermal transport in irradiated solids.<br/>In this work, we analyze the <i>SHI-induced damage</i> to wide-bandgap semiconducting ZnO single crystal by a hybrid simulation technique combining <i>ab initio</i> Monte-Carlo Time-Resolved Electron Kinetics (TREKIS) and molecular dynamics (MD), which is free from fitting parameters². In this approach, the evolution of electron dynamics of host Zn and O atoms is simulated following the initial impact of Bi ion on the ZnO lattice within the first 100 fs. The radial energy density distributed by ion to the lattice is obtained from TREKIS, the output of which is used to set the initial velocities for the classical MD model in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code³ to predict the 3D damage pattern to the initial zinc oxide hexagonal lattice during its relaxation on a time scale from 100 fs to hundreds of ps. Four different Zn-O interatomic potentials (IAPs) are considered in MD simulations. IAP determines both the ion-induced defect formation and the subsequent thermal conductivity (<i>k</i>) calculations. This TREKIS-MD method is compared with randomly distributed atomic displacements in the crystal formed by the Atomsk software⁴.<br/>Then the phonon thermal conductivity of the ion-damaged subsurface region of the ZnO lattice along the (0001) direction obtained from TREKIS-MD is calculated with equilibrium molecular dynamics (EMD) and is compared with the results from the Boltzmann transport equation relaxation time approximation (BTE-RTA), semi-analytical Klemens-Callaway and Rayleigh effective medium approximation models. The <i>k</i> of pristine ZnO obtained by BTE-RTA matches that found by EMD. The difference between the TREKIS-MD and randomly introduced point defects model is seen at high ion doses due to overlapped impinging ions. The <i>random defects model</i> fails at high ion doses and predicts further <i>k</i> decrease. On the contrary, the TREKIS-MD model demonstrates <i>k</i> saturation observed experimentally but overestimates the saturated <i>k</i> value. The convergence between TREKIS-MD and spatially-controlled time-domain thermoreflectance measurements of <i>k</i> can be tailored by the appropriate selection of the IAP. The described computational approach opens up an avenue for the design of thermal nanomaterials by controlling the radiation damage via monitoring the electronic excitation by SHIs and subsequent electron-lattice phonon relaxation.<br/>This work was funded by Nazarbayev University collaborative research program (CRP) grant 11022021CRP1504.<br/><b>References:</b><br/>1. J. H. O’Connell, G. Aralbayeva, V. A. Skuratov, M. Saifulin, A. Janse van Vuuren, A. Akilbekov, M. Zdorovets, <i>Mater Res Express</i>. <b>5</b>, 055015 (2018).<br/>2. R. A. Rymzhanov, N. Medvedev, J. H. O’Connell, V. A. Skuratov, A. Janse van Vuuren, S. A. Gorbunov, A. E. Volkov, <i>Nucl Instrum Methods Phys Res B</i>. <b>473</b> (2020), doi:10.1016/j.nimb.2020.04.005.<br/>3. A. P. Thompson, H. M. Aktulga, R. Berger, D. S. Bolintineanu, W. M. Brown, P. S. Crozier, P. J. in ’t Veld, A. Kohlmeyer, S. G. Moore, T. D. Nguyen, R. Shan, M. J. Stevens, J. Tranchida, C. Trott, S. J. Plimpton, <i>Comput Phys Commun</i>. <b>271</b> (2022), doi:10.1016/j.cpc.2021.108171.<br/>4. P. Hirel, <i>Comput Phys Commun</i>. <b>197</b>, 212–219 (2015).