Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci Low-energy channel for mass transfer in Pt crystal initiated by molecule impact Rita I. Babicheva a,f , Iman Evazzade b , Elena A. Korznikova c,g , Igor A. Shepelev d , Kun Zhou a, ⁎ , Sergey V. Dmitriev c,e a School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore b Department of Physics, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran c Institute for Metals Superplasticity Problems, Russian Academy of Sciences, 39 Khalturin St., Ufa 450001, Russia d Saratov State University, Astrakhanskaya St. 83, Saratov 410012, Russia e National Research Tomsk State University, 36 Lenin Prospekt, Tomsk 634050, Russia f Environmental Process Modelling Centre, Nanyang Environment & Water Research Institute, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, Singapore 637141, Singapore g Ufa State Aviation Technical University, Karl Marx Str. 12, 450008 Ufa, Russia ARTICLE INFO Keywords: Crystal lattice Mass transfer Point defect Crowdion Atom-surface collision Molecular dynamics ABSTRACT Crystal surface bombardment by atoms or molecules, neutral or ionized, occurs both in ambient conditions and in many technological operations, such as surface plasma treatment, ion implantation, etc. Recently, it was established that the impact of a molecule initiates the mass transfer in the one-dimensional Frenkel-Kontorova atomic chain more efficiently than that of a single atom. This is explained by the fact that the atom can initiate only a very sharp, fast-moving crowdion (anti-kink), which requires relatively high energy, while the molecule is able to initiate a less localized crowdion with considerably lower velocity and energy. In the current study, by means of molecular dynamics simulation, for the first time, this phenomenon is studied for a realistic 3D model of platinum crystal. We compare the efficiency of single Pt atom impact and Pt 2 molecule impact on the (1 0 1) surface of fcc Pt crystal for the initiation of mass transfer in the material by crowdions. It is revealed that in order to generate a crowdion moving inside the crystal, the properly oriented molecule needs an order of magnitude smaller energy than single atom. This considerable reduction of required energy happens when the molecule is oriented perpendicularly to the crystal surface and hits the crystal along a close-packed atomic row. Furthermore, it is revealed for the first time that the molecule with sufficiently large velocity can initiate the so- called supersonic 2-crowdion, which travels longer distances in the crystal than the classical supersonic crow- dion having same or even higher energy. Our results can be useful for understanding and prediction the mass transfer during technological applications where bombardment by atomic clusters is employed to modify and improve mechanical or functional properties of surfaces. 1. Introduction Crystal surface is exposed to bombardment by neutral or ionized atoms or atomic clusters either at ambient conditions or during surface processing by plasma surface treatment, ion implantation, secondary ion mass spectrometry [1–11], etc. Such bombardment can initiate desired or undesired crystal structure transformations near the surface due to the mass transfer inside the crystal. Mass transport by point defects in crystalline solids is responsible for many physical processes occurring during plastic deformation [12–18], heat treatment [19], irradiation [20–24], etc. Motion of vacancies is the main mechanism of thermally activated diffusion [19]. Self-interstitial atoms have higher energy and hence, their concentra- tion in the thermal equilibrium state is much smaller than that of va- cancies, but their contribution becomes more prominent in non-equi- librium processes. Self-interstitials in the form of dumbbells have relatively low mobility [25], but they are highly mobile when located in close-packed atomic rows creating so-called crowdions [26]. Interest- ingly, immobile interstitials usually have higher potential energy than standing crowdions [26,27]. Crowdions can be at rest or they can move with subsonic or supersonic speed [28–33]. Atomic displacements in a standing or subsonic crowdion in metals have a kink profile spanning https://doi.org/10.1016/j.commatsci.2019.03.022 Received 19 November 2018; Received in revised form 9 March 2019; Accepted 14 March 2019 ⁎ Corresponding author. E-mail address: kzhou@ntu.edu.sg (K. Zhou). Computational Materials Science 163 (2019) 248–255 0927-0256/ © 2019 Elsevier B.V. All rights reserved. T