Machine learning driven simulated deposition of carbon films: From low-density to diamondlike amorphous carbon

© 2020 American Physical Society. Amorphous carbon (a-C) materials have diverse interesting and useful properties, but the understanding of their atomic-scale structures is still incomplete. Here, we report on extensive atomistic simulations of the deposition and growth of a-C films, describing interatomic interactions using a machine learning (ML) based Gaussian approximation potential model. We expand widely on our initial work [M. A. Caro, Phys. Rev. Lett. 120, 166101 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.166101] by now considering a broad range of incident ion energies, thus modeling samples that span the entire range from low-density (sp2-rich) to high-density (sp3-rich, "diamondlike") amorphous forms of carbon. Two different mechanisms are observed in these simulations, depending on the impact energy: low-energy impacts induce sp- and sp2-dominated growth directly around the impact site, whereas high-energy impacts induce peening. Furthermore, we propose and apply a scheme for computing the anisotropic elastic properties of the a-C films. Our work provides fundamental insight into this intriguing class of disordered solids, as well as a conceptual and methodological blueprint for simulating the atomic-scale deposition of other materials with ML driven molecular dynamics