AVS 53rd International Symposium
    Thin Film Thursday Sessions
       Session TF-ThM

Paper TF-ThM7
Kinetic Pathways Leading to Layer-By-Layer Growth: A Multibllion Time-Step Molecular Dynamics Study

Thursday, November 16, 2006, 10:00 am, Room 2022

Session: Fundamentals in Thin Film Deposition
Presenter: V. Chirita, Linköping University, Sweden
Authors: V. Chirita, Linköping University, Sweden
D. Adamovic, Linköping University, Sweden
E.P. Münger, Linköping University, Sweden
L. Hultman, Linköping University, Sweden
J.E. Greene, University of Illinois, Urbana
Correspondent: Click to Email
We employ multibillion time-step embedded-atom method molecular dynamics simulations to study homoepitaxial growth of Pt(111) during low-energy (5 - 50 ev) Pt irradiation at 5 eV intervals. We deposit 5 monolayers at 1000K and with fluxes corresponding to deposition rates of 5x10@super 5@ µm/min and 5x10@super 4@ µm/min, i.e. only 3, respectively 2, orders of magnitude higher than experimental rates used in electron beam-physical vapor deposition (EB-PVD). To analyze the results we calculate normalized anti-phase intensities, as measured in reflection high-energy electron diffraction (RHEED), and detect a 3-dimensional (3D) growth mode for energies of up to 20 eV. However, for E = 20 eV and higher, the RHEED intensities signal the transition to layer-by-layer growth mode. In order to determine the mechanism responsible for the observed change in the growth mode we isolate, with unprecedented accuracy, the effects of irradiation-induced processes from thermally activated mass transport during deposition. We find that for all energies irradiation events are completed within 10 ps following impacts while thermal migration is not affected by the deposition energy. We provide direct evidence that the energy threshold observed at 20 eV (and observed in many experimental studies) is entirely due to the atomic processes induced by the irradiation process, in the first 10 ps following the arrival of energetic species. Adatom scattering, surface channeling, dimer formation and cluster disruption are identified as primary mechanisms responsible for 2-fold and 5-fold increases in intra-, respectively interlayer, mass transport rates as irradiation energy is increased from 10 to 20 eV. The same kinetic pathways, leading to an even more clear transition from 3D to layer-by-layer growth, are identified in µs-long (multibillion time step) MD simulations carried out at fluxes approaching experimental conditions. Our results should apply to most fcc (111) metallic planes and have added significance in the low-temperature regime, where thermal processes are exponentially depressed, as it will be discussed.