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Molecular Dynamics Studies of Low-Energy Atom Impact Phenomena on Metal Surfaces during Crystal Growth
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

It is a well-known fact in the materials science community that the use of low-energy atom impacts during thin film deposition is an effective tool for altering the growth behavior and for increasing the crystallinity of the films. However, the manner in which the incident atoms affect the growth kinetics and surface morphology is quite complicated and still not fully understood. This provides a strong incentive for further investigations of the interaction among incident atoms and surface atoms on the atomic scale. These impact-induced energetic events are non-equilibrium, transient processes which complete in picoseconds. The only accessible technique today which permits direct observation of these events is molecular dynamics (MD) simulations.

This thesis deals with MD simulations of low-energy atom impact phenomena on metal surfaces during crystal growth. Platinum is chosen as a model system given that it has seen extended use as a model surface over the past few decades, both in experiments and simulations. In MD, the classical equations of motion are solved numerically for a set of interacting atoms. The atomic interactions are calculated using the embedded atom method (EAM). The EAM is a semi-empirical, pair-functional interatomic potential based on density functional theory. This potential provides a physical picture that includes many-atom effects while retaining computational efficiency needed for larger systems.

Single adatoms residing on a surface constitute the smallest possible clusters and are the fundamental components controlling nucleation kinetics. Small two-dimensional clusters on a surface are the result of nucleation and are present during the early stages of growth. These surface structures are chosen as targets in the simulations (papers I and II) to provide further knowledge of the atomistic processes which occur during deposition, to investigate at which impact energies the different kinetic pathways open up, and how they may affect growth behavior. Some of the events observed are adatom scattering, dimer formation, cluster disruption, formation of three-dimensional clusters, and residual vacancy formation. Given the knowledge obtained, papers III and IV deal with growth of several layers with the aim to study the underlying mechanisms responsible for altering growth behavior and how the overall intra- and interlayer atomic migration can be controlled by low-energy atom impacts.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2006.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1028
Keyword [en]
Molecular dynamics simulations, Low energy Ion irradiation, Atomistic processes, Thin film growth
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-7165ISBN: 91-85523-56-9 (print)OAI: oai:DiVA.org:liu-7165DiVA: diva2:22231
Public defence
2006-06-08, Planck, Physics Building, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Note

On the day of the defence date the status of article II was Accepted.

Available from: 2006-08-29 Created: 2006-08-29 Last updated: 2017-01-11Bibliographically approved
List of papers
1. Low-energy ion irradiation during film growth: Kinetic pathways leading to enhanced adatom migration rates
Open this publication in new window or tab >>Low-energy ion irradiation during film growth: Kinetic pathways leading to enhanced adatom migration rates
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2005 (English)In: Applied Physics Letters, ISSN 0003-6951, Vol. 86, 211915- p.Article in journal (Refereed) Published
Abstract [en]

Embedded-atom molecular dynamics simulations are used to investigate the effects of low-energy self-ion irradiation of Pt adatoms on Pt(111). Here, we concentrate on self-bombardment dynamics, i.e., isolating and monitoring the atomic processes, induced by normally incident Pt atoms with energies E ranging from 5 to 50 eV, that can affect intra- and interlayer mass transport.. We find that adatom scattering, surface channeling, and dimer formation occur at all energies. Atomic intermixing events involving incident and terrace atoms are observed at energies 15  eV, while the collateral formation of residual surface vacancies is observed only with E>40  eV. The overall effect of low-energy self-ion irradiation is to enhance lateral adatom and terrace atom migration. ©2005 American Institute of Physics

Keyword
platinum, adsorbed layers, ion beam effects, molecular dynamics method, channelling, vacancies (crystal), diffusion, metallic thin films, surface structure
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13934 (URN)10.1063/1.1940122 (DOI)
Available from: 2006-08-29 Created: 2006-08-29 Last updated: 2016-08-31
2. Enhanced intra- and interlayer mass transport on Pt(111) via 5 - 50 eV Pt atom impacts on two-dimensional Pt clusters
Open this publication in new window or tab >>Enhanced intra- and interlayer mass transport on Pt(111) via 5 - 50 eV Pt atom impacts on two-dimensional Pt clusters
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2006 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 4, 2235-2243 p.Article in journal (Refereed) Published
Abstract [en]

Embedded-atom molecular dynamics simulations were used to investigate the effects of low-energy (5–50 eV) normally-incident self-ion irradiation of two-dimensional compact Pt3, Pt7, Pt19, and Pt37 clusters on Pt(111). We follow atomistic pathways leading to bombardment-induced intra- and interlayer mass transport. The results can be described in terms of three impact energy regimes. With E ≤ 20 eV, we observe an increase in 2D island dimensions and negligible residual point defect formation. As the impact energy is raised above 20 eV, we observe an increase in irradiation-induced lateral mass transport, a decrease in island size, and the activation of interlayer processes. For E ≥ 35 eV, this trend continues, but point defects, in the form of surface vacancies, are also formed. The results illustrate the richness of the dynamical interaction mechanisms occurring among incident energetic species, target clusters, and substrate atoms, leading to island preservation, reconfiguration, disruption and/or residual point defects formation. We discuss the significance of these results in terms of thin film growth.

Keyword
Ion bombardment; Platinum; Clusters; Atomistic dynamics
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13935 (URN)10.1016/j.tsf.2006.05.028 (DOI)
Available from: 2006-08-29 Created: 2006-08-29 Last updated: 2016-08-31
3. Kinetic pathways leading to layer-by-layer growth from hyperthermal atoms: A Multibillion time step molecular dynamics study
Open this publication in new window or tab >>Kinetic pathways leading to layer-by-layer growth from hyperthermal atoms: A Multibillion time step molecular dynamics study
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2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, 115418-115425 p.Article in journal (Refereed) Published
Abstract [en]

We employ multibillion time step embedded-atom molecular dynamics simulations to investigate the homoepitaxial growth of Pt(111) from hyperthermal Pt atoms (EPt=0.2–50eV) using deposition fluxes approaching experimental conditions. Calculated antiphase diffraction intensity oscillations, based on adatom coverages as a function of time, reveal a transition from a three-dimensional multilayer growth mode with EPt<20eV to a layer-by-layer growth with EPt≥20eV. We isolate the effects of irradiation-induced processes and thermally activated mass transport during deposition in order to identify the mechanisms responsible for promoting layer-by-layer growth. Direct evidence is provided to show that the observed transition in growth modes is primarily due to irradiation-induced processes which occur during the 10ps following the arrival of each hyperthermal atom. The kinetic pathways leading to the transition involve both enhanced intralayer and interlayer adatom transport, direct incorporation of energetic atoms into clusters, and cluster disruption leading to increased terrace supersaturation.

Place, publisher, year, edition, pages
American Physical Society, 2007
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-38795 (URN)10.1103/PhysRevB.76.115418 (DOI)45667 (Local ID)45667 (Archive number)45667 (OAI)
Note

The previous status of this article was Manuscript.

Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-01-11Bibliographically approved
4. Controlled intra- and interlayer mass transport during low-energy Pt(111) homoepitaxy
Open this publication in new window or tab >>Controlled intra- and interlayer mass transport during low-energy Pt(111) homoepitaxy
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(English)Manuscript (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-13937 (URN)
Available from: 2006-08-29 Created: 2006-08-29 Last updated: 2014-04-14

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