quantum mechanical description of displacement damage
DESCRIPTION
Quantum Mechanical Description of Displacement Damage. Matthew J. Beck 1 , Ryan Hatcher 1 , R.D. Schrimpf 2 , D.M. Fleetwood 2,1 , and S. T. Pantelides 1 1 Department of Physics and Astronomy 2 Department of Electrical Engineering and Computer Science - PowerPoint PPT PresentationTRANSCRIPT
Quantum Mechanical Description of Displacement
DamageMatthew J. Beck1, Ryan Hatcher1, R.D. Schrimpf2,
D.M. Fleetwood2,1, and S. T. Pantelides1
1Department of Physics and Astronomy2Department of Electrical Engineering and Computer Science
Vanderbilt University, Nashville, TN 37235 USA
MURI ReviewJune 13th, 2007
Support: AFOSR
Matthew J. Beck
[email protected] Review, June 2007
Introduction• NIEL, Kinchin-Pease — threshold
displacement energy• Molecular dynamics (MD) — full atomistic
dynamics– Limitation: empirical potentials
• >1 keV: Accurate methods exist• …but “terminal subclusters” are <1 keV
events! PKA
Secondary
Terminal Subclusters
Matthew J. Beck
[email protected] Review, June 2007
First-principles Molecular Dynamics
• State-of-the-art quantum mechanical calculations
• Density functional theory, local density approximation
• Cell sizes: 216 atoms• Calculation times: 100s of fs
Dynamic “messiness” @ 100 fs Red atoms: KE >
0.22 eV Black atoms: displaced > 0.2
Å
Matthew J. Beck
[email protected] Review, June 2007
Identifying Terminal Subclusters
15 eV displacement
PKA
Secondary
Terminal Subclusters
500 eV displacement
Matthew J. Beck
[email protected] Review, June 2007
Identifying Terminal Subclusters
500 eV
15-100 eVFr
act
ion o
f in
itia
l m
om
en
tum
Fraction of initial momentum along displacement direction
remaining
500 eV
15-100 eV
Time
Matthew J. Beck
[email protected] Review, June 2007
Identifying Terminal Subclusters
500 eV
<=100 eV
Fract
ion o
f in
itia
l m
om
en
tum
Fraction of initial momentum along displacement direction remaining
Time
Matthew J. Beck
[email protected] Review, June 2007
Damage Scaling with Energy• Natoms with KE > 0.22 eV N atoms with Δr > 1.17 Å
– Even small KE events contribute!– “Hot” atoms predict disordered atoms
Damage Scaling:• Density of secondary atoms
– independent of direction and energy
• Energy of secondary atoms – dependent on initial displacement energy
Note: 0.22 eV T m
SiRed (hot) atoms: KE > 0.22 eV Black atoms:
displaced > 0.2 Å
25 eV displacement: Dynamic
“messiness” @ 100 fs
Matthew J. Beck
[email protected] Review, June 2007
Damage Scaling with Energy
15 eV, 8 atoms
500 eV, 8 secondaries, 64 total atoms?
Melt cylinder along ion track!
Diameter for 500 eV ion: 3 nm
1.5 nm
Matthew J. Beck
[email protected] Review, June 2007
Experimental Melt Tracks
AFM image of recrystalized Si along glancing Pb ion tracks at the Si/SiO2 interface. White
arrow shows incident ion direction
A.F.M.J. Carvalho, et al., APL 90
073116 (2007)
Matthew J. Beck
[email protected] Review, June 2007
Conclusions• Quantum mechanical calculations are
effective tools for probing atomic scale dynamics of <1 keV displacements– Quantitatively identify terminal subclusters– Low energy displacements contribute to
dynamical damage formation
• Single displacement damage events can disorder volumes of atoms which are significant in highly scaled devices