1. S15-O-13
10~14, Sep., 2006
Jeju, Korea
IUMRS-ICA-2006
First-Principles Study on Stress Reduction Behavior & Bond Characteristics of Metal-Incorporated Amorphous Carbon Films
Jung-Hae Choi, Seung-Cheol Lee, and Kwang-Ryeol Lee
Future Technology Research Division Korea Institute of Science and Technology

2. Amorphous carbon (a-C) films
High hardness
High wear resistance
Low friction coefficient
Optical transparency
Chemical inertness
Smooth surface
Bio-compatibility
Protective coating
Bio materials
Video
Head Drum
Coronary
Artery Stent
Hard disk
Hip Joint

3. Disadvantages of a-C films
High residual compressive stress
(6~20 GPa)
poor adhesion
Hard disk
Before deposition
After deposition
Substrate bending
Delamination
M. W. Moon, Acta Mater., (2002).

4. Structure and property relationship
Substrate biasing
Post-annealing
Metal incorporation
; Ti, W, Mo, Cr, Al….
Hardness

5. Metal-incorporated a-C films
a-C:W
a-C:Ag
Not fully understood yet !!!
Mechanism ?
1.9 at. % W
2 nm
0.1 at. % Ag
A.-Y. Wang APL (2005).
Carbon (2006).
H.-W. Choi, unpublished work

6. Purpose of this work a-C; ; sp3, sp2, sp bonding Diamond
; ideal sp3 bonding
109.5o
≠109.5o
a-C; ; sp3, sp2, sp bonding
distorted sp3 ; primary cause of
the residual stress
The effect of metal incorporation on the stress reduction
 atomic bond characteristics ??
First-principles calculations
- the dependency of total energy of the system on the bond angle
- the electronic structure and its effects on the stress reduction
behavior of a-C films

7. Tetrahedron bond modelC
109.5o Me
tetrahedral bonding of
carbon(or Me)-carbon
structure relaxation
total energy calculation
; reference state
DEC-C
DEMe-C
90o~
130o C
90o~
130o Me
Bond angle distortion
bond distance relaxation
total energy calculation
Me; Mo, Ag, Al

8. Calculation condition by VASP
DFT scheme
Ecut = 550 eV
Exchange-correlation potential; GGA (PBE)
Projector Augmented-Wave (PAW) potential
Gaussian smearing factor = 0.05 eV
Spin-unrestricted calculations
Convergence = 10-5 eV
Ionic relaxation; CG method (force < 0.01 eV/Å)
Gamma point calculation (15x15x15 Å3)

9. Total energy change by the bond angle distortion
Increase in total energy drastically decreases
by Me-incorporation.
Noble metal shows lower increase in total energy
by the bond angle distortion than transition metal.
Al shows a negative energy change by the bond angle
distortion.

10. Charge density of HOMO C 4 5 3 2 1 z Covalent bonding [e/Å3] [Å]
rMax=1.05
d=1.54
Covalent bonding
[e/Å3]
[Å]

11. Charge density of HOMO C Mo Ag Al bonding nonbonding antibonding ionic
rMax=1.05
d=1.54
rMax=0.69
d=2.10
rMax=0.63
d=2.27
rMax=0.69
d=2.05
bonding
nonbonding
antibonding
ionic

12. Partial density of statesC Mo Ag Al
s, p, d
bonding
nonbonding
antibonding
ionic
s, p, d orbitals

13. a-C:Al films DE90 < 0 sp3 sp2 Residual stress Hardness
Young’s modulus
P. Zhang, J. Vac. Sci. & Tech. A (2002).

14. Summary C Mo C Mo Ag Al Ag Al d=1.54 d=2.10 Atomic bond structure
Sp3 fraction
Hardness
Residual compressive stress C Mo Al Ag C Mo
rMax=1.05
d=1.54
rMax=0.69
d=2.10 Al Ag
Atomic bond structure
 role of metal incorporation in a-C films
a guideline for the choice of a metal
element to control the residual stress of
a-C films without a substantial
degradation in the mechanical properties.
rMax=0.63
d=2.27
rMax=0.69
d=2.05