1. Jung-Hae Choi, Hyo-Shin Ahn, Seung-Cheol Lee & Kwang-Ryeol Lee
Third Conference
of the Asian Consortium
for Computational Materials Science
(ACCMS-3)
PC43
08-11, Sep., 2005
Beijing, China
Stress reduction behavior in metal incorporated amorphous carbon films ; First-principle approach
Jung-Hae Choi, Hyo-Shin Ahn,
Seung-Cheol Lee & Kwang-Ryeol Lee
Future Technology Research Division Korea Institute of Science and Technology
Seoul, KOREA

2. Tetrahedral amorphous carbon (ta-C) films
High fraction of tetrahedral (sp3) bonding
Advantages
- High hardness and wear resistance
Optical transparency
Chemical inertness
- Smooth surface
- Bio-compatibility
Hard coatings
Hard disk
Disadvantages
- High residual compressive stress (6~20 GPa) → poor adhesion
Delamination
Before deposition
After deposition
Substrate bending
M. W. Moon et al.,
Acta Mater., (2002).

3. Motivation reduction of residual compressive stress
in W-incorporated a-C:H films
prepared by a hybrid process
composed of ion-beam deposition and magnetron sputtering
1.9 at % W
W atoms are fully dissolved
in a-C matrix
Mechanism ?
Not fully understood yet !!!
A.-Y. Wang et al., APL (2005).

4. Purpose of this work Amorphous carbon Diamond ; distorted sp3
; ideal sp3 bonding
109.5o
≠109.5o
Amorphous carbon
; distorted sp3
+ sp2, sp bonding
Known as a primary cause of
the residual stress in a-C structure
to elucidate the dependency of total energy of the system on the bond angle & the electron density distribution and its effects on the stress reduction behavior of a-C films

5. Calculation condition by DMOL3
DFT scheme
Exchange-correlation potential; GGA (PBE)
Atomic orbital; double-zeta polarization basis set
Cutoff radius of atomic orbitals; 9 Å
All electron calculation
Spin consideration

6. 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

7. Total energy change by the bond angle distortion
Increase in total energy drastically decreases
by Me-incorporation.
Metal atoms having a filled d-shell (underlined atoms) show
lower increase in total energy by the bond angle distortion.
Al shows a similar behavior with noble metals.

8. Formation energy of Me-C tetrahedron
DEfM-C = (EtotM-C + EatomC) - (EtotC-C + EatomM) Me Me
Higher formation energy of Me-C tetrahedron
 weaker Me-C bond
 less angular dependency of total energy

9. Isosurface of electron density; C-C-tetrahedron
0.5
1.5
1.0
90o C
1.5
1.0
0.5
Inset values are the electron density [Å-3] of the isosurface

10. Iso-e- density surface ; Au-C-109
Isosurface of electron density; Au-C-tetrahedron
Iso-e- density surface ; Au-C-109
109.5o Au
0.2
0.4
0.5
90o Au
0.2
0.4
0.5
Inset values are the electron density [Å-3] of the isosurface

11. Isosurface of electron density right before it is separatedAg Ar Cd Au Al Zn Cu Pd C
109.5o

12. Isosurface of electron density right before it is separatedV Ti Ni Si Mn W Cr Mo Co Fe C
109.5o

13. electron density right before its isosurface is separated (res)
Weaker bonding
Lower angular dependency
of total energy
 stress reduction
Lower res
Lower shape anisotropy
of electron density

14. Larger atom incorporation in a-C structured
0.0 %
2.0 %
5.0 % Si C
MD of a-C:Si deposition
: Dimensional increase along the
surface normal by Si incorporation
 may release the strain
S.- H. Lee et al.. PA15 in ACCMS-3
Induce strain energy ?
Maybe not significant !

15. Summary
The stress reduction behavior in metal-incorporated amorphous carbon films was investigated by the first-principle calculation. Present calculations evidently show that the metal incorporation reduces the directionality of the bond, which results in the reduction of the residual stress caused by bond angle distortion in amorphous carbon network. The pivotal action of the metal atoms dissolved in the carbon matrix would be more significant when noble metals having filled d-shells, such as Au, Ag, or Cu, are incorporated. These atoms have a weak and more isotropic bond with carbon atoms as confirmed by the electron density distribution. Interestingly, Al also shows a very weak dependence of the energy on the bond angle. Electron density distribution of Al incorporated tetrahedron shows the similar behavior to that of noble metal-incorporated tetrahedron.