08-11, Sep., 2005Beijing, China

Stress reduction behavior in metal incorporated

amorphous carbon films; First-principle approach

Third Conference of the Asian Consortium for Computational Materials Science(ACCMS-3)

Jung-Hae Choi, Hyo-Shin Ahn, Seung-Cheol Lee & Kwang-Ryeol Lee

Future Technology Research DivisionKorea Institute of Science and Technology

Seoul, KOREA

choijh@kist.re.krhttp://diamond.kist.re.kr/DLC

PC43

Tetrahedral amorphous carbon (ta-C) films

• Advantages• Advantages

Hard disk

Before deposition

After deposition

DelaminationM. W. Moon et al., Acta Mater., 50 219 (2002).

- High residual compressive stress (6~20 GPa) → poor adhesion

High fraction of tetrahedral (sp3) bonding

Substrate bending

Hard coatings- High hardness and wear resistance

- Optical transparency

- Chemical inertness

- Smooth surface

- Bio-compatibility

• Disadvantages• Disadvantages

Motivation

1.9 at % W

A.-Y. Wang et al., APL 86 111902 (2005).

reduction of residual compressive stress in W-incorporated a-C:H filmsprepared by a hybrid process composed of ion-beam deposition and magnetron sputtering

W atoms are fully dissolved in a-C matrix

Not fully understood yet !!!Mechanism ?

Purpose of this work

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

Amorphous carbon; distorted sp3 + sp2, sp bonding

Diamond ; ideal sp3 bonding

109.5o

≠109.5o

Known as a primary cause of the residual stress in a-C structure

Known as a primary cause of the residual stress in a-C structure

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

Tetrahedron bond model

tetrahedral bonding of carbon(or Me)-carbon structure relaxation total energy calculation ; reference state

tetrahedral bonding of carbon(or Me)-carbon structure relaxation total energy calculation ; reference state

Bond angle distortion bond distance relaxation total energy calculation

Bond angle distortion bond distance relaxation total energy calculation

109.5o

Me

90o~130o

Me

90o~130o

C

109.5o

C

EC-C EMe-C

Total energy change by the bond angle distortion

3 4 5 6 7 8 9 10 11 12 13 14 15-1

0

1

2

Fe

Mn

V

ZnCd AlNi

Pd

Co

CuAgAu

MoCrW

Ti

Si

C

E90

o (e

V)

atomic group (# of valence e-)

2nd period 3rd period 4th period 5th period 6th period

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.

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.

Formation energy of Me-C tetrahedron

3 4 5 6 7 8 9 10 11 12 13 14 15

0

2

4

6

8

10

12

14

C

Si

Al

CdZn

AuAg

CuPd

NiCo

Fe

2nd period 3rd period 4th period 5th period 6th period

MnCrMoW

V

Ti

Ef M

e-C(e

V)

atomic group (# of valence e-)

EfM-C = (Etot

M-C + EatomC) - (Etot

C-C + EatomM)Ef

M-C = (EtotM-C + Eatom

C) - (EtotC-C + Eatom

M)

Me

Higher formation energy of Me-C tetrahedron weaker Me-C bond less angular dependency of total energy

Higher formation energy of Me-C tetrahedron weaker Me-C bond less angular dependency of total energy

Me

Isosurface of electron density; C-C-tetrahedron

90o

C

1.51.00.5

Inset values are the electron density [Å-3] of the isosurface

109.5o

C

0.5 1.51.0

Iso-e- density surface ; Au-C-109

0.5

Isosurface of electron density; Au-C-tetrahedron

109.5o

Au

90o

Au

0.40.2 0.5

0.2 0.4

Inset values are the electron density [Å-3] of the isosurface

Isosurface of electron density right before it is separated

109.5o

Ar 0.01 Cd 0.36 Ag 0.40 Au 0.40

Pd 0.58Cu 0.53Zn 0.45Al 0.45

C 1.50

Isosurface of electron density right before it is separated

Cr 0.72

109.5o

V 0.63 Ti 0.64 Ni 0.67 Si 0.72

Mo 0.72W 0.70Mn 0.70

Co 0.76 Fe 0.82 C 1.50

electron density right before its isosurface is separated (e

s)

Lower es

Lower shape anisotropy of electron density

Lower es

Lower shape anisotropy of electron density

Weaker bonding Lower angular dependency of total energy stress reduction

Weaker bonding Lower angular dependency of total energy stress reduction

3 4 5 6 7 8 9 10 11 12 13 14 150.2

0.4

0.6

0.8

1.4

1.6

C

Al

Si

ZnCd

CuAg/Au

NiPd

CoFe

MnV

Cr/Mo WTi

Ti

2nd period 3rd period 4th period 5th period 6th period

atomic group (# of valence e-)

es (A

-3)

Larger atom incorporation in a-C structure

3 4 5 6 7 8 9 10 11 12 13 14 151.1

1.2

1.3

1.4

1.5

1.6

1.7

Si

Al

Cd

Zn

Au

Ag

Cu

Pd

NiCo

Fe

Mn

WMo

Cr

VTi

Ti

3rd period 4th period 5th period 6th period

d Me-

C/d

C-C

atomic group (# of valence e-)

d

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

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 !

Induce strain energy ? Maybe not significant !

0.0 %

2.0 %

5.0 %

Si

C

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.