Diamondlike carbon DLC films High hardness High wear

Diamond-like carbon (DLC) films • High hardness • High wear resistance • Low friction coefficient • Optical transparency • Chemical inertness • Smooth surface • Bio-compatibility Hard disk Video Head Drum • Protective coating • Bio materials Coronary Artery Stent Hip Joint

Disadvantages of DLC films High residual compressive stress poor adhesion (6~20 GPa) Hard disk Before deposition After deposition Substrate bending Delamination M. W. Moon, Acta Mater. , 50 219 (2002).

H a rd n e s s Stress and 3 sp bond fraction

To reduce residual scomp in DLC films • Substrate biasing • Post-annealing • Metal atom incorporation ; Ti, W, Mo, Cr, Al….

W-incorporated DLC films 1. 9 at % W ? m s i han Mec Not fully understood yet !!! A. -Y. Wang APL 86 111902 (2005).

Purpose of this work ≠ 109. 5 o Diamond ; ideal sp 3 bonding DLC ; distorted sp 3 + sp 2, sp bonding Known as a primary cause of the residual stress in DLC structure dependency of total energy of the system on the bond angle & the electron density distribution and its effects on the stress reduction behavior of DLC films

Tetrahedron bond model 109. 5 o Me C DEMe-C DEC-C 90 o~ 130 o C tetrahedral bonding of carbon(or Me)-carbon à structure relaxation à total energy calculation ; reference state Me Bond angle distortion à bond distance relaxation à total energy calculation

Calculation condition § Code; DMOL 3 § Exchange-correlation potential; GGA (PBE) § Atomic orbital; double-zeta polarization basis set § Cutoff radius of atomic orbitals; 9 Å § All electron calculation § Spin consideration

Total energy change by the bond angle distortion

Formation energy of Me-C tetrahedron DEf. M-C = (Etot. M-C + Eatom. C) - (Etot. C-C + Eatom. M) Me DEf. M-C Me

Isosurface of electron density; C-C-tetrahedron 109. 5 o 0. 5 1. 0 1. 5 C 90 o C Inset values are the electron density [Å-3] of the isosurface

Isosurface of electron density right before it is separated V 0. 63 Ti 0. 67 Si 0. 64 Ni 0. 72 Mn 0. 70 W 0. 70 Cr 0. 72 Mo Co 0. 76 Fe 0. 82 C 1. 50 109. 5 o 0. 72

Isosurface of electron density right before it is separated 0. 40 Au 0. 36 Ag 0. 40 Ar 0. 01 Cd Al 0. 45 Zn C 0. 45 Cu 1. 50 109. 5 o 0. 53 Pd 0. 58

Electron density right before its isosurface is separated (res) § Lower re § Lower shape anisotropy of electron density s § Weaker bonding § Lower angular dependency of total energy stress reduction

W-incorporated DLC films C 1. 50 W 0. 70

Me-DLC films; Experimental Hardness Residual stress Young’s modulus By FCVA P. Zhang, J. Vac. Sci. & Tech. A. 20 390 (2002).

Conclusion C 1. 50 Mn 0. 70 Au 0. 40 Al 0. 45