26~27, Oct., 2006 Jeju ICC DLC , , Diamond-like carbon (DLC) films Amorphous Carbon Film Mixture of sp 1, sp 2 and sp 3 Hybridized Bonds High Content of Hydrogen (20-60%) Synonyms Diamond-like Carbon (Hydrogenated) amorphous carbon (a-C:H) i-Carbon Tetrahedral Amorphous Carbon (ta-C) ta-C sp 2 H sp 3 DAC PAC ta-C:H GA C No film High hardness High wear resistance Low friction coefficient Optical transparency Chemical inertness Smooth surface Bio-compatibility High hardness High wear resistance Low friction coefficient Optical transparency Chemical inertness Smooth surface Bio-compatibility Hard disk Video Head Drum Coronary Artery Stent Hip Joint Protective coating Bio materials Protective coating Bio materials Diamond-like carbon (DLC) films Disadvantages of DLC films Hard disk Before deposition After deposition M. W. Moon, Acta Mater., (2002). High residual compressive stress (6~20 GPa) High residual compressive stress (6~20 GPa) poor adhesion Substrate bending Delamination Structure and property relationship Hardness Substrate biasing Post-annealing Metal incorporation ; Ti, W, Mo, Cr, Al. Substrate biasing Post-annealing Metal incorporation ; Ti, W, Mo, Cr, Al. Metal-incorporated DLC films A.-Y. Wang APL (2005). Carbon (2006). 2 nm 0.1 at. % Ag 1.9 at. % W a-C:W a-C:Ag H.-W. Choi, unpublished work Not fully understood yet !!! Mechanism ? Purpose of this work The effect of metal incorporation on the stress reduction atomic bond characteristics ?? DLC ; sp 3, sp 2, sp bonding distorted sp 3 ; primary cause of the residual stress Diamond ; ideal sp 3 bonding o 109.5 o 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 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 o Me 90 o ~ 130 o Me 90 o ~ 130 o C o C E C-C E Me-C Me; Mo, Ag, Al Calculation condition by VASP DFT scheme E cut = 550 eV Exchange-correlation potential; GGA (PBE) Projector Augmented-Wave (PAW) potential Gaussian smearing factor = 0.05 eV Spin-unrestricted calculations Convergence = eV Ionic relaxation; CG method (force < 0.01 eV/) Gamma point calculation (15x15x15 3 ) 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. 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. Charge density of HOMO C Max =1.05 d= o z Covalent bonding [e/ 3 ] [] Charge density of HOMO MoAg Max =0.69 d=2.10 Max =0.63 d=2.27 C Max =1.05 d=1.54 bonding nonbonding antibonding Al Max =0.69 d=2.05 ionic Partial density of states s, p, d MoAg C Al bonding nonbonding antibonding ionic s, p, d orbitals Al a-C:Al films Residual stress Hardness Youngs modulus sp 3 sp 2 E 90 < 0 P. Zhang, J. Vac. Sci. & Tech. A (2002). Summary Mo Ag Max =0.69 d=2.10 Max =0.63 d=2.27 C Max =1.05 d=1.54 Al Max =0.69 d=2.05 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. 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. Hardness Sp fraction Sp 3 fraction Residual compressive stress C Mo Al Ag