Korea Institute of Science and Technology Seung-Hyeob Lee, Churl-Seung Lee, Seung-Cheol Lee, Kyu-Hwan Lee, and Kwang-Ryeol Lee Future Technology Research Division, Korea Institute of Science and Technology, Korea Institute of Science and Technology, P.O. Box, 131 Cheongryang, Seoul, Korea Structural Evolutions of Amorphous Carbon Films by Molecular Dynamics Simulation The International Conference On Metallurgical Coatings And Thin Films ICMCTF 2003

Korea Institute of Science and Technology IntroductionIntroduction  Tetrahedral Amorphous Carbon (ta-C) Film  Non-hydrogenated amorphous carbon  High ratio of sp 3 hybridized carbon bonds (60-80%)  High hardness, density, and wear resistance  Smooth surface, chemical inertness, optical transparency RMS roughness = 0.95nm

Korea Institute of Science and Technology MotivationMotivation  Problems of ta-C Film  High Residual Compressive Stress 6 – 20 GPa  Deterioration of Adhesion Self-delamination of a-C film Peeling off the a-C film

Korea Institute of Science and Technology Approach Approach  Atomic Scale Investigation using Computer Simulation  Investigation of structural evolutions and physical properties  Understanding of mechanical, chemical, thermal phenomena  Overcome the limitation of experiments  Various conditions Understanding the Relationship between Structure Evolution and Material Properties Understanding the Relationship between Structure Evolution and Material Properties

Korea Institute of Science and Technology Structural Modeling for ta-C Film  Subplantation Model  Generation rigid, dense phase by shallow subsurface implantation process by deposition of hyperthermal species Y. Lifshitz et al. Phys. Rev. Lett., 62 (1989) 1290  Thermal Spike Model  Generation stress state by localized melting due to adequate high incident beam energy and rapid chilling D. R. Mckenzie et al. Phys. Rev. Lett., 67 (1991) 773

Korea Institute of Science and Technology Purposes of This Work  Growth of a-C Film by Molecular Dynamics Simulation  Deposition of carbon atom with high energy  Observation of Structural Evolution  Investigation of Material Properties  Pair correlation function, bonding structure, density and stress

Korea Institute of Science and Technology MethodologyMethodology  Empirical Potential  Tersoff Potential J. Tersoff, Phys. Rev. Lett., 61 (1988)  Diamond Substrate  Number of atoms : 608  Temperature : 300K  Boundary condition : Y-Z axis  Carbon Deposition  Number of deposited atoms : 500 atoms  Incident kinetic energy : 1 ~ 300 eV  Time step : ~ 0.5 fs  Interval between carbon arrival : 1 ps  Full dynamics except fixed layer In the case of 75 eV

Korea Institute of Science and Technology Deposition Behavior of a-C Film Incident atomsSubstrate atoms 50 eV 150 eV 1 eV

Korea Institute of Science and Technology DensityDensity

Residual Stress and sp 3 Bond Fraction

Korea Institute of Science and Technology Distribution of Coordination Number 50 eV 150 eV 1 eV 100 eV Coordination Number

Korea Institute of Science and Technology Experimental Residual Stress J.-K. Shin et al, Appl. Phys. Lett., 27 (2001) Growth by Filtered Vacuum Arc Method

Korea Institute of Science and Technology Pair Correlation Function Satellite Site

Korea Institute of Science and Technology Comparison of Pair Correlation Function

Korea Institute of Science and Technology ConclusionsConclusions  The optimum incident energy for the highest residual stress, sp 3 bond ratio and density was in the rage from 50 to 75 eV, which is in good agreement with experimental observations.  At the optimum incident energy, significant amount of carbon atom was placed at a meta-stable site of distance 0.21 nm.  From the meta-stable site intensity, the atomic structure of the amorphous carbon film depended on the quenching rate of thermal spike due to the collision of energetic carbon atom.

Korea Institute of Science and Technology Potential Energy (Incident Energy Dependence) Potential Energy 1 eV 50 eV 300 eV

Korea Institute of Science and Technology Behavior of System Energy during Deposition 1 st Atom 2 nd Atom 5 th Atom3 rd Atom Bombardment occurs here! In the case of 50 eV

Korea Institute of Science and Technology Snapshot of Coordination and Residual Stress Min Max In the case of 75 eV

Korea Institute of Science and Technology ApplicationsApplications  Industrial Applications  Head drum of VCR, CD-R pressing die, chip carrying tools, forming dies, EMC molding cavity and so on.  Biological and Medical Applications  Artificial valve of the heart, hip joint, stent and so on.

Korea Institute of Science and Technology Behavior of System Energy during Deposition Bombardment occurs here! In the case of 75 eV Deposition atom added here