of Diamond-like Carbon Thin Film An Experimental Study of the Influence of Imperfections on the Buckling of Diamond-like Carbon Thin Film Myoung-Woon Moon, Kyu-Hwan Oh School of Materials Science and Engineering, Seoul National University, KOREA Princeton Materials Institute, Princeton University, USA Jin-Won Chung, Kwang-Ryeol Lee Future Technology Research Division Korea Institute of Science and Technology, KOREA R. Wang, A. G. Evans

Purpose and overviews Purpose Overview The observation on the sources of interface imperfection Defect, Free edge, Substrate Curvature Optimization of imperfection instability Overview (Characterization of defect on the interface) - Surface profile on defect site : Atomic Force Microscopy - Cross sectioning of defect site : Focus Ion Beam - Chemical analysis for defect : Auger Electron Spectroscopy Observation for the condition of defect-induced delamination

The Source of Imperfection

Introduction of Interface delamination General systems with Delamination or Buckle -Highly compressed film DLC or Diamond film on glass / Si Gold on copper film on sapphire Amorphous (hydrogenated ) Si film on glass/Si Stainless steel on polycarbonate Thermal Barrier Coatings system Interface delamination on Diamond-Like Carbon film Imperfection deriven Delamination Buckle deriven Delamination

Imperfection I – Interface defects The reflection of Small defects on the film surface after deposition 4 mm 10 mm 10 mm Large defects 10 mm 10 mm 10 mm 20 mm

Imperfection II - Free edge Free edge effect on delamination Free edge 5 mm 50 mm Delamination sequence from free edge ( t = Real time) t=5 sec t=1 sec 10 mm 200 mm Thickness of film h= 0.13 mm h= 0.80 mm

Imperfection III – Substrate Curvature effect “Substrate curvature plays a role of imperfection” J. W. Hutchinson, JMPS, 49, 2001 L > 1 The condition of Preferred Propagation direction Concave : axial Convex : circumferential

Observation on defect site

Experiments on defect effects  Deposition with CVD Diamond-like carbon films on glass substrates by PECVD with CH4 and C6H6 plus N2, Negative self bias voltage : -100 to -700V The film thickness : 0.13 ~ 0.46mm Residual compression : 1GPa and 3GPa  resulting in telephone cord buckles. AFM In tapping mode (Digital Instrument company).  Images of representative buckles and cross sectional profiles FIB Dual-Beam FIB (FEI Company, DB235).  Direct cut along the buckle (damage free)  To create the straight-sided buckle from telephone cord buckle. AES Auger Electron Spectroscopy  Chemical analysis on several defect sites  

Cross sections of defect sites - AFM Surface topology Profile of Cross section

Cross sectioning : small defect - FIB Defect Geometry Thickness of film h ~ 0.46mm Wavelength : 10 mm Amplitude : ~0.9 h Before cut After cut

Cross sectioning : Large defect - FIB Before cut After Defect Geometry Thickness of film h ~ 0.46mm Wavelength : 40 mm Amplitude : ~ 1.6 h Moon et al, Acta Mater., 2002

Chemical analysis underneath defect sites -AES Film surface (Refection of defect) Underneath film (Defect on substrate) 10 mm 5 mm - Auger electron spectroscopy-

Discussion and Summary

Energy release rate with imperfection size The condition of Delamination propagation Hutchinson, He, Evans, 2000, JMPS

Summary of Observation on defect sites =1.9GPa E=90~100GPa Sub-critical No delamination Stationary Delamination only Super-critical Propagation of delamination . * Weiderhorn, S. M., J. Am. Ceram. Soc., 1967, 50, 407.

Summary The source of imperfection on the interface Defect, Free edge, and substrate curvature effect The characterization of Defect AFM :Measurement of Profile of defect on the film surface FIB : Cross sectional analysis with fine AES : Chemical analysis on foreign defect on the interface The condition of Defect-induced delamination