An Experimental Study of the Influence of Imperfections on the Buckling of Diamond-like Carbon Thin FilmMyoung-Woon Moon, Kyu-Hwan Oh School of Materials Science and Engineering, Seoul National University, KOREAPrinceton Materials Institute, Princeton University, USA

Jin-Won Chung, Kwang-Ryeol LeeFuture Technology Research DivisionKorea Institute of Science and Technology, KOREA

R. Wang, A. G. EvansPrinceton Materials Institute, Princeton University, USA

PurposeThe observation on the sources of interface imperfection Defect, Free edge, Substrate CurvatureOptimization of imperfection instabilityPurpose and overviews 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

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

The reflection of Small defects on the film surface after depositionLarge defectsImperfection I Interface defects

t=1 sect=5 secFree edge effect on delaminationDelamination sequence from free edge ( t = Real time)Imperfection II - Free edgeThickness of film h= 0.13 mmh= 0.80 mm

Substrate curvature plays a role of imperfectionJ. W. Hutchinson, JMPS, 49, 2001Imperfection III Substrate Curvature effectL > 1 The condition of Preferred Propagation direction

Concave : axial Convex : circumferential

Observation on defect site

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

Experiments on defect effects

Cross sections of defect sites - AFMSurface topologyProfile of Cross section

Cross sectioning : small defect - FIBDefect Geometry

Thickness of film h ~ 0.46mm

Wavelength : 10 mmAmplitude : ~0.9 hBefore cut

After cut

Cross sectioning : Large defect - FIBDefect Geometry

Thickness of film h ~ 0.46mm

Wavelength : 40 mm Amplitude : ~ 1.6 hBefore cut

After cutMoon et al, Acta Mater., 2002

- Auger electron spectroscopy-Film surface(Refection of defect)Chemical analysis underneath defect sites -AESUnderneath film(Defect on substrate)

Discussion and Summary

Energy release rate with imperfection sizeHutchinson, He, Evans, 2000, JMPS The condition ofDelamination propagation

Sub-critical No delamination

Stationary Delamination only

Super-critical Propagation of delaminationSummary of Observation on defect sites* Weiderhorn, S. M., J. Am. Ceram. Soc., 1967, 50, 407.E=90~100GPa =1.9GPa .

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

Summary