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Mechanical Properties of diamond-like carbon films grown by plasma CVD

Mechanical Properties of diamond-like carbon films grown by plasma CVD. By: Liwei Wang Instructor: Dr. Y. Tzeng For: ELEC 7730 Date: Oct 17, 2003. Questions. How the hydrogen incorporation induced in the DLC film deposition effect the mechanical properties?

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Mechanical Properties of diamond-like carbon films grown by plasma CVD

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  1. Mechanical Properties of diamond-like carbon films grown by plasma CVD By: Liwei Wang Instructor: Dr. Y. Tzeng For: ELEC 7730 Date: Oct 17, 2003

  2. Questions • How the hydrogen incorporation induced in the DLC film deposition effect the mechanical properties? • What is the synergetic effect on the surface roughness of DLC films?

  3. Outline • Background Introduction • ---What is Diamond-like carbon (DLC) film? • ---Why DLC film? • DLC deposition techniques • ---How DLC films grow? • Mechanical Properties • ---What is the correlation between mechanical properties and the deposition condition?

  4. What is DLC? Carbon usually exists in several forms; graphite, diamond, and the new form of fullerines. All three of these forms are crystalline in structure but have varying properties based on the bonding order of the carbon atoms. Diamond-like carbon (DLC), on the other hand, is amorphous in structure, containing both SP2 and SP3 bonded carbon. As such, DLC has both diamond-like and graphitic properties. Hence the name diamond-like carbon (DLC).

  5. What is DLC? http://www.nippon-itf.co.jp/dlcen.html

  6. Why DLC film? • High hardness. • Due to the low temperature coating process, which makes them particularly attractive for applications where the substrate cannot experience elevated temperatures. it can be deposited not only on carburized steel or aluminum alloy, but also on many kinds of rubber and resin! • Low friction coefficient (about0.1) even without lubrication! http://www.nippon-itf.co.jp/dlcen.html

  7. Why DLC film? • High optical transparency. • High dielectric strength. • High thermal conductivity. • High chemical inertness, biocompatibility • High surface smoothness. Etc. The unique combination of those desirable characteristic and material properties make the DLC films attract widespread attention in both industrial and technical applications.

  8. DLC deposition techniques • DLC films have been prepared by a variety of methods and precursors, such as: • RF-Plasma assisted CVD (RF-PACVD) • DC-Plasma assisted CVD (DC-PACVD) • Plasma Enhanced CVD (PECVD) • Electron cyclotron resonance microwave plasma CVD (ECR-PACVD) • Sputtering • Vacuum arc deposition • Filtered - cathodic vacuum arc (FCVA) deposition • Ion beam deposition • From a variety of solid and gaseous source materials.

  9. The ECR-MPCVD Process • Lower, broad range of operating pressures. • High ionization efficiency • Wide range of achievable ion energies: • ----Intrinsic ion energies below values that can induce • radiation damage. • ----Higher energies can be achieved easily with assistance • of extraction grids, or substrate bias. • Electrodeless coupling of the electric power to the plasma • Directionality of the ion and even neutral beam. Alfred Grill, Gold Plasma in materials fabrication, IEEE Press, 1994

  10. The ECR-MPCVD system • Microwave generator • ---2.45Ghz • Permanent magnets • ---875gauss • RF generator • ---13.56Mhz • Additional magnets • Turbo pump http://www2.eng.cam.ac.uk/~www-edm/equip.html

  11. The ECR-MPCVD system A schematic of the commercial ECR-MPCVD system from ASTeX ASTeX AX2040 http://www.eng.uc.edu/~rsingh/pvd.htm

  12. ECR-MPCVD Process parameters Different process parameters such as: -- substrate bias, -- plasma gas composition, -- substrate temperature, -- pressure and plasma -- density Have great influence on the composition, crystal quality, properties of the deposited films.

  13. ECR-MPCVD Process parameters used in the DLC deposition

  14. Characterization of DLC film-Mechanical properties Raman spectroscopy Phase structural determination Atomic force microscope (AFM) Surface roughness Measured by: Film Harness Nanoindenter Tribological behaviors Tribometer

  15. Phase structural determination by Raman analysis Highly crystalline perfect graphite exhibits a sharp peak at 1580cm-1 ----G-peak Diamond exhibits a sharp peak at 1332cm-1 ----D-peak Raman sensitivity for sp2-C was reported to be more than a hundred times higher than that for sp3-C Therefore, most Raman analysis about DLC film is concerned with G-band (a band around 1580cm-1 ) P.L. Chen et al./Applied Surface Science 92 (1996) 30-34

  16. Raman spectra A broad skewed peak centered at ~ 1580cm-1 D-peak shifted from 1410cm-1 to 1365cm-1 G-peak shifted from 1585cm-1 -1545cm-1 when the magnitude of the bias voltage was increased. K.Y. Li et al. / Diamond and Related Materials 10 (2001) 1855 - 1861

  17. Surface roughness • Generally, DLC film surface roughness • Range from 2rms to 10rms. • Decrease with increasing negative bias voltage. • Because the surface roughness is a synergetic effect of • Ion bombardment • Formation of volatile hydrocarbon compounds.

  18. Surface roughness measured by AFM AFM image of DLC prepared in (a) -120 V and (b) -60 V K.Y. Li et al. / Diamond and Related Materials 10 (2001) 1861 - 1867

  19. Film Hardness • DLC films have a wide range of hardness • Range from 3GPa to 80GPa. • Increase with increasing negative bias voltage to certain level. • These differences are interrelated with • Kinetic energy of plasma constituents impinging on • substrate surface. • Subsequent hydrogen incorporation into carbon films.

  20. Film Hardness Monovalent hydrogen can serve as the terminating atoms in a carbon network. Develop softer and polymeric-like films with hardness below 4 GPa. Higher concentration of hydrogen will induce more hydrogen incorporation. K.Y. Li et al. / Diamond and Related Materials 10 (2001) 1861 - 1867

  21. Film Hardness Most mechanical properties of DLC films strongly depended on the kinetic energy of impinging particles. Higher substrate bias leads to intense impingement distorting the carbon planes and then reinstating by cross-linked sp3 carbon bonding Increase the fraction of sp3 sites and develop more diamond-like bonding environment. K.Y. Li et al. / Diamond and Related Materials 10 (2001) 1861 - 1867

  22. Film Hardness DLCA – Acetylene/Argon 3sccm /60sccm DLCM – Methane/Argon 6sccm /60sccm K.Y. Li et al. / Diamond and Related Materials 10 (2001) 1861 - 1867

  23. Conclusions • DLC film describes a variety of amorphous carbon materials. • Exhibit a wide range of mechanical and tribological behaviors controlled by the deposition process. • Provide great potential in both industrial and technology applications.

  24. Answers • Monovalent hydrogen can serve as the terminating atoms in a carbon network, which will help develop polymeric – like films. • It is a synergetic effect of ion bombardment and formation of volatile hydrocarbon compounds.

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