Question Bank



Graphite
  • Name the allotropes of carbon?
  • What is graphite and what are its crystallographic forms?
  • Describe the structure of graphite.
  • What are the three naturally occurring types of graphite?
  • What is HOPG?
  • Explain the lubricity of graphite.
  • What are the limitations of graphite?
  • What is graphene?
  • What is expanded graphite and what are its uses?
  • What is intercalated graphite?
  • What is xGnP?
Classification of Carbon Films
  • What is the difference between Sputtered a-C and ta-C?
  • Define DLC.
  • Write a short note on DLC describing its properties and applications.
  • Name the two most important variables that affect the structure and properties of DLC films.
  • What properties of DLC films are affected by the presence of hydrogen?
  • Hydrogen is an sp2 stabilizer. True/False?
  • How does the hydrogen content in DLC films affect their hardness and electrical properties?
  • Name some common alloying elements in DLCs. Why are DLCs alloyed/doped?
  • Name some methods for depositing DLC films.
  • Name two different sources of carbon in CVD of DLC films.
  • What kind of substrates provide good adhesion to DLC films?
  • How can you improve the adhesion of DLC films to silicide forming substrates?
  • What are nanostructured carbon films, how are they produced, and what are their applications?
Growth Mechanism of a-C:H Thin Films
  • What is NFC film and how can it be deposited ?
  • Expand XRR. What can it be used for?
  • What is the typical hydrogen content in a-C:H films? What does the hydrogen content strongly depend on?
  • How can one control the hydrogen content in a-C:H films?
  • How is the hydrogen content related to carbon bonding in a-C:H films?
  • What kind of carbon bonding will be observed at high ion energies (> 50 eV)?
  • What are polymer-like amorphous carbon films?
  • What is the effect of energy of impinging ions on film composition?
  • What is surface loss probability, and what are its values for sp1-, sp2-, and sp3- hybridized precursors ?
  • Explain the growth mechanism of a-C:H films with schematics.
Photoluminescence of Carbon Films
  • Define: Photoluminescence (PL) and Photostimulated Luminescence (PSL).
  • Describe the optical absorption phenomenon. Draw the log(absorption coefficient) vs photon energy plot, and mark the three absorption regimes.
  • Explain Beer-Lambert's law, Tauc's law, Urbach's tail.
  • Explain the optical absorption phenomenon by defects in materials.
  • What is the reason behind strong PL background in Raman spectra of hydrogenated carbon films?
  • How is the PL intensity related to hydrogen content in hydrogenated carbon films?
  • How is the PL intensity estimated in a Raman spectrum of hydrogenated carbon films?
Hydrogen Estimation in DLC Films
  • Name some techniques of hydrogen estimation in DLC films.
  • Expand: ERDA, EPES, REELS, SIMS, AES, XPS, NMR, ESCA.
  • Explain in detail the EPES technique. Derive the equations for FWHM and fraction of hydrogen content in a C-H-O ternary system.
  • What are the problems with the EPES technique.?
  • Explain in brief the REELS technique.
  • Explain in detail the Electron Rutherford Backscattering technique.
  • Explain in brief the ERDA technique.
Frictional Behavior of DLC
  • What is friction? Name and explain different varities of friction.
  • How do you determine friction?
  • What causes kinetic friction?
  • Define tribology.
  • What is superlubricity? Give an example.
  • Expand BAM. What makes BAM a special material?
  • Define wear? Name the different types of wear.
  • What are the standard instruments used to determine sliding friction coefficient and wear resistance?
  • What is Highly Crosslinked Polyethylene used for?
  • Name the factors that affect the friction and wear performance.
  • What is the typical range of friction coefficient for DLC films?
  • How does the hydrogen content affect the friction in DLC films?
  • Does the substrate rigidity/hardness affect the coefficient of friction of DLC films? If yes, how?
  • Pi-bonding decreases the coefficient of friction of DLC films. True/False?
Wear of DLC
  • Explain adhesive bonding.
  • What causes adhesive bonding in DLC films and how can it be reduced?
  • What causes friction in hydrogen-free DLC films in ultra-high vacuum?
  • What causes friction in a-C:H films in humid environment?
  • What causes friction in a-C:H films in dry/inert atmosphere?
  • How does the friction of DLC films vary with exposure time between subsequent sliding passes?
  • How does humidity affect the friction coefficient in hydrogenated DLC films?
  • What is the effect of hydrogen on coefficient of friction for DLC films in dry/inert atmosphere?
Hydrophobicity in DLC
  • Define wetting. What is the role of adhesive and cohesive forces in wetting of a material surface?
  • Define contact angle.
  • What is the relation between contact angle and wettability?
  • Define hydrophobic, hydrophilic, and superhydrophobic surfaces?
  • What is "Lotus Effect"?
  • What do you mean by high energy and low energy surfaces?
  • Name the factors that impact surface energy and wettability.
  • How can you increase or decrease the surface energy of DLC films?
  • How does the hydrophobicity of DLC films vary with carbon bonding (sp2 and sp3)?
  • How does the hydrogen content in plasma (during DLC film deposition) affect the contact angle of the DLC film?
  • Name some applications of hydrophobic DLC films.
  • What is thrombogenicity?
  • How is contact angle related to surface roughness?
  • What are the surface energies for graphite and diamond?
  • Hydrophobicity increases as the sp3 bonded carbon content increases in DLC films. Explain why this is so and why graphite has a greater contact angle than that of diamond (111).
  • Can the surface energy of a solid be calculated from contact angle measurements (sessile drop method)? If so, explain how this is accomplished.