Graphite [ Solutions ]
- Name the allotropes of carbon?
- What is graphite and what are its crystallographic forms?
- Draw and explain the structure of graphite.
- What are the three naturally occurring types of graphite?
- What is HOPG?
- Explain the lubricity of graphite.
- What is graphene?
- What is expanded graphite and what are its uses?
- What is intercalated graphite?
- What is xGnP?
- 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?
- How does the hydrogen content in DLC films affect their hardness and electrical properties?
- Why are DLCs doped? Name some common doping elements in DLCs.
- 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?
- 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.
- 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?
- 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.
- 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?
- 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?
- 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.
