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CNT Growth: Current Technology and its Limits

CNT Growth: Current Technology and its Limits. Presented by: Kevin McMullen February 23, 2009. Methods and Limitations. Barriers to industrial applications of nanotubes: Scalability of growth for quality nanotubes Defect-free growth of macroscopic length tubes

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CNT Growth: Current Technology and its Limits

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  1. CNT Growth: Current Technology and its Limits Presented by: Kevin McMullen February 23, 2009 Kevin McMullen

  2. Methods and Limitations • Barriers to industrial applications of nanotubes: • Scalability of growth for quality nanotubes • Defect-free growth of macroscopic length tubes • Control of tube location and order • Control of chirality and diameter Applied Materials SunFab PECVD 5.7 SWNT ~100μm long grown on Si columns (Chap 3, Carbon Nanotubes: Synthesis, Structure, Properties, and Applications) Kevin McMullen

  3. Methods and Limitations • Iijima grew first observed CNTs by arc-discharge • Laser ablation has produced low-defect SWCNT • Chemical Vapor Deposition (CVD) shows promise for scalability • Gaseous hydrocarbon feedstock • Temperatures around 1000°C required These methods require carbon to be evaporated from a solid source at temps in excess of 3000°C Kevin McMullen

  4. Plasma Enhanced Chemical Vapor Deposition (PECVD) Dense MWNT grown by PECVD (M. Meyyappan et al., Plasma Sources Sci. Tech. 2003) Schematic of a PECVD (M. Meyyappan et al., Plasma Sources Sci. Tech. 2003) Kevin McMullen

  5. PECVD Recipe • Procedures vary from lab to lab • Parameters from Maschmann paper: • Pressure: 10 Torr • Gas flow:10 sccm CH4, 50 sccm H2 • 300 W plasma • Temperature: 650-900 °C Average growth rate of tubes form Al-Fe-Al PAA substrate (M. R. Maschmann et al., Carbon 2007) Kevin McMullen

  6. Catalysts • Growth by CVD requires a catalyst • Common catalysts: Fe, Ni, Co, Mo • Good catalyst=high surface area and large pore volume • CNT diameter correlates to catalyst particle size Ni sputtered at shown times/rf powers Kevin McMullen

  7. Obtaining Order with an Engineered Substrate Photolithographic nickel catalyst on the substrate grows tubes in specified area. Also note transition from CNFs to CNTs. (M. Meyyappan et al., Plasma Sources Sci. Tech. 2003) SEM of CNTs grown on silicon pillars (Y. Homma et al., APL 2002) Kevin McMullen

  8. Order and Density on PAA Substrates Annealed 20 min @ 500°C Not Annealed 0.5nm Fe 1.0nm Fe 2.0nm Fe CNTs grown in porous anodic alumina (PAA) (M. R. Maschmann et al., Carbon 2007) Kevin McMullen

  9. Proposed Growth Mechanisms for MWCNTs • Many questions remain unanswered • During growth is end open or closed? TEM of open MWCNT (Chap 4, Carbon Nanotubes: Synthesis, Structure, Properties, and Applications) (a-c) TEM of MWCNTs with closed ends. (d) carbon filament and (e) fiber with catalyst particle at tip (Chap 4, Carbon Nanotubes: Synthesis, Structure, Properties, and Applications) Kevin McMullen

  10. Molecular Dynamics Simulations Tubes grow simultaneously with an open edge. Bonds between the open ends from “lip-lip” interactions that stabilize the configuration. There is a small, but finite probability that 2 pentagon defects will occur at the same time, thus closing the tube. (Images from Chap 4, Carbon Nanotubes: Synthesis, Structure, Properties, and Applications) Kevin McMullen

  11. Proposed Growth Mechanisms for SWCNTs • SWCNTs never grow without a catalyst Ni or Co Decoration Co or Ni catalyst atom “scoots” around the open edge to rearrange any pentagons to hexagons C60 (Images from Chap 4, Carbon Nanotubes: Synthesis, Structure, Properties, and Applications) Kevin McMullen

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