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Fig. 1. (Color online) Schematic of carbon nanostructures: (a) single sheet of graphite, (b) CNT consisting of concentric graphene sheets, and (c) CNF composed of stacked graphene cones at an angle alpha with respect to the axis of the fiber. The two primary CNF structures: (d) herringbone-type CNF and (e) bamboo-type CNF. (f) Representative VACNF composed of a Ni catalyst nanoparticle at the tip and a graphitic fiber body. [(a)–(e)] Adapted with permission from Ref. 5. First citation in article

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Fig. 2. Atomic-scale STM images of a CNF surface (a) before and (b) after oxygen plasma treatment. Reprinted with permission from Ref. 42, Copyright 2003 American Chemical Society. First citation in article

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Fig. 3. Typical noncontact tapping mode line profile of a phase image taken in the direction perpendicular to the axis of (a) an untreated “fresh” fiber on HOPG and (b) a fiber exposed to 5  min of oxygen plasma on HOPG. Reprinted in part with permission from Ref. 42, Copyright 2003 American Chemical Society. First citation in article

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Fig. 4. TEM of untreated (a) fishbone (herringbone) and (b) parallel (bamboo) CNFs with the corresponding IR spectroscopy results below. Adopted with permission from Ref. 47, Copyright 2002 Blackwell Publishing. First citation in article

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Fig. 5. IR spectra of untreated (CNF-U), oxidized (CNF-OX), anthranilic-acid-treated (CNF-AA) CNFs, and of a physical mixture of anthranilic acid and CNFs (AA-phys). Adopted with permission from Ref. 49, Copyright 2002 Blackwell Publishing. First citation in article

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Fig. 6. XPS sputter depth profile of a CNF treated in Ar/O plasma for 10  min. The table lists XPS atomic composition results for six nanofiber samples treated with different plasma conditions. The values in parentheses at the top of the table are the mean binding energies of the fit lines, given in eV. Reprinted with permission from Ref. 56, Copyright 2002 Elsevier. First citation in article

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Fig. 7. XPS results: (a) Fe 2p and (b) O 1s spectra of iron oxide coated CNFs, with (1) as-synthesized and (2) heated to 700  °C in hydrogen and helium (followed by exposure to air). Summary of surface compositions is summarized in the table. Reprinted in part with permission from Ref. 58, Copyright 2003 American Chemical Society. First citation in article

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Fig. 8. UPS He  II valence band spectra of the CNTs (solid line) and graphite (dotted line). Reprinted with permission from Ref. 59, Copyright 1999 American Physical Society. First citation in article

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Fig. 9. UPS spectra of (a) HOPG, (b) purified MWCNT film, (c) air oxidized MWCNT film and (d) plasma oxidized MWCNT film, with He  II 40.8  eV. Arrows indicate pi-derived density of states. Adopted with permission from Ref. 61, Copyright 1999 Elsevier. First citation in article

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Fig. 10. C KVV Auger spectra of HOPGn at normal emission and MWCNT, SWCNT, fullerene, quarterphenyl, and HOPG at an emission angle of 5°. Reprinted with permission from Ref. 63, Copyright 2005 Elsevier. First citation in article

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Fig. 11. TEM images of MWCNT samples (a) before and (b) after irradiation. (c) AES carbon KLL spectra from the nanotube samples is shown (A) before irradiation, (B) after 30  min sputter time, (C) after 210  min sputter time, and (D) graphite carbon. Adopted with permission from Ref. 64, Copyright 1999 Elsevier. First citation in article

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Fig. 12. SEM images of cylindrical CNFs deposited using (a) 20% C₂H₂:NH₃ gas ratio and (b) conical CNFs deposited using 75% C₂H₂:NH₃ gas ratio. Auger chemical composition analysis is presented in (c), where (1) is from the head of the cylindrical CNF in (a), (2) is from the body of the conical CNF in (a), (3) is from the head of the conical CNF in (b), and (4) is from the body of the conical CNF in (b). (d) Summary of Auger depth profiles of the substrate surface at various C₂H₂:NH₃ ratios. Adopted with permission from Ref. 68. First citation in article

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Fig. 13. SEM images of plasma-treated CNFs (a) before and (b) after a 5  min growth of secondary nanofibers. Reprinted in part with permission from Ref. 58, Copyright 2003 American Chemical Society. First citation in article

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Fig. 14. SEM images of CNFs grown from Cu-Ni alloys with (a) 81% Ni, (b) 39% Ni, and (c) 20% Ni. Adopted with permission from Ref. 70, Copyright 2005 Elsevier. First citation in article

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Fig. 15. (Color online) EDX line scan showing the elemental composition along the length of a conical nanofiber (grown from Cu₈₀Ni₂₀ catalyst) shown in the SEM image on the right. Reprinted with permission from Ref. 70, Copyright 1999 Elsevier. First citation in article

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Fig. 16. (Color online) EDX spectra (a) from the body of an argon treated fiber (b). FE measurements (c) of typical J-E curves for VACNFs treated with Ar plasma for various times. Adopted with permission from Ref. 71. First citation in article

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Fig. 17. STEM images and cartoons of the nanofiber outer wall structure: [(a) and (b)] using a Ni catalyst and [(c) and (d)] using a Pd catalyst. The white arrows in the STEM images point towards the catalyst particle at the tip of the fiber. Adopted with permission from Ref. 72. First citation in article

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Fig. 18. HRTEM images showing the surface morphology differences between (a) heat treated and (b) pyrolytically stripped, hollow CNFs. Adopted with permission from Ref. 40, Copyright 2005 Institute of Physics. First citation in article

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Fig. 19. (a) TEM image of Au-nanoparticle CNF composites after thermal activation at 300  °C. (b) HRTEM image showing a single nanoparticle on the CNF surface. Reprinted with permission from Ref. 51, Copyright 2004 American Chemical Society. First citation in article

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Fig. 20. (a) EELS analysis of a BN-coated pyrolytically stripped hollow CNF and (b) HRTEM image of a heat treated BN-coated hollow CNF. Adopted with permission from Ref. 74, Copyright 2004 Blackwell Publishing. First citation in article

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Fig. 21. (a) Surface hydrogen concentration as measured by D-SIMS and (b) FTIR spectra of a 1  MeV proton bombarded SWCNT film. Reprinted with permission from Ref. 75, Copyright 2003 American Chemical Society. First citation in article

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Fig. 22. TEM images of hollow CNFs (a) before and (b) after pyrrole deposition. Time-of-flight SIMS spectra of (c) untreated and (d) polymer treated CNFs. Adopted with permission from Ref. 79. First citation in article

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Fig. 23. (Color online) Temperature-programed desorption spectra of from CNFs treated with HNO₃ for 12  h at room temperature for (a) CO and (b) CO₂. The peak temperature (T_m) of the different types of surface oxygen complexes used in fitting were 280  °C for carboxyl, 460  °C for carboxylic anhydride, 520  °C for peroxide, 570  °C for hydroxyl, 620  °C and 720  °C for lactones, 660  °C for ether or carbonyl, 790  °C for carbonyl, and 930  °C for pyrone-type structures. Reprinted with permission from Ref. 81, Copyright 2007 Elsevier. First citation in article

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Fig. 24. Mass spectrum of (a) MWCNT initially, (b) MWCNT after heating in vacuum to 1000  °C for 10  min, (c) SWCNT rod initially, and (d) SWCNT rod after 40  h in vacuum. Na⁺, K⁺, and NaOH⁺ are adsorbed contaminants. Adopted with permission from Ref. 86, Copyright 2003 Japanese Journal of Applied Physics. First citation in article

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Fig. 25. (a) Low magnification TEM image of a conical CNT showing numerous graphite branches grown around the main tube; (b) a closer view of the tip where the hollow tube and catalyst particle decorating the tip are clearly visible. Adopted with permission from Ref. 87, Copyright 2000 Springer Science and Business Media. First citation in article

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Fig. 26. Schematic representation of the growth of (a) a CNF using conventional thermal CVD, (b) a vertically aligned carbon nanostructure using PECVD, and (c) a carbon nanocone formed due to additional precipitation of C on the outer walls during PECVD. Reprinted with permission from Ref. 88. First citation in article

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Fig. 27. Scanning electron images of (a) parylene-coated and (b) Al₂O₃ VACNFs. Reprinted in part with permission from Ref. 99, Copyright 2006 American Chemical Society. First citation in article

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Fig. 28. Schematic cross-section images of functionalized nanotubes coated via ALD: (a) Al₂O₃ ALD film, (b) multilayered Al₂O₃/W/Al₂O₃ ALD film, and (c) functionalized monolayer on an Al₂O₃ ALD seed layer. (d) TEM image of a multiwalled nanotube coated via ALD with a multilayer as shown in (b). Reprinted with permission from Ref. 100. First citation in article

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Fig. 29. (Color online) (a) Schematic illustration of the steps involved in the functionalization of CNFs and subsequent procedure for electroless deposition. (b) Chemical transformations involved in the nanofiber modification. Reprinted with permission from Ref. 105, Copyright 2006 American Chemical Society. First citation in article

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Fig. 30. (Color online) Illustration of biomolecular functionalization of a CNF with an amine-terminated oligonucleotide, first four bases shown of 5-amino-c6-G-GGG… (courtesy of M. Fuentes-Cabrera). Attachment upon the nanofiber is provided by an amide bond, such as that resulting from an EDC condensation reaction, at a putative nanofiber-COOH site. First citation in article