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1. In situ growth rate measurements and length control during chemical vapor deposition of vertically aligned multiwall carbon nanotubes
D. B. Geohegan, A. A. Puretzky, I. N. Ivanov, S. Jesse, G. Eres, and J.Y. Howe
Appl. Phys. Lett. 83, 1851 (2003). Download PDF file (320 kB)

Time-resolved reflectivity is employed as an in situ diagnostic in thermal chemical vapor deposition of vertically aligned arrays of multiwall carbon nanotubes (VAA–MWNT). Fabry–erot interference fringes and attenuation of a reflected HeNe laser beam are used to measure the length of VAA–MWNT throughout the first 3–8 µm of growth yielding in situ measurements of growth rates and kinetics and the capability to observe the onset and termination of growth. VAA–MWNT growth is characterized between 565 and 750 °C on Si substrates with evaporated Al/Fe/Mo multilayer catalysts and acetylene feedstock. Nanotube lengths were controlled by rapid evacuation of the chamber at predetermined reflectivities, and it was demonstrated that growth can be restarted at later times. The extinction coefficients of the VAA–MWNT were studied and correlated with nanotube wall structure. Growth rates for VAA–MWNT are found to vary depending on the catalyst preparation, temperature, and time. Both the highest growth rates (0.3 µm/s) and the tallest VAA–MWNT (0.75 mm long) were achieved at 730 °C. ©2003 American Institute of Physics.

2. Comment on "Single-Crystals of Single-Walled Carbon Nanotubes Formed by Self-Assembly"
M. F. Chisholm, Y. Wang, A. R. Lupini, G. Eres, A. A. Puretzky, B. Brinson, A. V. Melechko, D. B. Geohegan, H. Cui, M. P. Johnson, S. J. Pennycook, D. H. Lowndes, S. Arepalli, C. Kittrell, S. Sivaram, M. Kim, G. Lavin, J. Kono, R. Hauge, and R. E. Smalley
Science 300, 1236b (2003)   Download PDF file (308 kB)

Schlittler et al. (1) reported the production of single crystals of single-walled carbon nanotubes (SWCNTs) by the thermolysis of nanopatterned structures of alternating layers of C60 and nickel. Electron diffraction, high-resolution phase contrast imaging, and electron energy loss spectroscopy (EELS) were used to characterize the resulting crystals. In this comment, we report the reproduction of their experimental results; however, we disagree with their interpretation of the data. We suggest that the crystals formed in our experiments consist not of SWCNTs, but rather of calcium molybdenum oxide. ©2003 The American Association for the Advancement of Science.

3. Nucleation of Single-Walled Carbon Nanotubes
X. Fan, R. Buczko, A. A. Puretzky, D. B. Geohegan, J. Y. Howe, S. T. Pantelides, and S. J. Pennycook
Phys. Rev. Lett. 90, 145501 (2003)   Download PDF file (424 kB)

The nucleation pathway for single-wall carbon nanotubes on a metal surface is demonstrated by a series of total energy calculations using density functional theory. Incorporation of pentagons at an early stage of nucleation is energetically favorable as they reduce the number of dangling bonds and facilitate curvature of the structure and bonding to the metal. In the presence of the metal surface, nucleation of a closed cap or a capped single-wall carbon nanotube is overwhelmingly favored compared to any structure with dangling bonds or to a fullerene. ©2003 The American Physical Society

4. Growth behavior of carbon nanotubes on multilayered metal catalyst film in chemical vapor deposition
H. Cui, G. Eres, J. Y. Howe, A. Puretkzy, M. Varela, D. B. Geohegan and D. H. Lowndes

Chem. Phys. Lett. 374, 222 (2003).   Download PDF file (431 kB)

The temperature and time dependences of carbon nanotube (CNT) growth by chemical vapor deposition are studied using a multilayered Al/Fe/Mo catalyst on silicon substrates. Within the 600–1100 °C temperature range of these studies, narrower temperature ranges were determined for the growth of distinct types of aligned multi-walled CNTs and single-walled CNTs by using high-resolution transmission electron microscopy and Raman spectroscopy. At 900 °C, in contrast to earlier work, double-walled CNTs are found more abundant than single-walled CNTs. Defects also are found to accumulate faster than the ordered graphitic structure if the growth of CNTs is extended to long durations. (C) 2002 Elsevier Science B.V. All rights reserved.

5. Operation of individual integrally gated carbon nanotube field emitter cells
M. A. Guillorn, M. D. Hale, V. I. Merkulov, M. L. Simpson, G. Y. Eres, H. Cui, A. A. Puretzky , and D. B. Geohegan
Appl. Phys. Lett. 81, 2860 (2002)   Download PDF file (200 kB)

In this work, we examine the operation of individual field emitter cells contained in a field emitter array composed of integrally gated multiwalled carbon nanotube (MWNT)-based field emission cathodes. These devices were found to behave in a manner consistent with a multiple emission site model of Fowler-Nordheim field emission. These results show considerable variation in the operational characteristics of cells contained within the same array and indicate that data obtained from arrays of cells are not necessarily indicative of individual cell performance. (C) 2002 American Institute of Physics.

6. The electrodeposition of metal at metal/carbon nanotube junctions
D. W. Austin, A. A. Puretzky, D. B. Geohegan, P. F. Britt, M. A. Guillorn, and M. L. Simpson
Chem. Phys. Lett. 361, 525 (2002)   Download PDF file (424 kB)

We deposited a semiconducting single-walled carbon nanotube on Pd electrodes, and the initial charge transport measurements showed the usual large contact resistance between the electrodes and the nanotube. We electroplated Au over the electrodes with no obvious deposition of An along the sidewalls of the nanotube between the electrodes. Post deposition charge transport measurements indicated more than a factor of six decrease in the electrode/nanotube contact resistance, yet the semiconducting behavior of the nanotube was maintained. A significant difference in the post deposition I-V characteristics may be explained by an electronic or mechanical modification of the nanotube/electrode junction. (C) 2002 Elsevier Science B.V. All rights reserved.

7. Synthesis and characterization of single-wall carbon nanotube–amorphous diamond thin-film composites
H. Schittenhelm, D. B. Geohegan, G. E. Jellison, A. A. Puretzky, M. J. Lance, P. F. Britt

Appl. Phys. Lett. 81, 2097, (2002). Download PDF file (256 KB)


8. Investigations of single-wall carbon nanotube growth by time-restricted laser vaporization
Alex A. Puretzky, Henrik Schittenhelm, Xudong Fan, Michael J. Lance, Larry F. Allard, Jr., and David B. Geohegan

Phys. Rev. B 65, 245425 (2002) Download PDF file (1000 KB)



9. Condensed phase growth of single-wall carbon nanotubes from laser annealed nanoparticulates
D. B. Geohegan, H. Schittenhelm, X. Fan, and S. J. Pennycook, A. A. Puretzky, M. A. Guillorn, D. A. Blom and D. C. Joy

Appl. Phys. Lett. 78, 3307, (2001). Download PDF file (383 KB)


10. "Dynamics of single-wall carbon nanotube synthesis by laser vaporization"
A.A. Puretzky, D.B. Geohegan, X. Fan, S.J. Pennycook

Appl. Phys. A 70, 153, (2000). Download PDF file (531 KB)

11. In situ imaging and spectroscopy of single-wall carbon nanotube synthesis by laser vaporization
A. A. Puretzky, D. B. Geohegan, X. Fan, and S. J. Pennycook,

Appl. Phys. Lett. 76, 182, (2000). Download PDF file (304 KB)



12. "Imaging of Vapor Plumes Produced by Matrix Assisted Laser Desorption: A Plume Sharpening Effect"
A. A. Puretzky, D. B. Geohegan, G. B. Hurst, M. V. Buchanan and B. S. Luk'yanchuk

Phys. Rev. Lett. 83, 444, (1999). Download PDF file (553k)



13. "Gas-phase nanoparticle formation and transport during pulsed laser deposition of Y1Ba2Cu3O7 – d"
D. B. Geohegan, A. A. Puretzky, and D. J. Rader

Appl.Phys. Lett. 74, 3788 (1999) . Download PDF file (287k)


14.  "Time-Resolved Imaging  of Gas Phase Nanoparticle Synthesis by Laser Ablation" D.B. Geohegan, A.A. Puretzky, G. Duscher, and S.J. Pennycook

Appl.Phys. Lett. 72, 2987 (1998) . Download PDF file (195k)
15. "Photoluminescence from Gas-Suspended SiOx Nanoparticles Synthesized by Laser Ablation" D.B. Geohegan, A.A. Puretzky, G. Duscher, and S.J. Pennycook

Appl.Phys. Lett.73, 438 (1998) . Download PDF file (429k)

16.  "Dynamics of laser ablation plume penetration through low pressure background gases" David B. Geohegan and Alexander A. Puretzky

Appl.Phys. Lett.67, 197 (1995) . Download PDF file (312k)
17.  "Comparative diagnostics of ArF- and KrF-laser generated carbon plumes used for amorphous diamond-like carbon film deposition"  Puretzky, A.A.; Geohegan, D.B.; Jellison, G.E.J.; McGibbon, M.M.

Applied Surface Science, Vol: 96-98, pp. 859-865, (1996). Download PDF file (702k)
18.  "Laser ablation plume thermalization dynamics in background gases: Combined imaging, optical absorption and emission spectroscopy, and ion probe measurements"  Geohegan, D.B.; Puretzky, A.A.

Applied Surface Science, Vol: 96-98, pp. 131-138, (1996). Download PDF file (585k)
 

19. "Dynamics of Plume Propagation and Splitting during Pulsed-Laser Ablation"
R. F. Wood, K. R. Chen, J. N. Leboeuf, A. A. Puretzky, and D. B. Geohegan

Phys. Rev. Lett. 79, 1571, (1997). Download PDF file (130k)

An innovative new approach has been developed for modeling the expansion of laser-generated plumes into low-pressure gases where initially the mean free path may be long enough for interpenetration of the plume and background. The model is based on a combination of multiple elastic scattering and hydrodynamic formulations. Although relatively simple in structure, it gives excellent fits to new experimental data for Si in He and Ar, and provides for the first time a detailed, coherent explanation of the observed splitting of the plume into a fast and slow component. ©1997 The American Physical Society




20. "Accelerated expansion of laser-ablated materials near a solid surface"
K. R. Chen, J. N. Leboeuf, R. F. Wood, D. B. Geohegan, J. M. Donato, C. L. Liu, and A. A. Puretzky

Phys. Rev. Lett. 75, 4706, (1995).Download PDF file (163k)