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
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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 Science300, 1236b (2003) Download
PDF file (308 kB)
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)
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
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 6001100
°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 nanotubeamorphous
diamond thin-film composites
H. Schittenhelm, D. B. Geohegan, G. E. Jellison, A. A. Puretzky, M. J. Lance,
P. F. Britt
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
Thegrowth times of single-wall
carbon nanotubes (SWNT's) within a high-temperaturelaser-vaporization
(LV) reactor were measured and adjusted through in situimaging
of the plume of laser-ablated material using Rayleigh-scattered lightinduced
by time-delayed, 308-nm laser pulses. Short SWNT's were synthesizedby
restricting the growth time to less than 20 msfor ambient growth
temperatures of 7601100 °C. Statistical analysis of transmissionelectron microscope photographs indicated most-probable lengths of 3577
nm forthese conditions. Raman spectra (Eex = 1.96
and 2.41 eV) of theshort nanotubes indicate that they are well-formed
SWNT's. The temperatureof the particles in the vortex-ring-shaped
plume during its thermalizationto the oven temperature was estimated
by collecting its blackbodyemission spectra at different spatial
positions inside the oven andfitting them to Planck's law. These
data, along with detailedoven temperature profiles, were used to
deduce a complete pictureof the time spent by the plume at high
growthtemperatures (7601100 °C). The upper and lower limits
of the growthrates of SWNT's were estimated as 0.6 and 5.1 µm/sfor the typical nanosecond Nd:YAG laser-vaporization conditions used in
thisstudy. These measurements permit the completion of a general
pictureof SWNT growth by LV based on imaging, spectroscopy, andpyrometry of ejected material at different times after ablation, whichconfirms our previous measurements that the majority of SWNT growthoccurs at times greater than 20 ms after LV bythe conversion
of condensed phase carbon. The American Physical Society
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
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,
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
15. "Photoluminescence from Gas-Suspended
SiOx Nanoparticles Synthesized by Laser Ablation" D.B. Geohegan, A.A. Puretzky,
G. Duscher, and S.J. Pennycook
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.
A comparative study of ArF- and KrF-laser
generated carbon plasmas has been performed under PLD conditions of amorphous
diamond-like carbon (DLC) films. Gated-ICCD species-resolved imaging, luminescence
spectroscopy and ion probe diagnostics have revealed distinct differences between
the carbon plumes generated by ArF- and KrF-lasers. KrF-laser (6.7 J/cm) irradiation
produces a less energetic carbon plasma containing larger amounts of luminescent
C2 compared with ArF-laser ablation at the same energy fluence. Spectroscopic
ellipsometry and EELS analysis of the DLC films deposited on Si 100 and NaCl
substrates were utilized to characterize the high quality ArF- and KrF-laser
deposited films (up to 84% of sp bonded carbon for 7 J/cm ArF-laser DLC film).
The more energetic and highly-atomized ArF-laser carbon plasma appears to be
responsible for the better diamond-like properties.
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.
Combined diagnostic measurements are
employed to characterize the penetration of energetic ablation plumes through
background gases during a key transitional regime in which the ion flux is observed
(with fast ion probes) to split into distinct fast and slowed components. This
apparently general phenomenon occurs over a limited range of distances at ambient
pressures typically used for PLD (as reported for YBCO ablation into O2)
and may be important to film growth by PLD because a 'fast' component of ions
can arrive at the probe (or substrate) with little or no delay compared to propagation
in vacuum (i.e., high 10-100 eV kinetic energies). At longer distances, this
'fast' component is completely attenuated, and only slowed distributions of
ions are observed. Interestingly, this 'fast' component is easily overlooked
in imaging studies because the bright plume luminescence occurs in the slowed
distribution. Time- and spatially-resolved optical absorption and emission spectroscopy
are applied to experimentally determine the composition of the 'fast' and 'slow'
propagating plume components for a single-component target ablation (yttrium)
into an inert gas (argon) for correlation with quantitative imaging and ion
probe measurements. The yttrium/argon system was chosen because optical absorption
spectroscopy of both Y and Y was simultaneously possible and the inert nature
of argon. Experimental results for several other systems, including Si/Ar, Si/He,
YBCO/O2 are presented to illustrate variations in scattering mechanisms.
Species-resolved imaging of YO and Ba is presented for the YBCO/O2
system to illustrate the similarities and differences in the spatial regions
of observed luminescence. These measurements confirm that, in addition to the
bright significantly-slowed front which has been described by shock or drag
propagation models, a fast-component of target material is transmitted to extended
distances for some ambient pressures with near-initial velocities.
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
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