5 research outputs found
Concentration Measurement of Length-Fractionated Colloidal Single-Wall Carbon Nanotubes
The determination of the carbon concentration of single-wall
carbon
nanotubes (SWCNTs) in a given dispersion is a basic requirement for
many studies. The commonly used optical absorption-based concentration
measurement is complicated by the spectral change due to variations
in nanotube chirality and length. In particular, the origin of the
observed length-dependent spectral change and its effect on concentration
determination has been the subject of considerable debate. Here, we
use length-fractionated DNA-wrapped SWCNTs to establish the relationship
between SWCNT carbon concentration and optical absorption spectra
by directly quantifying the amount of wrapping DNA and, independently,
the DNA/carbon nanotube mass ratio. We find that SWCNT carbon concentrations
derived from either the E<sub>11</sub> peak or spectral baseline deviate
significantly from the SWCNT carbon concentrations derived from the
DNA measurement method. Instead, SWCNT carbon concentrations derived
from the spectral integration of the E<sub>11</sub> optical transition
region match most closely with the DNA-derived SWCNT carbon concentrations.
We also observe that shorter SWCNT fractions contain more curved carbon
nanotubes, and propose that these defective nanotubes are largely
responsible for the observed spectral variation with nanotube length
Chirality-Dependent Vapor-Phase Epitaxial Growth and Termination of Single-Wall Carbon Nanotubes
Structurally
uniform and chirality-pure single-wall carbon nanotubes
are highly desired for both fundamental study and many of their technological
applications, such as electronics, optoelectronics, and biomedical
imaging. Considerable efforts have been invested in the synthesis
of nanotubes with defined chiralities by tuning the growth recipes
but the approach has only limited success. Recently, we have shown
that chirality-pure short nanotubes can be used as seeds for vapor-phase
epitaxial cloning growth, opening up a new route toward chirality-controlled
carbon nanotube synthesis. Nevertheless, the yield of vapor-phase
epitaxial growth is rather limited at the present stage, due in large
part to the lack of mechanistic understanding of the process. Here
we report chirality-dependent growth kinetics and termination mechanism
for the vapor-phase epitaxial growth of seven single-chirality nanotubes
of (9, 1), (6, 5), (8, 3), (7, 6), (10, 2), (6, 6), and (7, 7), covering
near zigzag, medium chiral angle, and near armchair semiconductors,
as well as armchair metallic nanotubes. Our results reveal that the
growth rates of nanotubes increase with their chiral angles while
the active lifetimes of the growth hold opposite trend. Consequently,
the chirality distribution of a nanotube ensemble is jointly determined
by both growth rates and lifetimes. These results correlate nanotube
structures and properties with their growth behaviors and deepen our
understanding of chirality-controlled growth of nanotubes
Rod Hydrodynamics and Length Distributions of Single-Wall Carbon Nanotubes Using Analytical Ultracentrifugation
Because of their repetitive chemical
structure, extreme rigidity,
and the separability of populations with varying aspect ratio, SWCNTs
are excellent candidates for use as model rodlike colloids. In this
contribution, the sedimentation velocities of length and density sorted
single-wall carbon nanotubes (SWCNTs) are compared to predictions
from rod hydrodynamic theories of increasing complexity over a range
of aspect ratios from <50 to >400. Independently measuring all
contributions to the sedimentation velocity besides the shape factor,
excellent agreement is found between the experimental findings and
theoretical predictions for numerically calculated hydrodynamic radius
values and for multiterm analytical expansion approximations; values
for the hydrodynamic radii in these cases are additionally found to
be consistent with the apparent hydrated particle radius determined
independently by buoyancy measurements. Lastly, we utilize this equivalency
to calculate the apparent distribution of nanotube lengths in each
population from their sedimentation coefficient distribution without
adjustable parameters, achieving excellent agreement with distributions
from atomic force microscopy. The method developed herein provides
an alternative for the ensemble measurement of SWCNT length distributions
and others rodlike particles
Bright Fraction of Single-Walled Carbon Nanotubes through Correlated Fluorescence and Topography Measurements
Correlated measurements of fluorescence
and topography were performed
for individual single-walled carbon nanotubes (SWNTs) on quartz using
epifluorescence confocal microscopy and atomic force microscopy (AFM).
Surprisingly, only ∼11% of all SWNTs in DNA-wrapped samples
were found to be highly emissive on quartz, suggesting that the ensemble
fluorescence quantum yield is low because only a small population
of SWNTs fluoresces strongly. Qualitatively similar conclusions were
obtained from control studies using a sodium cholate surfactant system.
To accommodate AFM measurements, excess surfactant was removed from
the substrate. Though individual SWNTs on nonrinsed and rinsed surfaces
displayed differences in fluorescence intensities and line widths,
arising from the influence of the local environment on individual
SWNT optical measurements, photoluminescence data from both samples
displayed consistent trends
High-Resolution Length Fractionation of Surfactant-Dispersed Carbon Nanotubes
Length fractionation of colloidal single-wall carbon
nanotube (SWCNT)
dispersions is required for many studies. Size-exclusion chromatography
(SEC) has been developed as a reliable method for high-resolution
length fractionation of DNA-dispersed SWCNTs but has not been applied
to surfactant-dispersed SWCNTs due to their lower dispersion stability
and tendency to adsorb onto SEC stationary phases. Here, we report
that SEC length fractionation can be achieved for bile salt dispersed
SWCNTs by using porous silica-based beads as the stationary phase
and bile salt solution as the mobile phase. We demonstrate that the
SEC length sorting method can be combined with existing ultracentrifugation
SWCNT sorting methods to produce “orthogonally sorted”
samples, including length sorted semiconducting SWCNTs, which are
important for electronics applications as well as length sorted empty-core
SWCNTs. Importantly, we show that unlike simple length fractionation
by SEC or any other method, orthogonal sorting produces samples of
consistent quality for different length fractions, with similar UV–vis-nearIR
absorption and Raman spectral features