8 research outputs found
Broadband tunable, polarization-selective and directional emission of (6,5) carbon nanotubes coupled to plasmonic crystals
We
demonstrate broadband tunability of light emission from dense (6,5)
single-walled carbon nanotube thin films via efficient coupling to
periodic arrays of gold nanodisks that support surface lattice resonances
(SLRs). We thus eliminate the need to select single-walled carbon
nanotubes (SWNTs) with different chiralities to obtain narrow linewidth
emission at specific near-infrared wavelengths. Emission from these
hybrid films is spectrally narrow (20–40 meV) yet broadly tunable
(∼1000–1500 nm) and highly directional (divergence <1.5°).
In addition, SLR scattering renders the emission highly polarized,
even though the SWNTs are randomly distributed. Numerical simulations
are applied to correlate the increased local electric fields around
the nanodisks with the observed enhancement of directional emission.
The ability to control the emission properties of a single type of
near-infrared emitting SWNTs over a wide range of wavelengths will
enable application of carbon nanotubes in multifunctional photonic
devices
Understanding Charge Transport in Mixed Networks of Semiconducting Carbon Nanotubes
The
ability to select and enrich semiconducting single-walled carbon nanotubes
(SWNT) with high purity has led to a fast rise of solution-processed
nanotube network field-effect transistors (FETs) with high carrier
mobilities and on/off current ratios. However, it remains an open
question whether it is best to use a network of only one nanotube
species (monochiral) or whether a mix of purely semiconducting nanotubes
but with different bandgaps is sufficient for high performance FETs.
For a range of different polymer-sorted semiconducting SWNT networks,
we demonstrate that a very small amount of narrow bandgap nanotubes
within a dense network of large bandgap nanotubes can dominate the
transport and thus severely limit on-currents and effective carrier
mobility. Using gate-voltage-dependent electroluminescence, we spatially
and spectrally reveal preferential charge transport that does not
depend on nominal network density but on the energy level distribution
within the network and carrier density. On the basis of these results,
we outline rational guidelines for the use of mixed SWNT networks
to obtain high performance FETs while reducing the cost for purification
Broadband Tunable, Polarization-Selective and Directional Emission of (6,5) Carbon Nanotubes Coupled to Plasmonic Crystals
Controlled In Situ PbSe Quantum Dot Growth around Single-Walled Carbon Nanotubes: A Noncovalent PbSe-SWNT Hybrid Structure
We developed a simple method of synthesizing
noncovalently linked
hybrids of PbSe quantum dots (QDs) and single-walled carbon nanotubes
(SWNTs). The PbSe QDs grow around the SWNTs without any linker molecule
or chemical modification of the SWNTs. We are able to control the
size and shape of the QDs attached to the SWNTs by varying the synthesis
conditions and elucidate the three-dimensional (3D) morphology and
atomic structure of the half-ring-shaped PbSe QDs bonded to the SWNTs
using scanning transmission electron microscopy (STEM) tomography
and high-resolution transmission electron microscopy (HRTEM). The
PbSe QDs not only assemble on the SWNT bundles, but they actually
grow around them. The growth of the PbSe QDs around SWNT sidewalls
is favored over the growth of spherical particles in solution, probably
due to dipole stabilization by the large π-electron system of
the SWNTs
Effect of Polymer Molecular Weight and Solution Parameters on Selective Dispersion of Single-Walled Carbon Nanotubes
The selective dispersion of single-walled carbon nanotube
species
(n,m) with conjugated polymers such as polyÂ(9,9-dioctylfluorene) (PFO)
and polyÂ(9,9-dioctylfluorene-<i>co</i>-benzothiadiazole)
(F8BT) in organic solvents depends not only on the type of solvent
but also on the molecular weight of the polymer. We find an increasing
amount of nanotubes and altered selectivities for dispersions with
higher molecular weight polymers. Including the effects of different
aromatic solvents, we propose that solution viscosity is one of the
factors influencing the apparent selectivity by changing the reaggregation
rate of the single-walled carbon nanotubes (SWNT). The type of solvent,
polymer molecular weight, concentration, and viscosity should thus
be taken into account when screening for new polymers for selective
SWNT dispersion
Polymer-Sorted Semiconducting Carbon Nanotube Networks for High-Performance Ambipolar Field-Effect Transistors
Efficient selection of semiconducting
single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples
is crucial for their application as printable and flexible semiconductors
in field-effect transistors (FETs). In this study, we use atactic
polyÂ(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative
with asymmetric side-chains, for the selective dispersion of semiconducting
SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs.
Lowering the molecular weight of the dispersing polymer leads to a
significant improvement of selectivity. Combining dense semiconducting
SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide
hybrid dielectric enables transistors with balanced ambipolar, contact
resistance-corrected mobilities of up to 50 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>, low ohmic contact resistance,
steep subthreshold swings (0.12–0.14 V/dec) and high on/off
ratios (10<sup>6</sup>) even for short channel lengths (<10 μm).
These FETs operate at low voltages (<3 V) and show almost no current
hysteresis. The resulting ambipolar complementary-like inverters exhibit
gains up to 61