21 research outputs found
<i>In Situ</i> Formation of Carbon Nanotubes Encapsulated within Boron Nitride Nanotubes <i>via</i> Electron Irradiation
We report experimental evidence of the formation by <i>in situ</i> electron-irradiation of single-walled carbon nanotubes (C-NT) confined within boron nitride nanotubes (BN-NT). The electron radiation stemming from the microscope supplies the energy required by the amorphous carbonaceous structures to crystallize in a tubular form in a catalyst-free procedure, at room temperature and high vacuum. The structural defects resulting from the interaction of the shapeless carbon with the BN nanotube are corrected in a self-healing process throughout the crystallinization. Structural changes developed during the irradiation process such as defects formation and evolution, shrinkage, and shortness of the BN-NT were <i>in situ</i> monitored. The outer BN wall provides a protective and insulating shell against environmental perturbations to the inner C-NT without affecting their electronic properties, as demonstrated by first-principles calculations
Dynamic HAADF-STEM Observation of a Single-Atom Chain as the Transient State of Gold Ultrathin Nanowire Breakdown
Ultrathin
chemically grown gold nanowires undergo irremediable
structural modification under external stimuli. Thanks to dynamic
high-angle annular dark-field imaging, electron-beam-induced damage
was followed, revealing the formation of linear chains of gold atoms
as well as reactive clusters on the side, opening fascinating prospects
for applications in both catalysis and electronic transport
Dynamic HAADF-STEM Observation of a Single-Atom Chain as the Transient State of Gold Ultrathin Nanowire Breakdown
Ultrathin
chemically grown gold nanowires undergo irremediable
structural modification under external stimuli. Thanks to dynamic
high-angle annular dark-field imaging, electron-beam-induced damage
was followed, revealing the formation of linear chains of gold atoms
as well as reactive clusters on the side, opening fascinating prospects
for applications in both catalysis and electronic transport
Dynamic HAADF-STEM Observation of a Single-Atom Chain as the Transient State of Gold Ultrathin Nanowire Breakdown
Ultrathin
chemically grown gold nanowires undergo irremediable
structural modification under external stimuli. Thanks to dynamic
high-angle annular dark-field imaging, electron-beam-induced damage
was followed, revealing the formation of linear chains of gold atoms
as well as reactive clusters on the side, opening fascinating prospects
for applications in both catalysis and electronic transport
Dynamic HAADF-STEM Observation of a Single-Atom Chain as the Transient State of Gold Ultrathin Nanowire Breakdown
Ultrathin
chemically grown gold nanowires undergo irremediable
structural modification under external stimuli. Thanks to dynamic
high-angle annular dark-field imaging, electron-beam-induced damage
was followed, revealing the formation of linear chains of gold atoms
as well as reactive clusters on the side, opening fascinating prospects
for applications in both catalysis and electronic transport
Quaternary Chalcogenide-Based Misfit Nanotubes LnS(Se)-TaS(Se)<sub>2</sub> (Ln = La, Ce, Nd, and Ho): Synthesis and Atomic Structural Studies
We
have synthesized quaternary chalcogenide-based misfit nanotubes LnS(Se)-TaS<sub>2</sub>(Se) (Ln = La, Ce, Nd, and Ho). None of the compounds described
here were reported in the literature as a bulk compound. The characterization
of these nanotubes, at the atomic level, has been developed via different
transmission electron microscopy techniques, including high-resolution
scanning transmission electron microscopy, electron diffraction, and
electron energy-loss spectroscopy. In particular, quantification at
sub-nanometer scale was achieved by acquiring high-quality electron
energy-loss spectra at high energy (∼between 1000 and 2500
eV). Remarkably, the sulfur was found to reside primarily in the distorted
rocksalt LnS lattice, while the Se is associated with the hexagonal
TaSe<sub>2</sub> site. Consequently, these quaternary misfit layered
compounds in the form of nanostructures possess a double superstructure
of La/Ta and S/Se with the same periodicity. In addition, the interlayer
spacing between the layers and the interatomic distances within the
layer vary systematically in the nanotubes, showing clear reduction
when going from the lightest (La atom) to the heaviest (Ho) atom.
Amorphous layers, of different nature, were observed at the surface
of the nanotubes. For La-based NTs, the thin external amorphous layer
(inferior to 10 nm) can be ascribed to a Se deficiency. Contrarily,
for Ho-based NTs, the thick amorphous layer (between 10 and 20 nm)
is clearly ascribed to oxidation. All of these findings helped us
to understand the atomic structure of these new compounds and nanotubes
thereof
Atomic Structural Studies on Thin Single-Crystalline Misfit-Layered Nanotubes of TbS-CrS<sub>2</sub>
Various nanotubes
from ternary misfit compounds have been reported
in recent years. In the present work, the detailed atomic structure
and chemical configuration of misfit-layered nanotubes based on the
TbS-CrS<sub>2</sub> are reported. These analyses have been developed
via different transmission electron microscopy techniques, including
high-resolution scanning transmission electron microscopy, electron
diffraction, and electron energy loss spectroscopy. These structural
analyses show that two different kinds of nanotubes can be produced:
a “regular” nanotube and a “wavy” one.
Both kinds of nanotubes show the alternating arrangements of the TbS
and CrS<sub>2</sub> subsystems; however, the wavy ones present a nearly
periodically deficiency in terbium. In addition to the structural
investigation, the chemical analyses have proved that the outer layer
of both kinds of nanotubes is composed of the elements Cr and S. All
these findings helped to understand the growth mechanism during the
sulfurization reaction taking place in the synthesis process
Strontium Cobalt Oxide Misfit Nanotubes
Low-dimensional
misfit layered compounds have been found to have ultralow thermal
conductivity, which is attributed to their unique structure and the
low dimensionality. There are a few studies reporting the preparation
of sulfide-based misfit nanotubes but only one study on oxide-based
analogs. In this investigation, we report a new oxide-based misfit
nanotube derived from misfit layered strontium cobaltite. Thorough
structural investigation by electron microscopy techniques, including
electron diffraction, aberration corrected high-resolution (scanning)
transmission electron microscopy, and electron energy-loss spectroscopy
along with density functional theory calculations show that these
nanotubes consist of alternating layers of SrCoO<sub>2</sub> and CoO<sub>2</sub>. We have studied systematically the effect of base concentration
on the structure and composition of the nanotubes, which reveals the
importance of misfit stress to tightly roll the structure into tubular
form and thus control the synthesis. Electronic structure calculations
find that the structures are semiconducting with a ferrimagnetic ground
state. Our studies further extend the family of bulk misfit layered
oxides into the 1D realm with potential applications in thermoelectric
and electronic devices
Nanotubes from Oxide-Based Misfit Family: The Case of Calcium Cobalt Oxide
Misfit
layered compounds (MLCs) have generated significant interest
in recent years as potential thermoelectric materials. MLC nanotubes
could reveal behavior that is entirely different from the bulk material.
Recently, new chemical strategies were exploited for the synthesis
of nanotubular forms of chalcogenide-based MLCs, which are promising
candidates for thermoelectric materials. However, analogous synthesis
of oxide-based MLC nanotubes has not been demonstrated until now.
Here, we report a chemical strategy for synthesis of cobalt-oxide-based
misfit nanotubes. A combination of high-resolution (scanning) transmission
electron microscopy (including image simulations), spatially resolved
electron energy-loss spectroscopy, electron diffraction, and density
functional theory (DFT) calculations is used to discover the formation
of a phase within these nanotubes that differs significantly from
bulk calcium cobaltite MLCs. Furthermore, DFT calculations show that
this phase is semiconducting with a band gap in excess of 1 eV, unlike
bulk calcium cobaltite MLCs, which are known to be metallic. Through
systematic experiments, we propose a formation mechanism for these
nanotubes that could also apply more generally to realizing other
oxide-based MLC nanotubes
Synthesis and Optical Properties of Homogeneous Nanoshurikens
During the last years the controlled
synthesis of Au nanoparticles
(NPs) has almost become a reality, and structures such as spheres,
cubes, rods, decahedra, or octahedra can be prepared with <i>a la carte</i> dimensions in a very homogeneous manner. However,
the fabrication of spiked particles, the most efficient plasmonic
NPs, with controllable geometric parameters remains elusive. Here
we show how to prepare highly homogeneous spiked nanoparticles composed
of a penta-twinned core and five tips. These nanoparticles, reminiscent
of ninja nanoshurikens (throwing stars), exhibit the ability to concentrate
large electromagnetic fields at the apexes of the tips upon illumination.
The apexes also present high affinity for analytes, giving rise to
an unprecedented capacity for quantitative optical ultradetection
with SERS