10 research outputs found
In Situ Visualization of Self-Assembly of Charged Gold Nanoparticles
Self-assembly
of Au nanoparticles (NPs) coated with positively
charged cetyltrimethylammonium ions (CTA<sup>+</sup>) and negatively
charged citrate ions in aqueous liquid cell was investigated by in
situ transmission electron microscopy (TEM). Under electron illumination
in TEM, the hydrated electrons will reduce the overall positive charges
of the CTA<sup>+</sup> covered Au NPs and decrease the repulsive electrostatic
forces among NPs, leading to assembly of individual NPs into one-dimensional
structures. On the contrary, the negatively charged Au NPs coated
with citrate ions are steady in liquid cell regardless of electron
beam intensity
Solvent-Mediated End-to-End Assembly of Gold Nanorods
We demonstrate a new method for the bottom-up assembly of anisotropic nanoparticles, showing that alkanethiol molecules can induce controlled end-to-end assembly of gold nanorods in mixed water/acetonitrile solutions. The assembly is driven by solvent-mediated interactions among hydrophobic alkanethiol ligands selectively bound to the ends of the nanorods and among hydrophilic cetyltrimethylammonium bromide (CTAB) surfactants on the sides of the rods. It occurs only when the gold-nanorod samples have been aged for approximately two weeks. We compare the kinetics of solvent-mediated assembly using undecanethiol ligands to assembly processes driven by covalent bonding using α,ω-undecanedithiol ligands and processes driven by hydrogen bonding using 11-mercaptoundecanoic acid ligands. Our experiments demonstrate the different assembly mechanisms involved as well as the conditions needed to obtain selective end-to-end assembly
Strong Resistance to Bending Observed for Nanoparticle Membranes
We demonstrate how gold nanoparticle
monolayers can be curled up into hollow scrolls that make it possible
to extract both bending and stretching moduli from indentation by
atomic force microscopy. We find a bending modulus that is 2 orders
of magnitude larger than predicted by standard continuum elasticity,
an enhancement we associate with nonlocal microstructural constraints.
This finding opens up new opportunities for independent control of
resistance to bending and stretching at the nanoscale
Size-Dependent Coherent-Phonon Plasmon Modulation and Deformation Characterization in Gold Bipyramids and Nanojavelins
Localized
surface plasmon resonances (LSPRs) arising from metallic
nanoparticles offer an array of prospective applications that range
from chemical sensing to biotherapies. Bipyramidal particles exhibit
particularly narrow ensemble LSPR resonances that reflect small dispersity
of size and shape but until recently were only synthetically accessible
over a limited range of sizes with corresponding aspect ratios. Narrow
size dispersion offers the opportunity to examine ensemble dynamical
phenomena such as coherent phonons that induce periodic oscillations
of the LSPR energy. Here, we characterize transient optical behavior
of a large range of gold bipyramid sizes, as well as higher aspect
ratio nanojavelin ensembles with specific attention to the lowest-order
acoustic phonon mode of these nanoparticles. We report coherent phonon-driven
oscillations of the LSPR position for particles with resonances spanning
670 to 1330 nm. Nanojavelins were shown to behave similarly to bipyramids
but offer the prospect of separate control over LSPR energy and coherent
phonon oscillation period. We develop a new methodology for quantitatively
measuring mechanical expansion caused by photogenerated coherent phonons.
Using this method, we find an elongation of approximately 1% per photon
absorbed per unit cell and that particle expansion along the lowest
frequency acoustic phonon mode is linearly proportional to excitation
fluence for the fluence range studied. These characterizations provide
insight regarding means to manipulate phonon period and transient
mechanical deformation
Self-Assembled Nanoparticle Drumhead Resonators
The self-assembly of nanoscale structures
from functional nanoparticles
has provided a powerful path to developing devices with emergent properties
from the bottom-up. Here we demonstrate that freestanding sheets self-assembled
from various nanoparticles form versatile nanomechanical resonators
in the megahertz frequency range. Using spatially resolved laser-interferometry
to measure thermal vibrational spectra and image vibration modes,
we show that their dynamic behavior is in excellent agreement with
linear elastic response for prestressed drumheads of negligible bending
stiffness. Fabricated in a simple one-step drying-mediated process,
these resonators are highly robust and their inorganic–organic
hybrid nature offers an extremely low mass, low stiffness, and the
potential to couple the intrinsic functionality of the nanoparticle
building blocks to nanomechanical motion
Kinetic Pathway of Palladium Nanoparticle Sulfidation Process at High Temperatures
A significant
issue related to Palladium (Pd) based catalysts is
that sulfur-containing species, such as alkanethiols, can form a PdS<sub><i>x</i></sub> underlayer on nanoparticle surface and subsequently
poison the catalysts. Understanding the exact reaction pathway, the
degree of sulfidation, the chemical stoichiometry, and the temperature
dependence of this process is critically important. Combining energy-filtered
transmission electron microscopy (EFTEM), X-ray diffraction (XRD),
and X-ray absorption spectroscopy experiments at the S <i>K-</i>, Pd <i>K</i>-, and <i>L</i><sub>2,3</sub>-edges,
we show the kinetic pathway of Pd nanoparticle sulfidation process
with the addition of excess amount of octadecanethiol at different
temperatures, up to 250 °C. We demonstrate that the initial polycrystalline
Pd-oleylamine nanoparticles gradually become amorphous PdS<sub><i>x</i></sub> nanoparticles, with the sulfur atomic concentration
eventually saturating at Pd/S = 66:34 at 200 °C. This final chemical
stoichiometry of the sulfurized nanoparticles closely matches that
of the crystalline P<sub>16</sub>S<sub>7</sub> phase (30.4% S), albeit
being structurally amorphous. Sulfur diffusion into the nanoparticle
depends strongly on the temperature. At 90 °C, sulfidation remains
limited at the surface of nanoparticles even with extended heating
time; whereas at higher temperatures beyond 125 °C, sulfidation
occurs rapidly in the interior of the particles, far beyond what can
be described as a core–shell model. This indicates sulfur diffusion
from the surface to the interior of the particle is subject to a diffusion
barrier and likely first go through the grain boundaries of the nanoparticle
Electrooxidative Tandem Cyclization of Activated Alkynes with Sulfinic Acids To Access Sulfonated Indenones
An
electrooxidative direct arylsulfonlylation of ynones with sulfinic
acids via a radical tandem cyclization strategy has been developed
for the construction of sulfonated indenones under oxidant-free conditions.
This method provides a simple and efficient approach to prepare various
sulfonylindenones in good to excellent yields, demonstrating the tremendous
prospect of utilizing electrocatalysis in oxidative coupling. Notably,
this reaction could be easily scaled up with good efficiency
Low-Pressure Flow Chemistry of CuAAC Click Reaction Catalyzed by Nanoporous AuCu Membrane
Click chemistry has
been widely used in bioconjugation, polymer
synthesis, and the development of new anticancer drugs. Here, we report
a nanoporous membrane made of AuCu alloy nanowires, which can effectively
catalyze copperÂ(I)-catalyzed 1,3-dipolar cycloaddition between azide
and terminal alkyne (CuAAC) in flow condition with pressure less than
one bar. Comparison studies of the nanowires before and after the
reaction using X-ray photoelectron spectroscopy reveal Cu(0) and CuÂ(I)
are main species that promote the reaction. This simple strategy can
be used to synthesize a variety of compounds with triazole linkage
and extended to gram level chemical production
Phonon-Driven Oscillatory Plasmonic Excitonic Nanomaterials
We
demonstrate that coherent acoustic phonons derived from plasmonic
nanoparticles can modulate electronic interactions with proximal excitonic
molecular species. A series of gold bipyramids with systematically
varied aspect ratios and corresponding localized surface plasmon resonance
energies, functionalized with a J-aggregated thiacarbocyanine dye
molecule, produces two hybridized states that exhibit clear anticrossing
behavior with a Rabi splitting energy of 120 meV. In metal nanoparticles,
photoexcitation generates coherent acoustic phonons that cause oscillations
in the plasmon resonance energy. In the coupled system, these photogenerated
oscillations alter the metal nanoparticle’s energetic contribution
to the hybridized system and, as a result, change the coupling between
the plasmon and exciton. We demonstrate that such modulations in the
hybridization are consistent across a wide range of bipyramid ensembles.
We also use finite-difference time domain calculations to develop
a simple model describing this behavior. Such oscillatory plasmonic-excitonic
nanomaterials offer a route to manipulate and dynamically tune the
interactions of plasmonic/excitonic systems and unlock a range of
potential applications
Binary Transition-Metal Oxide Hollow Nanoparticles for Oxygen Evolution Reaction
Low-cost transition
metal oxides are actively explored as alternative materials to precious
metal-based electrocatalysts for the challenging multistep oxygen
evolution reaction (OER). We utilized the Kirkendall effect allowing
the formation of hollow polycrystalline, highly disordered nanoparticles
(NPs) to synthesize highly active binary metal oxide OER electrocatalysts
in alkali media. Two synthetic strategies were applied to achieve
compositional control in binary transition metal oxide hollow NPs.
The first strategy is capitalized on the oxidation of transition-metal
NP seeds in the presence of other transition-metal cations. Oxidation
of Fe NPs treated with Ni (+2) cations allowed the synthesis of hollow
oxide NPs with a 1–4.7 Ni-to-Fe ratio via an oxidation-induced
doping mechanism. Hollow Fe–Ni oxide NPs also reached a current
density of 10 mA/cm<sup>2</sup> at 0.30 V overpotential. The second
strategy is based on the direct oxidation of iron–cobalt alloy
NPs which allows the synthesis of hollow Fe<sub><i>x</i></sub>Co<sub>100–<i>x</i></sub>-oxide NPs where <i>x</i> can be tuned in the range between 36 and 100. Hollow Fe<sub>36</sub>Co<sub>64</sub>-oxide NPs also revealed the current density
of 10 mA/cm<sup>2</sup> at 0.30 V overpotential in 0.1 M KOH