8 research outputs found
Integrated Computational and Experimental Structure Refinement for Nanoparticles
Determining the three-dimensional
(3D) atomic structure of nanoparticles
is critical to identifying the structures controlling their properties.
Here, we demonstrate an integrated genetic algorithm (GA) optimization
tool that refines the 3D structure of a nanoparticle by matching forward
modeling to experimental scanning transmission electron microscopy
(STEM) data and simultaneously minimizing the particle energy. We
use the tool to create a refined 3D structural model of an experimentally
observed ∼6000 atom Au nanoparticle
Integrated Computational and Experimental Structure Refinement for Nanoparticles
Determining the three-dimensional
(3D) atomic structure of nanoparticles
is critical to identifying the structures controlling their properties.
Here, we demonstrate an integrated genetic algorithm (GA) optimization
tool that refines the 3D structure of a nanoparticle by matching forward
modeling to experimental scanning transmission electron microscopy
(STEM) data and simultaneously minimizing the particle energy. We
use the tool to create a refined 3D structural model of an experimentally
observed ∼6000 atom Au nanoparticle
Integrated Computational and Experimental Structure Refinement for Nanoparticles
Determining the three-dimensional
(3D) atomic structure of nanoparticles
is critical to identifying the structures controlling their properties.
Here, we demonstrate an integrated genetic algorithm (GA) optimization
tool that refines the 3D structure of a nanoparticle by matching forward
modeling to experimental scanning transmission electron microscopy
(STEM) data and simultaneously minimizing the particle energy. We
use the tool to create a refined 3D structural model of an experimentally
observed ∼6000 atom Au nanoparticle
Integrated Computational and Experimental Structure Refinement for Nanoparticles
Determining the three-dimensional
(3D) atomic structure of nanoparticles
is critical to identifying the structures controlling their properties.
Here, we demonstrate an integrated genetic algorithm (GA) optimization
tool that refines the 3D structure of a nanoparticle by matching forward
modeling to experimental scanning transmission electron microscopy
(STEM) data and simultaneously minimizing the particle energy. We
use the tool to create a refined 3D structural model of an experimentally
observed ∼6000 atom Au nanoparticle
Ionic Layer Epitaxy of Nanometer-Thick Palladium Nanosheets with Enhanced Electrocatalytic Properties
Large
surface area-to-volume ratio with plenty of accessible electrochemically
active sites presents metal nanosheets a highly efficient catalyst
material. However, a facile and effective synthesis of metal nanosheets
with nanoscale thicknesses, macroscopic sizes, and desired crystal
facets is still a grand challenge. Here, we report the synthesis of
free-standing Pd nanosheets by ionic layer epitaxy (ILE), which employs
a cationic oleylamine monolayer at the water–air interface
as a soft template to guide the nanosheet growth. The Pd nanosheets
exhibited a quasi-square morphology with a uniform thickness of ∼2
nm and sizes ranging from 1 to 6 μm. Owing to the extremely
large surface-to-volume ratio and the exposure of mixed surface crystal
facets, the Pd nanosheets exhibited high activity in formic acid oxidation
compared to the commercial Pd black and other reported Pd nanostructures.
This work presents a simple and effective way to prepare metal nanosheets
with nanometer-scale thickness control
Atomic Layer Epitaxy of h‑BN(0001) Multilayers on Co(0001) and Molecular Beam Epitaxy Growth of Graphene on h‑BN(0001)/Co(0001)
The direct growth of hexagonal boron
nitride (h-BN) by industrially
scalable methods is of broad interest for spintronic and nanoelectronic
device applications. Such applications often require atomically precise
control of film thickness and azimuthal registry between layers and
substrate. We report the formation, by atomic layer epitaxy (ALE),
of multilayer h-BN(0001) films (up to 7 monolayers) on Co(0001). The
ALE process employs BCl<sub>3</sub>/NH<sub>3</sub> cycles at 600 K
substrate temperature. X-ray photoelectron spectroscopy (XPS) and
low energy electron diffraction (LEED) data show that this process
yields an increase in h-BN average film thickness linearly proportional
to the number of BCl<sub>3</sub>/NH<sub>3</sub> cycles, with BN layers
in azimuthal registry with each other and with the Co(0001) substrate.
LEED diffraction spot profile data indicate an average BN domain size
of at least 1900 Ã…. Optical microscopy data indicate the presence
of some domains as large as ∼20 μm. Transmission electron
microscopy (TEM) and ambient exposure studies demonstrate macroscopic
and microscopic continuity of the h-BN film, with the h-BN film highly
conformal to the Co substrate. Photoemission data show that the h-BN(0001)
film is p-type, with band bending near the Co/h-BN interface. Growth
of graphene by molecular beam epitaxy (MBE) is observed on the surface
of multilayer h-BN(0001) at temperatures of 800 K. LEED data indicate
azimuthal graphene alignment with the h-BN and Co(0001) lattices,
with domain size similar to BN. The evidence of multilayer BN and
graphene azimuthal alignment with the lattice of the Co(0001) substrate
demonstrates that this procedure is suitable for scalable production
of heterojunctions for spintronic applications
Metastable Intermediates in Amorphous Titanium Oxide: A Hidden Role Leading to Ultra-Stable Photoanode Protection
Metastable
intermediates represent a non-equilibrium state of matter
that may impose profound impacts to materials properties beyond our
understandings of monolithic and equilibrium systems. Here, we report
a discovery of hidden metastable intermediates in amorphous TiO<sub>2</sub> thin films and their critical role in electrochemical damage.
These intermediates have a non-bulk crystal-like structure and exhibit
significantly higher electrical conductivity than both the amorphous
and the crystalline phases. When these TiO<sub>2</sub> films are applied
to protect Si photoelectrochemical (PEC) photoanodes, the intermediates
can induce localized high electrical currents that largely accelerate
the etching of the TiO<sub>2</sub> film and the Si electrode underneath.
The intermediates can be effectively suppressed by raising their nucleation
barrier via reducing the film thickness from 24 to 2.5 nm. The homogeneous
amorphous TiO<sub>2</sub>-film-coated
Si photoanodes achieved more than 500 h of PEC water oxidation at
a steady photocurrent density of over 30 mA·cm<sup>–2</sup>
Pore Structure and Bifunctional Catalyst Activity of Overlayers Applied by Atomic Layer Deposition on Copper Nanoparticles
We
present a model system, based on spherical nonporous supports,
to facilitate the characterization of supported metal catalysts stabilized
by atomic layer deposition (ALD) against sintering and leaching under
liquid-phase conditions. Calcination at high temperatures (973 K)
produces pores in the ALD overcoat, and we image these pores using
scanning transmission electron microscopy and electron energy loss
spectroscopy (STEM/EELS). We determine the size of these pores to
be ∼1 nm using small-angle X-ray scattering (SAXS). Finally,
we demonstrate the use of ALD to synthesize novel bifunctional catalysts
by the addition of an acidic oxide layer to the stabilizing overcoat