3 research outputs found
Confined Etching within 2D and 3D Colloidal Crystals for Tunable Nanostructured Templates: Local Environment Matters
We report the isotropic
etching of 2D and 3D polystyrene (PS) nanosphere <i><i>hcp</i></i> arrays using a benchtop O<sub>2</sub> radio frequency plasma
cleaner. Unexpectedly, this slow isotropic etching allows tuning of
both particle diameter and shape. Due to a suppressed etching rate
at the point of contact between the PS particles originating from
their arrangement in 2D and 3D crystals, the spherical PS templates
are converted into polyhedral structures with well-defined hexagonal
cross sections in directions parallel and normal to the crystal <i>c</i>-axis. Additionally, we found that particles located at
the edge (surface) of the <i><i>hcp</i></i> 2D
(3D) crystals showed increased etch rates compared to those of the
particles within the crystals. This indicates that 2D and 3D order
affect how nanostructures chemically interact with their surroundings.
This work also shows that the morphology of nanostructures periodically
arranged in 2D and 3D supercrystals can be modified via gas-phase
etching and programmed by the superlattice symmetry. To show the potential
applications of this approach, we demonstrate the lithographic transfer
of the PS template hexagonal cross section into Si substrates to generate
Si nanowires with well-defined hexagonal cross sections using a combination
of nanosphere lithography and metal-assisted chemical etching
High-Performance Lithium-Ion Batteries with High Stability Derived from Titanium-Oxide- and Sulfur-Loaded Carbon Spherogels
This study presents
a novel approach to developing high-performance
lithium-ion battery electrodes by loading titania-carbon hybrid spherogels
with sulfur. The resulting hybrid materials combine high charge storage
capacity, electrical conductivity, and core-shell morphology, enabling
the development of next-generation battery electrodes. We obtained
homogeneous carbon spheres caging crystalline titania particles and
sulfur using a template-assisted sol-gel route and carefully treated
the titania-loaded carbon spherogels with hydrogen sulfide. The carbon
shells maintain their microporous hollow sphere morphology, allowing
for efficient sulfur deposition while protecting the titania crystals.
By adjusting the sulfur impregnation of the carbon sphere and varying
the titania loading, we achieved excellent lithium storage properties
by successfully cycling encapsulated sulfur in the sphere while benefiting
from the lithiation of titania particles. Without adding a conductive
component, the optimized material provided after 150 cycles at a specific
current of 250 mA g–1 a specific capacity of 825
mAh g–1 with a Coulombic efficiency of 98%
Setting Directions: Anisotropy in Hierarchically Organized Porous Silica
Structural
hierarchy, porosity, and isotropy/anisotropy are highly
relevant factors for mechanical properties and thereby the functionality
of porous materials. However, even though anisotropic and hierarchically
organized, porous materials are well known in nature, such as bone
or wood, producing the synthetic counterparts in the laboratory is
difficult. We report for the first time a straightforward combination
of sol–gel processing and shear-induced alignment to create
hierarchical silica monoliths exhibiting anisotropy on the levels
of both, meso- and macropores. The resulting material consists of
an anisotropic macroporous network of struts comprising 2D hexagonally
organized cylindrical mesopores. While the anisotropy of the mesopores
is an inherent feature of the pores formed by liquid crystal templating,
the anisotropy of the macropores is induced by shearing of the network.
Scanning electron microscopy and small-angle X-ray scattering show
that the majority of network forming struts is oriented towards the
shearing direction; a quantitative analysis of scattering data confirms
that roughly 40% of the strut volume exhibits a preferred orientation.
The anisotropy of the material’s macroporosity is also reflected
in its mechanical properties; i.e., the Young’s modulus differs
by nearly a factor of 2 between the directions of shear application
and perpendicular to it. Unexpectedly, the adsorption-induced strain
of the material exhibits little to no anisotropy