5 research outputs found
Multiparameter and Parallel Optimization of ReaxFF Reactive Force Field for Modeling the Atomic Layer Deposition of Copper
In this study, we
aim to develop a ReaxFF reactive force field
for simulating the reaction mechanism of copper atomic layer deposition
(ALD). To achieve this, we optimized the Cu/C, Cu/H, and Cu/N parameters
of ReaxFF and extended the existing Cu potential to describe Cu/C/H/O/N
interactions involved in Cu ALD. The parametrization procedure was
implemented through an efficient multiparameter and parallel optimization
scheme based on the Taguchi method. Using the newly developed Cu potential,
we performed reactive molecular dynamics (RMD) simulations on an āabbreviatedā
ALD cycle using a [CuĀ(<sup><i>i</i></sup>Pr-amd)]<sub>2</sub> (<sup><i>i</i></sup>Pr-amd = <i>N</i>,<i>N</i>ā²-diisopropylacetamidinate) or CuĀ(dmap)<sub>2</sub> (dmap = dimethylamino-2-propoxide) precursor with the H radical
as a coreactant. In the first half-cycle, the [CuĀ(<sup><i>i</i></sup>Pr-amd)]<sub>2</sub> precursor is found to adsorb dissociatively
on the Cu surface as CuĀ(<sup><i>i</i></sup>Pr-amd) monomers.
During the second half-cycle, H radicals partly eliminate precursor
fragments to the gas phase, but some intermediates such as C<sub>5</sub>H<sub>12</sub>N<sub>2</sub> and C<sub>2</sub>H<sub>4</sub>N remain
on the surface and may become a source of contamination. On the other
hand, the CuĀ(dmap)<sub>2</sub> precursor dissociates into CuĀ(dmap)
and dmap on the Cu surface. The second half-cycle is initiated through
a hydrogen transfer reaction, which completely eliminates the dmap
ligands to the gas phase. In general, our RMD simulations suggest
that the surface chemistry of CuĀ(dmap)<sub>2</sub> during the ALD
is simpler and cleaner than that of [CuĀ(<sup><i>i</i></sup>Pr-amd)]<sub>2</sub>
Bimodal Mesoporous Carbon Nanofibers with High Porosity: Freestanding and Embedded in Membranes for LithiumāSulfur Batteries
We
demonstrate a synthetic approach for highly ordered hexagonal
mesoporous carbon nanofibers with bimodal porosity, with an extremely
high surface area and a high inner pore volume of 1928 m<sup>2</sup>/g and 2.41 cm<sup>3</sup>/g, respectively. A tubular silica template
acts as an alternative fiber template for anodic alumina membranes.
The sulfur cathode fabricated with the nanofibers shows much better
electrochemical performance compared with our previously reported
BMC-1/S cathodes by achieving a more homogeneous sulfur distribution
in the carbon nanofiber framework. It is also noted that the variation
of porous architectures of the carbon framework (i.e., low volumetric
ratio of small mesopores over the total pore volume) results in very
different electrochemistry, suggesting the significance of porosity
optimization for sulfur electrodes
<i>In Situ</i> SAXS Study on a New Mechanism for Mesostructure Formation of Ordered Mesoporous Carbons: Thermally Induced Self-Assembly
A new mechanism for mesostructure formation of ordered
mesoporous
carbons (OMCs) was investigated with in situ small-angle X-ray scattering
(SAXS) measurements: thermally induced self-assembly. Unlike the well-established
evaporation-induced self-assembly (EISA), the structure formation
for organicāorganic self-assembly of an oligomeric resol precursor
and the block-copolymer templates Pluronic P123 and F127 does not
occur during evaporation but only by following a thermopolymerization
step at temperatures above 100 Ā°C. The systems investigated here
were cubic (<i>Im</i>3Ģ
<i>m</i>), orthorhombic <i>Fmmm</i>) and 2D-hexagonal (plane group <i>p</i>6<i>mm</i>) mesoporous carbon phases in confined environments, as
thin films and within the pores of anodic alumina membranes (AAMs),
respectively. The thin films were prepared by spin-coating mixtures
of the resol precursor and the surfactants in ethanol followed by
thermopolymerization of the precursor oligomers. The carbon phases
within the pores of AAMs were made by imbibition of the latter solutions
followed by solvent evaporation and thermopolymerization within the
solid template. This thermopolymerization step was investigated in
detail with in situ grazing incidence small-angle X-ray scattering
(GISAXS, for films) and in situ SAXS (for AAMs). It was found that
the structural evolution strongly depends on the chosen temperature,
which controls both the rate of the mesostructure formation and the
spatial dimensions of the resulting mesophase. Therefore the process
of structure formation differs significantly from the known EISA process
and may rather be viewed as thermally induced self-assembly. The complete
process of structure formation, template removal, and shrinkage during
carbonization up to 1100 Ā°C was monitored in this in situ SAXS
study
A Photoactive Porphyrin-Based Periodic Mesoporous Organosilica Thin Film
A novel
optoelectroactive system based on an oriented periodic mesoporous
organosilica (PMO) film has been developed. A tetra-substituted porphyrin
silsesquioxane was designed as a precursor, and the porphyrin macrocycles
were covalently incorporated into the organosilica framework without
adding additional silica sources, using an evaporation-induced self-assembly
process. The synthesized PMO film has a face-centered orthorhombic
porous structure with a 15 nm pore diameter. This large pore size
enables the inclusion of electron-conducting species such as [6,6]-phenyl
C<sub>61</sub> butyric acid methyl ester in the periodic mesopores.
Optoelectronic measurements on the resulting interpenetrating donorāacceptor
systems demonstrate the light-induced charge generation capability
and hole-conducting property of the novel porphyrin-based PMO film,
indicating the potential of PMO materials as a basis for optoelectroactive
systems
Oriented Thin Films of a Benzodithiophene Covalent Organic Framework
A mesoporous electron-donor covalent organic framework based on a benzodithiophene core, BDT-COF, was obtained through condensation of a benzodithiophene-containing diboronic acid and hexahydroxytriphenylene (HHTP). BDT-COF is a highly porous, crystalline, and thermally stable material, which can be handled in air. Highly porous, crystalline oriented thin BDT-COF films were synthesized from solution on different polycrystalline surfaces, indicating the generality of the synthetic strategy. The favorable orientation, crystallinity, porosity, and the growth mode of the thin BDT-COF films were studied by means of X-ray diffraction (XRD), 2D grazing incidence diffraction (GID), transmission and scanning electron microscopy (TEM, SEM), and krypton sorption. The highly porous thin BDT-COF films were infiltrated with soluble fullerene derivatives, such as [6,6]-phenyl C<sub>61</sub> butyric acid methyl ester (PCBM), to obtain an interpenetrated electron-donor/acceptor hostāguest system. Light-induced charge transfer from the BDT-framework to PCBM acceptor molecules was indicated by efficient photoluminescence quenching. Moreover, we monitored the dynamics of photogenerated hole-polarons <i>via</i> transient absorption spectroscopy. This work represents a combined study of the structural and optical properties of highly oriented mesoporous thin COF films serving as host for the generation of periodic interpenetrated electron-donor and electron-acceptor systems