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 “abbreviated” ALD cycle using a [Cu­(^<i>i</i>Pr-amd)]₂ (^<i>i</i>Pr-amd = <i>N</i>,<i>N</i>′-diisopropylacetamidinate) or Cu­(dmap)₂ (dmap = dimethylamino-2-propoxide) precursor with the H radical as a coreactant. In the first half-cycle, the [Cu­(^<i>i</i>Pr-amd)]₂ precursor is found to adsorb dissociatively on the Cu surface as Cu­(^<i>i</i>Pr-amd) monomers. During the second half-cycle, H radicals partly eliminate precursor fragments to the gas phase, but some intermediates such as C₅H₁₂N₂ and C₂H₄N remain on the surface and may become a source of contamination. On the other hand, the Cu­(dmap)₂ precursor dissociates into Cu­(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 Cu­(dmap)₂ during the ALD is simpler and cleaner than that of [Cu­(^<i>i</i>Pr-amd)]₂

Bimodal Mesoporous Carbon Nanofibers with High Porosity: Freestanding and Embedded in Membranes for Lithium–Sulfur 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 m²/g and 2.41 cm³/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 organic–organic 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 °C. The systems investigated here were cubic (<i>Im</i>3̅<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 °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 C₆₁ butyric acid methyl ester in the periodic mesopores. Optoelectronic measurements on the resulting interpenetrating donor–acceptor 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 C₆₁ butyric acid methyl ester (PCBM), to obtain an interpenetrated electron-donor/acceptor host–guest 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