Nicole Grobert

Choosing a suitable potential model to study dynamic processes in novel structures is an ambitious task often relying on chemical intuition. This paper addresses this challenge through a case study of diaphites, diamond–graphite nanocomposites, that are the only naturally occurring crystalline form of carbon featuring both sp ³ and sp ² hybridized atoms. As their synthesis is expensive and difficult to control, molecular dynamics (MD) simulations of their formation would be highly valuable. However, none of the available carbon potentials explicitly includes diaphites in their parameterization. Here, we benchmark several well-established carbon potentials (Tersoff 1989, Tersoff 1994, REBO-II, LCBOP-I, AIREBO, AIREBO-M, GAP-20, ACE) against ab initio MD (AIMD) at the PBE+D2 level of theory. Comparison of structural labeling disqualified Tersoff 1989, Tersoff 1994, REBO-II, AIREBO, and AIREBO-M. To enable long-timescale simulations on systems of a few thousand atoms, an ML-AIMD model was developed using AIMD acceleration with an on-the-fly Gaussian Approximation Potential (GAP). ML-AIMD accurately reproduced AIMD results and was therefore used as a benchmark. Extended testing revealed that ACE is the most transferable and computationally efficient potential for MD simulations of diaphites, reproducing the sp ² fraction across all temperatures at a cost at least four times lower than GAP-20. LCBOP-I performed comparably below 2000 K and remains preferable when computational resources are limited. The presented benchmarking framework efficiently identifies the most suitable potentials and provides a general strategy for selecting MD models for novel materials.

Molecular dynamics simulations identify collision-induced interfacial bonding as a feasible alternative to conventional high-pressure synthesis of diamond–graphite nanocomposites, offering improved control over structure and composition.

A novel heterostructured hexagonal‐boron nitride (h‐BN) flake‐coating on multi‐wall carbon nanotubes (MWCNT/BN) is reported and synthesized by chemical vapor deposition (CVD). Comprehensive characterization using X‐ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM), combined with electron energy loss spectroscopy (EELS), revealed the atomic structure and growth mechanism, which is further validated by molecular dynamics simulations. The resulting MWCNT/BN structure comprises three distinct layers: an inner carbon nanotube (CNT) core, coaxial BN nanotubes (BNNTs) surrounding the CNT core, and outer BN flakes extending from the BNNTs. We propose that BN layers first form coaxial BNNTs on the CNT surface; as deposition proceeds, BN accumulation generate in‐plane and out‐of‐plane compressive stresses in the h‐BN layers. When these stresses exceed a critical threshold, local buckling or cracking occurs, BN flakes emerge and grow further. This work elucidates, for the first time, the formation mechanism of BN nanoflakes on MWCNTs and confirms that the structure is a van der Waals heterostructure. The approach also offers a new route for synthesizing coaxial MWCNT@BN with only a few h‐BN layers. Notably, the BN flake coatings provide efficient phonon transport pathways and a large surface area, making this heterostructure highly promising for applications in thermal dissipation.

Atomic-scale wetting governs material formation at the nanoscale but remains poorly understood under confinement, where classical capillarity models fail. The growth of metallic nanowires within multi-wall carbon nanotubes (MWCNTs) exemplifies this challenge, requiring precise control over wetting, nucleation, and vapour-phase condensation. Here we show that nanowire formation proceeds through a two-stage mechanism: curvature-driven nucleation at open tube ends followed by capillary-driven elongation sustained by continuous vapour condensation. Using in situ atomic-resolution transmission electron microscopy (ARTEM) coupled with a deep learning convolutional neural network (CNN) capable of classifying liquid, solid and intermediate Sn _x O phase transitions, we directly capture the cascade of thermally induced nanowire growth within CNTs. Growth requires a wetting interface (contact angle, θ x O and the nanotube wall—conditions not described by Kelvin or Lucas–Washburn models. These results establish a predictive framework for vapour-phase nanowire encapsulation, linking nanoscale wetting dynamics to the fabrication of advanced nanomaterials.

Using megahertz x-ray free electron laser imaging with x-ray pulses of ~25 femtoseconds and a machine-learning strategy, we have conducted comprehensive in situ imaging studies on the dynamics of cavitation bubble clouds in ultrasound fields at the SPB/SFX beamline of the European XFEL. The research unambiguously revealed the quasi-simultaneous implosion of multiple bubbles and simultaneous collapse of bubble cloud in nanosecond scale and their dynamic impacts onto two-dimensional (2D) materials for layer exfoliation. We have also performed multiphysics modeling to simulate the shock wave emission, propagation, impact, and stresses produced. We elucidated the critical conditions for producing instant or fatigue exfoliation and the effects of bonding strengths and structural defects on the exfoliation rate. The discoveries have filled the long-standing missing knowledge gaps in the underlying physics of exfoliating 2D materials in ultrasound fields, providing a solid theoretical foundation for optimizing and scaling-up operation to produce 2D materials in a much more cost-effective and sustainable way.

Advanced fibers enable the fabrication of structures and composites for applications reliant on lightweight, oxidation resistant, mechanically strong, and electrically insulating materials, e.g. in all forms of land, air, and space transportation and in applications within extreme environments. Hexagonal boron nitride (h-BN) fibers harness these advantages, and in addition, offer ultra-high-strength-to-weight ratio and low density. Yet, existing precursors for polymer-derived BN fibers are limited to insoluble and air/moisture sensitive polyborazylenes, hindering fiber production at scale. In this contribution, we report a reliable, controllable, and scalable synthesis methodology for producing pure micro- and nano-h-BN fibers, offering a competitive alternative to NASA’s energy-intensive h-BN nanotubes production. The single-source precursor, N-methyl polyaminoborane (PMeAB), plays a pivotal role in this process. The catalytic, and scalable, synthesis of PMeAB with controlled molecular weights (M _w = 110,500–290,500 g·mol⁻¹) enables the production of h-BN fibers by electrospinning method and thermolysis under ammonia. PMeAB molecular weight and concentration were identified as key factors dictating the viscosity and surface tension, and thus influencing the overall spinnability of the PMeAB solution. We reveal that the subsequent formation of a cross-linked intermediate during PMeAB thermolysis is essential to retain the fibrous morphology during the conversion to h-BN fibers. Comprehensive characterization demonstrated the purity and homogeneity of the h-BN fibers, with ~ 97 at.% of B and N contents combined throughout the fiber body. This newly disclosed route to h-BN fibers offers a route to potentially valuable multifunctional filler material for advanced lightweight composites suitable for applications in extreme environments.

Atomic-scale wetting plays a crucial role in the fabrication of materials at the nanoscale, yet remains poorly understood under confinement, in which classical capillarity models fail. The growth of metallic nanowires inside multi-wall carbon nanotubes (MWCNTs) presents a particular challenge, as it requires precise control over wetting, nucleation, and vapour-phase condensation. Here, we show that nanowire formation within MWCNTs follows a two-stage mechanism: nucleation at open ends of the multi-wall nanotube, driven by the curved carbon walls, followed by capillary-driven elongation sustained by continuous condensation. Using in situ atomic-resolution transmission electron microscopy (ARTEM) combined with a deep learning convolutional neural network (CNN) capable of differentiating liquid and solid SnO, as well as intermediate SnOₓ phases, we track nanowire growth at the atomic scale. Mechanistically, we reveal that growth requires the formation of a wetting interface (contact angle < 90°) between the liquid precursor and the nanotube wall – a condition that classical models, such as Kelvin and Lucas–Washburn, fail to capture. Instead, these confined systems are dominated by nucleation kinetics, vapour flux, and interfacial condensation, which collectively drive the time-dependent filling observed in our ARTEM experiments. These findings establish a predictive framework for nanowire growth under confinement, providing a scalable approach to advanced nanomaterials where nanoscale wetting drives vapour-phase condensation, with potential implications for the manufacture of catalytic, energy, nanoelectronics, and quantum materials.

Creating sustainable and stable semiconductors for energy conversion via catalysis, such as water splitting and carbon dioxide reduction, is a major challenge in modern materials chemistry, propelled by the limited and dwindling reserves of platinum group metals. Two-dimensional hexagonal borocarbonitride (h-BCN) is a metal-free alternative and ternary semiconductor, possessing tunable electronic properties between that of hexagonal boron nitride (h-BN) and graphene, and has attracted significant attention as a nonmetallic catalyst for a host of technologically relevant chemical reactions. Herein, we use density functional theory to investigate the stability and optoelectronic properties of phase-separated monolayer h-BCN structures, varying carbon concentration and domain size. We find that, on average, a higher C content reduces the energetic cost of carbon inclusion per atom, as an increasingly graphitized network lowers the overall energy of the structure. Using functional HSE06, we show how the electronic bandgap of h-BN can be reduced from 5.94 to 1.61 eV with significant substitution of C in the domain (C at. % ∼ 44%) adding to the weight of evidence that suggests these segregated h-BCN systems can easily be customized. We use the location of conduction and valence band edges with respect to the potentials of HER, OER and CO₂ reduction to assess the catalytic suitability of these materials, identifying three structures with appropriate band edges for these catalytic reactions. Finally, the photoactivity of the structures is assessed through TD-DFT calculations, and we propose two candidates for photocatalysis based on the segregated h-BCN system.

Nanofibrous active layers offer hierarchical control over molecular structure, and the size and distribution of electron donor:acceptor domains, beyond conventional organic photovoltaic architectures. This structure is created by forming donor pathways via electrospinning nanofibers of semiconducting polymer, then infiltrating with an electron acceptor. Electrospinning induces chain and crystallite alignment, resulting in enhanced light‐harvesting and charge transport. Here, the charge transport capabilities are predicted, and charge separation and dynamics are evaluated in these active layers, to assess their photovoltaic potential. Through X‐ray and electron diffraction, the fiber nanostructure is elucidated, with uniaxial elongation of the electrospinning jet aligning the polymer backbones within crystallites orthogonal to the fiber axis, and amorphous chains parallel. It is revealed that this structure forms when anisotropic crystallites, pre‐assembled in solution, become oriented along the fiber– a configuration with high charge transport potential. Competitive dissociation of excitons formed in the photoactive nanofibers is recorded, with 95%+ photoluminescence quenching upon electron acceptor introduction. Transient absorption studies reveal that silver nanoparticle addition to the fibers improves charge generation and/or lifetimes. 1 ns post‐excitation, the plasmonic architecture contains 45% more polarons, per exciton formed, than the bulk heterojunction. Therefore, enhanced exciton populations may be successfully translated into additional charge carriers.

Electrospinning has been applied to produce ceramic fibers using sol gel-based spinning solutions consisting of ceramic precursors, a solvent, and a polymer to control the viscosity of the solution. However, the addition of polymers to the spinning solution makes the process more complex, increases the processing time, and results in porous mechanically weak ceramic fibers. Herein, we develop a coelectrospinning technique, where a nonspinnable sol (2, ZrO₂, SiO₂, and Al₂O₃. The polycrystalline TiO₂ fibers possess excellent flexibility and a high Young's modulus reaching 54.3 MPa, solving the extreme brittleness problem of the previously reported TiO₂ fibers. The single-component ZrO₂ fibers exhibit a Young's modulus and toughness of 130.5 MPa and 11.9 KJ/m³, respectively, significantly superior to the counterparts prepared by conventional sol-gel electrospinning. We also report the creation of ceramic fibers in micro- and nanospring morphologies and examine the formation mechanisms using thermomechanical simulations. The fiber assemblies constructed by the helical fibers exhibit a density-normalized toughness of 3.5-5 times that of the straight fibers due to improved fracture strain. This work expands the selection of the electrospinning solution and enables the development of ceramic fibers with more attractive properties.