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In situ atomistic insight into the growth mechanisms of single layer 2D transition metal carbides

Publisher galley / uncorrected proof PDF for the Nature Communications MXene growth article; the science matches 2018sang-nat-situ-atomistic.

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Prose summarizes the publication identified by doi. For citation-ready text and figures, prefer the version-of-record PDFs on 2018sang-nat-situ-atomistic or 2018sang-nat-situ-atomistic-2.

Summary

In situ aberration-corrected STEM with heating shows homoepitaxial growth of hexagonal TiC adlayers on defunctionalized Ti₃C₂ MXene above roughly 500 °C, yielding Ti₄C₃- and Ti₅C₄-like compositions. Density functional theory and ReaxFF hybrid force-biased Monte Carlo and molecular dynamics rationalize adatom diffusion, binding, and step energies for Frank–van der Merwe growth of a single carbide layer. This galley ingest slug duplicates the scientific narrative on 2018sang-nat-situ-atomistic while recording PDF provenance for the uncorrected proof file named in pdf_path.

Methods

STEM and electron energy-loss spectroscopy use in situ heating in ultrahigh vacuum (order 10⁻⁹ Torr), annealing Ti₃C₂Tₓ flakes above 500 °C to remove terminators and nucleate TiC islands, with elemental mapping to distinguish carbide adlayers from bare Ti metal. Simulations combine DFT supercell energetics for h-TiC adlayers on Ti₃C₂ with ReaxFF-based hybrid fbMC/MD to capture bond-making and bond-breaking during growth on MXene surfaces.

Instrument settings, temperature schedules, EELS acquisition parameters, and simulation cell/sampling details are given in papers/Xiahan_Nature_Comm_MXene_defect_2018_galley.pdf and the version-of-record article PDFs cross-linked from 2018sang-nat-situ-atomistic.

Atomistic modeling (DFT + ReaxFF fbMC/MD). Same protocol family as the version-of-record article: DFT on slab/supercell models of defunctionalized Ti\(_3\)C\(_2\) with h-TiC adlayers, plus ReaxFF-based hybrid force-biased Monte Carlo / molecular dynamics (fbMC/MD) to capture bond-making/bond-breaking during Frank–van der Merwe growth. Engine: molecular dynamics with ReaxFF in the hybrid fbMC/MD workflow (N/A — specific MD engine name not in this note’s excerpt). System: periodic supercells containing the MXene template and adlayer (N/A — atom counts from article/SI). PBC: three-dimensional periodic supercells for DFT and coupled fbMC/MD as described in Nature Communications Methods. Ensemble / timestep / production length: canonical finite-temperature sampling is used in the published fbMC/MD workflow as described in Nature Communications Methods (N/A — whether the authors label the segment explicitly as NVT vs another thermostat formulation should be confirmed from the PDF/SI rather than this galley ingest page). Thermostat / barostat: N/A — not stated in the indexed galley excerpt used here. Temperature: thermal driving aligned with the microscopy conditions discussed (~500 °C with beam assistance; 1000 °C thermal-only in the abstract narrative). Pressure (hydrostatic): N/A — not used in the atomistic models summarized here. Electric field in MD: N/A — not used as a classical MD bias (STEM beam effects are experimental). Enhanced sampling: fbMC/MD (Monte Carlo bond events + MD); N/A — umbrella / metadynamics / replica exchange not indicated in the indexed text for this work.

Findings

Homoepitaxial TiC monolayers grow in a Frank–van der Merwe mode with Ti and C supplied from the MXene flake; h-TiC adlayers appear above 500 °C with beam assistance and at 1000 °C thermally. DFT highlights a balance of low adatom diffusion barriers, high h-Ti surface energy, step-edge penalties, and strong h-TiC binding that favors layered growth. EELS supports C-rich adlayer stoichiometry versus bare Ti metal.

The combined STEM/theory storyline emphasizes layer-by-layer carbide accretion on defunctionalized MXene rather than metal islanding alone, consistent with the binding/step cost balance summarized in the DFT section.

Limitations

Proof PDFs can differ in wording and figure quality from the journal version. Electron-beam effects couple to thermal driving forces, and reactive force-field kinetics remain approximate versus experiment.

Wiki prose here is a navigation aid. Definitive numbers, protocol details, and figure-level claims should be taken from the peer-reviewed article at pdf_path (and any Supporting Information cited there), not from this page alone.

Relevance to group

Multiple van Duin group contributors co-author; this slug records ingest provenance for the galley-stage file bytes.

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