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Nanoindentation of monolayer Tin+1CnTx MXenes via atomistic simulations: The role of composition and defects on strength

Summary

MXenes—2D transition-metal carbides/nitrides—are promising solution-processable conductors; mechanical properties depend on composition, surface termination, and defects. This work performs ReaxFF-based simulated nanoindentation in LAMMPS on oxygen-terminated Ti₃C₂O₂ and Ti₂CO₂ monolayers, extracting Young’s moduli from force–displacement curves for pristine sheets and sheets with Ti and C vacancies. OVITO visualizes deformation modes. The study positions defect-containing MXenes against graphene oxide benchmarks for modulus in wet-chemistry 2D processing contexts. The simulated indentation workflow parallels nanoindentation interpretations used in experiments, enabling direct comparison to mechanically tested MXene flakes when defect populations are documented. Compositional comparisons between Ti₃C₂O₂ and Ti₂CO₂ illustrate how MXene family members can differ sharply in stiffness, motivating property maps that treat termination and stoichiometry as first-class variables alongside defect density.

Methods

1 — MD application (simulated nanoindentation). ReaxFF (Ti₃C₂Tₓ-compatible parametrization cited in Computational Materials Science) is used in LAMMPS with QEq-style charge equilibration and documented nonbond cutoffs (see article). PBC: periodic in-plane monolayer cells of oxygen-terminated Ti₃C₂O₂ and Ti₂CO₂; a rigid spherical indenter (10 nm diameter) advances at 10 m·s⁻¹ along the surface normal while recording force–displacement curves (OVITO visualization). Ensemble: NVT at 1 K to suppress thermal noise during modulus extraction. Timestep: 0.25 fs. Defect models: additional Ti₃C₂O₂ cells include ~1 % Ti vacancies and ~10 % C vacancies simultaneously as in the abstract. Duration / staging: follow the staged relaxation + indentation protocol in the paper (exact ps/ns windows in Methods/figures). Thermostat / temperature control: the manuscript states the temperature was maintained at 1 K throughout indentation within the canonical (NVT) ensemble (see Comput. Mater. Sci. Methods for the corresponding LAMMPS controls). Barostat / pressure: N/A — NVT indentation without hydrostatic NPT barostat control. Electric fields / enhanced sampling: N/A — not used.

2 — Force-field training. N/A — applies a published MXene ReaxFF parametrization with DFT training heritage referenced in the article.

3 — Static QM. N/A — not a DFT-only study.

Findings

Outcomes: reported Young’s moduli are ~466 GPa (pristine Ti₃C₂O₂) and ~983 GPa (pristine Ti₂CO₂); combined Ti + C vacancies reduce Ti₃C₂O₂ to ~386 ± 31 GPa in the quoted defective model.

Comparisons: defective Ti₃C₂O₂ is compared to graphene oxide moduli cited for solution-processed 2D materials.

Sensitivity: composition (n+1,n family member) and vacancy loading strongly shift stiffness extracted from indentation slopes.

Limitations: 1 K sampling suppresses thermal effects; rigid indenter + classical ReaxFF omit explicit electronic plasticity.

Corpus honesty: moduli and defect percentages are taken from the abstract on pdf_path; verify against Comput. Mater. Sci. tables.

Limitations

1 K indentation suppresses thermal phonon contributions; rigid indenter and classical ReaxFF omit explicit electronic plasticity and charge transfer beyond the model. MXene terminations beyond O are not exhaustively sampled here. Young’s modulus extraction from indentation curves depends on contact radius definitions and elastic assumptions—use the article analysis pipeline when comparing to experiment. MXene literature evolves quickly; treat numerical moduli as illustrative ReaxFF predictions unless paired with experimental mechanical datasets from the same synthesis generation. Indentation rate effects are not explored across orders of magnitude in the excerpted protocol summary shown on this wiki page alone.

Relevance to group

Demonstrates ReaxFF nanoindentation protocols for MXene mechanical screening alongside 2D TMD and carbon mechanics pages; useful when contrasting solution-processable carbide sheets with oxide ceramic simulations in the corpus.

Citations and evidence anchors

  • DOI: 10.1016/j.commatsci.2018.10.033 — papers/ReaxFF_others/Plummer_Anasori_Gogotsi_MXene_indentation_2019.pdf; extract normalized/extracts/2018plummer-computationa-nanoindentation-monolayer_p1-2.txt.