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Reactive molecular dynamics simulations on SiO2-coated ultra-small Si nanowires

Evidence and attribution

Authority of statements

Prose sections below (Summary, Methods, Findings, etc.) are curated summaries of the publication identified by doi, title, and pdf_path in the front matter above. They are not new primary claims by this wiki.

For definitive numerical values, reaction schemes, and interpretations, use the peer-reviewed article (and optional records under normalized/papers/ when present)—not this page alone.

Summary

Ultra-small Si nanowires (Si-NWs) with oxide shells are important for quantum-confined Si optoelectronics, but dry oxidation pathways and self-limiting thicknesses are hard to control at the nanometer scale. This study uses ReaxFF MD to follow oxidation of (100) Si-NWs with initial diameters 1.0–3.0 nm from 300–1200 K. Two temperature-dependent regimes are reported: at high T, ultrathin SiO\(_2\) nanowires (fully oxidized structures in the classification used in the paper); at low T, Si core | ultrathin SiO\(_2\) core–shell morphologies. The crossover temperature decreases linearly with increasing curvature (smaller diameter). Interfacial stress drives self-limiting oxidation, depending on initial radius and temperature—linking mechanics to process windows for morphology control.

Methods

Force-field training (ReaxFF)

Parent FF / elements: ReaxFF with the Si/SiO\(_2\) parameter set employed by Buehler et al. (as cited in the article), trained extensively against Si and SiO\(_2\) phases. SiO\(_x\) suboxides with \(x < 2\) were not explicit training targets; the authors note prior planar Si|SiO\(_2\) work still gave reasonable agreement with DFT and experiment for suboxide species.

QM reference, training set, optimization, reference data: N/A — this publication applies an existing Si/SiO\(_2\) ReaxFF parametrization to nanowire oxidation rather than reporting a new fit workflow; any additional QM benchmarks are in the cited ReaxFF references (see pdf_path).

MD application (atomistic oxidation)

Engine / code: Reactive molecular dynamics with ReaxFF (indexed excerpt and abstract); N/A — standalone MD program name not recovered from normalized/extracts/2012khalilov-venue-c2nr32387g_p1-2.txt—confirm in pdf_path.

System size & composition: (100) Si nanowires with initial diameters 1.0–3.0 nm under dry thermal oxidation in the 300–1200 K window; the indexed text describes diameter via averaged radial positions of surface atoms (exact stoichiometries and gas-phase O\(_2\) loading per case are in pdf_path).

Boundaries / periodicity: Periodic boundary conditions along the wire (z) axis with a 1 nm unit-cell repeat to mimic an infinitely long nanowire (Computational details in the article; excerpt p. 2).

Ensemble: N/A — NVE/NVT/NPT label not recovered from the indexed excerpt (verify pdf_path).

Timestep: N/A — not recovered from the indexed excerpt (verify pdf_path).

Duration / stages: N/A — equilibration/production schedule not recovered from the indexed excerpt; reactive trajectories are discussed on ps accessible timescales in line with typical ReaxFF oxidation surveys—verify staging in pdf_path.

Thermostat: N/A — thermostat type and coupling constants not recovered from the indexed excerpt (verify pdf_path).

Barostat / pressure control: N/A — NPT barostat not stated in the indexed excerpt for these nanowire runs.

Temperature: 300–1200 K oxidation window; individual production temperatures follow the paper’s parameter sweep.

Pressure / stress: Interfacial stress is analyzed in the article as part of the self-limiting oxidation argument; N/A — externally imposed hydrostatic pressure control is not described in the indexed excerpt.

Electric field: N/A — not used for the oxidation MD in the indexed excerpt.

Replica / enhanced sampling: N/A — not indicated in the indexed excerpt.

Static QM / DFT-only

N/A — central results are ReaxFF MD on nanowires, not a standalone static DFT study (DFT appears as validation context in the ReaxFF literature cited by the authors).

Findings

The simulations report two temperature regimes for ultra-small wires: high temperature yields fully oxidized ultrathin SiO₂ nanowire-like products (terminology as used in the paper), whereas lower temperature yields Si core | ultrathin SiO₂ shell core–shell morphologies. The crossover temperature decreases approximately linearly with increasing curvature (smaller diameter), linking nanoscale effects to process windows. Interfacial stress is identified as driving self-limiting oxidation, depending on initial Si-NW radius and oxidation temperature, consistent with stress-gated oxidation arguments discussed in the introduction. The work positions ReaxFF as an atomistic bridge between mechanics and oxidation for sub-3 nm (100) Si wires under dry conditions.

Limitations

  • 1 nm axial periodicity approximates an infinitely long wire; real wires have length, facets, and defects not fully captured.
  • Dry oxidation only; wet chemistry pathways differ.

Relevance to group

van Duin-group coauthored ReaxFF on Si oxidation at nanowire scale—ties to electronics Si/SiO\(_2\) processing literature.

Citations and evidence anchors

  • DOI: 10.1039/c2nr32387g
  • Text-aligned pointer: normalized/extracts/2012khalilov-venue-c2nr32387g_p1-2.txt