Skip to content

Fluorination of graphene enhances friction due to increased corrugation

Evidence and attribution

Authority of statements

Prose below summarizes the peer-reviewed Nano Letters article identified by doi and pdf_path. This page is not a substitute for the full paper (figures, quantitative friction trends, and simulation details).

Summary

FFM on patterned CVD graphene with XeF\(_2\) fluorination is combined with LAMMPS ReaxFF+QEq sliding simulations (Pt tip on G/FG). Fluorination raises nanoscale friction (several-fold to ~9× in places) and disorders stick–slip on FG versus ordered lattice friction on G. The authors attribute the enhancement primarily to larger interfacial energy corrugation from localized charge at F sites (Prandtl–Tomlinson picture), not increased puckering (Just Accepted PDF).

Methods

Experiments: CVD graphene on Cu, transferred to SiO\(_2\)/Si, patterned with photoresist, and fluorinated in XeF\(_2\) (60–1200 s, ~30 °C, 1 Torr XeF\(_2\), 35 Torr N\(_2\) carrier, pulse mode) so uncovered regions become FG while resist-protected areas stay pristine. After resist strip, friction force microscopy (FFM) compares G vs FG under dry N\(_2\) (RH < 2%); Raman (532 nm) characterizes fluorination. AFM: RHK UHV350 and Asylum MFP-3D; Mikromasch CSC37 Si tips with Sader-calibrated stiffness and a diamagnetic lateral-force calibrator.

MD (LAMMPS): A hemispherical Pt(111) asperity (1,626 atoms, radius 2.3 nm) slides on graphene or FG supported on a stepped Pt(181) substrate (5,280 atoms, ~10 × 6 × 1.2 nm³) at 10 K, mimicking substrate roughness. ReaxFF with QEq charge equilibration each step; Berendsen thermostat; Δt = 0.5 fs; PBC in-plane. Normal load set by initial tip–film height; top 3 tip layers constrained to slide direction only. A virtual atom 40 Å ahead links through a spring (K = 80 N/m) to mimic lateral compliance; drag speed 2 m/s. Static friction from peak lateral force; energy corrugation maps from tip–sample interaction energy vs position (Nano Lett. Methods; Just Accepted PDF).

1 — MD application (tip-on-film sliding)

  • Engine / code: LAMMPS with ReaxFF + QEq each step (Methods above; papers/ReaxFF_others/Li_Shenoy_Fluor_graphene_NanoLetters_2014.pdf).
  • System / composition: Pt tip (1,626 atoms) on graphene or fluorinated graphene on Pt(181) support (5,280 atoms); ~10 × 6 × 1.2 nm³ cell (Methods).
  • Boundaries / periodicity: PBC in-plane (Methods).
  • Ensemble / thermostat / temperature: NVT-class framing with Berendsen thermostat at 10 K (Methods).
  • Timestep: 0.5 fs (Methods).
  • Duration / stages / equilibration lengths: N/A — total trajectory lengths not copied into this wiki note (Nano Lett. Methods).
  • Barostat / pressure control: N/A — not stated as constant-pressure dynamics in the excerpted Methods above; normal load is set geometrically via tip–film height (Methods).
  • Shear / strain: 2 m/s lateral drive via spring-coupled virtual atom (K = 80 N/m, 40 Å offset) (Methods).
  • Electrostatics: QEq each step (Methods); N/A — cutoffs/precision details not copied here (full article).
  • Electric field: N/A — not indicated in the excerpted Methods above.
  • Replica / enhanced sampling: N/A — not indicated in the excerpted Methods above.

Findings

FFM shows μ\(_\text{FG}\) much larger than μ\(_\text{G}\) (e.g. ~6–7× in a representative boundary scan; monotonic increase with fluorination across samples). MD reproduces greatly increased peak friction on FG and μ\(_\text{FG}\)/μ\(_\text{G}\) ~7.3–8.0:1 without increased puckering of FG (ruling out puckering as the dominant mechanism). Interaction-energy corrugation grows strongly with F content (e.g. ~12.9 meV on pristine vs ~206 meV on a C\(_8\)F model at 0 nN load in one comparison). The authors interpret friction enhancement via Prandtl–Tomlinson behavior (E\(_0\) vs contact stiffness) and localized negative charge on F increasing potential roughness—consistent with AFM trends and prior hydrogenation MD (Just Accepted PDF).

Limitations

The registered PDF is a “Just Accepted”–era extract in the corpus; partial text extraction. Quantitative comparison to experiment should be taken from the final typeset article when available.

Relevance to group

Tribology and 2D materials context; not a van Duin-group ReaxFF methods paper—kept as neighboring graphene functionalization / mechanics literature.

Citations and evidence anchors

  • https://doi.org/10.1021/nl502147t — Communication title and DOI as in front matter.

Reader notes (navigation)

  • Corpus also registers a second path for the same DOI: paper:2014nanoletters-venue-paper (duplicate PDF ingest).