Atomistic Mechanisms of Temperature-Dependent Ion Track Formation in Gallium Nitride under Swift Heavy Ion Irradiation

Chaohui He; Chuanjian Yao; Hang Zang; Huan He; Jianan Wei; Jiayu Liang; Shaowei He; Tan Shi; Wenlong Liao; Xiaojun Fu

arxiv: 2604.24288 · v1 · submitted 2026-04-27 · ❄️ cond-mat.mtrl-sci

Atomistic Mechanisms of Temperature-Dependent Ion Track Formation in Gallium Nitride under Swift Heavy Ion Irradiation

Jiayu Liang , Shaowei He , Wenlong Liao , Tan Shi , Hang Zang , Yonghong Li , Xiaojun Fu , Chuanjian Yao

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Chaohui He Jianan Wei Huan He

This is my paper

Pith reviewed 2026-05-08 03:06 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci

keywords gallium nitrideswift heavy ionsion tracksmolecular dynamicstwo-temperature modelradiation damagenanobubblestemperature effects

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The pith

Swift heavy ion tracks in gallium nitride shift from broken segments to continuous channels as temperature rises through crystal decomposition.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper investigates how temperature affects the formation of ion tracks when gallium nitride is hit by swift heavy ions. Using combined models of electron and atom motion, the simulations reveal that higher temperatures make the tracks change shape: starting as separate segments at low heat, becoming lines of small bubbles at medium heat, and turning into solid tunnels at high heat. The reason is that the material breaks down along the ion path into clusters of gallium atoms and nitrogen molecules, which then rearrange. This matters because gallium nitride is used in high-power electronics and space tech that must withstand radiation and heat, so knowing these atomic changes helps predict and improve material durability. The study also notes that new crystal structures form near the tracks, potentially creating weak spots for electrical leaks.

Core claim

The simulations demonstrate a temperature-driven morphological transition of ion tracks in GaN, evolving from discontinuous segments under low electronic stopping to continuous tracks with isolated nanobubbles and finally to fully continuous channels at higher temperatures and stopping powers. At the atomic level, the wurtzite structure decomposes into Ga clusters and N2 molecules, with Ga-rich regions and recrystallized phases near bubble interfaces and N2 in bubble cores. Zincblende nanodomains form around the tracks, correlating with dislocation networks.

What carries the argument

The coupled two-temperature model and molecular dynamics simulations that track electronic energy loss and the resulting atomic rearrangements leading to track formation.

Load-bearing premise

The chosen interatomic potentials and two-temperature model parameters correctly describe the electronic stopping and atomic movements in GaN over the studied temperature range without needing special adjustments.

What would settle it

Direct experimental observation of ion tracks in GaN irradiated at different temperatures showing no morphological change or no evidence of Ga clusters and N2 molecules would contradict the simulated transition.

read the original abstract

The radiation tolerance of gallium nitride under extreme conditions is critical for its deployment in next-generation electronic and optoelectronic devices, yet the microscopic mechanisms governing swift heavy ion induced damage at elevated temperatures remain poorly understood. Therefore, this study employs a coupled approach including the two-temperature model and molecular dynamics simulations to resolve the entire processes of ion track generation induced by swift heavy ions irradiation across a wide temperature range. A temperature-driven morphological transition of ion tracks, evolving from discontinuous segments to continuous tracks composed of isolated nanobubbles, and ultimately to fully continuous channels is observed. Under lower electronic stopping loss of 430 MeV Kr irradiation, increasing temperature significantly enhances track visibility, enlarges track radii and promotes nanobubble formation. For higher electronic stopping conditions of 1171 MeV Ta irradiation, continuous ion tracks consisting of discontinuous nanobubbles (~1.5 nm radius) emerge already at 300 K, followed by a thermally activated transition into continuous channels with further radial expansion. At the atomic scale, SHI irradiation induces decomposition of wurtzite GaN into Ga clusters and N2 molecules along the ion trajectory, with Ga-rich regions and recrystallized wurtzite phases accumulating near bubble interfaces, while N2 preferentially segregates within bubble cores. Additionally, zincblende nanodomains nucleate around ion tracks and exhibit strong spatial correlation with radiation-induced dislocation networks, particularly screw dislocations, providing potential pathways for leakage current and increased susceptibility to single-event burnout.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The simulations map a temperature-driven shift in GaN ion tracks from discontinuous segments to continuous nanobubble channels with Ga/N2 decomposition, but the results rest on unvalidated 2TM-MD parameters at high temperatures.

read the letter

This paper runs coupled two-temperature model and molecular dynamics simulations to track how swift heavy ions damage gallium nitride across a temperature range. The central observation is a clear morphological progression: discontinuous tracks at lower temperatures give way to continuous tracks made of isolated nanobubbles and finally to fully continuous channels as temperature rises. They also describe the wurtzite lattice breaking down into gallium clusters and N2 molecules along the track, with zincblende nanodomains appearing near dislocation networks, especially screw dislocations. The trends differ by ion type, with higher stopping power (Ta) producing continuous features even at 300 K while lower stopping power (Kr) shows stronger temperature sensitivity in track radius and bubble formation. These atomic-scale pictures of segregation and recrystallization are the main addition relative to earlier GaN track studies. The workflow is straightforward and the reported changes in morphology and composition are presented without obvious internal contradictions. The work supplies useful visual and quantitative detail on how temperature modulates damage visibility and extent, which could help people thinking about radiation effects in GaN devices for power or space use. The soft spot is that the entire temperature-transition story depends on the accuracy of the electronic stopping powers, electron-phonon coupling, and the interatomic potential once local temperatures spike along the track. The abstract gives no sign of validation against measured track radii at multiple temperatures, alternative potentials, or ab initio checks for the high-temperature decomposition and bubble energetics. Standard potentials fitted at lower temperatures often produce unreliable bond-breaking or clustering behavior above a few thousand K, so the reported Ga clusters, N2 segregation inside bubbles, and zincblende correlation could be artifacts. Without those cross-checks the mechanistic claims stay provisional. This is the sort of computational study that radiation-damage modelers and GaN device engineers would want to see. It adds concrete simulation output on a relevant material even if the model choices need scrutiny. It deserves a serious referee so the community can evaluate the parameter set and decide how far to trust the high-temperature results.

Referee Report

2 major / 2 minor

Summary. The manuscript employs a coupled two-temperature model (TTM) and molecular dynamics (MD) simulation framework to investigate swift heavy ion (SHI) track formation in wurtzite GaN across a wide temperature range. It reports a temperature-driven morphological transition: under 430 MeV Kr irradiation, tracks evolve from discontinuous segments to continuous structures with isolated nanobubbles; under 1171 MeV Ta irradiation, continuous nanobubble tracks (~1.5 nm radius) form at 300 K and transition to fully continuous channels with radial expansion at higher temperatures. At the atomic scale, the simulations show decomposition of GaN into Ga clusters and N2 molecules along the track, with Ga-rich regions and recrystallized wurtzite near bubble interfaces, N2 segregation in bubble cores, and nucleation of zincblende nanodomains correlated with dislocation networks.

Significance. If the TTM-MD results hold under rigorous validation, the work would provide valuable atomic-scale mechanistic insight into temperature-dependent radiation damage in GaN, a material of interest for high-power electronics. The reported morphological transitions and decomposition pathways could inform models of track annealing and defect evolution. However, the manuscript does not report any cross-validation of the electronic stopping powers, electron-phonon coupling, or interatomic potential against ab initio calculations or experimental track radii at multiple temperatures, which limits the strength of the central claims.

major comments (2)

[Methods] Methods section (assumed §2 or §3): The choice of interatomic potential and TTM parameters (electronic stopping, electron-phonon coupling strength) is not validated for the high-temperature regime (> several thousand K) relevant to track formation and GaN decomposition. Standard potentials fitted to ground-state properties can yield spurious bond-breaking or bubble energetics; no comparison to ab initio MD, alternative potentials, or experimental track radii at elevated temperatures is provided, leaving the temperature-transition claim dependent on an untested assumption.
[Results] Results (assumed §4): The reported track radii, nanobubble sizes (~1.5 nm), and morphological transitions are presented without quantitative error bars or sensitivity analysis to TTM parameters. It is unclear whether the observed transition from discontinuous segments to continuous channels is robust or sensitive to small changes in the electronic energy deposition profile or potential cutoff.

minor comments (2)

[Abstract] Abstract and introduction: The phrase 'parameter-free' is not used, but the workflow description would benefit from explicit statement of all free parameters in the TTM-MD coupling.
[Figures] Figure captions (assumed): Ensure all simulation snapshots include scale bars, temperature labels, and clear indication of which irradiation condition (Kr or Ta) is shown.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive review of our manuscript. The comments on methodological validation and quantitative robustness of the results are well taken. We have prepared revisions to address these points directly while preserving the core findings of the temperature-dependent track morphology and atomic-scale decomposition mechanisms.

read point-by-point responses

Referee: [Methods] Methods section (assumed §2 or §3): The choice of interatomic potential and TTM parameters (electronic stopping, electron-phonon coupling strength) is not validated for the high-temperature regime (> several thousand K) relevant to track formation and GaN decomposition. Standard potentials fitted to ground-state properties can yield spurious bond-breaking or bubble energetics; no comparison to ab initio MD, alternative potentials, or experimental track radii at elevated temperatures is provided, leaving the temperature-transition claim dependent on an untested assumption.

Authors: We acknowledge that explicit high-temperature validation of the interatomic potential and TTM parameters against ab initio MD is not reported in the original manuscript. The potential selected is a widely adopted many-body potential for GaN that reproduces key ground-state and defect properties; prior literature has applied it to radiation-damage simulations, including bond-breaking events. To address the referee’s concern, the revised manuscript will include an expanded Methods subsection that (i) cites existing ab initio benchmarks for GaN decomposition energetics and high-temperature behavior, (ii) discusses the known limitations of classical potentials in the extreme-temperature regime, and (iii) notes the scarcity of experimental track-radius data above room temperature. A limited sensitivity test of the electron-phonon coupling strength will also be added. We cannot, however, perform new large-scale ab initio MD for the full track-formation process within the scope of this study. revision: partial
Referee: [Results] Results (assumed §4): The reported track radii, nanobubble sizes (~1.5 nm), and morphological transitions are presented without quantitative error bars or sensitivity analysis to TTM parameters. It is unclear whether the observed transition from discontinuous segments to continuous channels is robust or sensitive to small changes in the electronic energy deposition profile or potential cutoff.

Authors: We agree that the original presentation lacked quantitative uncertainty measures and robustness checks. In the revised manuscript we will (i) report track radii and nanobubble diameters with standard deviations obtained from at least five independent simulations per temperature and ion species, (ii) include a dedicated sensitivity subsection that varies the electronic energy deposition profile within the experimental uncertainty of the stopping-power tables and the potential cutoff radius, and (iii) demonstrate that the discontinuous-to-continuous morphological transition remains qualitatively unchanged under these variations. These additions will be placed in the Results section and supported by new supplementary figures. revision: yes

Circularity Check

0 steps flagged

No circularity: simulation outcomes are not redefined inputs

full rationale

The paper reports direct outputs from coupled two-temperature model plus molecular dynamics simulations of swift heavy ion tracks in GaN across temperatures. Track morphologies, nanobubble sizes, Ga-cluster formation, N2 segregation, and zincblende domain nucleation are simulation results under stated interatomic potentials and electronic stopping parameters; none are shown to be fitted to the target observables and then relabeled as predictions. No self-citation load-bearing steps, uniqueness theorems, or ansatz smuggling appear in the derivation chain. The modeling is self-contained computational work whose validity rests on external validation of potentials rather than internal redefinition.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claims rest on standard interatomic potentials and electronic stopping models whose accuracy at high temperature is assumed rather than re-derived; no new entities are postulated.

axioms (1)

domain assumption The two-temperature model parameters and chosen interatomic potentials remain valid across the simulated temperature range for GaN.
Invoked to justify the coupled simulation approach described in the abstract.

pith-pipeline@v0.9.0 · 5606 in / 1249 out tokens · 55524 ms · 2026-05-08T03:06:49.455002+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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https://doi.org/10.3390/ma13163627. (3) Xue, Y.; Ding, L.; Yang, X.; Chen, W.; Huang, Z.; Xue, Y.; Wang, T.; Liu, C.; Li, B.; Luo, Y.; Hao, P.; Ju, G.; Chen, Z.; Shen, B. In Situ Transmission Electron Microscopy Observation of N Ion Radiation Damage in the GaN Material at High Temperature. Applied Physics Letters 2025, 127 (13), 132102. https://doi.org/10...

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https://doi.org/10.1007/s00214-014-1447-z. (24) Waseda, Y.; Suzuki, K. Structure Factor and Atomic Distribution in Liquid Metals by X‐ray Diffraction. Physica Status Solidi (b) 1972, 49 (1), 339–347. https://doi.org/10.1002/pssb.2220490132. (25) Di Cicco, A.; Filipponi, A. Three-Body Distribution Function in Liquids: The Case of Liquid Gallium. Journal of...

work page doi:10.1007/s00214-014-1447-z 1972