Tan Shi

Molybdenum disulfide (MoS ₂ ) is a prototypical transition metal dichalcogenide semiconductor with excellent optical and electrical properties. In this study, the irradiation behavior of monolayer and multilayer MoS ₂ was compared under irradiation with 2 MeV protons at 300 K, at fluences of 1 × 10 ^14, 1 × 10 ¹⁵ , and 5 × 10 ¹⁵ protons cm ⁻² . Raman spectroscopy revealed that the intensity of the longitudinal acoustic mode, indicative of structural defects, increased with irradiation fluence only in monolayer MoS ₂ , and both the in-plane ( E 2g 1 ) and out-of-plane ( A 1g ) vibrational modes showed minimal sensitivity to irradiation in both samples. Photoluminescence (PL) measurements revealed a strong suppression of direct-transition emission in monolayer MoS ₂ after irradiation, whereas enhanced PL near the A- and B-exciton energies was observed in multilayer MoS ₂ . X-ray photoelectron spectroscopy revealed no notable oxidation in MoS ₂ , but the Mo 3d and S 2p binding energies were slightly increased in monolayer MoS ₂ . Kelvin probe force microscopy showed opposite trends in the MoS ₂ –SiO ₂ work-function difference for monolayer and multilayer samples, indicating competing effects of surface adsorption, charge transfer, and electronic property modifications induced by irradiation defects. Molecular dynamics simulations further elucidate irradiation-induced defect formation, including point defects, sputtering, and defect clustering. These results provide insights into the irradiation behavior of MoS ₂ and its layer-dependent property modifications.

This work systematically unveils the nanoscale surface damage dynamics in gallium nitride by investigating the atomistic mechanisms of hillock formation. The results identify two distinct hillock morphologies dependent on electronic energy loss (Se) values. Bell-shaped hillocks form under 18.2 keV/nm Kr irradiation, whereas crater-rim hillocks with central holes emerge under 40.2 keV/nm Ta irradiation. Microstructural analysis reveals that Ga-rich hillocks are accompanied by the generation of metastable zincblende nanodomains. These nanodomains preferentially aggregate around the periphery or sidewalls of the hillocks and exhibit a high spatial correlation with screw dislocations. Further temperature-dependent studies indicate that elevated temperatures significantly enlarge the overall dimensions of the hillock structures without altering their fundamental morphologies. Notably, under Ta irradiation above 1200 K, the high temperatures drastically reduce the viscosity and surface tension of liquid gallium. This enhanced fluidity of the transient molten phase promotes the formation of penetrating nanochannels.

Primary knock-on atom (PKA) spectra provide the fundamental link between neutron irradiation environments and atomistic radiation damage. In reactor pressure vessels (RPVs), neutron attenuation and moderation produce substantial through-wall variations in PKA spectra. In this work, position-dependent PKA spectra representative of different locations across the RPV wall and thermal shield were combined with molecular dynamics simulations to investigate the influence of spectral evolution on primary radiation damage in an Fe–1at.% Ni model alloy. The damage-energy contribution of the PKA spectrum was found to be concentrated within an intermediate energy range of ~10–200 keV, with progressive spectral softening shifting the dominant contribution toward lower recoil energies through the vessel thickness. Spectrum-weighted analysis showed that the surviving defects per NRT displacement exhibit only a modest dependence on spectral position. In contrast, the nature of the surviving damage exhibits pronounced spectral sensitivity. Harder spectra near the inner wall and thermal shield promote spatially extended cascades, subcascade formation, and larger defect clusters, whereas softer outer-wall spectra predominantly generate isolated defects and small clusters. High-energy cascades also enhance Ni incorporation into interstitial clusters, indicating increased local chemical redistribution within cascade-affected regions. These results demonstrate that neutron spectral evolution influences not only the quantity of primary radiation damage but also its evolving character, with potential implications for long-term microstructural evolution in RPV materials.

Multi-principal element alloys (MPEAs) generally exhibit high radiation tolerance because the substantial lattice distortion associated with atomic size mismatch and chemical disorder may enhance the migration energy barriers. The atomic size mismatch effects are less understood because of the complex coupling among defect production, chemical redistribution, and structural instability under irradiation. Here, a Nb–Zr–Ti–V alloy with a body centered cubic structure is used as a model system to elucidate the role of atomic size mismatch in irradiation-induced defect evolution under helium ion irradiation. First-principles density functional calculations show that Frenkel pairs associated with smaller Nb and V atoms have significantly lower formation energies than those involving oversized Zr, indicating that increasing Nb and V contents reduces the energetic barrier for vacancy production and accelerate helium bubble nucleation, which is exanimated in our experiments. Under irradiation, coupled vacancy and interstitial fluxes toward bubbles produce inverse Kirkendall-type radiation-induced segregation, with V enrichment near bubble interiors and pronounced Zr accumulation in the surrounding matrix. The Zr enrichment near bubbles triggers a Bain-path–related BCC→FCC (FCT) transformation and the formation of plate-like radiation-induced precipitates. These precipitates act as strong defect sinks, enhancing vacancy trapping and helium bubble growth and establishing a positive feedback loop between precipitation and bubble evolution. These results highlight atomic size mismatch as a key parameter controlling irradiation tolerance in BCC MPEAs and provide mechanistic guidance for designing radiation-resistant BCC alloys.