Decoupling sublattice dynamics in low-dose neutron-irradiated 4H-SiC via two-component density functional theory guided positron annihilation spectroscopy

Abstract

Silicon carbide (SiC) is a premier candidate for nuclear applications, yet characterizing the nascent damage from low-dose neutron irradiation remains a challenge due to the complex behavior of its two sublattices. A typical example is that the standard S–W parameter analysis method for Positron Annihilation Doppler Broadening Spectroscopy (PADBS) is insensitive to low-density vacancy-type defects in materials. In this study, we investigate 4H-SiC subjected to 14 MeV fusion neutron fluences of 1 × 1013–2 × 1013 n/cm2. We report a distinct inconsistency: while the positron lifetime (τ) obtained from Positron Annihilation Lifetime Spectroscopy indicates a measurable evolution in defect characteristics, standard S and W parameters obtained from PADBS remain seemingly static. By combining experimental data with Two-Component Density Functional Theory calculations, we demonstrate that this stagnation is an artifact caused by the overwhelming positron trapping cross section of silicon vacancies (VSi), which masks the carbon vacancies (VC) signal. By utilizing a chemically resolved P-parameter method, we successfully decouple the sublattice signatures, revealing a ∼4.4% decrease in the carbon-to-silicon vacancy ratio (VC/VSi). This shift provides direct evidence of preferential dynamic annealing on the carbon sublattice and the clustering of vacancies into VSi-like complexes, mechanisms previously invisible to standard S–W analysis. Most importantly, this study extends the application of PADBS, enabling the effective detection of initial damage characteristics at low doses.