Carbon-induced vacancy evolution and lattice dynamics in layered TlInS 2 crystals: A combined PALS, Raman, and MIKA study

In this work, the influence of carbon incorporation on vacancy-type defects and local structural properties of TlInS 2 crystals was investigated using positron annihilation lifetime spectroscopy (PALS), Raman spectroscopy, and MIKA calculations. The PALS results showed a decrease in τ 2 from 0.291 to 0.279 ns, accompanied by an increase in I 2 from 56.97% to 62.80%, indicating modification of vacancy-type trapping centers rather than the dominant formation of larger open-volume defects. MIKA calculations showed that the relaxed C S +V In configuration gives a positron lifetime of approximately 295 ps, close to the experimental τ 2 = 291 ± 4 ps, suggesting an In-vacancy-related environment for the dominant trapping state. Raman spectroscopy confirmed preservation of the characteristic vibrational features of TlInS 2 and the absence of new crystalline phases. Overall, carbon mainly modifies the local structural and electronic environment of vacancy-type defects while preserving the fundamental layered crystal framework of TlInS 2 .