Tuning the electronic properties of boron nitride nanotubes through carbon-, oxygen-, and vacancy-induced defects

The functionalization of low-dimensional materials has emerged as an effective strategy for tailoring their electronic and magnetic properties for advanced nanotechnology applications. In this work, density functional theory calculations were employed to investigate carbon-, oxygen-, and vacancy-related defects in insulating boron nitride nanotubes (BNNT) and semiconducting di-boron di-nitride nanotubes (B2N2NT) with (9,0) chirality. Monomers, dimers, trimers, larger carbon clusters, and carbon–oxygen and carbon–vacancy complexes were considered. In BNNT, defect incorporation generally reduces the band gap and, in several configurations, induces spin-polarized electronic states through defect-induced localized states near the Fermi level. In contrast, most functionalized B2N2NT systems exhibit increased band gaps, demonstrating enhanced semiconducting stability. Thermodynamic analysis indicates that larger carbon clusters are more favorable in BNNT, whereas smaller defect configurations dominate in B2N2NT. These results demonstrate that defect engineering provides an effective route for tuning boron nitride nanotubes for nanoelectronic, sensing, and spintronic applications.