Bandgap Engineering through Topological and Strain-Induced Changes in Tetragraphene.

The ability to modulate electronic properties in low-dimensional carbon materials is fundamental to developing next-generation flexible electronics. In this work, we perform a comprehensive first-principles investigation of tetragraphene nanotubes (TGNTs), exploring the interplay between curvature-induced topology and uniaxial strain. Two chiral families are examined: zigzag-like (, 0) and armchair-like (0, ) configurations. Our results show that all TGNTs remain semiconducting upon rolling, with direct band gaps at the Γ point. We show that (, 0) TGNTs undergo a semiconductor-to-metal transition under strain, while preserving the sp-sp hybridization, a phenomenon not previously reported for this class of materials. The nanotubes exhibit high Young's modulus values and direction-dependent fracture patterns, with a strong correlation between structural anisotropy and mechanical performance. These findings reveal the potential of TGNTs as versatile platforms for strain-tunable optoelectronic applications and highlight the importance of topological and mechanical control in the engineering of functional nanocarbon systems.