Characterizing Raman modes and gas sensing features of functionalized tetragonal graphyne quantum dots: A first principles study

Abstract

This theoretical work has availed the first-principles method to critically explore the characterizing Raman spectra of tetragonal graphyne quantum dots. The Raman spectra of these T-graphyne systems possess the fingerprint of both sp and sp2 bonded atoms. We have explored that sp atoms predominate in determining intense Raman peaks over 2000 cm−1. Group theoretical analysis also provides a different insight into the occurrence of Raman active modes in these systems. Furthermore, the energy preference guides us to substitutionally dope boron (B) and nitrogen (N) atoms into the most stable α-T graphyne structure. The doping process enhances the system's stability and reduces the energy gap to a value of 1.29 eV. The concentration and position of the BN pair in T graphynes can be identified from the intense BN stretching mode at ∼ 1890 cm−1. Moreover, angle-dependent polarized Raman analysis depicts the effect of parallel and perpendicular polarization on the vibrational modes of T-graphyne for different incident laser wavelengths of 532 nm, 633 nm, and 785 nm. The anisotropy in the period of polarization-dependent intensities can be used to identify the crystal orientation direction. Firm absorption peaks in the UV–Vis spectra are also discussed from the allowed electronic transitions. Furthermore, the BN doped α-T graphyne structure possesses a large dipole moment of 5.2 Debye and can adsorb carbon-monoxide (CO) molecules with fascinating recovery time. The I–V response of the adsorbed T-graphyne system exhibit reasonably good sensing behaviour within a bias range of 0.28–0.29 V. Our results on vibrational signatures, and gas sensing applications will serve as an essential benchmark for graphyne-related research.