Optical properties of hexagonal boron nanotubes by first-principles calculations

Abstract

We present optical properties of hexagonal boron nanotubes (BNTs) for different schemes of incident light in the framework of density functional theory. We have considered three models of small diameter (below 5 Å) BNTs namely armchair (3,3), zigzag (5,0), and chiral (4,2) consisting 12, 20, and 56 atoms, respectively. In this convolution, we have investigated various optical parameters such as static dielectric constant, plasma frequency, absorption coefficient, refractive index, reflectivity, and optical conductivity for unpolarized [100], parallel polarized [001], and perpendicular polarized light [100]. The parallel and perpendicular polarized lights ensure the anisotropic nature of BNTs. The study reveals the highest static dielectric constants for chiral BNTs correspond to parallel polarized and unpolarized light, indicating good dielectric materials. The highest absorption coefficient is reported for armchair (3,3) BNT among all the considered models. Moreover, small absorption is noticed in comparison to CNTs. The small electron energy loss is obtained for parallel polarized light in contrast to perpendicular ones. The static refractive index follows the same trend as that of static dielectric constant, i.e., (4,2)>(3,3)>(5,0) for unpolarized and parallel polarized lights. Whereas, for perpendicular polarized light, they exhibit different order, i.e., (3,3)>(5,0)>(4,2). However, the static and maximum refractive indices are obtained high for chiral (4,2) BNT correspond to parallel polarized light. Further, the reflectivity and conductivity of (3,3) BNT bring out to be the highest for all the incident light. The high conductivity is predicted for armchair and chiral BNTs correspond to parallel polarized light. These predictions proved to be promising candidate for field emission and opto-electronic devices. The present calculated findings are well compared with the available experimental and theoretical results of other nanotubes.