Predicting the optical properties of nanostructured metamaterials: single-walled carbon nanotube arrays
Aaron Sisto, Stanford University
Vertically aligned single-walled carbon nanotube (SWCNT) arrays, fabricated across macroscopic dimensions, have been found to exhibit unique optical properties not found in traditional bulk materials. However, an accurate, generalized method of modeling these systems has yet to be realized. A first-principles computational approach based on density functional theory, accounting for many-electron effects, is used in conjunction with classical electrodynamics simulations to understand the optical properties of CNT arrays in the visible and near IR. The first-principles approach includes the use of the GW and Bethe-Salpeter methods and the accuracy of these approximations is assessed through evaluation of the absorption spectra of individual SWCNTs. The electrodynamics results are found to be in agreement with experiments. We find that exceptionally low spectral and directional reflectance (< 2 percent) and high absorptance arise from both the anisotropy in the dielectric function of individual CNTs as well as the vertical alignment, sparseness and CNT length. Collectively, these characteristics allow light to enter the material at any incidence angle with very low reflectance and gradually become completely absorbed. Furthermore, the accuracy achieved by this predictive method facilitates the optimization of the effective optical properties through variation of macroscopic array parameters. By altering the array density or chirality distribution, absorption at specific wavelengths can be selectively enhanced.
Abstract Author(s): A. Sisto, X. Ruan, T. S. Fisher, J. B. Neaton