Near-perfect absorber consisted of a vertical array of single-wall carbon nanotubes and engineered multi-wall carbon nanotubes

An extensive study on the optical characteristics of vertically aligned single-wall carbon nanotubes (SWCNTs) and engineered multi-wall carbon nanotubes (MWCNTs) using finite-difference time-domain (FDTD) simulation technique is presented in this work. We investigated absorption characteristics for SWCNTs, MWCNTs, dual-diameter MWCNTs, and cone MWCNTs with the changes in the occupation area and incident angle of light in the visible wavelength range. The enhancement of absorption was achieved by changing the geometrical shapes. Our study suggests that 99.569 % of the total light energy is absorbed in SWCNT's and 99.883% in cone-shaped-top MWCNB with an occupation area of 20% and 50%, respectively, at 450 nm wavelength and 5000 nm tube height. Moreover, for both SWCNTs and MWCNTs, reflectance increases with the increase of the occupation area due to the larger reflecting top surface area. We found that a drastic reduction of absorption occurs as the angle between the tube axis of aligned carbon nanotubes (CNTs) and the incoming light source increases above 30 degrees. Our study will be valuable for further investigation of the optical properties of shape-engineered CNTs and will promote CNT-based ultra-broadband absorber devices and systems for multifunctional optoelectronic applications. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement