Alignment-Dependent Polarization Properties of Self-Assembled Carbon Nanotube Films

Abstract

Ordered self-assembled carbon nanotube (CNT) films exhibit outstanding anisotropic optoelectronic properties, subwavelength-scale thickness and high stability making them promising candidates for next-generation polarization photodetectors. The degree of alignment is a critical structural parameter for CNTs due to their exceptionally high aspect ratio and intrinsically one-dimensional nature. To investigate the polarization properties of self-assembled CNT films as a function of their alignment, we fabricated films with controlled alignment by modulating the density of active catalyst particles, with consideration of the crowding effect among adjacent CNTs during growth.Subsequently, the optical performance of the CNT films was evaluated under polarized light at a wavelength of 632 nm. The results indicate that as the degree of alignment, quantified by the Chebyshev orientation factor (COF), increases from 0.26 to 0.53, both the transmittance and the extinction ratio of a 700 nm-thick film improve significantly.Notably, when the degree of alignment reaches 0.61, the extinction ratio attains a remarkable value of 700. Under oblique incidence, the extinction ratio steadily increases with the incident angle, while the transmittance remains nearly constant. This unique phenomenon is attributed to the anisotropic structure of the film, where lateral alignment exhibits superior performance compared to top-surface alignment.