Revisiting THz absorption in GO and rGO liquid crystalline films

TL;DR

This study demonstrates that liquid crystalline GO and rGO films fabricated via vacuum filtration exhibit strong, tunable THz absorption with low reflectance, offering a practical alternative to metasurface-based absorbers for high-frequency applications.

Contribution

It introduces a simple vacuum filtration method to create GO and rGO liquid crystalline films with enhanced THz absorption properties, highlighting the role of LC phase in improving uniformity and absorption.

Findings

GO and rGO LC films show strong THz absorption (up to 50%).

Films are significantly smaller than the THz wavelength, enabling compact absorber design.

LC phase enhances film uniformity and absorption efficiency.

Abstract

With a swift progress in modern high-throughput communication systems, security, sensing and medicine utilizing THz range technologies, the demand for easy-to-fabricate, lightweight and high-performance absorbing materials has increased drastically. Notably, traditional approaches of eliminating unwanted radiation based on metasurfaces often face fabrication challenges limiting their practicality. In this study, we propose a straightforward approach for fabricating graphene oxide (GO) and reduced graphene oxide (rGO) liquid crystalline (LC) films via the vacuum filtration method and investigate their THz absorption characteristics. Here, the presence of LC phase in our electrochemically exfoliated GO and rGO LC films was confirmed by ellipsometric characterization. THz time-domain spectroscopy (TDS) measurements reveal that these films possess a low reflectance and transmittance confirming their strong absorptive properties within 0.4 - 1.6 THz frequency range for 2 micrometer thick GO and rGO LC films. Particularly, the GOLC film shows 37 % average absorption at a thickness of 2.12 micrometer, which is 221 times smaller than the central wavelength. Similarly, the rGOLC film reaches 50 % absorption with a 1.68 micrometer thickness, 279 times smaller than the central wavelength. These findings provide valuable insights for development of GO- and rGO-based LC THz absorbers with highly tunable properties due to the ordering of GO flakes. Specifically, the LC phase of GO contributes to the formation of more uniform films with enhanced absorption due to the compact stacking and denser packing, compared to conventional GO films with randomly oriented GO flakes.