Enhanced Performance of Al, Sb and Al/Sb Nanosheets Designed as Dielectric Lenses for Terahertz Applications

Abstract

Herein, aluminum (Al), antimony (Sb), and aluminum-coated antimony (Al/Sb) nanosheets are fabricated using the thermal evaporation technique under a vacuum pressure of 10−5 mbar. Structural and morphological investigations of these films have shown their amorphous growth, including nanograins embedded in an amorphous medium. Optically, while Al nanosheets exhibited free carrier absorption due to their metallic nature, Sb and Al/Sb nanosheets demonstrated semiconductor characteristics with energy band gaps of 1.10 eV and 0.60 eV, respectively. Additionally, Al nanosheets recorded a sufficiently large dielectric constant and optical conductivity values exceeding 76 and 24 (Ωcm)−1, respectively, at an incident photon energy (E) of 1.13 eV. Coating Sb nanosheets with Al enhanced the dielectric properties of Sb, increasing the dielectric constant and optical conductivity values from 3.6 to ~ 14.0 and from 0.40 (Ωcm)−1 to 4.86 (Ωcm)−1, respectively, at E = 1.13 eV. Moreover, the optical conductivity fitting according to the Drude-Lorentz model showed that the nanosheets under study are suitable for plasmonic interactions and performed as terahertz band filters, exhibiting terahertz cutoff frequencies in the range of 0.69–14.95 THz. Although the charge carriers' drift mobility in Al nanosheets is very low due to the high charge carrier concentration, coating these nanosheets onto Sb increased the drift mobility of charge carriers in Sb nanosheets. The optical and dielectric analyses presented in this work indicate the potential of Al, Sb, and Al/Sb nanosheets for use as dielectric lenses and terahertz band filters.