Tunable transparent terahertz absorber for sensing and radiation warming

Abstract

The lack in efficient functional devices has hindered plenty practical applications in terahertz (THz) band. In this work, we developed transparent THz absorber by employing trilayer Salisbury screen structure. Monolayer graphene and indium tin oxide (ITO) glass were spaced by a thin dielectric film, forming a transparent THz absorber. Assisted by ion gel, the carrier density of graphene layer can be effectively tuned through small external electrical gating (−2.5 V-2.5 V), with a modulation depth reaching to 100%. Taking advantage of the strong π−π interaction between graphene and external molecules containing π electrons, our fabricated transparent THz absorber enabled diphenylamine (DPA) detection. The adsorbed DPA molecule moves Fermi level of graphene toward Dirac point, performing a limit of detection of 5.5 ng. Moreover, by transferring the absorbed radiation into heat, our fabricated absorber can serve as a radiation warming device. The surface temperature of transparent THz absorber is 0.7 °C higher than that of glass in IR radiation environment. Note that the absorber is highly transparent in visible band, it will not prevent photosynthesis process of plants. Thereby, the THz absorbers have potential practical applications in diverse fields including wave manipulation, molecule sensing, and radiation warming.