Carbon‐based terahertz absorbers: Materials, applications, and perspectives

Abstract

Terahertz (THz) waves are nowadays used in a multitude of applications ranging from medicine, telecommunication, security surveillance, to fast sensing and imaging. Along with the most apparent aspects of the potential applications, there is also a flip side of the coin: the effects of unwanted electromagnetic pollution on various elements of the environment. Therefore, an effective shielding of THz radiation, preferably with an appreciable amount of absorption, is one of the milestones for the further development of terahertz technology. This review briefly outlines the main aspects of the area of research in terahertz absorbers, materials used, and their specific applications. Particular attention has been paid to the use of carbon‐based materials as terahertz absorbers, needed to fill the gap between the well‐known components across absorption coefficient 10–100 cm −1  for a refractive index 3–5. An example of such a class of materials is that of the organic or hybrid organic–inorganic polymers whose pyrolysis in an inert atmosphere gives black materials containing a residual free carbon phase. The carbon phase is a random network of covalent bonds in which carbon atoms are mainly in sp 2  hybridization state. The absorption of THz radiation is strongly dependent on the state of arrangement of C‐sp 2 , the amount of carbon, and the graphitic carbon domain size.