A Review on Thin-film Sensing with Terahertz Waves

Abstract

In the past two decades, the development and steady improvement of terahertz technology has motivated a wide range of scientific studies designed to discover and develop terahertz applications. Terahertz sensing is one such application, and its continued maturation is virtually guaranteed by the unique properties that materials exhibit in the terahertz frequency range. Thinfilm sensing is one branch of this effort that has enjoyed diverse development in the last decade. Deeply subwavelength sample thicknesses impose great difficulties to conventional terahertz spectroscopy, yet sensing those samples is essential for a large number of applications. In this article we review terahertz thin-film sensing, summarizing the motivation, challenges, and state-of-the-art approaches based predominately on terahertz time-domain spectroscopy. 246 J Infrared Milli Terahz Waves (2012) 33:245-291 Keywords Terahertz · THz · Thin-film · Sensing · Time-domain spectroscopy · Terahertz interferometry · Terahertz differential time-domain spectroscopy · Terahertz goniometry · Terahertz ellipsometry · Parallel plate waveguide · Microstrip transmission line · Filter · Metamaterial · Metasurface · Split-ring · Resonator · Frequency selective surface · Surface wave · Zenneck wave · Surface plasmon polariton · Hole array · Sensitivity · Quality factor

Precise Determination of Thicknesses of Multilayer Polyethylene Composite Materials by Terahertz Time-Domain Spectroscopy

“…The internal structure of the fibers is connected with polyethylene molecules, and it should be underlined that the THz range of radiation corresponds to the molecular interaction of hydrogen bonding, van der Waals interactions, and lattice interactions [34,35]. Another factor that should be taken into account is the influence of the strain and deformations that arise during the whole composite production process: fiber drawing, tape forming, and finally, hot pressing [36].…”

Terahertz gas sensor based on absorption-induced transparency

“…The patterning of different holes (periodically arranged or not) with different shapes and sizes on the same sample, each one designed for covering one of several characteristic wavelengths of a single molecular compound (or a mixture of them) might lead to multispectral detection based on AIT. Therefore, the AIT configuration might become a complementary method to existing ones for applications in sensing at THz [13].…”

“…The AIT-based gas detector consists in a metallic hole array (HA), placed on top of a dielectric substrate (see Figure 2a) where the molecules to be detected are released in the air region, in contact with the HA (see Figure 2c). Our approach relies on the appearance of spectral features in transmission and reflection induced by the molecular specimen when this fills the holes [11], conversely to those approaches designed to feature strong resonances at the absorption energies of the molecules [12] and, with typical functionalities based on accurately measuring spectral shifts in the presence of a given substance [13]. To illustrate our proposal we have chosen the HCN gas as the substance to be detected in the air region.…”

Plasmonic behavior of III-V semiconductors in far-infrared and terahertz range

“…Utilizing the terahertz range for better and faster communications [1][2][3], sensing [4], medicine [5] and security [6] has created a need for devices, capable of operating in the desired frequency range of 0.1-30 THz. One of the principles that can serve as the basis of guiding, coupling and modulating THz waves is the surface plasmon -an interface wave propagating at the boundary of negative (conductive) and positive (dielectric) permittivity material.…”