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The photon energy of terahertz waves is of the order of a few milli-electronvolts and is much lower than the thermal energy of ~ 26 meV at room temperature. However, the fast and sensitive detection of terahertz waves is notoriously difficult at ambient conditions. Moreover, the material flexibility is also very important within existing terahertz technologies for development of wearable and portable terahertz devices. We experimentally demonstrate that multiwall carbon nanotube flexible paper (MWCNT-FP) is one of the potential candidates to be used for terahertz detectors at room temperature. For the first time, MWCNT-FP sample is measured over a wide frequency band ranging from 0.02 to 4.5 THz at room temperature as compared to previously reported materials that demonstrate prominent frequency response between 0.2 and 2.5 THz. The MWCNT-FP sample delivered wide band absorption between 0.02 and 4.0 THz. Over the transmission, a high absorption peak is detected at 1.0 THz. The optical density spectrum is observed around 1.25 and 3.37 THz in the low-frequency regime and high-frequency regime, respectively. The present results suggest the potential application of MWCNT-FP as a wearable THz detector.

Through time of non-destructive measurement of individual layer of materials or paint layers at nano-scale, non-contact terahertz technique is a very good approach. In this research work, the cerium oxide (CeO2) thin film is deposited on sapphire (c-Al2O3) substrate having thickness of 430 µm by using RF magnetron sputtering technique. A terahertz pulses incident on the CeO2 film, layer of CeO2 interface with substrate. Some amount of incident pulse transmits and rest will reflect with respect to transmission mode and reflection mode, respectively. In the reflection mode, the time elapsed between the arrival and departure of cerium oxide layer is directly proportional to the thickness of the layer as a function of wavelength. The thickness of CeO2 is measured about 35.83 µm using terahertz spectroscopy. This study shows that terahertz spectroscopy is an experimental approach and possible to measure thickness of thin film for non-destructive measurement.

The massless Dirac electron shows a linear energy dispersion in topological insulators (TIs) and these materials posses interesting properties such as high mobility, tuneable density and protection against backscattering over the time reversal symmetry and strong spin-orbit interaction. The flexibility is also an important parameter for development of wearable devices specially THz detector for imaging and quantum devices for optoelectronics applications. In this research work first time Bi2Te3 TIs thin film is fabricated on inhouse develop metallic multi wall carbon nanotubes flexible paper (MWCNT-FP) and characterized by terahertz-time domain spectroscopy acquired at room temperature. This research work delivers exclusive opportunities to explore interesting phenomena in topological surface states and topological phase transition in Bi2Te3 TIs thin film. Here, we measured terahertz absorption, optical density conductance and conductivity. An excellent broad band absorption is observed between 0.02 and 3.0 THz. The real conductance level is scientifically quite linear below 3.0 meV and thereafter certain increase. Similar trend is observed for the study of an imaginary conductance with respect to photon energy. The optical conductivity is observed in the range of 0.02–2.0 THz.