Debanjan Polley

Polarizing effect of aligned nanoparticles in terahertz frequency region

We report the polarizing behavior of aligned Ni nanoparticles (NPs) having average diameter of 165±15 nm in ~210 μm thick polyvinyl alcohol (PVA) matrix in the frequency range of 0.2-1.6 THz. The NPs have been prepared via a wet chemical route and then aligned in PVA film by using an external magnetic field. When the polarization of THz electric field is parallel to the NPs alignment direction, a strong THz absorption is observed whereas a minimum THz absorption is noticed for the corresponding perpendicular configuration. Degree of polarization is calculated to be 0.9±0.08. Considering the good polarizing performance, ease of preparation, durability, and low maintenance, this aligned NP system is a perfect candidate to emerge as a potential THz polarizer.

Controllable terahertz conductivity in single walled carbon nanotube/polymer composites

Terahertz (THz) conductivity of single walled carbon nanotube (SWNT)/poly-vinyl alcohol (PVA) composites has been studied in the frequency window of 0.3–2.0 THz. SWNT/PVA composite films with a constant thickness of 300 ± 20 μm are grown by dispersing required amount of SWNT in PVA solution via a slow drying process at room temperature under ambient condition. THz time domain spectroscopic measurements have been performed in transmission geometry at room temperature under N2 atmosphere and THz conductivity spectra have been extracted from the time domain data. It is found that conductivity of these samples can be efficiently tuned by changing the length of the SWNTs and also the SWNT weight fraction. For the highest weight fraction at a frequency of 1.5 THz, longer SWNT sample (average length ∼ 15 μm) showed 80% increased conductivity than its shorter counterpart (average length ∼ 2 μm) of the same diameter (1–2 nm). Shielding effectiveness of the samples has also been engineered by simply changing the ef...

Efficient terahertz anti-reflection properties of metallic anti-dot structures

We report the use of micrometer-sized copper (Cu) anti-dot structures as a novel terahertz (THz) anti-reflection coating (ARC) material and their superior performance over conventionally used metallic (Cu) thin films. Cu anti-dot structures of two different thicknesses (7 and 10 nm) with varying anti-dot diameters (100, 200, and 300 μm, inter-anti-dot separation fixed at 100 μm) are deposited on silicon substrates by RF magnetron sputtering and e-beam evaporation. The anti-reflection performance of these samples is studied in the frequency range of 0.3-2.2 THz. While continuous metallic (Cu) thin film minimizes the Fabry-Perot (FP) peak, it also suppresses the primary transmission peak, reducing the advantage due to the former effect. On the contrary, the anti-dot arrays reduce both the absolute amplitude of the FP peak and the amplitude ratio (AR) of the FP peak to the primary peak, making them a superior material for ARC applications. The AR can be further manipulated by varying the anti-dot size. A universal conductivity phase-matching condition, which is a prerequisite for the disappearance of the FP peak, is observed in these samples. The enhanced anti-reflection performance promotes these anti-dot structures as an efficient terahertz ARC material.

Nickel nanochain composite: An improved terahertz shielding material

Terahertz (THz) shielding effectiveness (SE) of nickel nanochains (NiNC), multiwalled carbon nanotubes (MWNT) and their composites in poly-vinyl alcohol have been studied in the frequency range of 0.4-1.8 THz at room temperature. NiNC of diameter ~ 300 nm and length ~ 4 μm are synthesized by reducing nickel chloride salt with hydrazine hydrate in ethylene glycol medium. NiNC and MWNT+NiNC composites show 130% and 260% increased SE at 1 THz than MWNT composites, respectively. Such a large increment in SE depicts that NiNC can easily replace the universally known MWNT composites as cost effective materials with higher shielding efficiency for the applications in THz shielding devices.

Fabrication and Characterization of 2-D Magnetic Antidot Arrays for Application in Magnonic Crystals

Investigation on magnetic properties of 2-D arrays of magnetic antidots with and without magnetic anisotropy has been performed. Antidots are fabricated and characterized by SEM, MFM, VSM, Static-MOKE and verified the results by micromagnetic simulation.