Dispersive Spectrometry At Terahertz Frequencies for Probing the Quality of NbTiN Superconducting Films

 Khudchenko, A., B. N. R. Lap, K. I. Rudakov, R. Hesper, V. P. Koshelets, P. N. Dmitriev, A. Chekushkin et al. "Dispersive Spectrometry At Terahertz Frequencies for Probing the Quality of NbTiN Superconducting Films." IEEE Transactions on Applied Superconductivity 32, no. 4 (2022): 1-6.

Abstract:

We present the quality measurements of thick (thicker than London penetration depth) NbTiN superconducting films at Terahertz frequencies using a Dispersive Fourier Transform Spectrometer (DFTS). The reflected RF signal from the tested film was measured in time domain, allowing us to separate it from other reflections. The complex conductivity of the film depends on frequency and determines the reflection coefficient. By comparing the film reflection in superconducting state (film temperature below Tc) with that of the normal state (film temperature above Tc), we characterized the film quality at terahertz frequencies, and directly probed the energy of the superconducting gap of the tested film. The experimental results were fitted using the extended Mattis-Bardeen theory and th obtained film parameters show a good agreement with the literature. In addition to the DFTS, we have also measured the properties of NbTiN film using Time Domain Spectroscopy (TDS). It is shown that both TDS and DFTS provide similar results, and both techniques can be used for the quality control of thick NbTiN films. The superconducting gap determined from the measurements by both DFTS and TDS are in good agreement for both solid and meshed films showing that there is no remarkable degradation in the film quality due to technological processes of lift-off or ion etching.

for full paper see 

https://ieeexplore.ieee.org/abstract/document/9699055/authors#authors

Terahertz-infrared spectroscopy of wafer-scale films of single-walled carbon nanotubes treated by plasma

Zhukov, S. S., E. S. Zhukova, A. V. Melentev, B. P. Gorshunov, A. P. Tsapenko, D. S. Kopylova, and Albert G. Nasibulin. "Terahertz-infrared spectroscopy of wafer-scale films of single-walled carbon nanotubes treated by plasma." Carbon 189 (2022): 413-421.

Abstract

We investigated terahertz-infrared electrodynamic properties of wafer-scale films composed of plasma-treated single-walled carbon nanotubes (SWCNTs) and films comprising SWCNTs grown with different lengths. The spectra of complex conductance of the films were measured at frequencies 5–20 000 cm−1 and in the temperature interval 5–300 K. Terahertz spectral response of films of pristine SWCNTs is well described with the Drude conductivity model and a plasmon resonance located at ≈100 cm−1. Stepwise treatment of the films with oxygen plasma led to a gradual suppression of the Drude spectral weight from the low-frequency side. For films with the nanotubes shorter than 1 μm, i.e., close to electrons mean free path and localization length, scattering of charge carriers at the nanotubes edges is shown to additionally contribute to the carriers scattering rate and to the damping of plasmon resonance. The temperature coefficient of ac resistance (ac TCR) in both kinds of films is found to strongly increase in amplitude during cooling and frequency decrease. The values of ac TCR increase in films with longer time of plasma treatment and nanotubes with shorter length but reach saturation in films with exposure time longer than ≈100 s or composed from SWCNTs shorter than 1 μm.

for full paper see 

https://www.sciencedirect.com/science/article/abs/pii/S0008622321012355

… For terahertz and infrared experiments commercial TeraView time-domain spectrometer… complex (amplitude and phase) transmission coefficient measured with the TeraView time-domain …

Polymer pellet fabrication for accurate THz-TDS measurements

Murphy, Keir N., Mira Naftaly, Alison Nordon, and Daniel Markl. "Polymer pellet fabrication for accurate THz-TDS measurements." Applied Sciences 12, no. 7 (2022): 3475.

for full paper see https://www.mdpi.com/2076-3417/12/7/3475/htm

Abstract

We investigate fabrication of compacts using polytetrafluoroethylene (PTFE) and polyethylene (PE), and the effect of compaction conditions on their terahertz transmission properties. The conditions used to fabricate compressed powder samples for terahertz time-domain spectroscopy (THz-TDS) can impact the accuracy of the measurements and hence the interpretation of results. This study investigated the effect of compaction conditions on the accuracy of the THz-TDS analysis. Two polymers that are commonly used as matrix materials in terahertz spectroscopy studies were explored using a compaction simulator and a hydraulic press for sample preparation. THz-TDS was used to determine the refractive index and loss coefficient to compare the powder compacts (pellets) to the values of solid material. Sample porosity, axial relaxation and tensile strength were measured to assess the material’s suitability for terahertz spectroscopy. It was found that PTFE is the preferable material for creating THz-TDS samples due to its low porosity and high tensile strength. PE was found to show significant porosity at all compaction pressures, making it an unsuitable material for the accurate determination of optical parameters from THz-TDS spectroscopy measurements. The larger particle sizes of PE resulted in compacts that exhibited significantly lower tensile strength than those made from PTFE making handling and storage difficult.

Keywords: terahertz time domain spectroscopy; sample preparation; polymers; porosity

"2.2.3. THz-TDS Measurements

THz-TDS measurements were carried out on a commercial system (TeraPulse Lx, Teraview), with a frequency (ν$$) resolution of 0.04 THz. All measurements were performed in a nitrogen-purged chamber. Sample thickness (L) was measured using a micrometer (±0.005mm$$) prior to the TDS measurement and was used for the calculation of the frequency-dependent refractive index (n(ν))$$ and loss coefficient (α(ν))$$."

Detecting Crystallinity Using Terahertz Spectroscopy in 3D Printed Amorphous Solid Dispersions

Santitewagun, Supawan, Rishi Thakkar, J. Axel Zeitler, and Mohammed Maniruzzaman. "Detecting Crystallinity Using Terahertz Spectroscopy in 3D Printed Amorphous Solid Dispersions." Molecular Pharmaceutics (2022). 

for full paper see https://pubs.acs.org/doi/full/10.1021/acs.molpharmaceut.2c00163#

Abstract

This study demonstrates the applicability of terahertz time-domain spectroscopy (THz-TDS) in evaluating the solid-state of the drug in selective laser sintering-based 3D printed dosage forms. Selective laser sintering is a powder bed-based 3D printing platform, which has recently demonstrated applicability in manufacturing amorphous solid dispersions (ASDs) through a layer-by-layer fusion process. When formulating ASDs, it is critical to confirm the final solid state of the drug as residual crystallinity can alter the performance of the formulation. Moreover, SLS 3D printing does not involve the mixing of the components during the process, which can lead to partially amorphous systems causing reproducibility and storage stability problems along with possibilities of unwanted polymorphism. In this study, a previously investigated SLS 3D printed ASD was characterized using THz-TDS and compared with traditionally used solid-state characterization techniques, including differential scanning calorimetry (DSC) and powder X-ray diffractometry (pXRD). THz-TDS provided deeper insights into the solid state of the dosage forms and their properties. Moreover, THz-TDS was able to detect residual crystallinity in granules prepared using twin-screw granulation for the 3D printing process, which was undetectable by the DSC and XRD. THz-TDS can prove to be a useful tool in gaining deeper insights into the solid-state properties and further aid in predicting the stability of amorphous solid dispersions.

To learn more about terahertz applications visit www.teraview.com 

Theoretical and experimental analysis of the dielectric properties of 3D orthogonal woven GFRP composites in the terahertz frequency range

 Nsengiyumva, Walter, Shuncong Zhong, Longhui Zheng, Bing Wang, Xueqi Lin, Xibin Fu, and Zhike Peng. "Theoretical and experimental analysis of the dielectric properties of 3D orthogonal woven GFRP composites in the terahertz frequency range." Optik 260 (2022): 169105.

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0030402622004697

Abstract

A novel method to calculate the dielectric constant (${\epsilon }_r^{\prime }$) of three-dimensional orthogonal woven glass fiber-reinforced polymer-matrix (3DOW-GFRP) composites in the terahertz (THz) frequency range is developed and experimentally verified using the THz time-domain spectroscopy (THz-TDS). The dielectric anisotropy is demonstrated through simulation by considering a single propagation direction of the THz waves and three different fiber orientations in unidirectional GFRP composites. Simulation results are compared to those obtained from the classic rule-of-mixture equations to determine the representative equations for the three different cases of fiber orientations in the ($x,y,z$)-coordinate system and a new model is developed to calculate ${\epsilon }_r^{\prime }$ of 3DOW-GFRP composites based on electromagnetic modeling principles. As opposed to previously reported lumped circuit models, our model addresses the issue of orthogonality of fiber and considers the shape and spatial disposition of the composite with respect to the polarization direction of the THz waves for accurate determination of ${\epsilon }_r^{\prime }$. A comparison between the measured and calculated ${\epsilon }_r^{\prime }$ indicates that the proposed method is highly accurate with ≤ 2.68% maximum error, while the latter reaches 7.82% for the classic rule-of-mixture equations. This method is potentially useful for the design of 3DOW-GFRP with desired ${\epsilon }_r^{\prime }$ for applications such as electromagnetic shielding and electrostatic discharging structures.

"… (TeraView TPS 4000) is employed to measure the dielectric properties of 3DOW-GFRP composite samples. Fig. 2 presents the photograph of the experimental setup and the schematic diagram of the operation of the TeraView … frequency of 50 Hz …"

for more information about TeraView's products visit www.teraview.com