Single-particle and collective excitations of polar water molecules confined in nano-pores within a cordierite crystal lattice

 Belyanchikov, M. A., Z. V. Bedran, M. Savinov, P. Bednyakov, P. Proschek, J. Prokleska, V. A. Abalmasov et al. "Single-particle and collective excitations of polar water molecules confined in nano-pores within a cordierite crystal lattice." Physical Chemistry Chemical Physics 24, no. 11 (2022): 6890-6904.

Abstract

Recently, the low-temperature phase of water molecules confined within nanocages formed by the crystalline lattice of water-containing cordierite crystals has been reported to comprise domains with ferroelectrically ordered dipoles within the a, b-planes which are antiferroelectrically alternating along the c-axis. In the present work, comprehensive broad-band dielectric spectroscopy is combined with specific heat studies and molecular dynamics and Monte Carlo simulations in order to investigate in more detail the collective modes and single-particle excitations of nanoconfined water molecules. From DFT-MD simulations we reconstruct the potential-energy landscape experienced by the H2O molecules. A rich set of anisotropic temperature-dependent excitations is observed in the terahertz frequency range. Their origin is associated with the complex rotational/translational vibrations of confined H2O molecules. A strongly temperature dependent relaxational excitation, observed at radio-microwave frequencies for the electric field parallel to the crystallographic a-axis, E||a is analyzed in detail. The temperature dependences of loss-peak frequency and dielectric strength of the excitation together with specific heat data confirm a ferroelectric order–disorder phase transition at T0 ≈ 3 K in the network of H2O dipoles. Additional dielectric data are also provided for polarization E||b, too. Overall, these combined experimental investigations enable detailed conclusions concerning the dynamics of the confined water molecules that develop within their microscopic energy landscapes.

for full paper see 

https://pubs.rsc.org/en/content/articlelanding/2022/cp/d1cp05338h/unauth

… For terahertz measurements, a time-domain TeraView 3000 spectrometer was employed to directly determine the spectra of the real ε' and imaginary ε" parts of the dielectric permittivity from the complex (amplitude and phase) transmission …

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 …