Abstract-Vibrational Response of Felodipine in the THz Domain: Optical and Neutron Spectroscopy Versus Plane-Wave DFT Modeling

Katarzyna Łuczyńska, Kacper Drużbicki,Tomasz Runka, Norbert Pałka, Jan Węsicki

https://link.springer.com/article/10.1007/s10762-019-00634-9

We present a joint experimental and computational terahertz (THz) spectroscopy study of the most stable polymorph (form I) of an antihypertensive pharmaceutical solid, felodipine (FLD). The vibrational response has been analyzed at room temperature by combining optical (THz-TDS, FT-IR, THz-Raman) and neutron (INS) terahertz spectroscopy. With the challenging example of a large and flexible molecular solid, we illustrate the complementarity of the experimental techniques. We show how the results can be understood by employing ab initio modeling and discuss current progress in the field. To this end, we employ plane wave formulation of density functional theory (plane wave DFT) along with harmonic lattice dynamics calculations (HLD) and ab initio molecular dynamics (AIMD) simulations. Based on a comprehensive theoretical analysis, we discover an inconsistency in the commonly accepted structural model, which can be linked to a distinct librational dynamics of the side ester chains. As a result, only a moderate agreement with the experimental spectra can be achieved. We, therefore, propose an alternative structural model, effectively accounting for the influence of the large-amplitude librations and allowing for a comprehensive analysis of the vibrational resonances up to 4.5 THz. In that way, we illustrate the applicability of the computationally supported THz spectroscopy to detect subtle structural issues in molecular solids. While the provided structural model can be treated as a guess, the problem calls for further revision by means of high-resolution crystallography. The problem also draws a need of extending the THz experiments toward low-temperature conditions and single-crystal samples. On the other hand, the studied system emerges as a challenge for the DFT modeling, being extremely sensitive to the level of the theory used and the resulting description of the intermolecular forces. FLD form I can be, hence, considered as a testbed for the use of more sophisticated theoretical approaches, particularly relying on an advanced treatment of the van der Walls forces and going beyond zero-temperature conditions and harmonic approximation.

Abstract-AlGaAs/GaAs Terahertz Quantum Cascade Laser with Gold-Based Metal – Metal Waveguide

Anna Szerling, Kamil Kosiel, Piotr Prokaryn, Michał Szymański, Artur Trajnerowicz, Maciej Sakowicz, Piotr Karbownik, Mariusz Płuska, Michał Walczakowski, Norbert Pałka,

https://link.springer.com/chapter/10.1007/978-94-024-1093-8_17

In this chapter, we report the fabrication of Al0.15Ga0.85As/GaAs ~3 THz frequency quantum cascade laser (QCL). Its operation is based on 3-quantum-well (3QW) modules, where the GaAs QWs are separated by Al0.15Ga0.85As barriers. The laser’s active region is build by stacking the 228 modules. The lasers were fabricated as gold-gold waveguide devices and were gold-gold mounted on GaAs receptor wafers. The 300 nm Au/5 nm Ti claddings were made by sputtering, for which we used 8 × 10−3 mbar pressure level and 50 W generator power. The wafer-bonding process was performed in the temperature range 350–400 °C. The structures were wet etched into ridges with widths in the range 50–160 microns and lengths 1.8 mm. The lasers operated with threshold current densities ~650 A/cm2 at 77 K, when fed by 100–300 ns current pulses supplied with 300–1000 Hz repetition frequencies.

Abstract-Moisture detection in composites by terahertz spectroscopy

Paweł Malinowski1, Norbert Pałka2, Szymon Opoka1, Tomasz Wandowski1 and Wiesław Ostachowicz1,3

http://iopscience.iop.org/1742-6596/628/1/012100

The application of Glass Fibre Reinforced Polymers (GFRP) in many branches of industry has been increasing steadily. Many research works focus on damage identification for structures made out of such materials. However, not only delaminations, cracks or other damage can have a negative influence of GFRP parts performance. Previous research proved that fluid absorption influences the mechanical performance of composites. GFRP parts can be contaminated by moisture or release agent during manufacturing, while fuel, hydraulic fluid and moisture ingression into the composite can be the in-service treats. In the reported research authors focus on moisture detection. There are numerous sources of moisture such as post manufacturing NDT inspection with ultrasonics coupled by water or exposition to moisture during transportation and in service. An NDT tool used for the research is a terahertz (THz) spectrometer. The device uses an electromagnetic radiation in the terahertz range (0.1-3 THz) and allows for reflection and transmission measurements. The spectrometer is equipped with moving table that allows for XY scanning of large objects such as GFRP panels. In the conducted research refractive indices were experimentally extracted from the materials of interest (water and GFRP). Time signals as well as C-scans were analysed for samples with moisture contamination. In order to be sure that the observed effects are related to moisture contamination reference measurements were conducted. The obtained results showed that the THz NDT technique can detect moisture hidden under a GFRP with multiple layers.

Abstract-Polymorphism of Resorcinol Explored by Complementary Vibrational Spectroscopy (FT-RS, THz-TDS, INS) and First-Principles Solid-State Computations (Plane-Wave DFT)

Kacper Drużbicki *†‡§, Edward Mikuli †, Norbert Pałka ∥, Sławomir Zalewski ⊥, and Mirosława D. Ossowska-Chruściel ⊥

† Department of Chemical Physics, Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Cracow, Poland

‡ Department of Radiospectroscopy, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan, Poland

§ Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russian Federation

∥ Institute of Optoelectronics, Military University of Technology, Gen. S. Kaliskiego 2, 00-908 Warsaw, Poland

⊥ Department of Technology and Chemical Physics, Institute of Chemistry, University of Natural Sciences and Humanities, 3-go Maja 54, 08-110 Siedlce, Poland

J. Phys. Chem. B, Article ASAP

DOI: 10.1021/jp507241j

Publication Date (Web): January 7, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/jp507241j

The polymorphism of resorcinol has been complementary studied by combining Raman, time-domain terahertz, and inelastic neutron scattering spectroscopy with modern solid-state density functional theory (DFT) calculations. The spectral differences, emerging from the temperature-induced structural phase transition, have been successfully interpreted with an emphasis on the low-wavenumber range. The given interpretation is based on the plane-wave DFT computations, providing an excellent overall reproduction of both wavenumbers and intensities and revealing the source of the observed spectral differences. The performance of the generalized gradient approximation (GGA) functionals in prediction of the structural parameters and the vibrational spectra of the normal-pressure polymorphs of resorcinol has been extensively examined. The results show that the standard Perdew, Burke, and Ernzerhof (PBE) approach along with its “hard” revised form tends to be superior if compared to the “soft” GGA approximation.

Abstract-Polymorphism of Resorcinol Explored by Complementary Vibrational Spectroscopy (FT-RS, THz-TDS, INS) and First Principles Solid-State Computations (Plane-Wave DFT)

Kacper Druzbicki , Edward Mikuli , Norbert Pałka ,Sławomir Zalewski , and Mirosława Danuta Ossowska-Chruściel

J. Phys. Chem. B, Just Accepted Manuscript

DOI: 10.1021/jp507241j

Publication Date (Web): January 7, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/jp507241j?journalCode=jpcbfk

The polymorphism of resorcinol has been complementary studied by combining Raman, time-domain terahertz and inelastic neutron scattering spectroscopy with modern solid-state density functional theory (DFT) calculations. The spectral differences, emerging from the temperature-induced structural phase transition, have been successfully interpreted with an emphasis on the low-wavenumber range. The given interpretation is based on the plane-wave DFT computations, providing an excellent overall reproduction of both wavenumbers and intensities and revealing the source of the observed spectral differences. The performance of the generalized gradient approximation (GGA) functionals in prediction of the structural parameters and the vibrational spectra of the normal-pressure polymorphs of resorcinol has been extensively examined. The results show that standard PBE along with its ‘hard’ revised form tend to be superior if compared to the ‘soft’ GGA approximation.