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10 pages, 4959 KiB

Open AccessArticle

Intermolecular Hydrogen-Bond Interactions in DPPE and DMPC Phospholipid Membranes Revealed by Far-Infrared Spectroscopy

by Valeria Conti Nibali, Caterina Branca, Ulderico Wanderlingh and Giovanna D’Angelo

Appl. Sci. 2021, 11(21), 10038; https://doi.org/10.3390/app112110038 - 27 Oct 2021

Cited by 6 | Viewed by 2292

The vibrational signature in the far-infrared region of two different phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), was investigated as a function of relative humidity from 0 to 75% in order to evaluate the effect of headgroup composition on the formation of intermolecular interactions. [...] Read more.

The vibrational signature in the far-infrared region of two different phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), was investigated as a function of relative humidity from 0 to 75% in order to evaluate the effect of headgroup composition on the formation of intermolecular interactions. The substructures of the frequency region between 50 and 300 cm⁻¹ were identified, and changes in the frequency and intensity of the related vibrations with hydration were analyzed. Interestingly, in PE, two additional vibrational bands with respect to PC were found at 162 and 236 cm⁻¹ and assigned to intermolecular hydrogen bonds between the hydrogen-bond-donating groups,

{- NH}_{3}^{+}

, and hydrogen-bond-accepting groups, —P—O− and —COO, of adjacent molecules. The presence of these interactions also affected the penetration of water, severely reducing the hydration capability of PE lipids. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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14 pages, 3603 KiB

Open AccessFeature PaperArticle

Electric Field and Temperature Effects on the Ab Initio Spectroscopy of Liquid Methanol

by Giuseppe Cassone, Sebastiano Trusso, Jiri Sponer and Franz Saija

Appl. Sci. 2021, 11(12), 5457; https://doi.org/10.3390/app11125457 - 12 Jun 2021

Cited by 2 | Viewed by 2311

Abstract

Although many H-bonded systems have been extensively investigated by means of infrared (IR) spectroscopy, the vibrational response to externally applied electric fields of polar liquids remains poorly investigated. However, local electric fields along with quantum-mechanical interactions rule the behavior of H-bonded samples at [...] Read more.

Although many H-bonded systems have been extensively investigated by means of infrared (IR) spectroscopy, the vibrational response to externally applied electric fields of polar liquids remains poorly investigated. However, local electric fields along with quantum-mechanical interactions rule the behavior of H-bonded samples at the molecular level. Among the many H-bonded systems, liquid methanol holds a key place in that it exhibits a very simple H-bond network where, on average, each molecule acts as a single H-bond donor and, at the same time, as a single H-bond acceptor. Here we report on the IR spectra emerging from a series of state-of-the-art ab initio molecular dynamics simulations of bulk liquid methanol under the action of static and homogeneous electric fields. In addition, the same analysis is here conducted in the absence of the external field and for different temperatures. Although some electric-field-induced effects resemble the response of other polar liquids (such as the global contraction of the IR spectrum upon field exposure), it turns out that, distinctly from water, the “electrofreezing” phenomenon is unlikely to happen in liquid methanol. Finally, we provide atomistic analyses magnifying the completely different nature of electric-field- and temperature-induced effects on bulk liquid methanol and on its vibrational response. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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8 pages, 13795 KiB

Open AccessArticle

Metal-Organic Hybrid Metamaterials for Spectral-Band Selective Active Terahertz Modulators

by Hyung Keun Yoo, Soo Bin Cho, Sae June Park, Yeong Hwan Ahn, Chul Kang, In-Wook Hwang and Joong Wook Lee

Appl. Sci. 2021, 11(6), 2765; https://doi.org/10.3390/app11062765 - 19 Mar 2021

Cited by 3 | Viewed by 2169

Abstract

Optically controlled spectral-band selective terahertz (THz) modulators based on metal-organic hybrid metamaterials were investigated. An artificially structured material, which consists of two single split-ring resonators put together on the split gap side, was patterned on a silicon substrate to generate frequency-selective properties. An [...] Read more.

Optically controlled spectral-band selective terahertz (THz) modulators based on metal-organic hybrid metamaterials were investigated. An artificially structured material, which consists of two single split-ring resonators put together on the split gap side, was patterned on a silicon substrate to generate frequency-selective properties. An active layer of an organic thin film (fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester, also called PCBM) was deposited on the metamaterial-silicon structure for modulating the transmission of incident THz radiation. The metal-organic hybrid metamaterials enabled active control of spectral bands present in the transmission spectra of THz waves. In addition, the changes in the photo-excited carrier density due to the transfer of charges between the layers were quantitatively analyzed by simulation results. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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14 pages, 5224 KiB

Open AccessFeature PaperArticle

Mail Inspection Based on Terahertz Time-Domain Spectroscopy

by Daniel Molter, Daniel Hübsch, Thorsten Sprenger, Korbinian Hens, Konstantinos Nalpantidis, Frank Platte, Garik Torosyan, René Beigang, Joachim Jonuscheit, Georg von Freymann and Frank Ellrich

Appl. Sci. 2021, 11(3), 950; https://doi.org/10.3390/app11030950 - 21 Jan 2021

Cited by 6 | Viewed by 13785

Abstract

One of the most prominent applications of terahertz time-domain spectroscopy is the spectral investigation of materials covered by visibly opaque objects. Therefore, terahertz waves are well suited to inspect the content of mail. We report on our work on mail inspection in this [...] Read more.

One of the most prominent applications of terahertz time-domain spectroscopy is the spectral investigation of materials covered by visibly opaque objects. Therefore, terahertz waves are well suited to inspect the content of mail. We report on our work on mail inspection in this spectral range including machine design, optical layouts, data analysis, and implementations. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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13 pages, 3836 KiB

Open AccessFeature PaperArticle

Performance Evaluation of a THz Pulsed Imaging System: Point Spread Function, Broadband THz Beam Visualization and Image Reconstruction

by Marta Di Fabrizio, Annalisa D’Arco, Sen Mou, Luigi Palumbo, Massimo Petrarca and Stefano Lupi

Appl. Sci. 2021, 11(2), 562; https://doi.org/10.3390/app11020562 - 8 Jan 2021

Cited by 21 | Viewed by 3752

Abstract

Terahertz (THz) technology is a promising research field for various applications in basic science and technology. In particular, THz imaging is a new field in imaging science, where theories, mathematical models and techniques for describing and assessing THz images have not completely matured [...] Read more.

Terahertz (THz) technology is a promising research field for various applications in basic science and technology. In particular, THz imaging is a new field in imaging science, where theories, mathematical models and techniques for describing and assessing THz images have not completely matured yet. In this work, we investigate the performances of a broadband pulsed THz imaging system (0.2–2.5 THz). We characterize our broadband THz beam, emitted from a photoconductive antenna (PCA), and estimate its point spread function (PSF) and the corresponding spatial resolution. We provide the first, to our knowledge, 3D beam profile of THz radiation emitted from a PCA, along its propagation axis, without the using of THz cameras or profilers, showing the beam spatial intensity distribution. Finally, we evaluate the THz image formation on a test-sample composed by a regular linen natural pattern. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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6 pages, 622 KiB

Open AccessFeature PaperArticle

Refractive Indices of Ge and Si at Temperatures between 4–296 K in the 4–8 THz Region

by Mira Naftaly, Steve Chick, Guy Matmon and Ben Murdin

Appl. Sci. 2021, 11(2), 487; https://doi.org/10.3390/app11020487 - 6 Jan 2021

Cited by 3 | Viewed by 3194

Abstract

Refractive indices of high resistivity Si and Ge were measured at temperatures between 4–296 K and at frequencies between 4.2–7.7 THz using a Fourier-transform spectrometer (FTS) in transmission mode. A phenomenological model of the temperature dependence of the refractive index is proposed. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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12 pages, 817 KiB

Open AccessFeature PaperArticle

Characterisation of Biological Materials at THz Frequencies by Attenuated Total Reflection: Lard

by Zoltan Vilagosh, Alireza Lajevardipour, Dominique Appadoo, Soon Hock Ng, Saulius Juodkazis and Andrew W. Wood

Appl. Sci. 2020, 10(23), 8692; https://doi.org/10.3390/app10238692 - 4 Dec 2020

Cited by 7 | Viewed by 2883

Abstract

The penetration depth of an evanescent wave in Attenuated Total Reflection (ATR) is dependent on the wavelength of the radiation utilised. At THz frequencies, the penetration depth into biological tissues is in the order of 0.1 to 0.5 mm; rendered pig lard was [...] Read more.

The penetration depth of an evanescent wave in Attenuated Total Reflection (ATR) is dependent on the wavelength of the radiation utilised. At THz frequencies, the penetration depth into biological tissues is in the order of 0.1 to 0.5 mm; rendered pig lard was used as a model sample in this study. A method for the direct measurement of the evanescent wave penetration depth is presented which allows for the estimation of the dispersion of the complex refractive index by using the reflection of the evanescent wave from varying sample depths. The method employs frustrated total internal reflection, and has been demonstrated by using the THz/Far-IR beamline at the Australian synchrotron, and modelled using finite difference time domain (FDTD) simulations. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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9 pages, 1981 KiB

Open AccessArticle

Tunable Dual Broadband Terahertz Metamaterial Absorber Based on Vanadium Dioxide

by Xiao-Fei Jiao, Zi-Heng Zhang, Tong Li, Yun Xu and Guo-Feng Song

Appl. Sci. 2020, 10(20), 7259; https://doi.org/10.3390/app10207259 - 17 Oct 2020

Cited by 40 | Viewed by 3146

Abstract

With the rapid development of terahertz technology, tunable high-efficiency broadband functional devices have become a research trend. In this research, a dynamically tunable dual broadband terahertz absorber based on the metamaterial structure of vanadium dioxide (VO₂) is proposed and analyzed. The [...] Read more.

With the rapid development of terahertz technology, tunable high-efficiency broadband functional devices have become a research trend. In this research, a dynamically tunable dual broadband terahertz absorber based on the metamaterial structure of vanadium dioxide (VO₂) is proposed and analyzed. The metamaterial is composed of patterned VO₂ on the top layer, gold on the bottom layer and silicon dioxide (SiO₂) as the middle dielectric layer. Simulation results show that two bandwidths of 90% absorption reach as wide as 2.32 THz from 1.87 to 4.19 THz and 2.03 THz from 8.70 to 10.73 THz under normal incidence. By changing the conductivity of VO₂, the absorptance dynamically tuned from 2% to 94%. Moreover, it is verified that absorptance is insensitive to the polarization angle. The physical origin of this absorber is revealed through interference theory and matching impedance theory. We further investigate the physical mechanism of dual broadband absorption through electric field analysis. This design has potential applications in imaging, modulation and stealth technology. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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11 pages, 1480 KiB

Open AccessArticle

Nonlinear TeraHertz Transmission by Liquid Water at 1 THz

by Fabio Novelli, Chun Yu Ma, Nidhi Adhlakha, Ellen M. Adams, Thorsten Ockelmann, Debasish Das Mahanta, Paola Di Pietro, Andrea Perucchi and Martina Havenith

Appl. Sci. 2020, 10(15), 5290; https://doi.org/10.3390/app10155290 - 30 Jul 2020

Cited by 18 | Viewed by 4537

Abstract

The solvation properties of liquid water originate from the transient network of hydrogen-bonded molecules. In order to probe the coupling between the different modes of this network, nonlinear terahertz (THz) spectroscopy techniques are required. Ideally, these techniques should use a minimal volume and [...] Read more.

The solvation properties of liquid water originate from the transient network of hydrogen-bonded molecules. In order to probe the coupling between the different modes of this network, nonlinear terahertz (THz) spectroscopy techniques are required. Ideally, these techniques should use a minimal volume and capitalize on sensitive field-resolved detection. Here we performed open aperture z-scan transmission experiments on static liquid cells, and detect the THz fields with electro-optical techniques. We show that it is possible to quantify the nonlinear response of liquid water at ~1 THz even when large signals originate from the sample holder windows. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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9 pages, 3924 KiB

Open AccessArticle

Reconfigurable Terahertz Metamaterial Using Split-Ring Meta-Atoms with Multifunctional Electromagnetic Characteristics

by Yuhang Liao and Yu-Sheng Lin

Appl. Sci. 2020, 10(15), 5267; https://doi.org/10.3390/app10155267 - 30 Jul 2020

Cited by 11 | Viewed by 3047

Abstract

We propose a reconfigurable terahertz (THz) metamaterial (RTM) to investigate its multifunctional electromagnetic characteristics by moving the meta-atoms of split-ring resonator (SRR) array. It shows the preferable and capable adjustability in the THz frequency range. The electromagnetic characteristics of the proposed RTM device [...] Read more.

We propose a reconfigurable terahertz (THz) metamaterial (RTM) to investigate its multifunctional electromagnetic characteristics by moving the meta-atoms of split-ring resonator (SRR) array. It shows the preferable and capable adjustability in the THz frequency range. The electromagnetic characteristics of the proposed RTM device are compared and analyzed by moving the meta-atoms in different polarized transverse magnetic (TM) and transverse electric (TE) modes. The symmetrical meta-atoms of RTM device exhibit a resonant tuning range of several tens of GHz and the asymmetrical meta-atoms of RTM device exhibit the better tunability. Therefore, an RTM device with reconfigurable meta-atoms possesses the resonance shifting, polarization switching, electromagnetically induced transparency (EIT) switching and multiband to single-band switching characteristics. This proposed RTM device provides the potential possibilities for the use of THz-wave optoelectronics with tunable resonance, EIT analog and tunable multiresonance characteristics. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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9 pages, 4733 KiB

Open AccessArticle

Tunable Terahertz Metamaterial Using an Electric Split-Ring Resonator with Polarization-Sensitive Characteristic

by Tao Xu and Yu-Sheng Lin

Appl. Sci. 2020, 10(13), 4660; https://doi.org/10.3390/app10134660 - 6 Jul 2020

Cited by 16 | Viewed by 3442

Abstract

We present a tunable terahertz (THz) metamaterial using an electric split-ring resonator (eSRR), which exhibits polarization-sensitive characteristics. The proposed eSRR is composed of double symmetrical semicircles and two central metal bars. By changing the lengths of two metal bars, the electromagnetic responses can [...] Read more.

We present a tunable terahertz (THz) metamaterial using an electric split-ring resonator (eSRR), which exhibits polarization-sensitive characteristics. The proposed eSRR is composed of double symmetrical semicircles and two central metal bars. By changing the lengths of two metal bars, the electromagnetic responses can be tuned and switched between dual-band and triple-band resonances in transverse magnetic (TM) mode. Furthermore, by moving the bottom metal bar to change the gap between the two metal bars, the first resonance is stable at 0.39 THz, and the second resonance is gradually blue-shifted from 0.83 to 1.33 THz. The tuning range is 0.50 THz. This means that the free spectrum ranges (FSR) could be broadened by 0.50 THz. This proposed device exhibits a dual-/triple-band switch, tunable filter, tunable FSR and polarization-dependent characteristics. It provides an effective approach to perform tunable polarizer, sensor, switch, filter and other optoelectronics in THz-wave applications. Full article

(This article belongs to the Special Issue Advances of THz Spectroscopy)

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