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Terahertz Vibrational Spectroscopy in Advanced Materials
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Terahertz Vibrational Spectroscopy in Advanced Materials

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Physics".

Deadline for manuscript submissions: 20 August 2025 | Viewed by 4821

Special Issue Editor

Prof. Dr. Seiji Kojima

E-Mail Website
Guest Editor
Division of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
Interests: THz time-domain spectroscopy; THz time-domain ellipsometry; Raman spectroscopy; Brillouin scattering; neutron scattering; low-energy excitations; relaxation processes; structural glasses; complex liquids; disordered materials ; multiferroics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Vibrational spectroscopy may be defined as an identification tool to measure the various vibrational energies related to atomic bonds, interactions, and structures in materials. It covers infrared (IR), Raman, and inelastic neutron spectroscopies. These spectroscopies have been extensively used to study elementary excitations in the THz range such as phonon, polariton, magnon, exciton, plasmon, boson peak, etc. Traditional IR spectroscopy reported frequency-dependent absorbance or transmittance. In contrast, the coherent terahertz generation technique using a femtosecond pulse laser enables the unique determination of a complex dielectric constant, and terahertz time-domain spectroscopy (THz-TDS) has attracted much attention. Compared with traditional IR spectroscopy, THz-TDS has a great advantage in the THz range down to 0.1 THz. In Raman spectroscopy, the development of a super-notch filter enables the measurement down to 0.1 THz using a single-grating monochromator. These developments in both Raman and IR spectroscopy in the terahertz range have enhanced the study of terahertz vibrational properties in various materials. Cold neutrons have energies typically in the millielectron volts range, which are in the same order as the THz range. Investigations of various solid-state excitations, molecular relaxations, and dynamic processes by these advanced spectroscopies in the THz range provide new insights into physics, chemistry, mineralogy, geology, biology, pharmacy, medical science, life science, and engineering.

This Special Issue will be devoted to the terahertz vibrational spectroscopy of these various fields for hard and soft materials. Original research papers and review articles are cordially invited for submission. The topics of interest include but are not limited to, the following keywords: terahertz spectroscopy; infrared spectroscopy; Raman spectroscopy; neutron scattering; soft phonon; boson peak; polariton; plasmon; magnon; charge density wave; weak interactions; Fano resonance; polymorphism; polyamorphism; phase transition; reaction; field effects; extreme conditions.

Prof. Dr. Seiji Kojima
Guest Editor

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • terahertz spectroscopy
  • infrared spectroscopy
  • Raman spectroscopy
  • neutron scattering
  • soft phonon
  • boson peak
  • polariton
  • plasmon
  • magnon
  • charge density wave
  • weak interactions
  • Fano resonance
  • polymorphism
  • polyamorphism
  • phase transition
  • reaction
  • field effects
  • extreme conditions

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Published Papers (4 papers)

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Research

19 pages, 5369 KiB  
Article
Interactions of Terahertz Photons with Phonons of Two-Dimensional van der Waals MoS2/WSe2/MoS2 Heterostructures and Thermal Responses
by Jingwen Huang, Ningsheng Xu, Yumao Wu, Xue Ran, Yue Fang, Hongjia Zhu, Weiliang Wang, Huanjun Chen and Shaozhi Deng
Materials 2025, 18(7), 1665; https://doi.org/10.3390/ma18071665 - 4 Apr 2025
Viewed by 410
Abstract
The interaction between terahertz (THz) photons and phonons of materials is crucial for the development of THz photonics. In this work, typical two-dimensional (2D) van der Waals (vdW) transition metal chalcogenide (TMD) layers and heterostructures are used in THz time-domain spectroscopy (TDS) measurements, [...] Read more.
The interaction between terahertz (THz) photons and phonons of materials is crucial for the development of THz photonics. In this work, typical two-dimensional (2D) van der Waals (vdW) transition metal chalcogenide (TMD) layers and heterostructures are used in THz time-domain spectroscopy (TDS) measurements, low-wavenumber Raman spectroscopy measurements, calculation of 2D materials’ phonon spectra, and theoretical analysis of thermal responses. The TDS results reveal strong absorption of THz photons in the frequency range of 2.5–10 THz. The low-wavenumber Raman spectra show the phonon vibration characteristics and are used to establish phonon energy bands. We also set up a computational simulation model for thermal responses. The temperature increases and distributions in the individual layers and their heterostructures are calculated, showing that THz photon absorption results in significant increases in temperature and differences in the heterostructures. These give rise to interesting photothermal effects, including the Seebeck effect, resulting in voltages across the heterostructures. These findings provide valuable guidance for the potential optoelectronic application of the 2D vdW heterostructures. Full article
(This article belongs to the Special Issue Terahertz Vibrational Spectroscopy in Advanced Materials)
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10 pages, 2881 KiB  
Article
Observation of Boson Peak of Fragile Baltic Amber Glass by Terahertz Time-Domain Spectroscopy
by Toru Sasaki, Soo Han Oh, Tatsuya Mori and Seiji Kojima
Materials 2024, 17(23), 5956; https://doi.org/10.3390/ma17235956 - 5 Dec 2024
Viewed by 827
Abstract
Amber is a fragile (in Angell’s classification) natural glass that has performed maturation processes over geological time. The terahertz dynamics of Baltic amber that was about 40 million years old were studied by terahertz time-domain spectroscopy (THz-TDS) in the frequency range of 0.2 [...] Read more.
Amber is a fragile (in Angell’s classification) natural glass that has performed maturation processes over geological time. The terahertz dynamics of Baltic amber that was about 40 million years old were studied by terahertz time-domain spectroscopy (THz-TDS) in the frequency range of 0.2 and 6.0 THz. In general, the intensity of a boson peak is weak for fragile glass. In the terahertz transmission spectra of Baltic amber in the previous study, no boson peak was observed upon slow cooling. However, in the present study, upon rapid cooling down to 15 K, the boson peak was observed clearly at 0.36 THz by the suppression of ice nucleation of confined water. The dynamic correlation length determined by the boson peak frequency was compared with the static structure correlation length and the scale of the medium-range order as determined by the first sharp diffraction peak of X-ray diffraction (XRD) in the recent literature. It was found that the dynamic correlation length determined by THz-TDS was closely related to the static correlation length determined by the XRD analysis. Full article
(This article belongs to the Special Issue Terahertz Vibrational Spectroscopy in Advanced Materials)
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14 pages, 2127 KiB  
Article
The Effect of Cesium Incorporation on the Vibrational and Elastic Properties of Methylammonium Lead Chloride Perovskite Single Crystals
by Syed Bilal Junaid, Furqanul Hassan Naqvi and Jae-Hyeon Ko
Materials 2024, 17(12), 2862; https://doi.org/10.3390/ma17122862 - 12 Jun 2024
Viewed by 1042
Abstract
Hybrid organic-inorganic lead halide perovskites (LHPs) have emerged as a highly significant class of materials due to their tunable and adaptable properties, which make them suitable for a wide range of applications. One of the strategies for tuning and optimizing LHP-based devices is [...] Read more.
Hybrid organic-inorganic lead halide perovskites (LHPs) have emerged as a highly significant class of materials due to their tunable and adaptable properties, which make them suitable for a wide range of applications. One of the strategies for tuning and optimizing LHP-based devices is the substitution of cations and/or anions in LHPs. The impact of Cs substitution at the A site on the structural, vibrational, and elastic properties of MAxCs1−xPbCl3-mixed single crystals was investigated using X-ray diffraction (XRD) and Raman and Brillouin light scattering techniques. The XRD results confirmed the successful synthesis of impurity-free single crystals, which exhibited a phase coexistence of dominant cubic and minor orthorhombic symmetries. Raman spectroscopy was used to analyze the vibrational modes associated with the PbCl6 octahedra and the A-site cation movements, thereby revealing the influence of cesium incorporation on the lattice dynamics. Brillouin spectroscopy was employed to investigate the changes in elastic properties resulting from the Cs substitution. The incorporation of Cs cations induced lattice distortions within the inorganic framework, disrupting the hydrogen bonding between the MA cations and PbCl6 octahedra, which in turn affected the elastic constants and the sound velocities. The substitution of the MA cations with smaller Cs cations resulted in a stiffer lattice structure, with the two elastic constants increasing up to a Cs content of 30%. The current findings facilitate a fundamental understanding of mixed lead chloride perovskite materials, providing valuable insights into their structural and vibrational properties. Full article
(This article belongs to the Special Issue Terahertz Vibrational Spectroscopy in Advanced Materials)
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14 pages, 3592 KiB  
Article
Phonon Properties and Lattice Dynamics of Two- and Tri-Layered Lead Iodide Perovskites Comprising Butylammonium and Methylammonium Cations—Temperature-Dependent Raman Studies
by Mirosław Mączka, Szymon Smółka and Maciej Ptak
Materials 2024, 17(11), 2503; https://doi.org/10.3390/ma17112503 - 22 May 2024
Viewed by 1515
Abstract
Hybrid lead iodide perovskites are promising photovoltaic and light-emitting materials. Extant literature data on the key optoelectronic and luminescent properties of hybrid perovskites indicate that these properties are affected by electron–phonon coupling, the dynamics of the organic cations, and the degree of lattice [...] Read more.
Hybrid lead iodide perovskites are promising photovoltaic and light-emitting materials. Extant literature data on the key optoelectronic and luminescent properties of hybrid perovskites indicate that these properties are affected by electron–phonon coupling, the dynamics of the organic cations, and the degree of lattice distortion. We report temperature-dependent Raman studies of BA2MAPb2I7 and BA2MA2Pb3I10 (BA = butylammonium; MA = methylammonium), which undergo two structural phase transitions. Raman data obtained in broad temperature (360–80 K) and wavenumber (1800–10 cm−1) ranges show that ordering of BA+ cations triggers the higher temperature phase transition, whereas freezing of MA+ dynamics occurs below 200 K, leading to the onset of the low-temperature phase transition. This ordering is associated with significant deformation of the inorganic sublattice, as evidenced by changes observed in the lattice mode region. Our results show, therefore, that Raman spectroscopy is a very valuable tool for monitoring the separate dynamics of different organic cations in perovskites, comprising “perovskitizer” and interlayer cations. Full article
(This article belongs to the Special Issue Terahertz Vibrational Spectroscopy in Advanced Materials)
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