Editorial

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4 pages, 162 KiB

Open AccessEditorial

Raman Spectroscopy of Crystals

by Alexander Krylov

Crystals 2020, 10(11), 981; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10110981 - 29 Oct 2020

Cited by 1 | Viewed by 2858

Abstract

Raman spectroscopy is now finding wide-ranging application in pure and applied science [...] Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

Research

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24 pages, 7289 KiB

Open AccessArticle

Raman Spectra of Diphenylalanine Microtubes: Polarisation and Temperature Effects

by Alexander Krylov, Svetlana Krylova, Svitlana Kopyl, Aleksandr Krylov, Ferid Salehli, Pavel Zelenovskiy, Alexander Vtyurin and Andrei Kholkin

Crystals 2020, 10(3), 224; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10030224 - 20 Mar 2020

Cited by 14 | Viewed by 3748

Abstract

Diphenylalanine microtubes have remarkable physical properties that allow one to use them in electronics. In this work, we measured polarised temperature-dependent Raman spectra in self-assembled diphenylalanine microtubes grown from the solution. We observed the anomalous temperature behaviour of the Raman lines. Their temperature [...] Read more.

Diphenylalanine microtubes have remarkable physical properties that allow one to use them in electronics. In this work, we measured polarised temperature-dependent Raman spectra in self-assembled diphenylalanine microtubes grown from the solution. We observed the anomalous temperature behaviour of the Raman lines. Their temperature changes were minimal, which required a significant improvement in the resolution and stability of Raman measurements. The anomalies in the behaviour of the spectra at about 178 K, 235 K, 255 K, 278 K, 296 K, 398 K and 412 K were observed. The structural phase transition at 398 K is irreversible. This transition is associated with the release of water molecules from nanochannels. The irreversible phase transition has a temperature range of about 10 K. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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9 pages, 2159 KiB

Open AccessArticle

Raman Spectra of Quartz and Pb⁴⁺-Doped SiO₂ Crystals at Different Temperature and Pressure

by Xiuyan Chen, Wenjiang Feng, Guoying Zhang and Yan Gao

Crystals 2019, 9(11), 569; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9110569 - 30 Oct 2019

Cited by 8 | Viewed by 5221

Abstract

In order to seek for new Raman crystals, the manuscript presented the discussion on the Raman frequency of α-quartz, β-quartz, as well as Pb⁴⁺-doped SiO₂ crystals at different temperature and pressure. The results demonstrated that as the pressure increased, the [...] Read more.

In order to seek for new Raman crystals, the manuscript presented the discussion on the Raman frequency of α-quartz, β-quartz, as well as Pb⁴⁺-doped SiO₂ crystals at different temperature and pressure. The results demonstrated that as the pressure increased, the Raman lines shifted towards higher frequency for α-SiO₂ crystal, while for β-SiO₂ crystals, the main lines moved to lower frequency. Several new peaks were generated from the Pb⁴⁺-doped α-SiO₂ crystals. The Pb⁴⁺-doped β-SiO₂ crystals presented strong and ample Raman beams in the low-frequency range. The airfoil-shaped spectra appeared and broadened at high temperature and pressure. It could be inferred that the Pb⁴⁺-doped SiO₂ crystals were excellent Raman crystal candidates. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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7 pages, 598 KiB

Open AccessArticle

The Behavior of NH₃⁺ Torsional Vibration in Amino Acids: A Raman Spectroscopic Study

by André Luís de Oliveira Cavaignac, Ricardo Jorge Cruz Lima and Paulo Tarso Cavalcante Freire

Crystals 2019, 9(10), 517; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9100517 - 09 Oct 2019

Cited by 1 | Viewed by 2959

Abstract

In this work we present the continuation of studies carried out on the changes of geometric parameters of the hydrogen bonds in amino acid crystals subjected to temperature or pressure variations. Changes in geometric parameters of the hydrogen bonds are correlated with the [...] Read more.

In this work we present the continuation of studies carried out on the changes of geometric parameters of the hydrogen bonds in amino acid crystals subjected to temperature or pressure variations. Changes in geometric parameters of the hydrogen bonds are correlated with the temperature behavior of the Raman wavenumber of NH₃⁺ torsional band. Now four monocrystals, L-valine, L-isoleucine, taurine, and L-arginine hydrochloride monohydrate, are studied. Temperature evolution of the Raman wavenumber of NH₃⁺ torsional band, with positive slope (dν/dT = 0.023 cm⁻¹/K) of L-isoleucine, can be related to the stability of the crystal structure and the hydrogen bonds strengths on heating due to different temperature lattice parameters variation. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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12 pages, 3838 KiB

Open AccessArticle

Characterization of Coals and Coal Ashes with High Si Content Using Combined Second-Derivative Infrared Spectroscopy and Raman Spectroscopy

by Yanshan Yin, Huixia Yin, Zihua Wu, Caiwen Qi, Hong Tian, Wei Zhang, Zhangmao Hu and Leihua Feng

Crystals 2019, 9(10), 513; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9100513 - 02 Oct 2019

Cited by 55 | Viewed by 5030

Abstract

The organic and mineral components in two coals and resulting high-temperature ashes with high silicon content were characterized by second-derivative infrared spectroscopy, Raman spectroscopy, and X-ray diffraction (XRD). The infrared spectra of raw coals show weak organic functional groups bands but strong kaolinite [...] Read more.

The organic and mineral components in two coals and resulting high-temperature ashes with high silicon content were characterized by second-derivative infrared spectroscopy, Raman spectroscopy, and X-ray diffraction (XRD). The infrared spectra of raw coals show weak organic functional groups bands but strong kaolinite bands because of the relatively high silicates content. In contrast, the Raman spectra of raw coals show strong disordered carbon bands but no mineral bands since Raman spectroscopy is highly sensitive to carbonaceous phases. The overlapping bands of mineral components (e.g., calcite, feldspar, and muscovite) were successfully resolved by the method of second-derivative infrared spectroscopy. The results of infrared spectra indicate the presence of metakaolinite in coal ashes, suggesting the thermal transformation of kaolinite during ashing. Intense quartz bands were shown in both infrared and Raman spectra of coal ashes. In addition, Raman spectra of coal ashes show a very strong characteristic band of anatase (149 cm^–1), although the titanium oxides content is very low. Combined use of second-derivative infrared spectroscopy and Raman spectroscopy provides valuable insight into the analyses of mineralogical composition. The XRD results generally agree with those of FTIR and Raman spectroscopic analyses. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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13 pages, 5991 KiB

Open AccessArticle

Raman Characterization of Carrier Concentrations of Al-implanted 4H-SiC with Low Carrier Concentration by Photo-Generated Carrier Effect

by Tao Liu, Zongwei Xu, Mathias Rommel, Hong Wang, Ying Song, Yufang Wang and Fengzhou Fang

Crystals 2019, 9(8), 428; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9080428 - 17 Aug 2019

Cited by 7 | Viewed by 4592

Abstract

In this work, 4H SiC samples with a multilayer structure (shallow implanted layer in a lowly doped n-type epitaxial layer grown on a highly doped thick substrate) were investigated by Raman scattering. First, Raman depth profiling was performed to identify characteristic peaks for [...] Read more.

In this work, 4H SiC samples with a multilayer structure (shallow implanted layer in a lowly doped n-type epitaxial layer grown on a highly doped thick substrate) were investigated by Raman scattering. First, Raman depth profiling was performed to identify characteristic peaks for the different layers. Then, Raman scattering was used to characterize the carrier concentration of the samples. In contrast to the conventional Raman scattering measuring method of the Longitudinal Optical Plasmon Coupled (LOPC) mode, which is only suitable to characterize carrier concentrations in the range from 2 × 10¹⁶ to 5 × 10¹⁸ cm⁻³, in this work, Raman scattering, which is based on exciting photons with an energy above the band gap of 4H-SiC, was used. The proposed method was evaluated and approved for different Al-implanted samples. It was found that with increasing laser power the Al-implanted layers lead to a consistent redshift of the LOPC Raman peak compared to the peak of the non-implanted layer, which might be explained by a consistent change in effective photo-generated carrier concentration. Besides, it could be demonstrated that the lower concentration limit of the conventional approach can be extended to a value of 5 × 10¹⁵ cm⁻³ with the approach presented here. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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8 pages, 1479 KiB

Open AccessArticle

Polarization Dependence of Low-Frequency Vibrations from Multiple Faces in an Organic Single Crystal

by Irena Nemtsov, Hagit Aviv, Yitzhak Mastai and Yaakov R. Tischler

Crystals 2019, 9(8), 425; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9080425 - 16 Aug 2019

Cited by 7 | Viewed by 3520

Abstract

Recent developments in optical filters have enabled the facile use of Raman spectroscopy for detection of low frequency (LF) vibrational modes. LF-Raman spectroscopy offers fast and sensitive characterization of LF vibrations, and enables the measurement of single microcrystals and detection of defects. It [...] Read more.

Recent developments in optical filters have enabled the facile use of Raman spectroscopy for detection of low frequency (LF) vibrational modes. LF-Raman spectroscopy offers fast and sensitive characterization of LF vibrations, and enables the measurement of single microcrystals and detection of defects. It is useful for probing intermolecular interactions in crystals, which are lower in energy, such as hydrogen bonds, shear modes, and breathing modes. Crystal excitation from multiple faces allows learning the orientation of intermolecular interactions, as polarization dependence varies with the polarizability of the interactions along the planes. Elucidating the orientations of the intermolecular interactions in organic crystals is essential for guiding the reactions or adsorption to a specific crystal face. In this study, we investigated the dependence of the LF-Raman signal intensity on the orientation of an organic single microcrystal of L-alanine. Three incident beam directions provided the orientations of the intermolecular interactions by analyzing the corresponding LF-Raman spectra. The signal intensity correlated well with the proximity between the incident beam’s direction and the orientations of the intermolecular interactions. Excellent compatibility was found between the spectra and simulated orientations based on structural information. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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19 pages, 1939 KiB

Open AccessArticle

Anomalous Behaviors of Spin Waves Studied by Inelastic Light Scattering

by Hua-Yi Hou, Ming Yang, Jin Qiu, In-Sang Yang and Xiang-Bai Chen

Crystals 2019, 9(7), 357; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9070357 - 14 Jul 2019

Cited by 6 | Viewed by 4031

Abstract

Magnonics, an emerging research field, aims to control and manipulate spin waves in magnetic materials and structures. However, the current understanding of spin waves remains quite limited. This review attempts to provide an overview of the anomalous behaviors of spin waves in various [...] Read more.

Magnonics, an emerging research field, aims to control and manipulate spin waves in magnetic materials and structures. However, the current understanding of spin waves remains quite limited. This review attempts to provide an overview of the anomalous behaviors of spin waves in various types of magnetic materials observed thus far by inelastic light scattering experiments. The anomalously large asymmetry of anti-Stokes to Stokes intensity ratio, broad linewidth, strong resonance effect, unique polarization selection, and abnormal impurity dependence of spin waves are discussed. In addition, the mechanisms of these anomalous behaviors of spin waves are proposed. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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14 pages, 3305 KiB

Open AccessArticle

Resonance Raman Spectroscopy of Mn-Mg_k Cation Complexes in GaN

by Andrii Nikolenko, Viktor Strelchuk, Bogdan Tsykaniuk, Dmytro Kysylychyn, Giulia Capuzzo and Alberta Bonanni

Crystals 2019, 9(5), 235; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9050235 - 04 May 2019

Cited by 6 | Viewed by 4707

Abstract

Resonance Raman analysis is performed in order to gain insight into the nature of impurity-induced Raman features in GaN:(Mn,Mg) hosting Mn-Mg_k cation complexes and representing a prospective strategic material for the realization of full-nitride photonic devices emitting in the infra-red. It is [...] Read more.

Resonance Raman analysis is performed in order to gain insight into the nature of impurity-induced Raman features in GaN:(Mn,Mg) hosting Mn-Mg_k cation complexes and representing a prospective strategic material for the realization of full-nitride photonic devices emitting in the infra-red. It is found that in contrast to the case of GaN:Mn, the resonance enhancement of Mn-induced modes at sub-band excitation in Mg co-doped samples is not observed at an excitation of 2.4 eV, but shifts to lower energies, an effect explained by a resonance process involving photoionization of a hole from the donor level of Mn to the valence band of GaN. Selective excitation within the resonance Raman conditions allows the structure of the main Mn-induced phonon band at ~670 cm⁻¹ to be resolved into two distinct components, whose relative intensity varies with the Mg/Mn ratio and correlates with the concentration of different Mn-Mg_k cation complexes. Moreover, from the relative intensity of the 2LO and 1LO Raman resonances at inter-band excitation energy, the Huang-Rhys parameter has been estimated and, consequently, the strength of the electron-phonon interaction, which is found to increase linearly with the Mg/Mn ratio. Selective temperature-dependent enhancement of the high-order multiphonon peaks is due to variation in resonance conditions of exciton-mediated outgoing resonance Raman scattering by detuning the band gap. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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Review

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49 pages, 7491 KiB

Open AccessReview

Raman Scattering: From Structural Biology to Medical Applications

by Alexey V. Vlasov, Nina L. Maliar, Sergey V. Bazhenov, Evelina I. Nikelshparg, Nadezda A. Brazhe, Anastasiia D. Vlasova, Stepan D. Osipov, Vsevolod V. Sudarev, Yury L. Ryzhykau, Andrey O. Bogorodskiy, Egor V. Zinovev, Andrey V. Rogachev, Ilya V. Manukhov, Valentin I. Borshchevskiy, Alexander I. Kuklin, Jan Pokorný, Olga Sosnovtseva, Georgy V. Maksimov and Valentin I. Gordeliy

Crystals 2020, 10(1), 38; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst10010038 - 15 Jan 2020

Cited by 27 | Viewed by 10729

Abstract

This is a review of relevant Raman spectroscopy (RS) techniques and their use in structural biology, biophysics, cells, and tissues imaging towards development of various medical diagnostic tools, drug design, and other medical applications. Classical and contemporary structural studies of different water-soluble and [...] Read more.

This is a review of relevant Raman spectroscopy (RS) techniques and their use in structural biology, biophysics, cells, and tissues imaging towards development of various medical diagnostic tools, drug design, and other medical applications. Classical and contemporary structural studies of different water-soluble and membrane proteins, DNA, RNA, and their interactions and behavior in different systems were analyzed in terms of applicability of RS techniques and their complementarity to other corresponding methods. We show that RS is a powerful method that links the fundamental structural biology and its medical applications in cancer, cardiovascular, neurodegenerative, atherosclerotic, and other diseases. In particular, the key roles of RS in modern technologies of structure-based drug design are the detection and imaging of membrane protein microcrystals with the help of coherent anti-Stokes Raman scattering (CARS), which would help to further the development of protein structural crystallography and would result in a number of novel high-resolution structures of membrane proteins—drug targets; and, structural studies of photoactive membrane proteins (rhodopsins, photoreceptors, etc.) for the development of new optogenetic tools. Physical background and biomedical applications of spontaneous, stimulated, resonant, and surface- and tip-enhanced RS are also discussed. All of these techniques have been extensively developed during recent several decades. A number of interesting applications of CARS, resonant, and surface-enhanced Raman spectroscopy methods are also discussed. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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37 pages, 9722 KiB

Open AccessEditor’s ChoiceReview

Raman Scattering in Non-Stoichiometric Lithium Niobate Crystals with a Low Photorefractive Effect

by Nikolay Sidorov, Mikhail Palatnikov and Alexandra Kadetova

Crystals 2019, 9(10), 535; https://0-doi-org.brum.beds.ac.uk/10.3390/cryst9100535 - 17 Oct 2019

Cited by 14 | Viewed by 4086

Abstract

Raman spectra of lithium niobate single crystals strongly doped by zinc and magnesium, it has been established, contain low-intense bands with frequencies 209, 230, 298, 694, and 880 cm⁻¹. Ab ignition calculations fail to attribute these bands to fundamental vibrations of [...] Read more.

Raman spectra of lithium niobate single crystals strongly doped by zinc and magnesium, it has been established, contain low-intense bands with frequencies 209, 230, 298, 694, and 880 cm⁻¹. Ab ignition calculations fail to attribute these bands to fundamental vibrations of A₂ symmetry type unambiguously. Such vibrations are prohibited by the selection rules in the space group C_3V⁶ (R3c). Ab initio calculations also proved that low-intense “extra” bands with frequencies 104 and 119 cm⁻¹ definitely do not correspond to vibrations of A₂ symmetry type. We have paid special attention to these extra bands that appear in LiNbO₃ single crystals Raman spectra despite the fact that they are prohibited by the selection rules. In order to do so, we have studied a number of lithium niobate single crystals, both nominally pure and doped, by Raman spectroscopy. We have assumed that some “extra” bands correspond to two-particle states of acoustic phonons with a total wave vector equal to zero. We have also detected a Zn concentration area (0.05–0.94 mol.% ZnO in a crystal) where doped crystal structure is more ordered: The order of alternation of the main, doping cations, and vacancies along the polar axis is increased, and oxygen octahedra are less distorted. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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