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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (25 June 2023) | Viewed by 27911

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Special Issue Editors

Prof. Dr. Chiara Castiglioni

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Guest Editor

Department of Chemistry, Materials and Chemical Engineering Giulio Natta, Politecnico di Milano, Milan, Italy
Interests: vibrational spectroscopy; organic functional materials; carbon nanostructures; semi-conducting polymers

Dr. Bernardo A. Nogueira

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Guest Editor

CQC, Department of Chemistry, University of Coimbra, P-3004-535 Coimbra, Portugal
Interests: molecular structure; color polymorphism; Raman spectroscopy

Special Issue Information

Dear Colleagues,

In his Nobel Lecture (December 11, 1930), Chandrasekhara V. Raman foresaw an exceptionally promising scenario for the application of Raman spectroscopy (RS) in the study of material properties. At the end of his speech, he observed: “The universality of the phenomenon, the convenience of the experimental technique and the simplicity of the spectra obtained enable the [Raman] effect to be used as an experimental aid to the solution of a wide range of problems in physics and chemistry. Indeed, it may be said that it is this fact which constitutes the principal significance of the effect. The frequency differences determined from the spectra, the width and character of the lines appearing in them, and the intensity and state of polarization of the scattered radiations enable us to obtain an insight into the ultimate structure of the scattering substance. As experimental research has shown, these features in the spectra are very definitely influenced by physical conditions, such as temperature and state of aggregation, by physico-chemical conditions, such as mixture, solution, molecular association, and polymerization, and most essentially by chemical constitution. It follows that the new field of spectroscopy has practically unrestricted scope in the study of problems relating to the structure of matter. We may also hope that it will lead us to a fuller understanding of the nature of light, and of the interactions between matter and light.”

These words anticipated the success of Raman spectroscopy (RS), the widespread application of which in research emerged during the 1970s due to major technical and technological advances. Currently, RS is fundamental in the study of crystalline materials and nanostructures, specifically due to the dependence of Raman scattering on both incident light and crystal sample features. Particularly, Raman spectra depend on the incident light geometry mode (backscattering, transmission, etc.), on the excitation wavelength, the polarization of the incident and scattered light, on the crystal sample symmetry and orientation and, of course, on its peculiar vibrational states.

RS studies of crystalline materials and nanostructures are often non-destructive, and allow the investigation in a broad set of conditions, from vacuum to high pressures, cryogenic and high temperatures and under the influence magnetic and electric fields. Several advanced Raman techniques are now available for the investigation of crystalline materials and nanostructured materials, such as surface-enhanced Raman spectroscopy (SERS), spatially offset Raman spectroscopy (SORS), stimulated Raman spectroscopy (SRS), polarized Raman spectroscopy (PRS), and resonance Raman spectroscopy (RRS), among others.

Additionally, the prediction and theoretical interpretation of the Raman activity of crystalline materials is now much more effective, particularly with the development of computational techniques that are able to predict solid-state properties (e.g., the fully periodic DFT methods). Moreover, the effect of reducing the dimensionality and/or the crystal size, as well as the role of structural and chemical defects, can be investigated by means of Raman experiments and interpreted with the help of theoretical modelling.

This Special Issue on “Raman spectroscopy of crystalline materials and nanostructures” is therefore dedicated to both theoretical and experimental novel research where Raman spectroscopy is applied to investigate crystalline materials and nanostructures.

Prof. Dr. Chiara Castiglioni
Dr. Bernardo A. Nogueira
Guest Editors

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Keywords

Raman spectroscopy
crystals and crystal polymorphs
liquid crystals
crystalline and semi-crystalline materials
nanostructured materials
theoretical modelling and Raman spectra prediction
nonlinear Raman spectroscopy
surface-enhanced Raman spectroscopy
advanced Raman techniques
Raman mapping and Raman spectroscopy in operando

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Published Papers (13 papers)

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Editorial

Jump to: Research, Review

3 pages, 157 KiB

Open AccessEditorial

Raman Spectroscopy of Crystalline Materials and Nanostructures

by Bernardo A. Nogueira and Chiara Castiglioni

Crystals 2024, 14(3), 251; https://doi.org/10.3390/cryst14030251 - 3 Mar 2024

Viewed by 2649

Abstract

One of the biggest challenges in the field of material science lies in understanding the structure and behavior of crystalline materials and nanostructures [...] Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

Research

Jump to: Editorial, Review

10 pages, 959 KiB

Open AccessArticle

Pressure-Induced Neutral to Ionic Phase Transition in TTF-Fluoranil, DimethylTTF-Fluoranil and DimethylTTF-Chloranil: A Comparative THz Raman Study

by Elena Ferrari, Francesco Mezzadri and Matteo Masino

Crystals 2023, 13(10), 1428; https://doi.org/10.3390/cryst13101428 - 26 Sep 2023

Cited by 1 | Viewed by 1095

Abstract

The Neutral to Ionic phase Transition (NIT) that occurs in few mixed stack charge transfer cocrystals at high pressure or low temperature is a charge instability combined with a structural instability. The lattice contraction, which increases the 3D Coulomb interactions, favors a higher degree of charge transfer. Due to Peierls instability, this leads to the dimerization of the stack, breaking its inversion symmetry. The 3D interactions also determine the arrangement of the adjacent dimerized polar stacks, making the ionic phase ferroelectric or antiferroelectric. The role of these parameters that modulate the NIT has been widely studied in Tetrathiafulvalene-haloquinone cocrystals. Here, we compare the high-pressure behavior of three of them: the newly synthesized TTF-FA and DMTTF-FA with the known DMTTF-CA and isostructural DMTTF-FA. We followed the evolution of the lattice phonons via THz Raman spectroscopy, assessing the pressure-dependent structural changes. While the FA-based crystals undergo strong first-order NIT, DMTTF-CA shows a continuous transition. The high-pressure behavior of each crystal is also compared with the low-temperature behavior. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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13 pages, 2294 KiB

Open AccessEditor’s ChoiceArticle

Vibrational Properties of the Potassium Titanyl Phosphate Crystal Family

by Sergej Neufeld, Uwe Gerstmann, Laura Padberg, Christof Eigner, Gerhard Berth, Christine Silberhorn, Lukas M. Eng, Wolf Gero Schmidt and Michael Ruesing

Crystals 2023, 13(10), 1423; https://doi.org/10.3390/cryst13101423 - 25 Sep 2023

Viewed by 1815

Abstract

The crystal family of potassium titanyl phosphate (KTiOPO

_{4}

The crystal family of potassium titanyl phosphate (KTiOPO

_{4}

) is a promising material group for applications in quantum and nonlinear optics. The fabrication of low-loss optical waveguides, as well as high-grade periodically poled ferroelectric domain structures, requires a profound understanding of the material properties and crystal structure. In this regard, Raman spectroscopy offers the possibility to study and visualize domain structures, strain, defects, and the local stoichiometry, which are all factors impacting device performance. However, the accurate interpretation of Raman spectra and their changes with respect to extrinsic and intrinsic defects requires a thorough assignment of the Raman modes to their respective crystal features, which to date is only partly conducted based on phenomenological modelling. To address this issue, we calculated the phonon spectra of potassium titanyl phosphate and the related compounds rubidium titanyl phosphate (RbTiOPO

_{4}

) and potassium titanyl arsenate (KTiOAsO

_{4}

) based on density functional theory and compared them with experimental data. Overall, this allows us to assign various spectral features to eigenmodes of lattice substructures with improved detail compared to previous assignments. Nevertheless, the analysis also shows that not all features of the spectra can unambigiously be explained yet. A possible explanation might be that defects or long range fields not included in the modeling play a crucial rule for the resulting Raman spectrum. In conclusion, this work provides an improved foundation into the vibrational properties in the KTiOPO

_{4}

material family. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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15 pages, 3491 KiB

Open AccessArticle

Flux Growth and Raman Spectroscopy Study of Cu₂CrBO₅ Crystals

by Evgeniya Moshkina, Evgeniy Eremin, Maxim Molokeev, Dieter Kokh and Alexander Krylov

Crystals 2023, 13(10), 1415; https://doi.org/10.3390/cryst13101415 - 23 Sep 2023

Viewed by 1123

Abstract

Multicomponent flux systems based on both Li₂WO₄-B₂O₃-Li₂O-CuO-Cr₂O₃ and Bi₂O₃-MoO₃-B₂O₃-Na₂O-CuO-Cr₂O₃ were studied in order to grow [...] Read more.

Multicomponent flux systems based on both Li₂WO₄-B₂O₃-Li₂O-CuO-Cr₂O₃ and Bi₂O₃-MoO₃-B₂O₃-Na₂O-CuO-Cr₂O₃ were studied in order to grow Cu₂CrBO₅ crystals. The conditions for Cu₂CrBO₅ crystallization were investigated by varyingthe component ratios, and the peculiarities of their interaction were characterized by studying the formation sequence of high-temperature crystallizing phases. Special attention was paid to the problem of Cr₂O₃ solubility. Phase boundaries between CuCrO₂, Cu₂CrO₄, and Cu₂CrBO₅ were considered. The crystal structure of the obtained samples was studied viasingle crystal and powder X-ray diffraction. The chemical composition of the grown crystals was examined using the EDX technique. Anactual ratio of Cu:Cr = 1.89:1.11 was found for Cu₂CrBO₅ grown from the lithium-tungstate system, which showed a small deviation from 2:1, implying the presence of a part of bivalent Cr²⁺ in the samples. Anomalies in the thermal dependence of magnetization were analyzed and compared with the previously obtained data for Cu₂CrBO₅. The anomaly at T_C ≈ 42 K and the antiferromagnetic phase transition at T_N ≈ 119 K were considered. Polarized Raman spectra of Cu₂CrBO₅ were obtained for the first time, and a comparative analysis of the obtained data with other monoclinic and orthorhombic ludwigites is presented. Along with the polarized room temperature spectra, the thermal evolution of Raman modes near the antiferromagnetic phase transition temperature T_N ≈ 119 K is provided. The influence of the magnetic phase transition on the Raman spectra of Cu₂CrBO₅ is discussed. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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13 pages, 3156 KiB

Open AccessArticle

Nanoscale Study of the Polar and Electronic Properties of a Molecular Erbium(III) Complex Observed via Scanning Probe Microscopy

by Maxim Ivanov, Arkadiusz Grempka, Arseniy Buryakov, Timur Nikitin, Licínia L. G. Justino, Rui Fausto, Paula M. Vilarinho and José A. Paixão

Crystals 2023, 13(9), 1331; https://doi.org/10.3390/cryst13091331 - 31 Aug 2023

Cited by 1 | Viewed by 1233

Abstract

We successfully synthesized millimeter-sized single crystals of the molecular erbium(III) complex Er(acac)₃(cphen), where acac = acetylacetonate and cphen = 5-chloro-1,10-phenanthroline. The novelty of this work stems from the exhaustive examination of the polar and electronic properties of the obtained samples at the macro-, micro-, and nanoscale levels. The single crystal X-ray diffraction method demonstrates the monoclinic (noncentrosymmetric space group P2₁) crystallographic structure of the synthesized samples and scanning electron microscopy exhibits the terrace–ledge morphology of the surface in erbium(III) crystals. By using the piezoelectric force microscopy mode, the origin of the polar properties and the hyperpolarizability in the synthesized samples were assigned to the internal domain structure framed by the characteristic terrace–ledge topography. The direct piezoelectric coefficient (~d33) was found to be intensely dependent on the local area and was measured in the range of 4–8 pm/V. A nanoscale study using the kelvin probe force and capacitance force (dC/dz) microscopy modes exposed the effect of the Er ions clustering in the erbium(III) complex. The PFM method applied solely to the Er ion revealed the corresponding direct piezoelectric coefficient (~d33) of about 4 pm/V. Given the maximum piezoelectric coefficient in the erbium(III) complex at 8 pm/V, we highlight the significant importance of the spatial coordination between the lanthanide ion and the ligands. The polar coordination between the lanthanide ion and the nitrogen and oxygen atoms was also corroborated by Raman spectroscopy supported by the density functional theory calculations. The obtained results can be of paramount importance for the application of molecular erbium(III) complex crystals in low-magnitude magnetic or electric field devices, which would reduce the energy consumption and speed up the processing switching in nonvolatile memory devices. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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12 pages, 3175 KiB

Open AccessArticle

Determination of Thermal Damage Threshold in THz Photomixers Using Raman Spectroscopy

by Martin Mikulics, Roman Adam, Genyu Chen, Debamitra Chakraborty, Jing Cheng, Anthony Pericolo, Ivan Komissarov, Daniel E. Bürgler, Sarah F. Heidtfeld, John Serafini, Stefan Preble, Roman Sobolewski, Claus M. Schneider, Joachim Mayer and Hilde H. Hardtdegen

Crystals 2023, 13(8), 1267; https://doi.org/10.3390/cryst13081267 - 17 Aug 2023

Cited by 3 | Viewed by 1680

Abstract

The increase of device lifetime and reliability of THz photomixers will play an essential role in their possible future application. Therefore, their optimal work conditions/operation range, i.e., the maximal incident optical power should be experimentally estimated. We fabricated and tested THz photomixer devices based on nitrogen-implanted GaAs integrated with a Bragg reflector. Raman spectroscopy was applied to investigate the material properties and to disclose any reversible or irreversible material changes. The results indicate that degradation effects in the photomixer structures/material could be avoided if the total optical power density does not exceed levels of about 0.7 mW/µm² for 100 min of operation. Furthermore, the investigations performed during 1000 min of optical exposure on the photomixer devices’ central region comprising interdigitated metal-semiconductor-metal (MSM) structures suggest a reversible “curing” mechanism if the power density level of ~0.58 mW/µm² is not exceeded. Long-term operation (up to 1000 h) reveals that the photomixer structures can withstand an average optical power density of up to ~0.4 mW/µm² without degradation when biased at 10 V. Besides the decrease of the position of the A_1g (LO) Raman mode from ~291 cm⁻¹ down to ~288 cm⁻¹ with increasing optical power density and operation time, broad Raman modes evolve at about 210 cm⁻¹, which can be attributed to degradation effects in the active photomixer/MSM area. In addition, the performed carrier lifetime and photomixer experiments demonstrated that these structures generated continuous wave sub-THz radiation efficiently as long as their optimal work conditions/operation range were within the limits established by our Raman studies. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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11 pages, 2263 KiB

Open AccessArticle

Investigation of Calcium and Magnesium Phosphate Crystals in Stones Treated with Diammonium Hydrogen Phosphate Conservation Product: Potential of Micro-Raman Spectroscopy

by Claudia Conti, Léa Cutard, Alessandra Botteon, Luigi Brambilla, Nicoletta Marinoni, Marco Realini, Maria Catrambone, Elena Possenti and Chiara Colombo

Crystals 2023, 13(8), 1212; https://doi.org/10.3390/cryst13081212 - 5 Aug 2023

Cited by 3 | Viewed by 1635

Abstract

This study is aimed at investigating crystals (calcium and magnesium phosphates) formed due the interaction of an inorganic conservation treatment (diammonium hydrogen phosphate—DAP) with carbonatic (calcitic and dolomitic) stones through micro-Raman Spectroscopy. The addressed questions concern (i) the identification of magnesium and calcium phosphate minerals crystallized within dolomitic stone samples with a different degree of conservation state and treated with two different DAP solution molarities and (ii) the distinction of complex calcium phosphate mixtures (hydroxyapatite—HAP and octa calcium phosphate—OCP) crystallized within a calcarenite stone treated with DAP. A statistically relevant number of Raman spectra have been acquired in sample cross sections and curve fitting analysis has been performed for the in-depth interpretation of data. The outcomes indicate that Raman Spectroscopy is an effective alternative method for the identification of poorly crystalline calcium phosphates (not easily detectable with X-ray diffraction), even when scarcely present in mixture with magnesium phosphates. Evidence of the Raman analytical capability and high potential to distinguish HAP and OCP in calcitic stones are also presented and discussed. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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11 pages, 2345 KiB

Open AccessArticle

Water Adsorption on MgO Surfaces: A Vibrational Analysis

by Maria Dekermenjian, Alexandre Merlen, Andreas Ruediger and Michel Rérat

Crystals 2023, 13(8), 1153; https://doi.org/10.3390/cryst13081153 - 25 Jul 2023

Cited by 2 | Viewed by 1582

Abstract

Using DFT calculations, we have considered different adsorption configurations of water molecules on MgO surfaces. In some cases, we have observed a chemical reaction between water and the surface, with the formation of hydroxyl groups. We have systematically compared the calculated Raman spectra of the final optimized structures with the measured spectra from MgO nanoparticles. Our results confirm the high reactivity of MgO surfaces with water. Some obtained structures can be considered precursors for the transformation of MgO into Mg(OH)₂. We suggest that some of them could be identified using Raman spectroscopy. Our study confirms the high potentiality of Raman spectroscopy, associated with numerical calculations, for the study of chemical reactivity of nanoparticles. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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10 pages, 1604 KiB

Open AccessArticle

Combining UV-Vis and Resonance Raman Spectroscopy to Characterize Molecular Aggregation

by Valentina Sesti, Micol D’Antonio, Andrea Lucotti, Paola Moretti, Rossella Castagna, Chiara Bertarelli and Matteo Tommasini

Crystals 2023, 13(7), 1141; https://doi.org/10.3390/cryst13071141 - 22 Jul 2023

Cited by 1 | Viewed by 1989

Abstract

In this work, we use UV-Vis and Raman spectroscopy to correlate the intensity of selected transitions to the onset of aggregation phenomena. Through TDDFT calculations, we rationalize the formation of H-aggregates and their influence on the observed changes in the UV-Vis spectra. A correlation between Raman intensity and the molar absorption coefficient is experimentally observed and theoretically rationalized. We develop this method by considering Disperse Orange 3 (DO3), a well-known push–pull azobenzene dye with strong optical absorption in the blue–green region of the visible spectrum, and the known tendency to form H-aggregates. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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16 pages, 24086 KiB

Open AccessArticle

Crystallization Kinetics: Relationship between Crystal Morphology and the Cooling Rate—Applications for Different Geological Materials

by Namık Aysal, Yiğit Kurt, Hüseyin Öztürk, Gulce Ogruc Ildiz, Mehmet Yesiltas, Davut Laçin, Sinan Öngen, Timur Nikitin and Rui Fausto

Crystals 2023, 13(7), 1130; https://doi.org/10.3390/cryst13071130 - 19 Jul 2023

Cited by 3 | Viewed by 3293

Abstract

Crystal morphology is controlled by several physicochemical parameters such as the temperature, pressure, cooling rate, nucleation, diffusion, volatile composition, and viscosity. The development of different crystal morphologies is observed as a function of the cooling rate in many different rock types (i.e., glassy volcanic rocks, and archeometallurgical slags). Crystallization is a two-stage kinetic process that begins with the formation of a nucleus and then continues with the accumulation of ions on it. The shapes of the crystals depend on the degree of undercooling (ΔT), and euhedral crystals, having characteristic forms that reflect their crystallographic internal structure, that grow just below their liquidus temperature. In this study, crystal morphologies in different minerals (e.g., quartz, sanidine, olivine, pyroxene, magnetite, etc.) that had developed in silicic volcanic rocks (spherulites) and slags from ancient mining were investigated and characterized using optical microscopy, X-ray diffraction, and Fourier-transform infrared (FTIR), Raman, and scanning electron microscope-energy dispersive X-ray fluorescence (SEM-EDX) spectroscopic techniques. Depending on the increase in the cooling rate, quartz, feldspar, olivine, pyroxene, and magnetite minerals were found to crystallize in subhedral, skeletal, dendritic, spherical, bow-tie and fibrous forms in glassy volcanic rocks and archeometallurgical slags. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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11 pages, 1890 KiB

Open AccessArticle

Surface-Enhanced Raman Spectroscopy of Benzylpenicillin Using Silver Nanocrystals Modified with Moroccan Plant Extracts

by Yasmine Fernine, Natércia C. T. Martins, Mustapha Taleb and Tito Trindade

Crystals 2023, 13(7), 1105; https://doi.org/10.3390/cryst13071105 - 16 Jul 2023

Cited by 1 | Viewed by 1424

Abstract

Green chemical routes for the synthesis of colloidal metal nanocrystals have been of great interest, namely in the context of nanosciences associated with biological applications. Among these methods, the synthesis of metal colloids using medicinal plant extracts originates nanocrystals having surfaces modified with chemical compounds of biological origin, which can be further explored in association with conventional pharmaceutics. In this context, the development of spectroscopic methods that seeks for understanding the potential benefits of using formulations that contain natural compounds and metal nanoparticles with therapeutic properties is of relevance. This research describes the chemical synthesis of silver colloids via the reduction of Ag(I) in the presence of distinct aqueous plant extracts. The selected extracts were obtained from Moroccan plants that have been used in traditional therapeutic practices over the centuries. The method led to stable colloids comprising polydispersed Ag nanocrystals that show surface-enhanced Raman scattering (SERS) activity. As an illustrative scenario, these colloids have been applied to the SERS detection of the natural β-lactam antibiotic benzylpenicillin, also known as penicillin G (PG). Our results indicate that all the Ag colloids tested with the different plant extracts are SERS-active for PG without showing detrimental interference from chemical adsorbates originated from the extracts. Therefore, this spectroscopic method can be further explored for monitoring nanoformulations of pharmaceuticals and metal colloids obtained using biological synthesis. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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13 pages, 4734 KiB

Open AccessArticle

Crystal Structure, Raman Spectroscopy and Optical Property Study of Mg-Doped SnO₂ Compounds for Optoelectronic Devices

by K. K. Singha, P. P. Singh, R. Narzary, A. Mondal, M. Gupta, V. G. Sathe, D. Kumar and S. K. Srivastava

Crystals 2023, 13(6), 932; https://doi.org/10.3390/cryst13060932 - 9 Jun 2023

Cited by 10 | Viewed by 2158

Abstract

Researchers have been consistently looking for new materials that can be integrated in optoelectronic and spintronic devices. In this research, we investigated the crystalline structure, Raman, and optical characteristics of Mg-doped SnO₂ compounds. The solid-state reaction technique was utilized to produce polycrystalline samples of Sn_1−xMg_xO₂ (0 ≤ x ≤ 0.10) for their potential use in optoelectronics devices. It was discovered that all the compounds were synthesized into a tetragonal rutile-type structure of SnO₂. The analysis of these samples using Raman spectroscopy provided more evidence, supporting the creation of the tetragonal rutile phase of SnO₂ and the successful integration of Mg ions in SnO₂. The measurements of the optical properties, such as absorbance and transmittance, carried out with a UV-Vis spectrophotometer demonstrated that the optical band gap widened with the increase in the magnesium doping concentration in SnO₂. In addition, it was noticed that increasing the quantity of magnesium doping concentration led to an increase in the transmittance value from 83% to 91%. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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Review

Jump to: Editorial, Research

15 pages, 13690 KiB

Open AccessReview

Raman Spectroscopy of 2D MoS₂ Interacting with Metals

by Francesco Tumino, Paolo D’Agosta, Valeria Russo, Andrea Li Bassi and Carlo Spartaco Casari

Crystals 2023, 13(8), 1271; https://doi.org/10.3390/cryst13081271 - 17 Aug 2023

Cited by 8 | Viewed by 5138

Abstract

The research on molybdenum disulphide (MoS

_{2}

) has progressed remarkably in the last decade, prompted by the increasing interest for this material as a potential candidate in future ultrathin optoelectronic devices. MoS

_{2}

is a layered semiconductor with a gap in the [...] Read more.

The research on molybdenum disulphide (MoS

_{2}

) has progressed remarkably in the last decade, prompted by the increasing interest for this material as a potential candidate in future ultrathin optoelectronic devices. MoS

_{2}

is a layered semiconductor with a gap in the visible region, which can be exfoliated down to the mono-layer form. Since the discovery of the exceptional optoelectronic properties of 2D MoS

_{2}

, Raman spectroscopy has been extensively used as a tool to characterize the structure and thickness of MoS

_{2}

films. Recent works on MoS

_{2}

-metal interfaces have shown that Raman spectra are significantly affected by the interaction with metals. However, a complete understanding of how such interaction modifies the MoS

_{2}

vibrational properties is still lacking. Studying this subject with both experimental and theoretical methods will provide fundamental insight into the interface physics of MoS

_{2}

-metal systems, which is crucial for the fabrication of metal contacts and for the development of metal-assisted synthesis methods. This review summarizes the main results concerning Raman spectroscopy studies of heterosystems between MoS

_{2}

and transition metals, providing both a basis and directions for future research. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystalline Materials and Nanostructures)

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