Advertisement

Potential of Raman spectroscopy towards understanding structures of carbon-based materials and perovskites

  • Premkumar Selvarajan
  • Goutam Chandra
  • Susmita Bhattacharya
  • Sanchita Sil
  • Ajayan VinuEmail author
  • Siva UmapathyEmail author
Review Article

Abstract

Sp3 and sp2 hybridised carbon materials have been exploited for myriad applications owing to their unique electronic features. Novel carbon materials and its composites are synthesised by researchers with improved physico-chemical properties for various applications. These novel materials need to be characterised to decipher the structures. Vibrational spectroscopic studies have been used to understand the lattice dynamics of such carbon materials for the last six decades. Raman spectroscopy in particular has been a unique technique in such investigations as it provides bond-specific information at a molecular level which is desirable in understanding the microstructure of carbon. In this review, we highlight the potential of Raman spectroscopy to study the microstructure of different carbon allotropes such as graphene, carbon nanotubes, fullerene, and carbon nitride and its composites. In addition, perovskites has been receiving a lot of attention recently as the scientific community has realised their potential in the areas of material science and energy storage and conversion. This review also covers a few aspects of Raman spectroscopic studies of oxide and halide perovskites.

Keywords

Raman spectroscopy Graphene Carbon nanotubes Fullerene C60 C70 Carbon nitride Composites Perovskites 

1 Introduction

The living world is characterised by three building blocks, namely carbon, hydrogen and oxygen. Of these elements, carbon possesses a unique property of catenation. This is the result of little energy difference between the 2s and 2p electrons which allows interaction of the individual orbitals to yield hybridised orbitals. This forms the foundation of its ability to exist in different ‘avatars’ or allotropes such as the sp3 hybridised diamond. However, when sp2 hybridised, it results in a plethora of structure. Graphite which may be considered to occupy the top of the allotrope hierarchy, consisting of numerous layers of sp2 carbon in a hexagonal network where each carbon atom shares covalent bonds with three neighbouring carbon atoms. Of particular significance is a one-atom-thick sp2 network of carbon atoms which forms the most fascinating material, i.e., graphene. This is the building block for many other allotropes. For instance, when a single layer of graphene is rolled up, it results in a 1-D single-walled carbon nanotube. Multiple concentric rolled cylinders lead to the formation of a multi-walled carbon nanotube. In addition, “buckyball” or buckminsterfullerene, a 0-D material which is comprised of sp2-sp3 nanocarbon structure (C60) has attracted attention of the research community [1].The exceptional physico-chemical properties of these materials attract applications in the field of catalysis, semiconductor devices, biomedical applications etc. [2, 3, 4, 5, 6]. Carbon materials (graphene; carbon nanotubes, CNTs; etc.) are found to exhibit best performances and emerge as potential shielding materials. Cao and co-workers have recently reviewed [2] the studies in the field of electromagnetic attenuation and advancement towards enhancement using graphene and its hybrid materials due to their fascinating properties. Blackburn et al. have described the utilisation of CNTs as emerging thermoelectric energy harvesting materials and conversion of waste heat to voltage [3]. Authors have tried to establish the understanding of SWCNTs as an efficient thermoelectric-energy convertor based on their unique structural, electrical and thermal properties. They have illustrated that CNT-based composites even show higher performance having immense potential for future devices. Composites of carbon material are well known for their catalytic activity. A unique and facile technique reported by Mori et al. describes the large-scale fabrication of 2-D carbon nanomaterials [4] by carbonisation of self-assembly of molecular units of 9,9′,10,10′-tetra-butoxy-cyclo[6]-paraphenylene-[2]-3,6-phenanthrenylene (CPPhen). It has been demonstrated that the addition of simply pyridine into the CPPhen solution as a dopant gives rise easily to very high N-doped carbon nanosheets which would be useful for high-performance catalytic applications. Boron carbon nitrides (BCN) emerge as a new type of boron and nitrogen substituted carbon-based nanocomposites that found applications in the field of hydrogen evolution reaction (HER), oxygen reduction reaction (ORR) and supercapacitor [5]. Several nanocomposites of BCN covalently cross-linked with 2-d materials such as C3N4, MoS2 and MoSe2 have also been explored and found an interesting visible light controlled catalytic activity towards HER.

Akin to carbon-based materials, perovskite structure (ABY3)–based materials have a range of stoichiometries and allotropes, which offer vast applications in heterogeneous catalysis, electrocatalysis, photocatalysis, photovoltaics, white-light emitting diodes, piezoelectric etc. [6, 7]. Moreover in perovskites, phase transformation caused by physical properties such as temperature and pressure as well as chemical modification caused by the substitution on A, B and Y; oxygen vacancy; doping and partially mixed at A and/or B and/or Y position lead to the different properties and thus different applications. Ulaganathan et al. described the impact of light photons on 2-d materials [8] such as graphene, graphene oxide, other 2-d materials and perovskite by luminescence, light-induced photo-doping effect and applications towards their device performance. They also discussed that it is much easy to control the electrical properties with the appropriate functionalisation of 2-d materials. This further helps us to fulfill the current demand of optoelectronics devices. Hence, spectroscopic techniques such as Raman spectroscopy are a prerequisite to monitor bonding nature, phase transition, oxygen vacancy and structural-related intrinsic properties of these exotic materials.

Raman spectroscopy has been the technique of choice for the researchers to understand the molecular structure of these carbon allotropes [9, 10, 11, 12]. Figure 1 depicts the trends in publication pertaining to Raman spectroscopic studies of various carbon materials. The records clearly show an increasing trend in the number of papers published in the last four and a half decades with respect to Raman spectroscopy of carbon materials as obtained from the web of science. The pie chart suggests that the maximum contribution is from graphene and CNT followed by graphite and diamond. Individual plots of publication records of the last three decades indicate an increasing trend in Raman spectroscopic studies of these materials.
Fig. 1

Trend of Raman spectroscopy–based publications of various carbon materials from web of science. The pie chart suggests that the maximum contribution is from graphene and CNT followed by graphite and diamond. Individual plots show an increasing trend in Raman spectroscopic studies of these materials

The allotropes of carbon have myriad features which lend their uniqueness and are manifested in several applications. For instance, charcoal has a high surface area which effectively utilised for catalysis, filtration etc. However, graphite is a crystalline carbon and is used for an entirely different set of applications such as refractory materials, in batteries and lubricants. On the other hand, diamond is the hardest known material and is used in cutting tools, optical components and so on. The more recently discovered allotropes such as SWCNT, MWCNT, fullerenes and graphene have different properties altogether and are being exploited in almost all fields of materials science and nanotechnology. Details of the structural features obtained by Raman spectroscopy for these materials have been discussed in the subsequent sections. The choice of Raman as a characterisation tool can be understood by Fig. 2 which shows the Raman spectra of representative carbonaceous materials. One can easily discern the unique spectral features which arise in different carbon allotropes. It provides a fingerprint of the material under observation. Therefore, Raman-based techniques have become the workhorse for characterisation of carbon-based systems. Consequently, the hybridisation, chemical impurities, elastic constants, crystal disorder, number of graphene layers, and many other properties of graphitic materials have been studied using Raman spectroscopy [9, 11, 12, 13]. In the last couple of decades, many novel carbon materials such as carbon nitrides and carbon nanocomposites have been developed. Raman spectroscopy has been employed as a tool to identify the formation of such materials at molecular level.
Fig. 2

Representative Raman spectra of different carbon materials and specific features

The objective of this review is to provide an overview of the potential of this technique towards understanding the structure of exotic carbon materials including carbon nitrides and carbon nanocomposites. The subsequent sections discuss Raman spectroscopic studies of different allotropes of carbon. Several examples have been taken to elucidate how Raman spectra can be used for determining layers in case of graphene or defects present in carbon materials. Recent literatures reveal that perovskites are emerging as fascinating materials for applications in catalysis, fuel cells, optoelectronics, solar cells, semiconductors and electrochemical sensing. Our laboratory is actively engaged in Raman spectroscopic studies of different oxide perovskites. Therefore, a section on perovskites, covering the study of oxide and halide perovskites using Raman spectroscopy has been added.

2 Exotic allotropes of carbon

2.1 Graphene (monolayer and few-layer)

Graphene [14, 15, 16] is a mono-atomic layer of C-atoms arranged into a 2D honeycomb lattice serves as an elementary block for graphitic materials such as 0D fullerenes, 1D nanotubes or stacked 3D graphite. The most fascinating feature of graphene is that, the electronic energy dispersion is conical in shape up to ~ 1 eV. At Dirac point, two inverted cones of CB and VB (conduction and valence bands respectively) touch each other. In neutral graphene, the Fermi energy exactly crosses the Dirac point. When dopped, electrons and holes can move through the mono-atomic layer with a velocity vF~106m/s, a minor fraction of the speed of light. The velocity of electrons (e) and holes (h) is energy-independent and they (e and h) behave as massless particles and antiparticles. Perfect e–h symmetry, Berry phase, chirality (absence of intra-valley and inter-valley back scattering), and zero rest mass of graphene make it as a unique candidate for the scientific community. In contrast to monolayer graphene, the energy dispersion is parabolic in bilayer graphene. It has finite density of states (DOS) at zero energy. The e and h are considered to have finite mass. Trilayer graphene is considered as an arrangement of massless single layer and massive bilayer sub-bands. Thus, as witnessed by the experiment and theory, few-layer graphene flakes with less than ten layers each demonstrate a characteristic band structure [17, 18]. The layers can be stacked as in graphite, or have any orientation. This gives rise to the appearance of a Dirac spectrum (a wealth of electronic properties) even in few layers of graphene.

Figure 3a describes the top view of the unit cells in mono, bilayer, and trilayer graphene. Monolayer graphene belongs to the D6h point group [19] with two atoms (A, B) in the unit cell (Fig. 3.i.a). The atoms in it can move in plane as well as out of plane. Therefore, the total degree of freedom is three (x, y, z). Thus, there will be a total of six branches (three optical and three acoustic). In monolayer graphene, the q = 0 phonon, known as Γ phonon, related to the irreducible representations as E2g, B2g, E1u, and A2u. Among them, E2g and B2g are the optical modes but E1u and A2u are the acoustic modes. In the case of graphite, there are four atoms per unit cell, and only half of them have fourth neighbours that either lie directly above or below in adjacent layers. Therefore, the two atoms of the unit cell in each layer now become inequivalent. Bilayer graphene has four atoms in the unit cell (A1, B1) and (A2, B2) (Fig. 3.i.b) and belongs to D3d point group [19]. As a result, vibration of a bilayer graphene can be achieved by combining in phase or out of phase vibration of two single layers. For monolayer and few-layer graphene, the Raman fingerprints are different and have been thoroughly investigated in the literature [10, 20, 21, 22, 23, 24, 25]. Due to momentum conservation, in a first order Raman process, we can only probe the Γ phonons. Among the Γ phonons only the doubly degenerate E2g mode is Raman active which is called G mode. In a standard Raman spectrum of monolayer graphene, the symmetry allowed G mode appears at 1583 cm−1. Other modes are at 1350 cm−1 (D mode), 1620 cm−1 (D′ mode), 2680 (2D mode), 2950 (D+G), 3245 (2D′) and 4290 cm−1 (2D+G). The mode observed at 1350 cm−1, termed as the D mode, is disorder-activated Raman mode and is related to the TO branch near the Brillion zone K point. Due to double resonance, even in the absence of D band, 2D band is observed, as presence of defect is not mandatory for the observation of the 2D band at 2680 cm−1. In few layer graphene, single layer optical modes become Davydov doublets, i.e. E2g emerges as an infrared-active E1u and a Raman-active E2g, B2g becomes an infrared-active A2u, and an inactive B2g. Thus, for few layer graphene/graphite, vibrational features are, Γ = 2(A2u + B2g + E1u + E2g). Now, there are two Raman-active E2g modes, each doubly degenerate. The high-frequency E2g mode is responsible for the above-mentioned G peak, while the low frequency E2g or S mode is a doubly degenerate rigid layer shear mode, which involves the relative motion of atoms in adjacent planes. The C peak is not expected to be dispersive with excitation energy, as observed in case of D, D′ and 2D′ peaks and their overtones [24]. In bilayer graphene, the peak position of the G mode remains unaltered as single layer graphene. However, the 2D bands in bilayer graphene split into four bands originated due to different phonon-assisted intervalley transition. In case of bilayer graphene, it has been pointed out [26, 27] that the Raman process considered to be fully resonant, is more dominant than the double resonance process. Figure 3 ii (a, b, c) describes the corresponding 2D-band line shape and variation in their different contributory components corresponding to the different number of layers (mono, bi, tri) of a graphene sample with ABA stacking. In literature, there are a large number of reports highlighting 2D band line shape analysis that as a useful and fast method to quantify the layer number of graphene and also provides information about the stacking order [28, 29, 30, 31]. These Raman fingerprint allows us to visualise directly the spatial distribution of Bernal (ABA) and rhombohedral (ABC) stacking. Other than the 2D band evolution, systematic shift in shear mode (S peak), and layer breathing mode (B) at 90 cm−1 and 1720 cm−1 (B i.e. A1g or A′, combination mode of LO and ZO′ respectively) mode having multiple peaks with unique line shape [32, 33, 34, 35, 36, 37] are also reported to illustrate clear signature of layer number and stacking order in graphene. Figure 4a) and b) describe stacking sequence in graphene a) Bernel (ABA) and Rhombohedral (ABC) respectively. Each letter mentioned in the stacking sequences describes individual layer. The atomic coordinates on the basal plane in the graphene honeycomb lattice (I: 0, 0; II: 1/3, 2/3; III: 2/3, 1/3) are shown in the Fig. 4a) and b) by dashed lines. The rectangle with solid lines describes unit cell in each stacking. Following linear chain model (LCM), a systematic variation in low frequency, S and B mode can be estimated for different stacking/layer orientation and layer number in FLG. Considering the nearest neighbour interaction and weak next nearest neighbour interaction, the frequency of S and B mode can be expressed as a function of layer number described below:
Fig. 3

(i) Upper panel describes top view of the real-space unit cell of a) monolayer graphene (1-LG) representing the in-equivalent A and B atoms where a1 and a2 are the unit vectors. b) For bilayer graphene (2-LG). c) Same for trilayer. Lower panel: ii) Corresponding 2D-band line shape that determine the number of layers of 2-d graphene system with ABA stacking. Reproduced with the permission from Phys. Rev. B 79, 125,426 (2009)

Fig. 4

Two major stacking sequence in graphene a) Bernel (ABA) b) rhombohedral (ABC). Each letter in the stacking sequences describes one layer. Three atomic coordinates on the basal plane in the graphene honeycomb lattice [I:(0, 0); II: (1/3, 2/3); III: (2/3, 1/3)] are shown by dashed lines. The rectangle with solid lines describes unit cell in each stacking. From bond polarisibility model-calculated thickness dependence variation in shear (S) and breathing (B) mode in FLG, (c) S modes in ABA stacking, (d) S modes in ABC stacking, and (e) B modes in ABA or ABC stacking. Dashed lines highlight the evolution of modes with frequency. Reproduced with the permission from Nanoscale, 2017, 9, 15,340

$$ \omega\ \left({S}_{NN-i}\right)=\frac{1}{\pi c}\sqrt{\frac{\kappa_{\parallel }}{m_{\mathrm{monolayer}}}}\ \mathit{\sin}\left(\frac{i\pi}{2N}\right) $$
(1a)
$$ \omega\ \left({B}_{NN-i}\right)=\frac{1}{\pi c}\sqrt{\frac{\kappa_{\perp }}{m_{\mathrm{monolayer}}}}\ \mathit{\sin}\left(\frac{i\pi}{2N}\right) $$
(1b)
where, κand κ the interlayer force coupling per unit area parallel and perpendicular to the FLG plane, mmonolayer is the monolayer mass per unit area, c speed of light, N layer number, and i = 1,2, … .(N-1). For graphite ω (SBulk) and ω (BBulk) are 43.5 and 128 cm−1 respectively. The theoretically predicted variation of S and B mode in FLG as obtained from interlayer bond polarisability model [35] for different stacking order are shown in Fig. 4(c–e) . With the advanced instrumentation (using long pass edge filters), even the evidence of twist-angle-dependent softening of the shear coupling in Bernel stacked twisted FLG can be easily detected [38].

2.1.1 Recent progress and applications of graphene

The emergence of low dimensional materials has suggested that the components of modern electronic and optoelectronic devices such as p-n junction diode, field-effect transistor (FET), solar cells, and devices used in various medical, chemical and industrial processes, can be scaled down to atomic thicknesses. Under a magnetic field, graphene transistor of few atomic layer was found to be capable of detecting THz and IR waves in a very wide band of frequencies (0.76–33 THz) and the detection frequency can be tuned by changing the magnetic field [39]. Following the revolution, in the same year, resonant tunnelling and negative differential conductance were also reported in graphene transistors which are composed of two graphene electrode separated by a few atomic layer–thick boron nitride barrier. The device offers the prospect of ultra-fast transit times and has potential for applications in high-frequency and logic devices [40]. A very interesting observation highlights strong reconstruction of graphene’s electronic spectrum when graphene is placed on hexagonal-boron nitride (h-BN), and it experiences a superlattice (Moiré) potential. The reconstruction of graphene’s electronic spectrum with new superlattice Dirac points emerging at sub-eV energies depends on the layer stacking angle (θ) between graphene and h-BN. The developed strain distribution with the same periodicity of the Moiré potential, is reflected by 2D band Raman feature of graphene, as it is sensitive to the misalignment between graphene and h-BN lattices [41]. The authors suggested that the Raman finger print can be used to recognise graphene superlattices with a specific misalignment angle below 2°. Bilayer graphene has also been widely used for making devices. When placed under the influence of electric field across the two layers, breaking the inversion symmetry of the lattice [42, 43], band gap opening is observed. Thus, in bilayer graphene FET, the band gap enhances the on-off ratio, making it a potential candidate for logic devices. The interaction between e-s of different layers of twisted bilayer graphene (TBG), generate van Hove singularities (vHs) in the density of states (DOS), whose energies are governed by the twisting angle, θ [44, 45]. TFG (twisted few-layer graphene) can be formed by the accidental folding of graphene flakes during the exfoliation process [25, 33] or by the transfer of graphene flakes onto other graphene flakes, or during growth of FLG by chemical vapour deposition [36]. It was found that t(1 + 1) LG and t(1 + 3) LG display resonant spectral features around 2.0 eV in comparison with Bernel-stacked 2LG and 4LG as observed from the optical contrast [25]. These features correspond to the energies of vHss in the joint density of states (JDOSs) of all optically allowed transitions in t(1 + 1) LG and t(1 + 3)LG. Thus, S and B modes are observed in the Raman spectra as when the laser energy, EL matches the energies of the vHss. The alterations in symmetry and Raman activity as well as the presence of vHs energies of JDOS in TFGs make the S and B modes observable when EL matches the corresponding VHS energies. The mismatch in periodicity between two twisted layers leads to change in symmetry and Raman activity that mostly affects shear interactions [33]. Recently, Eleil et al. showed that intra-layer and inter-layer electron-phonon (e–ph) interactions in samples of TBG can be distinguished by their Raman features [46]. They have also highlighted on probing the intra-layer process in graphene/h-BN by using Raman spectroscopy. It was found that in the intra-layer process, the e–ph scattering occurs in a graphene layer and the other layer (graphene or h-BN) imposes a periodic potential that backscatters the excited electron. On the contrary, the e–ph scattering occurs between states in the Dirac cones of adjacent graphene layers for the inter-layer process. The appearance of new phonon peaks and their intensity provides the strength of the interaction between monolayer graphene and the substrate/any periodic layer.

Electron-phonon coupling (EPC) is a fundamental interaction which influences electron mobility, thermal conductivity and many other phenomena in material physics. In atomically thin heterostructures, the interaction can include electrons in the same layer (intra-layer e–ph interaction) or in adjacent layers (inter-layer e–ph interaction). Graphene-based van der-Waal heterostructures (vdWHs) formed by vertically stacking other types of 2-d materials (e.g., transition metal dichalcogenide (TMD) with finite band gap) with graphene flakes, have attracted a significant interest [47]. In general, graphene flakes (with high mobility) are conventionally used as electrodes to achieve higher performance in vdWH-based devices because they have fewer defects compared with devices directly deposited on metal contacts [48, 49]. An atomically sharp and non-damaged interface and a modified interfacial coupling are essential to the high performance of TMD/graphene vdWHs–based devices, such as field-effect tunnelling transistors [48], photovoltaics, logic transistors, and memory devices [49, 50, 51]. In some cases, the charge transfer efficiency of monolayer graphene [52] are combined with a direct band gap of monolayer MoS2 or WS2 in a MoS2/graphene or WS2/graphene vertical heterostructure to prepare efficient photo detectors, where e s and h s are spontaneously generated and separated [53, 54, 55, 56]. The doping level and the carrier density (ne or nh) of graphene can be easily quantified by the spectral parameters of Raman spectroscopy [23]. The charge transfer between the graphene and MoS2 flakes is revealed by the G and 2D modes of graphene flakes. Apart from these high frequency modes, the S, B modes are much more sensitive to the interfacial coupling in vdWHs [57]. In some cases due to low EPC, the B modes are absent. Therefore, we suggest that the charge transfer and interface coupling between graphene and TMDs in the heterostructures can be determined by the modified signature of the graphene constituent as the spectral parameters of graphene are more sensitive to its doping level and interface coupling.

2.2 Carbon nanotube

For one-dimensional (1-d) materials, excitonic effects can be observed even at ambient temperature where the excitonic binding energy (B.E) ~ 0.3–0.5 eV is much greater than the thermal energy (kBT~26 meV) [58]. Because of the localised wavefunction of an exciton, the intensity of the optical process is boosted significantly, and thus, Raman spectroscopic feature in single-walled nanotubes (SWNTs) is controlled by excitons from photoexcited eh pairs.

The journey of SWNTs started with the discovery of multi-walled carbon nanotubes (MWNTs). MWNTs were first detected by the transmission electron microscopy (TEM) in carbon-arc soot by Iijima in 1991 [59]. These μm-long tubes having external diameter from 2 to 20 nm comprised two or more concentric shells. Almost after 2 years of the discovery of MWNTs, SWNTs with a single shell of carbon atoms were discovered [60, 61]. The typical diameter of these SWNTs is ~ 1 nm, in contrast to MWNTs. Later rigorous work supported the bulk production of ~ 1 nm diameter SWNTs [62]. The bulk production of these nanotubes paved the way to explore the-nanotubes chemical, mechanical and electrical properties by numerous experimental methods. The orientation of the six-membered carbon rings in the honeycomb lattice relative to the axis of nanotube is an interesting and essential fact about the structure of carbon-based nanotubes. Carbon nanotubes are primarily classified as achiral and chiral ones. An achiral nanotube has a mirror plane perpendicular to the tube axis and they can be classified as, armchair and zig-zag nanotubes. Considering the layer thickness, a double-walled carbon nanotube (DWNT) can be considered to be one type of MWNT for which the inter-layer interaction between the inner and outer nanotubes is generally considered.

Resonance Raman scattering (RRS) is widely used for the sample evaluation and characterisation of carbon nanotubes as it is a noncontact and non-destructive tool, which is operated in ambient condition. The RRS intensity reflects strong chirality and diameter dependence [63]. Figure 5 highlights that by tuning the excitation energies of the laser EL, we can observe resonance-enhancement associated with the Raman intensity from which one can precisely assign (n, m) values related to individual SWNTs. Thus, by combining experiment and theory, the population of specific chiral indices (n, m) in nanotube sample can be found out. Different Raman features are found to be sensitive to chiral indices (n, m) specifying the chiral vector, such as a) the radial breathing mode (RBM) all the C-atoms are vibrating in-phase in the radial direction, b) the G-band, neighbouring atoms are vibrating in opposite directions along the surface of the tube as in 2-d graphite, c) the disorder induced D-band, dispersive in nature and d) its 2nd-order-related harmonic G′-band. Among these four characteristics, the RBM is the one which is found to be more sensitive to the nanotube diameter (dt), In 2002, G D Mohan [64] explained the relationship of diameter of nanotube and its RBM mode considering oscillations of a thin hollow cylinder. With the idea obtained from experimental understanding and theoretical model an expression
$$ {\omega}_{RBM}=\frac{A}{d_t}+B $$
where ωRBM is the vibration frequency, and constants A and B differ for individual tubes and bundle tubes [65, 66]. In determination of the diameter, some authors consider [67, 68, 69] only the constant A, while, the constant B is believed to describe the additional interaction in bundles of nanotubes [66].
Fig. 5

Radial breathing modes (RBM) related to different chiral-index at three standard laser lines EL, 514, 752, and 785 nm. In the middle panel, the spectra consist of two RBMs of each which can only be resolved by changing the excitation energy. Reproduced with the permission from Phys. Rev. B 72, 205,438 (2005)

In a standard Raman spectrum of SWNT, the low frequency regions (100–400 cm1) display the RBM feature, for the resonance window of EL. The graphite like G band between 1500 and 1600 cm1, is associated with the highest-frequency optical phonon modes at the Γ-point in the Brillouin zone. In the case of nanotubes, the band splits into G+ and Gpeaks. Figure 6 describes the RBM mode and G band feature of three isolated semiconducting and metallic tubes in resonance with laser energy. The downshifted G (TO) band in semiconducting tubes [70] can be reasonably explained by simple curvature effect. Although, in metallic tubes, the large downshift and the linewidth of the G(LO) mode is related to the enriched EPC interaction due to electron confinement in 1-d between the LO phonon and the e-h excitations, termed as non-adiabatic Kohn anomaly [71, 72]. The D-band at 1350 cm1 is induced by the presence of amorphous carbon remaining from the synthesis or by symmetry-breaking defects in the nanotube structure. The G′-band, the overtone of the D-band (which we can also observe in highly oriented graphite) is also found at around 2600 cm1.
Fig. 6

RBM, G Band in semiconducting and metallic nanotube of different chiral index. Reproduced with the permission from Phys. Rev. B 65, 155,412 (2002)

Many Raman studies on these MWNTs were carried out but they cannot highlight characteristic Raman spectral features which are different from that of graphite. In a typical experimental observation, the splitting of the G band in MWNTs is very small in intensity and the effective Raman shift smeared out due to the diameter distribution within the individual MWNTs, compared with SWNTs and the variation between different tubes in an ensemble of MWNTs. Therefore, the G-band in MWNT exhibits a weakly asymmetric mode featuring close to the graphite frequency of 1582 cm−1 [73]. The larger inner diameter (> 2 nm) of He-arc or CVD grown MWNTs gives huge defects in CVD grown-MWNTs which makes it difficult to observe their nanoscale characteristic features (i.e. features different from graphite). After successful preparation of highly graphitised MWNTs by H-arc discharge evaporation, with very thin inner diameters of ~ 1 nm [74], observation of Raman active vibration modes in the low-frequency region becomes easier. Multiple G-band splitting effects are more clearly observed in individual MWNT than for SWNTs by compensating the environmental effect [75].

2.2.1 Recent progress and applications of carbon nanotube

An understanding of interaction associated with optical phonon modes and the charge carriers, specifically the dimensionless EPC parameter, is important to have an idea about the electron-transport mechanisms in nanotubes for device-based application. It is well studied in the literature that due to the nonadiabatic effect, in metallic tubes [76, 77, 78] the G-peak position increases both for e- as well as h-doping, whereas the linewidths of these bands illustrate decrease for both types of doping. Raman characteristics of the G and G′ bands have different doping dependences in doped semiconducting nanotubes. The e-h asymmetry in the G+ and G modes can be explained in terms of non-adiabatic effects along with the lattice-relaxation contribution. The G mode is blue-shifted compared with the G+ mode and the dependency of the EPC matrix elements on wave vector k clarifies this observation. It was also observed that the shift of the G′ band is significantly altered as compared with the G+ and Gmodes, and there is a red shift on e-doping but no shift on h-doping [79]. Again for looking into the charge transport phenomena, let us focus our attention to a gate-tunable p-n heterojunction diode fabricated by vertical stacking of direct band gap semiconducting SWNTs and single-layer MoS2 as p-type and n-type semiconductors, respectively. Using the system, one can achieve a wide range of charge transport behaviour with an applied gate bias. With the applied field, the charge transport can be modulated from insulating to rectifying with forward-to-reverse bias current ratios exceeding 104 [80]. We believe the photoresponse of the heterojunction can be mapped by their corresponding Raman features. The excitonic optical transitions characterised by Raman excitation profiles in SWNTs are still being studied by the scientific community [81]. In an effectively one-dimensional system, the physical wave function is compressed and as a result of instability in the system, some new phases of the material is observed. Theoretician predicted 1D carbon nanotube can behave as “excitonic insulator” [82, 83] but the observation of this phenomena experimentally still remains unexplored.

For low production cost and more chemical resistance compared with SWNTS, MWNTs are profitably used to make composite materials enhancing their mechanical, thermal and electrical properties [84, 85]. The stress transfer efficiencies of the MWNTs in the composite can be analysed by their second-order disordered induced Raman characteristics, G′ [85]. DWNT and TWNT (triple-walled nanotube) have become a new candidate of interest in recent years. Raman spectral characteristics of the RBMs, D and G bands for individual and bundled DWNT, TWNTs have been reported [86, 87]. Figure 7 shows that the frequency, width, and intensity variations of the triplet structure of G′ band from bundled TWNTs can be methodically analysed [88] by tuning EL, the excitation energy. The obtained result shed new light on the general understanding of the featured G′ band in FWNT (few-walled nanotube structure) systems. Here, we would like to point out another interesting study on MWNT that clarifies the innermost tubes in the MWNT systems host the Al4C3 nanoparticles and that these nanoparticles are efficient electron donors to the MWNTs. The electronic structure calculations indicate that both Al4C3-filled armchair and Al4C3-filled zigzag systems show metallic behaviours, originating from the doping of the MWNTs, are triggered by the encapsulated Al4C3 nanoparticles [89]. Recently, Kennedy et al. reported synthesis of ZnO incorporated CNTs [90] which can be used as a promising cathode material for field emission–based displays. The estimation of relative concentration of ZnO present in the CNT sample (below the detectable level) was quantified using intensity ratio of D and G band.
Fig. 7

The low frequency (a) resonant RBMs of an individual TWNT on a Si/SiO2 substrate Raman peak ~ 303 cm−1 is the signature of the substrate. Lower panel cartoon gives an idea of preparation technique and the estimated diameter of tubes for the two inner nanotubes. b The G′ band spectra of the individual TWNT shown in cartoon (a) acquired with five different excitation energies. Each Raman spectrum depicts three well-resolved G′ lines originated from the three concentric nanotubes when excited by EL values of 2.11 and 2.41 eV. The inset in (b) reflects the G′ line separations ih (open circles) and ho (closed circles), where i, h and o refer to the innermost, host, and outermost nanotube. By increasing EL, the Raman intensity of each G′ line shift towards higher frequencies, as well as an increase in the G′ peak widths, as described in the inset. Reproduced with the permission from Phys. Rev. B 91, 075402 (2015)

2.3 Fullerene

Buckminster fullerenes or ‘buckyballs’ were experimentally observed using mass spectrometry of carbon clusters by Kroto et al. in 1985 [91]. Since its discovery, tremendous efforts R&D efforts were undertaken to understand its structure and properties. Raman spectroscopy was an indispensable tool for analysis of fullerenes. Fullerenes produce prominent Raman peaks due to their high symmetry. These peaks are sensitive to doping or polymerisation which can be easily discerned in a Raman spectrum of fullerene [92]. Raman spectra of pristine and polymerised C60 and C70 fullerenes are discussed in the following sections.

2.3.1 C60

Benzigar et al. have demonstrated a synthesis route for highly crystalline mesoporous C60 of large surface area and extremely ordered form using mesoporous silica (SBA-15) as the template at high temperature. The solvent used here has played two important roles, one in the polymerisation and other in the crystallisation of C60 molecules. The specific capacitance of this material is measured and noted to be much higher than that of commercially available carbon materials and carbon nanotubes. The product material having high surface area, high stability and conducting wall is established as a striking metal-free electrode for supercapacitors and fuel cells applications. In the field of material research and energy applications, the authors believe that this ultimate product will bring a revolution.

The synthesised material was characterised using Raman spectroscopy. The Raman spectra in the 200–1800 cm−1 region of Pristine C60, mesoporous C60 synthesised using mesoporous silica prepared at 100 °C (MFC60-100), MFC60-130 and MFC60-150 are shown in Fig. 7 [93]. The characteristic of pristine C60 monomer is evident from the prominent peak that appears at 1466 cm−1. Distinct spectral changes were observed in this characteristic peak after the polymerisation which can be clearly visualised as a sharp fall in the intensity and 2 cm−1 red shift (1464 cm−1) of this vibrational mode (Fig. 8) attributed to pentagonal pinch A2g mode of C60 [94]. Additionally, appearance of two broad peaks at 1350 cm−1 (D-band) and 1590 cm−1 (G-band) assigned to E1g and B1g vibrational modes, respectively, and the complete disappearance of 495.5 cm−1 mode attributed to A1g vibrational mode is due to the polymerisation. The defect-related information in graphitic carbon materials is directly connected with the D and G vibrational modes via ID/IG ratio. The values of ID/IG ratio for all the samples were calculated and it was found that this value was 0.82 for MFC60-130. This reduction in the ID/IG ratio, therefore, leads to the confirmation of resonance of the covalent bonds which in turn converts the sp3 bonding to sp2 form. To get more details about the polymerisation, deconvolution of the Raman spectra of the samples was performed with Lorentzian function. This deconvolution analysis reveals that the pristine C60 contains only monomer characteristic feature at 1466 cm−1. On the other hand, MFC60-130 contains 1464 and 1460 cm−1 modes corresponding to dimer and linear chains, respectively, establishing C60 polymerisation and cross-linking in the wall.
Fig. 8

a Raman spectra of C60 precursor and mesoporous C60. Inset shows the magnified Raman spectra of the four samples in the region 1450–1475 cm−1. Renishaw, InVia system was utilised to collect the Raman spectra using 100× objective at room temperature using an Ar+ ion laser line of 514 nm with compatible gratings

2.3.2 C70

In another study, the authors have reported a new technique towards the fabrication of highly crystalline fullerene C70 having high order of mesoporosity by nanohard templating method using SBA-15 with the help of highly concentrated C70 fullerene precursor in solution. A simple fabrication strategy of highly crystalline fullerene C70 of highly ordered mesoporosity has been demonstrated in their study. A very high crystallinity and specific surface area of highly ordered mesoporous structured materials have been fabricated by this simple approach. It is highly beneficial for energy applications and very important to mention here that the order, nature and size of this mesoporous structure are controlled by tuning template pore diameter. The application of this novel material in the field of energy storage and conversion has also been demonstrated in this work.

To prove structural changes due to polymerisation of fullerene C70, Raman spectroscopy is in general utilised as the confirmative analytical technique by the researcher. The Raman spectra of C70 precursor, MFC70-100, MFC70-130, MFC70-150 and MFC70-200 in the range of 500–1750 cm−1 are shown in Fig. 9A [95]. The finger-print features of C70 including the main characteristic modes at 260, 456, 701, 737 and 1564 cm−1 assigned to A1′, A1′, E1″, E1″ and E2′ vibrational features, respectively, of D5h symmetry were observed in the range 200–1600 cm−1 as per previous literature [96, 97, 98, 99]. The Raman spectrum of C70 precursor is similar as compared with already available spectrum in the literature with a strong feature at 1562 cm−1 implies the monomeric form of fullerene C70. Different vibrational features of MFC70 samples were found to be shifted and broadened as compared with their original C70 precursor due to the carbonisation process. Most importantly, the single mode at 1562 cm−1 which is the characteristic feature of monomer breaks into two distinct modes appeared at 1545 and 1562 cm−1, the unique signature exhibited due to the reduced symmetry upon polymerisation of C70. It is noteworthy that a clear broadened mode appears at 1598 cm−1 after the carbonisation process attributed also to the reduced symmetry due to the polymerisation of C70. High pressure synthesis of nonporous C70 polymers also shows the same results [100]. To get more details about the intermolecular bond formation, deconvolution analysis of Raman mode was performed using Lorentzian function (Fig. 9B). This peak deconvolution method on the Raman spectrum C70 precursor clearly shows the presence of two modes at 1509 and 1562 cm−1 in the region (1495–1675 cm−1) under analysis. To gain insights about the induced changes in the Raman spectrum due to polymerisation, the broad envelop has been deconvoluted further. After this deconvolution analysis, it is found that the Raman spectrum of MFC70-150 consists of four component peaks appeared around 1510, 1545, 1562, and 1598 cm−1 as depicted in Fig. 9B.
Fig. 9

a Raman spectrum of (a) C70 precursor, (b) MFC70-100, (c) MFC70-130, (d) MFC70-150, and (e) MFC70–200. Inset depicts the magnified version of region of peak splitting. b Deconvoluted Raman spectrum of (a) C70 precursor and (b) MFC70–150. Renishaw, InVia system was utilised to collect the Raman spectra using 100× objective at room temperature using an Ar+ ion laser line of 514 nm with compatible gratings

The induced spectral changes confirm the formation of intermolecular-bonded crystalline polymerised C70 in the wall of mesoporous polymerised MFC70 materials. Similar type of intermolecular bonds was also evidenced from the deconvolution analysis for other three MFC70 materials. This study reveals that the simple strategy adopted by the authors could be further utilised for constructing of highly ordered crystalline structure of fullerenes. In addition, these nanochannels and hollow cores of this crystalline matrix can further be designed with desired functional groups for their potential applications in the fields of catalysis, sensing, electronic devices etc.

3 Emerging carbon materials and their composites

Critical need of green materials in the field of energy and environmental applications has become the central focus to the scientific community concerning the protection and conservation of the conventional energy sources, nature etc., and hence attracted the global attention. As mentioned earlier, the carbonaceous materials including graphene, CNTs, fullerenes, carbon dots and carbon nitrides are potential candidates because of their many advantages over others such as high stability, metal-free, non-toxic and cost-effective. In this search, several graphene-based nanocomposites cross-linked with graphitic-carbon nitride (g-C3N4) and other materials have been investigated and found their numerous applications in energy generation, energy conversion, energy storage (such as supercapacitors, fuel cells and batteries), catalysis (hydrogen evolution and oxygen reduction), sensor and electronics [101, 102, 103, 104, 105, 106, 107, 108, 109]. g-C3N4 is one of the promising candidates which is evolving as the next generation emergent materials having fascinating properties for numerous applications as mentioned above [101, 103, 104, 105, 107, 108, 110, 111]. Electron-rich g-C3N4-based materials have gained continuing and increasing attention due to their theoretical structural prediction due to the above-mentioned excellent properties and tremendous applications [112]. In a recent study, Khamlich et al. have illustrated a supercapacitor of advanced kind, constructed by using 3d nickel foam-graphene/zinc hydroxychlo-ride nanosheets (NiF-G/ZHCNs) composite electrode materials, having high electrochemical performance. This can help us to meet the increasing demand of the current electronic market by developing improved, green and cheaper energy storage devices [109].

Raman spectroscopy, a selection rule-dependent technique to investigate such materials is particularly sensitive to microstructure of the atoms. The detailed characteristics of graphene have already been discussed in the previous section. g-C3N4 consists of sp2 carbon and nitrogen atoms with triazine group. The lattice of graphitic crystal possesses hexagonal (dihedral) D46h prismatic point group symmetry. Vibrational analysis shows that this symmetry gives rise to vibrational features as per following irreducible representation:
$$ {\Gamma}_{\mathrm{vib}}={\mathrm{A}}_{2\mathrm{u}}+{2\mathrm{B}}_{2\mathrm{g}}+{\mathrm{E}}_{1\mathrm{u}}+{2\mathrm{E}}_{2\mathrm{g}} $$
(2)

Here, E-symmetry modes are associated with in-plane vibrations while A and B symmetry modes exhibit out-of-plane vibrations of atoms, respectively. Among these vibrational modes, only two E2g vibrations are Raman-active and appeared around 47 and 1582 cm−1, respectively. On the other hand, A2u and E1u vibrations are infra-red (IR)-active and are usually located at 868 and 1588 cm−1, respectively. The other B2g modes are not optically active.

Due to several drawbacks of pristine g-C3N4, such as rapid recombination of e-h pairs, small specific surface area and low visible light utilisation efficiency, the practical applications are hindered [113, 114]. Therefore, there is an increasing demand of facile and reliable approach to prepare the modified g-C3N4 with improved physiochemical properties and photocatalytic activities. The unique two dimensional (2-d) layered structure of g-C3N4 is suitable for hybridising with other elements. During recent time, several research groups have opted different methods to enhance the visible light photocatalytic performance of g-C3N4 by formation of surface coupling hybridisation utilising graphene, constructing of mesoporous structures, doping with metal or non-metal species and sensitising with organic dyes. Development of heterostructures exhibits a great potential because of its efficient electron–hole pair’s separation and transfer the charge carriers across the heterostructure interface to prevent the recombination and to promote the photocatalytic performance of g-C3N4 [115, 116].

3.1 Carbon nitride and its graphene composites

The Raman spectra in the 200–1750 cm−1 region of mesoporous carbon nitride (MCN)-11, MCN-11-G1, MCN-11-G2, MCN-11-G3, MCN-11-G4, bulk triazole-based C3N5 and bulk g-C3N4 are shown in Fig. 10 [90]. The peaks appear at 260, 316, 472, 715, 753, 980, 1233 and 1562 cm−1 (as shown in Fig. 10) are the distinct Raman characteristic features of g-C3N4 and attributed to the breathing modes of the triazine ring presence in the structure [117]. The additional vibration modes at 402, 650, 853 and 1276 cm−1 (as shown in the Fig. 10) attributed to the breathing modes of the triazole ring [118], appear in case of bulk triazole-based C3N5, MCN-11, MCN-11-G1, MCN-11-G2, MCN-11-G3 and MCN-11-G4 samples which imply the presence of the triazole moiety in the structure. The hybridisation of graphene with carbon nitride introduces disorder and the degree of disorderliness is directly correlated to ID/IG ratio. Here, it is pertinent to mention that the highest ID/IG ratio was observed in MCN-11-G3 among all the hybrids. These results in turn confirm that the most homogeneous hybridisation degree of graphene and carbon nitride components is possessed by this (MCN-11-G3) sample [119, 120].
Fig. 10

Raman spectra of (i) MCN-11, (ii) MCN-11-G1, (iii) MCN-11-G2, (iv) MCN-11-G3 and (v) MCN-11-G4, (vi) bulk triazole-based C3N5 and (vii) bulk g-C3N4 in the region of (a) 200–1095 cm−1 and (b) 1095–1750 cm−1, respectively. Renishaw, InVia system was utilised to collect the Raman spectra using 100× objective at room temperature using 830 nm diode laser with compatible gratings

In this work, the authors provide the first demonstration of the fabrication of triazole-based MCN and its graphene hybrids [115]. Spectroscopic studies and systematic theoretical (DFT) calculations affirm that the stabilised tetrazole-derived C3N5 structure consists of one and two triazole and triazine moieties, respectively. Contrast to bulk g-C3N4, better oxygen reduction reaction (ORR) activity along with enhanced diffusion limiting current density has been observed in bulk triazole-based C3N5. This is mainly ascribed to increased O2 adsorption in the triazole moiety on active carbons neighbouring N–N bond. This is also attributed to electron contribution from triazole moiety of sp2 hybridised N to the carbon nitride matrix pi–pi conjugation. Enhancement in decline of over potential is further attained by forming of hybrids between 3D triazole-based MCN structure and homogeneous graphene with strong electronic coupling.

3.2 NiF-G/ZHCN composite

An easy hydrothermal synthesis procedure has been adopted to prepare NiF-G/ZHCN composite electrode materials by depositing ZHCNs on NiF-G [109]. Raman spectroscopy has been employed to characterise this composite materials. The Raman spectrum of NiF-G/ZHCNs shows two clear signatures of mono to few layers graphene at 1583 and 2718 cm−1 assigned to the G and 2D bands, respectively having ratio I2D/IG is 0.69. The smaller D band intensity at around 1353 cm−1 indicates the high purity of the graphene material. The two comparatively less intense vibrational features 482 and 721 cm−1 characterise the Zn5(OH)8Cl2·H2O–based nanomaterial. Two distinct modes around 284 and 347 cm−1 attribute Zn–Cl and Zn–O stretching vibrations clearly indicate the bonding of Zn with chlorine and oxygen atoms, respectively in ZHCNs. The existence of several less intense Raman features around 2981 and 3012 cm−1 and 592, 926, 1077, 1128 and 1456 cm−1 attribute to the O–H stretching modes and multiple-phonon resonant Raman scattering processes, respectively in ZHCNs.

We strongly believe that there are scopes for designing of a novel group of materials with enhanced properties for electrocatalysis, rechargeable cells, solar cells, and supercapacitors utilising these unique hybrid materials.

4 Emergent non-carbon material

4.1 Perovskites

Perovskite is a family of compounds with general composition formula ABY3, where A is a large cation, B is a medium-sized cation and Y is an anion. A ion is twelvefold coordinated with Y anion and B ion is octahedrally coordinated by Y ions. The ideal perovskite possesses cubic crystal structure with a Pm\( \overline{3} \)m space group. However, most of the perovskites are distorted due to the BX6 octahedral distortions, B-cation displacements and BX6 octahedra tilting and exhibits different crystal structures (mostly orthorhombic and tetragonal) and space groups depending upon the distortion [121]. Perovskites exhibit entirely different properties depending upon the chemical composition, and therefore utilised in extensive applications. For example, oxide perovskites (ABO3) are well known for their potential applications in ferroelectrics, dielectrics, piezoelectric, photo catalysis, and super conductors. Halide perovskites (ABX3) demonstrate their vital importance in solar cells. Moreover, different ABY3-related structures like layered perovskite, double or triple perovskite influence the physical properties. In addition, parameters such as A, B and Y site doping, oxygen deficiencies, ordering in A or B site, temperature and pressure also affect their physical properties.

Hence, sensitive and non-destructive spectroscopic techniques are required to understand and probe the structural changes in perovskites. Vibrational and X-ray diffraction (XRD) techniques provide important information about the crystalline nature. Among them, Raman spectroscopic technique is a non-destructive and sample preparation free efficient tool which provides information regarding static and dynamic local disorder of crystal structure as well as the occurrence of structural transformation caused by external parameters. The subsequent sections provide details of how Raman spectroscopy can be adopted to study different kinds of perovskites.

4.1.1 Raman spectral analysis of oxide perovskites

In ABO3 perovskites, Raman peaks originate from ordered as well as disordered matrix. Group theory analysis allows separating the ordered regions from the disordered matrix. In general, the ideal simple cubic perovskite structure ABO3 with Pm\( \overline{3} \)m space group all the vibrational modes are Raman inactive. Whereas it is observed that in the cubic perovskite with Fm\( \overline{3} \)m space group, four first-order modes are Raman-active, i.e. A1g + Eg + 2F2g [122]. Tetragonal structure with P4/mbm space group shows four first-order Raman-active modes such as A1g + B1g + B2g + Eg [123]. Orthorhombic structure Pbnm and Pnma symmetry perovskites also have four first-order Raman-active modes such as Ag + B1g + B2g + B3g [124]. Similarly, rhombohedral structure with R\( \overline{3} \)c symmetry space group has five Raman active modes such as A1g + 4Eg [125]. Raman active frequencies per irreducible representations are dependent upon the number of structural formula units in the unit cell.

Table 1 represents the Raman active vibrational species and their corresponding vibrational frequencies of different oxide perovskites [123, 124, 126, 127, 128, 129]. Monitoring and probing the order and disorder nature of ABO3 perovskites are crucial as physical and chemical properties of ABO3 perovskites are highly sensitive to ordering in the B-site. Raman spectroscopy has a potential to probe the ordering in the B-site of perovskite structured relaxor ferroelectric oxides. In these cases, XRD technique fails to probe the ordering nature in B-site. The ordering nature in B-site can be caused due to the chemical disordering (substitution of two unequal B cations), arbitrary fluctuations of B cations and external parameters such as temperature and pressure.
Table 1

Raman frequency of different oxide orthorhombic ABO3 perovskites

Species

TbFeO3 [102]

DyFeO3 [102]

HoFeO3 [102]

TmFeO3 [102]

ErFeO3 [103]

YAlO3 [104]

GdAlO3 [99]

EuAlO3 [99]

SmAlO3 [99]

YMnO3 [101]

LaMnO3 [101]

CaMnO3 [100]

NdMnO3 [101]

Ag

109

110

109

110

112

 

95

89

78

    

140

140

139

140

140

 

146

  

151

140

  

157

160

159

160

163

150

 

160

   

160

 
     

197

232

 

200

188

198

184

205

273

270

270

273

273

278

313

301

286

288

257,284

243,278

245

329

332

340

346

345

345

368

352

345

323

 

322

335

406

409

425

434

424,434

412

   

396

   

480

489

495

506

505

    

497

493

487

495

521

    

553

536

527

522

518

   

641

649

660

649

645

        

B1g

139

138

 

112

139

 

111

 

110

151

109

  
   

163

 

157

160

 

138

 

170

  
     

219

222

190

170

220

   
     

240

   

317

308

258

314

329

339

340

322

346

270,283

   

341

  

453

414

412

  

429

416

414

409

408

    

479

    

470

   

481

481

465

482

 

494

495

505

506

552

512

  

537

  

500

         

616

611

 

601

B2g

 

89

           
  

210

  

197

146

147

143

178

184

179

 
 

260

   

270

       
   

364

  

398

  

336

   

418

425

430

429

434,481

470

475

      
     

540

523

513

508

    

B3g

159

  

139

 

150

174

164

136

    
  

205

   

217

203

196

205

   

249

260

 

263

264

     

284

  

354

  

364

365

 

323

   

320

320

 

426

424

425,475

433,681

434

403

400

392

392

383

   
     

555

551

    

564

 
     

690

       
     

760

       
In disordered ABB′O3 complex perovskites, Raman spectral lines broaden in homogeneously due to the arbitrary fluctuations of B and B′ ions, which causes local environment spatial fluctuations. Hence, disordered nature can be probed by the Raman spectral linewidths [130]. Setter and Laulicht [129] probed the B-site disorder nature of ABB′O3 complex perovskites {Pb (Sc0.5Ta0.5)O3} via Raman spectroscopy. They identified that the Raman peaks observed at 60 and 365 cm−1 represent the chemical disordering and controlled induced chemical ordering of Pb (Sc0.5Ta0.5)O3 respectively. Broad Raman bands observed at 200–300 cm−1 and 500–600 cm−1 regions illustrate the arbitrary nature of B and B′ ions positions and a broad band appearing at 800–900 cm−1 reveals the ferro and para-electric nature of the system. Jianga et al. [131] investigated the ordering of B-site with respect to different substitutions at A-site and temperature by Raman spectroscopy. They probed the B-site ordering by monitoring A1g mode at higher frequencies since the frequency and the line shape represents the nature of B-site cations via B–O bond lengths. The narrower line width of A1g mode represents the higher B-site chemical order, which was observed at high temperature and optimum dopant at A site. Zhenga et al. [132] and Pokorny et al. [133] also monitored the A1g mode Raman spectral line to probe the B-site ordering for different oxide perovskites. Figure 11 a represents Raman spectra of BaTiO3 at different temperatures.
Fig. 11

a Raman spectra for BaTiO3 at different temperature (Reproduced with the permission from J. Appl. Phy. 109, 114,110 (2011)), (b) Raman spectra of Ba2MnWO6 recorded using different laser source (reproduced with the permission from J. Phys. Chem. B 110, 777, 2006) and (c) Raman spectra of organic-inorganic hybrid MAPb3-xClx perovskites single crystals (reproduced with the permission from Phys. Chem. Chem. Phys. 12, 18112, 2016)

McCarty et al. [134] probed the superconductivity nature of (BaK)BiO3 via Raman spectral analysis. Ba0.6K0.4BiO3 exhibits superconductive nature at 4 K, which shows the distinctive Fano line shape at 348 cm−1 due to the coupling between a high frequency optical phonon and a broad electronic continuum. For non-superconducting (BaK)BiO3, the high frequency optical phonon is uncoupled to the electronic states. Sarbajit et al. [135] observed the Fano asymmetry line shape in Raman spectra of SrTiO3 and Ca0.3Sr0.7TiO3 perovskite nanocubes due to the interference of an optical phonon with rapid polarisation fluctuations in the nanopolar domains. Kreisel et al. [136] has demonstrated that Raman spectroscopy is an effective tool to probe pressure-dependent characteristics in relaxor materials. They reported high-pressure Raman measurements of Na0.5Bi0.5TiO3 and observed occurrence of phase transition from rhombohedral to orthorhombic crystal structure caused due to change in the tilt system and the cation displacement. Raman spectral features reveal that the transition does not occur in a single step, but goes through an intermediate phase. The Raman frequency evolution of characteristic bands shows the phase transition path.

Zaghrioui et al. [137] reveal that symmetry breaking is also an important factor for metal to insulator transition in NdNiO3 via electron diffraction and Raman spectroscopic techniques. They observed that Raman peaks observed at 63, 300, 320, 400, 460 and 620 cm−1 might be markers to probe metal to insulator transition temperature. Chen et al. revealed that Ba (Mg1/3Ta2/3)O3, Ba (Mg1/3Nb2/3)O3 and Ba (Co1/3Nb2/3)O3 dielectric constant value is strongly associated with the Raman shift of A1g octahedral oxygen stretching modes and the linewidth of A1g stretch mode is related to the Q × f value [138].

4.1.2 Raman spectral analysis of double perovskite oxides

Double perovskite oxides of the type A2BB′O6 (where A is a cation, B and B′ are two transition-metal elements) attract research interest due to vastness of chemical compositional (A, B and B′ site) and promising technological applications. Depends upon the A and B site substitution, the double perovskite oxides materials have been utilised as magnetic materials, piezoelectric materials, dielectric resonators and so on. The A2BB′O6 double perovskite oxide structure has a three-dimensional network of alternating BO6 and B′O6 octahedra and larger size A-cations occupying the 12-coordinated interstitial spaces between the octahedra. The ideal double perovskite oxide has cubic structure with Fm-3m space group. However, due to the dissimilar A and B substitution, distortion in octahedral network, BO6 and B′O6 rotation distorted the ideal cubic structure even at room temperature. Hence, monitoring the B sites ordering, substitution effects, oxygen vacancy and phase transition by utilising Raman spectroscopy is most needed [139]. The site symmetry group analysis reveals that Fm-3m space group exhibits three Raman active symmetry species such as A1g, 2F2g, and Eg. In general, the A1g and F2g modes are strong Raman active modes and the Eg mode is a weak Raman active mode. The A1g and Eg modes correspond to the BO6 octahedra symmetric stretching and twofold degenerate BO6 octahedra symmetric stretching mode. F2g modes are threefold degenerate, which correspond to the O–B–O octahedral bending and translation of the A cation.

Ezzahi et al. [140] investigated the possible phase transition of BaSrNiWO6, BaSrCoWO6 and BaSrMgWO6 with respect to temperature using XRD and Raman spectroscopy techniques. The XRD patterns divulge that the double perovskites belong to Fm-3m space group. Raman spectra indicate that the A cation (Ba2+/Sr2+) translational (F2g) and WO6 octahedra rotational modes appeared under 200 cm−1. O–W–O bending (F2g) vibrational modes appear in the range of 200–500 cm−1. W–O stretching vibrational modes (A1g) appears over 500 cm−1. Temperature-dependent studies indicate that all the vibrational modes show a monotonous decrease change in wavenumbers with increase in temperature due to the temperature-induced unit cell expansion. The monotonicity indicating that no phase transition occurred in the BaSrNiWO6, BaSrCoWO6 and BaSrMgWO6 perovskites up to the highest temperature [139].

Dias et al. [141] reported the Raman features of Ba2InTaO6 and Sr2InTaO6 perovskites. They observed that Ba-based perovskites fall in the tetragonal (P4/mnc) structure with D64h space group, which has four Raman active species with fourteen Raman active modes such as 3A1g, 3B1g, 2B2g and 6Eg. The Sr-based perovskites belong to the monoclinic (P21/n) structure with C52h space group, which has two Raman active species with twenty four Raman-active phonon modes such as 12Ag and 12Bg. Using Raman spectroscopy they proved no phase transition occurred for the Ba2InTaO6 and Sr2InTaO6 perovskites up to 77 K and revealed the fourteen and 24 Raman peaks at room temperature by Lorentzian line fitting. Manoun et al. probed the phase transition in Ba2 − xSrxZnWO6 double oxide perovskites with respect to increase in Sr concentration and temperature with the aid of XRD and Raman. The Ba2 − xSrxZnWO6 perovskite shows two phase transition with increase in Sr concentration (Cubic to tetragonal and tetragonal to monoclinic structure) and they reported that monitoring the trends in Raman vibrational shift with respect to Sr concentration is an effective way to probe the phase transition. Moreover full-width half maximum (FWHM) of Raman peak at 135 cm−1 with Raman shift reveals the phase transition caused by the temperature [142].

Fujioka et al. revealed the temperature and wavelength dependencies of Ba2MnWO6 and Sr2MnWO6 double perovskites using Raman spectroscopy, which disclosed an effective way to monitor the B site ordering with respect to temperature. This may be applicable for predicting B site ordering with respect to chemical composition. They used the two F2g modes to probe the ordering in B site. They found that the line widths of F2g modes were very narrow and almost constant against temperature change, which indicates that no evidence for compositional disorder at the B-cation site and proved that the F2g modes can be utilised as a marker to monitor B site ordering [143]. Raman spectra of Ba2MnWO6 obtained at different laser source were shown in Fig. 11b. Silva et al. showed that vibrational spectroscopy is a more efficient tool to probe the crystal structure of Ba3In2UO9 and Ba3In2WO9 double perovskites compare with XRD [144]. Iliev et al. also probed the strong spin-phonon coupling in La2NiMnO6 with aid of Raman spectroscopy. They observed a significant softening of the phonon mode (A1g), corresponds to the Ni/Mn–O6 octahedra stretching vibrations resulting from the spin-phonon coupling [145]. Filho et al. also probed the spin-phonon coupling in Y2NiMnO6 double perovskite by Raman spectroscopy. They observed oxygen octahedral symmetric stretching at 650 cm−1 as a most intense band, which exhibits an anomalous softening below the ferromagnetic transition caused by phonon renormalisation induced by the spin-phonon coupling [146], which spin-phonon coupling might be probed by monitoring the Ni/Mn-O6 stretching vibrational mode as a marker.

4.1.3 Raman spectral analysis of halide perovskites (ABX3)

Halide perovskites have a common chemical formula ABX3 where X site is occupied by halogens such as I, Br and Cl, B site is occupied by small size cations (compare to A site) like Pb and Sn and A site is occupied by larger size cations. Generally, in three-dimensional ABX3 perovskites, the A, B and X atoms, are located at the corner, body-centre and face-centre of the pseudocubic unit cell, respectively. In the ideal cubic structure, cation B has six nearest anions, which form corner-linked BX6 octahedra and cation A has twelve nearest anions. The ABX3 perovskites stability, crystal distortion, symmetry and formability are defined by the tolerance factor (t). For an ideal cubic ABX3 perovskites, tolerance factor should be close to 1 and the deviation from the value represents the crystal distortion and lower symmetry of the system. In general, if t has a value between 0.89 and 1, the halide perovskites may exist in cubic structure and the lesser value of t leads to tetragonal and orthorhombic structure. The t value higher than 1 destabilises the 3D perovskite network, which leads to two-dimensional or layered perovskites [147].

Organic-inorganic hybrid halide perovskites have attracted current research interest due to their promising potential applications as high-performance photovoltaics and optoelectronic materials. Methylammonium lead trihalide perovskite (CH3NH3PbX3 or MAPbX3, where X = Br, Cl, I), mixed halides (CH3NH3PbX′(3–x)X″x, where X′ and X″ are two different halogens) and mixed A site cations (A′A″ PbI3 where A′ and A″ are two different-sized cations) have emerged as the archetypical materials due to their constructive intrinsic properties such as direct bandgap with high molar extinction coefficient, higher power conversion efficiency, low trap densities, longer diffusion lengths and band gap tuning in the visible range [148, 149]. Understanding the structural dynamics within the perovskite structure is most needed, which plays critical role in assist charge separation, diffusion length and band gap tuning. In MAPbX3 perovskites, structural dynamics are caused by the MA cations orientational, conformational and rotational motions, which are responsible for the phase transitions, lower the exciton binding and impact on the separation and transportation of electrons and holes. Moreover, even though the MA cations do not directly contribute to the valence and conduction band structure, their orientation can distort the Pb-X octahedral framework, which affects thermal stability and electronic properties of the perovskite. To probe the octahedral distortion caused by the cation substitution in A and X sites, structural dynamics of MA cations and degradation mechanism of MAPbX3 perovskites, Raman spectroscopy is widely used owing to its versatility, powerful and non-contact nature to probe structural and compositional variations in MAPbX3 perovskites.

Quarti et al. reported low-frequency resonance Raman feature of MAPbI3 perovskite and assigned the vibrational modes utilising density functional theory (DFT) calculations. Understanding the lower vibrational modes of perovskites is important as it provides deep insight to understand the Pb-X framework as well as the local environment of MA cations. They observed two broad peaks at 62 and 94 cm−1 correspond to Pb–I inorganic cage bending and stretching vibrational modes respectively, which are identified as inorganic cage diagnostic modes. MA cations vibrational mode shows two Raman peaks at 119 and 154 cm−1. MA cations torsional mode observed as a broad and unresolved band at 200–340 cm−1 act as a marker to probe the orientational order of the organic cations because interactions between the MA cations and the inorganic counterpart affect the MA torsional mode [150].

Perez-Osorio et al. assigned all the vibrational modes of MAPbI3 perovskites by utilising first principles calculations. They assigned vibrational modes observed below 100 cm−1 to the Pb-I cage vibrations. MA cations librational, translational vibrational modes appeared in the region 60–175 cm−1 and MA torsional modes appeared at 402 cm−1. CH3NH3 rocking vibrational modes, C–N stretching, CH3 bending, NH3 bending, C–H stretching and N–H stretching vibrational modes are predicted in the region of 900, 1026, 1366, 1450, 2950 and 3050 cm−1 respectively [151]. Niemann et al. investigated the Raman and infrared spectra of hybrid organic−inorganic MAPbX3 (X = I, I2Br, Br, Br2Cl, BrCl2 and Cl) pure and mixed-halide perovskites. Blue shift was observed in most of the vibrational shift towards low atomic mass halides [152]. Xie et al. probed the MA cations interaction with inorganic halides in MAPbI3 and MAPbBr3–xClx single crystal perovskites via Raman spectroscopy and validated the results with CASTEP calculations. The restricted rotation vibrational mode of MA cations and N–H stretching vibrational mode of MA cations are taken as a marker to probe the MA cations and halogen interactions, because the restricted rotation vibrational mode generally appeared at 275 and 325 cm−1 in MAPbI3 and MAPbBr3 respectively which did not appear in MAI and MABr powder. The NH3 stretching vibrational mode of MA cations is splitted in MAPbBr perovskites, which is not observed in MABr powder. Doping of low level Cl concentration (x = 0.25) substantially diminishes the intensity of the MA cations restricted rotation mode and the vibrational mode is red-shifted (appeared at 325 cm−1) in MAPbBr2.5Cl0.5 single crystal. Likewise, blue shift was observed in the C–N stretching and NH3+ twisting and no significant changes were observed in CH3-related vibrations, which reveal that halides play a vital role in microenvironment of the PbX3 framework and the interactions of the organic cation (MA) with the PbX3 framework are fulfilled mainly via the N+–H–X hydrogen bonding interactions [153]. Raman spectra of MAPbBr3-xClx single crystal perovskites were shown in Fig. 11c, which illustrates the influence of halogen doping in MAPbBr3 vibrational frequencies.

Pistor et al. probed the degradation mechanism of MAPbI3 perovskites via Raman spectroscopy and proved that chemometric evaluation of Raman spectrum reveals not only the perovskite sample degradation, but also quantify and monitor it in real-time degradation. They used change in MA torsional mode (appeared at 175–450 cm−1), Pb-I cage vibrations and MA librational modes (appeared in the region 75–150 cm−1) with respect to heat and laser exposure as a marker to probe the degradation mechanism [154]. Ledinsky et al. suggested that Raman mapping is a powerful, fast and non-destructive tool to probe local in homogeneities of the halide concentrations in an organic-inorganic halide perovskite film as well as provide insight in the degradation of MAPbI3 perovskite film. They observed two Raman broad peaks at 52 and 110 cm−1 for freshly prepared non-degraded MAPbI3 perovskite film. When the perovskite film was exposed in ambient atmosphere two additional peaks were observed at 94 and 220 cm−1. To gain the deeper understanding of degradation mechanisms, Raman characteristic of the perovskite film were performed in a vacuum. Even though the samples were kept in a vacuum, the degraded films exhibit Raman signature, which closely match with the PbI. The Raman observation reveals that the MPbI3 perovskite films degrade without the water vapour, temperature and high intense exposure of the laser beam that also degrades the perovskites. In MAPbI3 − xBrx perovskite films, three Raman bands appeared at 139 ± 6, 151 ± 2 and 167 ± 1 cm−1 [155]. La-o-vorakiat et al. probed the phase transition from tetragonal to orthorhombic structural near-phase transition temperature near 160 K using time-resolved terahertz spectroscopy. They observed that the phonon modes evolved from two to four peaks depending upon the cooling rate and predicted the discontinuity in the Lorentz fitting parameters at the transition temperature, which defines tetragonal-to-orthorhombic transition [156].

Damle et al. studied the structural evaluation with respect to the incorporation of cesium (Cs) into the MAPbI3 hybrid perovskite structure as well as the change in optical properties with respect to the structural changes [120, 157]. They synthesised pure MAPbI3 and CsPbI3 as well as mixed A cations perovskites such as MA1 − xCsxPbI3 where x = 0.05, 0.24, 0.33, 0.59, 0.60 and 0.80. Formation of CsPbI3 was confirmed by the Raman peaks observed at 53 and 107 cm−1 corresponding to the Pb-I cage, which are not observed in CsI powder. For MAPbI3, the vibrational modes are observed at 64 and 107 cm−1. The Cs incorporated MAPbI3 (x = 0.04) makes the MAPbI3 structure rigid due to the Cs ionic size, which is evidenced by the red shift from 64 to 54 cm−1. Lower ionic size of Cs caused shrinking in unit cell; hence, Raman bands corresponding to the MA liberation and torsional modes are sharpened. Low-frequency Raman spectra of pure and cation mixed MAPbI3 perovskites reveal that Cs suppresses the anharmonic motion of the MA cations and local polar thermal phonon fluctuation, which leads to the appearance of new peaks, sharpening in peaks [156].

5 Conclusions

Summary of the unique features of 2-d carbon materials, composites and perovskites using Raman spectroscopy has been highlighted in Fig. 12. The quantum of information which can be obtained using this technique is indescribable. Raman spectroscopy has been the workhorse in characterising carbon materials.
Fig. 12

Schematic of the structures of different 2-d materials highlighted in the review and the features of Raman spectroscopy making it an indispensible characterisation tool for understanding these materials

In this review, we have provided the usefulness of Raman spectroscopy towards understanding the structures of various exotic carbon allotropes such as graphene, carbon nanotubes, fullerenes, carbon nitrides and their composites with graphene. We have collated data with respect to Raman spectroscopic studies of the mentioned carbon materials and have shown relevant examples to effectively analyse the Raman spectra of the materials. The recent trend in research and industry highlights layered carbon-based structures as the most versatile materials used in the modern field of ultrafast electronics, renewable energy as well as in purification and therapeutic purposes. Novel Raman spectroscopic techniques along with mathematical tools are making them possible to take the analysis to the next level. It is a sensitive and a specific technique for structural analysis by understanding electronic band structure of these low dimension “layer molecular crystals”. Raman spectral features such as band width, band shape and shift in Raman frequencies of different types of perovskites provide structural-related properties of a material. As an example in the THz range, phonon modes of perovskites are important because these phonons contribute to the photoconductivity in the same frequency range as the free carriers. Thus, extraction of vibrational mode and their evolution with temperature will help to understand the generation, transport and recombination of photo-generated carriers viable for the solar cell application. In addition, Raman spectroscopy acts as a standard tool to probe various applications and will continue to be one of the most important tools for the analysis of carbon materials.

References

  1. 1.
    A. Jorio, R. Saito, G. Dresselhaus, M.S. Dresselhaus, Raman spectroscopy in graphene related systems (John Wiley & Sons, 2010)Google Scholar
  2. 2.
    M. Cao, C. Han, X. Wang, M. Zhang, Y. Zhang, J. Shu, H. Yang, X. Fang, J. Yuan, J. Mater. Chem. C 6, 4586–4602 (2018)CrossRefGoogle Scholar
  3. 3.
    J.L. Blackburn, A.J. Ferguson, C. Cho, J.C. Grunlan, Adv. Mater. 30, 1704386 (2018)CrossRefGoogle Scholar
  4. 4.
    T. Mori, H. Tanaka, A. Dalui, N. Mitoma, K. Suzuki, M. Matsumoto, N. Aggarwal, A. Patnaik, S. Acharya, L.K. Shrestha, H. Sakamoto, K. Itami, K. Ariga Angew, Carbon nanosheets by morphology-retained carbonization of two-dimensional assembled anisotropic carbon nanorings. Chem. Int. Ed. 57, 9679–9683 (2018)CrossRefGoogle Scholar
  5. 5.
    C.N.R. Rao, K. Pramoda, Borocarbonitrides, BxCyNz, 2D nanocomposites with novel properties. Bull. Chem. Soc. Jpn. 92, 441–468 (2019)CrossRefGoogle Scholar
  6. 6.
    W.-J. Yin, B. Weng, J. Ge, Q. Sun, Z. Li, Y. Yan, Energy Environ. Sci. 12(442–462) (2019)Google Scholar
  7. 7.
    F.-C. Chen, Adv. Optical Mater 7, 1800662–1800686 (2019)CrossRefGoogle Scholar
  8. 8.
    R.K. Ulaganathan, Y.-H. Chang, D.-Y. Wang, S.-S. Li, Bull. Chem. Soc. Jpn. 91, 761–771 (2018)CrossRefGoogle Scholar
  9. 9.
    M.S. Dresselhaus, A. Jorio, M. Hofmann, G. Dresselhaus, R. Saito, Perspectives on carbon nanotubes and graphene raman spectroscopy. Nano Lett. 10(3), 751–758 (2010)CrossRefGoogle Scholar
  10. 10.
    A.C. Ferrari, Raman spectroscopy of graphene and graphite: Disorder, electron–phonon coupling, doping and nonadiabatic effects. Solid State Commun. 143, 47–57 (2007)CrossRefGoogle Scholar
  11. 11.
    S. Sil, R. Gautam, S. Umapathy, edited by V.P. Gupta (Elsevier) pp 117–146 (2018)Google Scholar
  12. 12.
    S. Sil, N. Kuhar, S. Acharya, S. Umapathy, is chemically synthesized graphene ‘really’ a unique substrate for SERS and fluorescence quenching? Sci. Rep. 3, 3336 (2013)CrossRefGoogle Scholar
  13. 13.
    M.S. Dresselhaus, A. Jorio, R. Saito, Characterizing graphene, graphite, and carbon nanotubes by Raman spectroscopy. Annu. Rev. Condens. Matter Phys. 1, 89–108 (2010)CrossRefGoogle Scholar
  14. 14.
    K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, A.A. Firsov, Electric field effect in atomically thin carbon films. Science 306, 666–669 (2004)CrossRefGoogle Scholar
  15. 15.
    K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, M.I. Katsnelson, I.V. Grigorieva, S.V. Dubonos, A.A. Firsov, Two-dimensional gas of massless Dirac fermions in graphene. Nature 438, 197–200 (2005)CrossRefGoogle Scholar
  16. 16.
    A.K. Geim, K.S. Novoselov, The rise of graphene. Nat. Mater. 6, 183–191 (2007)CrossRefGoogle Scholar
  17. 17.
    F. Guinea, A.H. Castro, N. Neto, M.R. Peres, Phys. Rev. B 73, 245426 (2006)CrossRefGoogle Scholar
  18. 18.
    M. Koshino, T. Ando, Electronic structures and optical absorption of multilayer graphenes. Solid State Commun. 149, 1123–1127 (2009)CrossRefGoogle Scholar
  19. 19.
    S. Reich, C. Thomsen, Phil. Trans. R. Soc. London A362, 2271 (2004)CrossRefGoogle Scholar
  20. 20.
    A.C. Ferrari, J.C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri, F. Mauri, S. Piscanec, D. Jiang, K.S. Novoselov, S. Roth, A.K. Geim, Raman spectrum of graphene and graphene layers. Phys. Rev. Lett. 97, 187401 (2006)CrossRefGoogle Scholar
  21. 21.
    D. Graf, F. Molitor, K. Ensslin, C. Stampfer, A. Jungen, C. Hierold, L. Wirtz, Nano Lett. 7, 238 (2007)CrossRefGoogle Scholar
  22. 22.
    Z. Ni, Y. Wang, T. Yu, Z.X. Shen, Raman spectroscopy and imaging of graphene. Nano Res. 1, 273–291 (2008)CrossRefGoogle Scholar
  23. 23.
    A. Das, S. Pisana, B. Chakraborty, S. Piscanec, S.K. Saha, U.V. Waghmare, K.S. Novoselov, H.R. Krishnamurthy, A.K. Geim, A.C. Ferrari, A.K. Sood, Nature Nanotech 3, 210 (2008)CrossRefGoogle Scholar
  24. 24.
    P.H. Tan, W.P. Han, W.J. Zhao, Z.H. Wu, K. Chang, H. Wang, Y.F. Wang, N. Bonini, N. Marzari, N. Pugno, G. Savini, A. Lombardo, A.C. Ferrari, The shear mode of multilayer graphene. Nat. Mater. 11, 294–300 (2012)CrossRefGoogle Scholar
  25. 25.
    J.-B. Wu, X. Zhang, M. Ijas, W.-P. Han, X.-F. Qiao, X.-L. Li, D.-S. Jiang, A.C. Ferrari, P.-H. Tan, Nat. Commun. 5, 5309 (2014)CrossRefGoogle Scholar
  26. 26.
    D.M. Basko, Phys. Rev. B 76, 081405(R) (2007)CrossRefGoogle Scholar
  27. 27.
    D.M. Basko, Theory of resonant multiphonon Raman scattering in graphene. Phys. Rev. B 78, 125418 (2008)CrossRefGoogle Scholar
  28. 28.
    L.M. Malard, M.H.D. Guimarães, D.L. Mafra, M.S.C. Mazzoni, A. Jorio, Group-theory analysis of electrons and phonons in N-layer graphene systems. Phys. Rev. B 79, 125426 (2009)CrossRefGoogle Scholar
  29. 29.
    L.M. Malard, M.A. Pimenta, G. Dresselhaus, M.S. Dresselhaus, Raman spectroscopy in graphene. Phys. Rep. 473, 51–87 (2009)CrossRefGoogle Scholar
  30. 30.
    Y. Hao, Y. Wang, L. Wang, Z. Ni, Z. Wang, R. Wang, C.K. Koo, Z. Shen, J.T.L. Thong, Probing layer number and stacking order of few-layer graphene by Raman spectroscopy. Small 6(2), 195–200 (2010)CrossRefGoogle Scholar
  31. 31.
    C.H. Lui, Z. Li, Z. Chen, P.V. Klimov, L.E. Brus, T.F. Heinz, Imaging stacking order in few-layer graphene. Nano Lett. 11, 164–169 (2011)CrossRefGoogle Scholar
  32. 32.
    S.K. Saha, U.V. Waghmare, H.R. Krishnamurthy, A.K. Sood, Phonons in few-layer graphene and interplanar interaction: a first-principles study. Phys. Rev. B 78, 165421 (2008)CrossRefGoogle Scholar
  33. 33.
    J.-B. Wu, Z.-X. Hu, X. Zhang, W.-P. Han, Y. Lu, W. Shi, X.-F. Qiao, M. Ijias, S. Milana, W. Ji, ACS Nano 9, 7440–7449 (2015)CrossRefGoogle Scholar
  34. 34.
    X. Luo, X. Lu, C. Cong, T. Yu, Q. Xiong, S.Y. Quek, Stacking sequence determines Raman intensities of observed interlayer shear modes in 2D layered materials – a general bond polarizability model. Sci. Rep. 5, 14565 (2015)CrossRefGoogle Scholar
  35. 35.
    L. Liang, A.A. Puretzky, B.G. Sumpter, V. Meunier, Interlayer bond polarizability model for stacking-dependent low-frequency Raman scattering in layered materials. Nanoscale 9, 15340–15355 (2017)CrossRefGoogle Scholar
  36. 36.
    M-L. Lin, T. Chen, W. Lu, Q-H. Tan, P. Zhao, H.-T. Wang, Y. Xu. P.-H. Tana. J. Raman Spectrosc., 49, 46–53 (2018)Google Scholar
  37. 37.
    C.H. Lui, L.M. Malard, S.H. Kim, G. Lantz, F.E. Laverge, R. Saito, T.F. Heinz, Nano Lett. 12, 5539–5544 (2012)CrossRefGoogle Scholar
  38. 38.
    M.-L. Lin, F.-R. Ran, X.-F. Qiao, J.-B. Wu, W. Shi, Z.-H. Zhang, X.-Z. Xu, K.-H. Liu, H. Li, P.-H. Tan, Ultralow-frequency Raman system down to 10 cm−1with longpass edge filters and its application to the interface coupling in t(2+2)LGs. Rev. Sci. Instrum. 87, 053122 (2016)CrossRefGoogle Scholar
  39. 39.
    Y. Kawano, Nanotechnology 24(21), 214004 (2013)CrossRefGoogle Scholar
  40. 40.
    L. Britnel, R.V. Gorbachev, A.K. Geim, L.A. Ponomarenko, A. Mishchenko, M.T. Greenaway, T.M. Fromhold, K.S. Novoselov, L. Eaves, Nature 4, 1794 (2013)Google Scholar
  41. 41.
    A. Eckmann, J. Park, H. Yang, D. Elias, A.S. Mayorov, G. Yu, R. Jalil, K.S. Novoselov, R.V. Gorbachev, M. Lazzeri, A.K. Geim, C. Casiragh, Raman fingerprint of aligned graphene/h-BN superlattices. Nano Lett. 13, 5242–5246 (2013)CrossRefGoogle Scholar
  42. 42.
    K.F. Mak, C.H. Lui, J. Shan, T.F. Heinz, Phys. Rev. Lett. 102, 256405 (2009)CrossRefGoogle Scholar
  43. 43.
    Y. Zhang, T.T. Tang, C. Girit, Z. Hao, M.C. Martin, A. Zettl, M.F. Crommie, Y. Ron, S. Wang, Nature 459, 820 (2009)CrossRefGoogle Scholar
  44. 44.
    J.M.B. Lopes dos Santos, N.M.R. Peres, A.H.C. Neto, Graphene bilayer with a twist: electronic structure. Phys. Rev. Lett. 99, 256802 (2007)CrossRefGoogle Scholar
  45. 45.
    K. Sato, R. Saito, C. Cong, T. Yu, M.S. Dresselhaus, Zone folding effect in Raman G-band intensity of twisted bilayer graphene. Phys. Rev. B 86, 125414 (2012)CrossRefGoogle Scholar
  46. 46.
    G.S.N. Elie, M.V.O. Moutinho, A.C. Gadelha, A. Righi, L.C. Campos, H.B. Ribeiro, P.-W. Chiu, K. Watanabe, T. Taniguchi, P. Puech, M. Paillet, T. Michel, P. Venezuela, M.A. Pimenta, Nat. Commun. 9, 1221 (2018)CrossRefGoogle Scholar
  47. 47.
    A.K. Geim, I.V. Grigorieva, Van der Waals heterostructures. Nature 499, 419–425 (2013)CrossRefGoogle Scholar
  48. 48.
    L. Britnell, R.V. Gorbachev, B.D. Jalil, R. Belle, F. Schedin, A. Mishchenko, T. Georgiou, M.I. Katsnelson, L. Eaves, S.V. Morozov, N.M. Peres, J. Leist, A.K. Geim, K.S. Novoselov, L.A. Ponomarenko, Field-effect tunneling transistor based on vertical graphene heterostructures. Science 335, 947–950 (2012)CrossRefGoogle Scholar
  49. 49.
    F. Withers, O. Del Pozo-Zamudio, A. Mishchenko, A.P. Rooney, A. Gholinia, K. Watanabe, T. Taniguchi, S.J. Haigh, A.K. Geim, A.I. Tartakovskii, K.S. Novoselov, Light-emitting diodes by band-structure engineering in van der Waals heterostructures. Nat. Mater. 14, 301–306 (2015)CrossRefGoogle Scholar
  50. 50.
    L. Britnell, R.M. Ribeiro, A. Eckmann, R. Jalil, B.D. Belle, A. Mishchenko, Y.J. Kim, R.V. Gorbachev, T. Georgiou, S.V. Morozov, A.N. Grigorenko, A.K. Geim, C. Casiraghi, A.H.C. Neto, K.S. Novoselov, Strong light-matter interactions in heterostructures of atomically thin films. Science 340, 1311–1314 (2013)CrossRefGoogle Scholar
  51. 51.
    T. Georgiou, R. Jalil, B.D. Belle, L. Britnell, R.V. Gorbachev, S.V. Morozov, Y.J. Kim, A. Gholinia, S.J. Haigh, O. Makarovsky, L. Eaves, L.A. Ponomarenko, A.K. Geim, K.S. Novoselov, A. Mishchenko, Vertical field-effect transistor based on graphene–WS2 heterostructures for flexible and transparent electronics. Nat. Nanotechnol. 8, 100–103 (2013)CrossRefGoogle Scholar
  52. 52.
    E. Pallecchi, F. Lafont, V. Cavaliere, F. Schopfer, D. Mailly, W. Poirier, A. Ouerghi, Sci. Rep. 4, 4558 (2014)CrossRefGoogle Scholar
  53. 53.
    C.J. Shih, Q.H. Wang, Y. Son, Z. Jin, D. Blankschtein, M.S. Strano, Tuning on–off current ratio and field-effect mobility in a MoS2–graphene heterostructure via Schottky barrier modulation. ACS Nano 8, 5790–5798 (2014)CrossRefGoogle Scholar
  54. 54.
    K. Roy, M. Padmanabhan, S. Goswami, T.P. Sai, G. Ramalingam, S. Raghavan, A. Ghosh, Graphene–MoS2 hybrid structures for multifunctional photoresponsive memory devices. Nat. Nanotechnol. 8, 826–830 (2013)CrossRefGoogle Scholar
  55. 55.
    T. Georgiou, R. Jalil, B.D. Belle, L. Britnell, R.V. Gorbachev, S.V. Morozov, Y.J. Kim, A. Gholinia, S.J. Haigh, O. Makarovsky, Nat. Nanotechnol. 8, 100 (2012)CrossRefGoogle Scholar
  56. 56.
    H. Henck, Z. Ben Aziza, D. Pierucci, F. Laourine, F. Reale, P. Palczynski, J. Chaste, M.G. Silly, F. Bertran, P. Le Fèvre, E. Lhuillier, T. Wakamura, C. Mattevi, J.E. Rault, M. Calandra, A. Ouerghi, Electronic band structure of two-dimensional WS2/Graphene van der Waals heterostructures. Phys. Rev. B 97, 155421 (2018)CrossRefGoogle Scholar
  57. 57.
    H. Li, J.-B. Wu, F. Ran, M.-L. Lin, X.-L. Liu, Y. Zhao, X. Lu, Q. Xiong, J. Zhang, W. Huang, H. Zhang, P.-H. Tan, Interfacial interactions in van der Waals heterostructures of MoS2 and graphene. ACS Nano 11, 11714–11723 (2017)CrossRefGoogle Scholar
  58. 58.
    C.D. Spataru, S. Ismail-Beigi, L.X. Benedict, S.G. Louie, Excitonic effects and optical spectra of single-walled carbon nanotubes. Phys. Rev. Lett. 92, 077402 (2004)CrossRefGoogle Scholar
  59. 59.
    S. Iijima, Helical microtubules of graphitic carbon. Nature 354, 56–58 (1991)CrossRefGoogle Scholar
  60. 60.
    S. Iijima, T. Ichihashi, Single-shell carbon nanotubes of 1-nm diameter. Nature 363, 603–605 (1993)CrossRefGoogle Scholar
  61. 61.
    D.S. Bethune, C.H. Kiang, M.S. de Vries, Cobalt-catalysed growth of carbon nanotubes with single-atomic-layer walls. Nature 363, 605–607 (1993)CrossRefGoogle Scholar
  62. 62.
    A. Thess, R. Lee, P. Nikolaev, Crystalline ropes of metallic carbon nanotubes. Science 273, 483–487 (1996)CrossRefGoogle Scholar
  63. 63.
    A. Jorio, R. Saito, J.H. Hafner, C.M. Lieber, M. Hunter, T. McClure, G. Dresselhaus, M.S. Dresselhaus, Structural (n,m) determination of isolated single-wall carbon nanotubes by resonant Raman scattering. Phys. Rev. Lett. 86, 1118–1121 (2001)CrossRefGoogle Scholar
  64. 64.
    G.D. Mahan, Oscillations of a thin hollow cylinder: carbon nanotubes. Phys. Rev. B 65, 235402 (2002)CrossRefGoogle Scholar
  65. 65.
    M.S. Dresselhaus, G. Dresselhaus, R. Saito, A. Jorio, Phys. Rep. 409, 47 (2005)CrossRefGoogle Scholar
  66. 66.
    J. Maultzsch, H. Telg, S. Reich, C. Thomsen, Radial breathing mode of single-walled carbon nanotubes: optical transition energies and chiral-index assignment. Phys. Rev. B 72, 205438 (2005)CrossRefGoogle Scholar
  67. 67.
    M.S. Dresselhaus, G. Dresselhaus, A. Jorio, A.G. Souza Filho, M.A. Pimenta, D.R. Saito, Acc. Chem. Res. 35, 1070 (2002)CrossRefGoogle Scholar
  68. 68.
    M.S. Dresselhaus, G. Dresselhaus, A. Jorio, A.G. Souza Filho, M.A. Pimenta, R. Saito, Carbon 40, 2043 (2002)CrossRefGoogle Scholar
  69. 69.
    M.S. Dresselhaus, A. Jorio, A.G. Souza Filho, G. Dresselhaus, Raman spectroscopy on one isolated carbon nanotube. R Saito. Physica B 323, 15–20 (2002)CrossRefGoogle Scholar
  70. 70.
    S. Piscanec, M. Lazzeri, J. Robertson, A.C. Ferrari, F. Mauri, Optical phonons in carbon nanotubes: Kohn anomalies, Peierls distortions, and dynamic effects. Phys. Rev. B 75, 035427 (2007)CrossRefGoogle Scholar
  71. 71.
    M. Lazzeri, S. Piscanec, F. Mauri, A.C. Ferrari, Phonon linewidths and electron-phonon coupling in graphite and nanotubes. J. Robertson. Phys. Rev. B 73, 155426 (2006)CrossRefGoogle Scholar
  72. 72.
    N. Caudal, A.M. Saitta, M. Lazzeri, F. Mauri, Kohn anomalies and nonadiabaticity in doped carbon nanotubes. Phys. Rev. B 75, 115423 (2007)CrossRefGoogle Scholar
  73. 73.
    A.M. Rao, A. Jorio, M.A. Pimenta, M.S.S. Dantas, R. Saito, G. Dresselhaus, M.S. Dresselhaus, Polarized Raman study of aligned multiwalled carbon nanotubes. Phys. Rev. Lett. 84, 1820–1823 (2000)CrossRefGoogle Scholar
  74. 74.
    X. Zhao, Y. Ando, L.C. Qin, H. Kataura, Y. Maniwa, R. Saito, Radial breathing modes of multiwalled carbon nanotubes. Chem. Phys. Lett. 361, 169–174 (2002)CrossRefGoogle Scholar
  75. 75.
    X. Zhao, Y. Ando, L.-C. Qin, H. Kataura, Y. Maniwa, R. Saito, Multiple splitting ofG-band modes from individual multiwalled carbon nanotubes. Appl. Phys. Lett. 81, 2550–2552 (2002)CrossRefGoogle Scholar
  76. 76.
    A. Das, A.K. Sood, A. Govindaraj, A.M. Saitta, M. Lazzeri, F. Mauri, C.N.R. Rao, Doping in carbon nanotubes probed by Raman and transport measurements. Phys. Rev. Lett. 99, 136803 (2007)CrossRefGoogle Scholar
  77. 77.
    H. Farhat, H. Son, G.G. Samsonidze, S. Reich, M.S. Dresselhaus, Phonon softening in individual metallic carbon nanotubes due to the Kohn anomaly. J. Kong. Phys. Rev. Lett. 99, 145506 (2007)CrossRefGoogle Scholar
  78. 78.
    Y. Wu, J. Maultzsch, E. Knoesel, B. Chandra, M. Huang, M.Y. Sfeir, L.E. Brus, J. Hone, T.F. Heinz, Variable electron-phonon coupling in isolated metallic carbon nanotubes observed by Raman scattering. Phys. Rev. Lett. 99, 027402 (2007)CrossRefGoogle Scholar
  79. 79.
    A. Das, A.K. Sood, Phys. Rev. B79, 235429 (2009)CrossRefGoogle Scholar
  80. 80.
    D. Jariwalaa, V.K. Sangwana, C.-C. Wua, P.L. Prabhumirashia, M.L. Geiera, T.J. Marksa, L.J. Lauhona, M.C. Hersama, PNAS 110, 18076 (2013)CrossRefGoogle Scholar
  81. 81.
    H.N. Tran, J.C. Blancon, J.R. Huntzinger, R. Arenal, V.N. Popov, A.A. Zahab, A. Ayari, A. San-Miguel, F. Vall’ee, N. Del Fatti, J.L. Sauvajol, M. Paillet, Phys. Rev. B 94, 075430 (2016)CrossRefGoogle Scholar
  82. 82.
    M. Rontani, Anomalous magnetization of a carbon nanotube as an excitonic insulator. Phys. Rev. B 90, 195415 (2014)CrossRefGoogle Scholar
  83. 83.
    D. Varsano, S. Sorella, D. Sangalli, M. Barborini, S. Corni, E. Molinari, M. Rontani, Nature Comm 8, 1461 (2017)CrossRefGoogle Scholar
  84. 84.
    H.D. Wagner, O. Lourie, Y. Feldman, R. Tenne, Stress-induced fragmentation of multiwall carbon nanotubes in a polymer matrix. Appl. Phys. Lett. 72, 188–190 (1998)CrossRefGoogle Scholar
  85. 85.
    L.S. Schadler, S.C. Giannaris, P.M. Ajayan, Appl. Phys. Lett. 73, 2 (1998)CrossRefGoogle Scholar
  86. 86.
    T.C. Hirschmann, P.T. Araujo, H. Muramatsu, X. Zhang, K. Nielsch, Y.A. Kim, M.S. Dresselhaus, Characterization of bundled and individual triple-walled carbon nanotubes by resonant Raman spectroscopy. ACS Nano 7, 2381–2387 (2013)CrossRefGoogle Scholar
  87. 87.
    T.C. Hirschmann, P.T. Araujo, H. Muramatsu, J.F. Rodriguez-Nieva, M. Seifert, K. Nielsch, Y.A. Kim, M.S. Dresselhaus, Role of intertube interactions in double- and triple-walled carbon nanotubes. ACS Nano 8, 1330–1341 (2014)CrossRefGoogle Scholar
  88. 88.
    T.C. Hirschmann, M.S. Dresselhaus, H. Muramatsu, M. Seifert, U. Wurstbauer, E. Parzinger, K. Nielsch, Y.A. Kim, P.T. Araujo, G′band in double- and triple-walled carbon nanotubes: a Raman study. Phys. Rev. B 91, 075402 (2015)CrossRefGoogle Scholar
  89. 89.
    P.T. Araujo, N.M. Barbosa Neto, M.E.S. Sousa, R.S. Angelica, S. Simoes, M.F.G. Vieira, M.S. Dresselhaus, M.A.L. dos Reis, Carbon 124, 348 (2017)CrossRefGoogle Scholar
  90. 90.
    J. Kennedy, F. Fang, J. Futter, J. Laveneur, P.P. Murmu, G.N. Panin, T.W. Kang, E. Manikandan, Diam. Relat. Mater. 71, 79 (2017)CrossRefGoogle Scholar
  91. 91.
    H.W. Kroto, J.R. Heath, S.C. Obrien, R.F. Curl, R.E. Smalley, Nature 318(6042), 162 (1985)CrossRefGoogle Scholar
  92. 92.
    K. Hans, R. Pfeiffer, M. Hulman, C. Kramberger, Phil. Trans. R. Soc. Lond. A 362, 2375 (2004)CrossRefGoogle Scholar
  93. 93.
    M.R. Benzigar, S. Joseph, H. Ilbeygi, D.H. Park, S. Sarkar, G. Chandra, S. Umapathy, S. Srinivasan, S.N. Talapaneni, A. Vinu, Highly crystalline mesoporous C60 with ordered pores: a class of nanomaterials for energy applications. Angew. Chem. Int. Ed. 57, 569–573 (2018)CrossRefGoogle Scholar
  94. 94.
    K. Ikeda, K. Uosaki, Resonance hyper-Raman scattering of fullerene C60 microcrystals. J. Phys. Chem. A 112, 790–793 (2008)CrossRefGoogle Scholar
  95. 95.
    M.R. Benzigar, S. Joseph, A.V. Baskar, D.H. Park, G. Chandra, S. Umapathy, S.N. Talapaneni, A. Vinu, Ordered mesoporous C70 with highly crystalline pore walls for energy applications. Adv. Funct. Mater. 28, 1803701 (2018)CrossRefGoogle Scholar
  96. 96.
    A.V. Soldatov, G. Roth, A. Dzyabchenko, D. Johnels, S. Lebedkin, C. Meingast, B. Sundqvist, M. Haluska, H. Kuzmany, Topochemical polymerization of C70 controlled by monomer crystal packing. Science 293, 680–683 (2001)CrossRefGoogle Scholar
  97. 97.
    J. Onoe, A. Nakao, K. Takeuchi, XPS study of a photopolymerized C60 film. Phys. Rev. B 55, 10051–10056 (1997)CrossRefGoogle Scholar
  98. 98.
    P. Sharma, R. Singhal, R. Vishnoi, R. Kaushik, M.K. Banerjee, D.K. Avasthi, V. Ganesan, Ion track diameter in fullerene C70 thin film using Raman active vibrational modes of C70 molecule. Vacuum 123, 35–41 (2016)CrossRefGoogle Scholar
  99. 99.
    D. Liu, M. Yao, L. Wang, Q. Li, W. Cui, B. Liu, R. Liu, B. Zou, T. Cui, B. Liu, J. Liu, B. Sundqvist, T. Wågberg, Pressure-induced phase transitions of C70 nanotubes. J. Phys. Chem. C 115, 8918–8922 (2011)CrossRefGoogle Scholar
  100. 100.
    L.J. Terminello, D.K. Shuh, F.J. Himpsel, D.A. Lapiano-Smith, J. Stöhr, D.S. Bethune, G. Meijer, Unfilled orbitals of C60 and C70 from carbon K-shell X-ray absorption fine structure. Chem. Phys. Lett. 182, 491–496 (1991)CrossRefGoogle Scholar
  101. 101.
    X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J.M. Carlsson, K. Domen, M. Antonietti, A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 8(1), 76–80 (2009)CrossRefGoogle Scholar
  102. 102.
    Z. Tong, D. Yang, Z. Li, Y. Nan, F. Ding, Y. Shen, Z. Jiang, Thylakoid-inspired multishell g-c3n4nanocapsules with enhanced visible-light harvesting and electron transfer properties for high-efficiency photocatalysis. ACS Nano 11(1), 1103–1112 (2017)CrossRefGoogle Scholar
  103. 103.
    X. Liu, L. Dai, Carbon-based metal-free catalysts. Nat. Rev. Mater. 1, 16064 (2016)CrossRefGoogle Scholar
  104. 104.
    Y. Zheng, Y. Jiao, Y. Zhu, L.H. Li, Y. Han, Y. Chen, A. Du, M. Jaroniec, S.Z. Qiao, Hydrogen evolution by a metal-free electrocatalyst. Nat. Commun. 5, 3783 (2014)CrossRefGoogle Scholar
  105. 105.
    K. Srinivasu, B. Modak, S.K. Ghosh, J. Phys. Chem. C 118(46), 26479 (2014)CrossRefGoogle Scholar
  106. 106.
    Q. Guo, Y. Zhang, J. Qiu, G. Dong, Engineering the electronic structure and optical properties of g-C3N4 by non-metal ion doping. J. Mater. Chem. C 4(28), 6839–6847 (2016)CrossRefGoogle Scholar
  107. 107.
    D. Das, S.L. Shinde, K.K. Nanda, ACS Appl. Mater. Interfaces 8(3), 2181 (2016)CrossRefGoogle Scholar
  108. 108.
    M. Tahir, C. Cao, N. Mahmood, F.K. Butt, A. Mahmood, F. Idrees, S. Hussain, M. Tanveer, Z. Ali, I. Aslam, ACS Appl. Mater. Interfaces 6(2), 1258–1265 (2013)CrossRefGoogle Scholar
  109. 109.
    S. Khamlich, Z. Abdullaeva, J.V. Kennedy, M. Maaza, Appl. Surf. Sci. 405, 329–336 (2017)CrossRefGoogle Scholar
  110. 110.
    Z. Tong, D. Yang, Z. Li, Y. Nan, F. Ding, Y. Shen, Z. Jiang, Thylakoid-inspired multishell g-C3N4 nanocapsules with enhanced visible-light harvesting and electron transfer properties for high-efficiency photocatalysis. ACS Nano 11(1), 1103–1112 (2017)CrossRefGoogle Scholar
  111. 111.
    Q. Guo, Y. Zhang, J. Qiu, G. Dong, Engineering the electronic structure and optical properties of g-C3N4by non-metal ion doping. J. Mater. Chem. C 4(28), 6839–6847 (2016)CrossRefGoogle Scholar
  112. 112.
    A.Y. Liu, M.L. Cohen, Science 245(4920), 841 (1989)CrossRefGoogle Scholar
  113. 113.
    A. Naseri, M. Samadi, A. Pourjavadi, A.Z. Moshfegh, S. Ramakrishna, Graphitic carbon nitride (g-C3N4)-based photocatalysts for solar hydrogen generation: recent advances and future development directions. J. Mater. Chem. A 5, 23406–23433 (2017)CrossRefGoogle Scholar
  114. 114.
    M. Zhang, Y.Y. Duan, H.Z. Jia, F. Wang, L. Wang, Z. Su, C.Y. Wang, Defective graphitic carbon nitride synthesized by controllable co-polymerization with enhanced visible light photocatalytic hydrogen evolution. Catal. Sci. Technol. 7, 452–458 (2017)CrossRefGoogle Scholar
  115. 115.
    I.Y. Kim, S. Kim, X. Jin, S. Premkumar, G. Chandra, N.S. Lee, G.P. Mane, S.J. Hwang, S. Umapathy, A. Vinu, Ordered mesoporous C3N5 with a combined triazole and triazine framework and its graphene hybrids for the oxygen reduction reaction (ORR). Angew. Chem. Int. Ed. 57, 17135–17140 (2018)CrossRefGoogle Scholar
  116. 116.
    W.C. Peng, X.Y. Li, Synthesis of MoS2/g-C3N4 as a solar light-responsive photocatalyst for organic degradation. Catal. Commun. 49, 63–67 (2014)CrossRefGoogle Scholar
  117. 117.
    Q. Xiang, J. Yu, M. Jaroniec, Preparation and enhanced visible-light photocatalytic H2-production activity of graphene/C3N4 composites. J. Phys. Chem. C 115, 7355–7363 (2011)CrossRefGoogle Scholar
  118. 118.
    M. Muniz-Miranda, F. Muniz-Miranda, S. Caporali, SERS and DFT study of copper surfaces coated with corrosion inhibitor. Beilstein. J. Nanotechnol 5, 2489–2497 (2014)CrossRefGoogle Scholar
  119. 119.
    I.Y. Kim, J.M. Lee, T.W. Kim, H.N. Kim, H. Kim, W. Choi, S.J. Hwang, A strong electronic coupling between graphene nanosheets and layered titanate nanoplates: a soft-chemical route to highly porous nanocomposites with improved photocatalytic activity. Small 8, 1038–1048 (2012)CrossRefGoogle Scholar
  120. 120.
    X. Jin, J. Lim, N.S. Lee, S.J. Hwang, A powerful role of exfoliated metal oxide 2D nanosheets as additives for improving electrocatalyst functionality of graphene. Electrochim. Acta 235, 720–729 (2017)CrossRefGoogle Scholar
  121. 121.
    C.J. Howarda, H.T. Stokes, Group-theoretical analysis of octahedral tilting in perovskites. Acta Cryst. B 54, 782–789 (1998)CrossRefGoogle Scholar
  122. 122.
    T. Runka, K. Łapsa, A. Łapin’ski, R. Aleksiyko, M. Berkowski, M. Drozdowski, J. Mol. Struct. 704, 281–285 (2004)CrossRefGoogle Scholar
  123. 123.
    T. Runka, M. Berkowski, M. Drozdowski, J. Mol. Struct. 792–793, 221 (2006)CrossRefGoogle Scholar
  124. 124.
    A. Chopelas, Single-crystal Raman spectra of YAlO3 and GdAlO3: comparison to several orthorhombic ABO3 perovskites. Phys. Chem. Miner. 38, 709–726 (2011)CrossRefGoogle Scholar
  125. 125.
    M.V. Abrashev, A.P. Litvinchuk, M.N. Iliev, R.L. Meng, V.N. Popov, V.G. Ivanov, R.A. Chakalov, C. Thomsen, Phys. Rev. B 59, 4146–4153 (1999)CrossRefGoogle Scholar
  126. 126.
    M.N. Iliev, M.V. Abrashev, H.G. Lee, V.N. Popov, Y.Y. Sun, C. Thomsen, R.L. Meng, C.W. Chu, Raman spectroscopy of orthorhombic perovskitelikeYMnO3andLaMnO3. Phys. Rev. B 57, 2872–2877 (1998)CrossRefGoogle Scholar
  127. 127.
    S. Venugopalan, M. Dutta, A.K. Ramdas, J.P. Remeika, Magnetic and vibrational excitations in rare-earth orthoferrites: a Raman scattering study. Phys. Rev. B 31, 1490–1497 (1985)CrossRefGoogle Scholar
  128. 128.
    N. Koshizuka, S. Ushioda, Inelastic-light-scattering study of magnon softening in ErFeO3. Phys. Rev. B 22, 5394–5399 (1980)CrossRefGoogle Scholar
  129. 129.
    M. Udagawa, K. Kohn, N. Koshizuka, T. Tsushima, K. Tsushima, Influence of magnetic ordering on the phonon Raman spectra in YCrO3 and GdCrO3. Solid State Commun. 16, 779–783 (1975)CrossRefGoogle Scholar
  130. 130.
    N. Setter, I. Laulicht, Appl. Spectrosc. 3, 526 (1987)CrossRefGoogle Scholar
  131. 131.
    F. Jianga, S. Kojima, C.I. Zhao, C. Feng, J. Appl. Phys. 88, 3608–3612 (2000)CrossRefGoogle Scholar
  132. 132.
    H. Zhenga, G.D.C. de Csete Gyorgyfalva, R. Quimby, H. Bagshaw, R. Ubic, I.M. Reaney, J. Yarwood, Raman spectroscopy of B-site order–disorder in CaTiO3-based microwave ceramics. J. Eur. Ceram. Soc. 23, 2653 (2003)CrossRefGoogle Scholar
  133. 133.
    J. Pokorny, U.M. Pasha, L. Ben, O.P. Thakur, D.C. Sinclair, I.M. Reaney, Use of Raman spectroscopy to determine the site occupancy of dopants in BaTiO3. J. Appl. Phys. 109, 114110 (2011)CrossRefGoogle Scholar
  134. 134.
    K.F. McCarty, H.B. Radousky, D.G. Hinks, Y. Zheng, A.W. Mitchell, T.J. Folkerts, R.N. Shelton, Electron-phonon coupling in superconductingBa0.6K0.4BiO3: a Raman scattering study. Phys. Rev. B 40, 2662–2665 (1989)CrossRefGoogle Scholar
  135. 135.
    S. Banerjee, R.D. Dae-In Kim, I.P. Robinson, Y. Herman, S. Mao, S. Wong, Appl. Phys. Lett. 89, 223130 (2006)CrossRefGoogle Scholar
  136. 136.
    J. Kreisel, A.M. Glazer, P. Bouvier, G. Lucazeau, High-pressure Raman study of a relaxor ferroelectric: the Na0.5Bi0.5TiO3perovskite. Phys. Rev. B 63, 174106 (2001)CrossRefGoogle Scholar
  137. 137.
    M. Zaghrioui, A. Bulou, P. Lacorre, P. Laffez, Electron diffraction and Raman scattering evidence of a symmetry breaking at the metal-insulator transition of NdNiO3. Phys. Rev. B 64, 081102 (2001)CrossRefGoogle Scholar
  138. 138.
    M.Y. Chen, C.T. Chia, I.N. Lin, L.J. Lin, C.W. Ahn, S. Nahm, Microwave properties of Ba(Mg1/3Ta2/3)O3, Ba(Mg1/3Nb2/3)O3 and Ba(Co1/3Nb2/3)O3 ceramics revealed by Raman scattering. J. Eur. Ceram. Soc. 26, 1965–1968 (2006)CrossRefGoogle Scholar
  139. 139.
    A. Hossain, P. Bandyopadhyay, S. Roy, An overview of double perovskites A2B′B″O6 with small ions at A site: synthesis, structure and magnetic properties. J. Alloys Compd. 740, 414–427 (2018)CrossRefGoogle Scholar
  140. 140.
    B.M. Ezzahi, A. Ider, L. Bih, S. Benmokhtar, M. Azrour, M. Azdouz, J.M. Igartua, P. Lazor, J. Mol. Struct. 985, 339 (2011)CrossRefGoogle Scholar
  141. 141.
    A. Dias, L.A. Khalam, M.T. Sebastian, R.L. Moreira, Raman-spectroscopic investigation of and perovskites. J. Solid State Chem. 180, 2143–2148 (2007)CrossRefGoogle Scholar
  142. 142.
    B. Manoun, A. Ezzahi, S. Benmokhtar, A. Ider, P. Lazor, L. Bih, J.M. Igartua, X-ray diffraction and Raman spectroscopy studies of temperature and composition induced phase transitions in Ba2−xSrxZnWO6 (0≤x≤2) double perovskite oxides. J. Alloys Compd. 533, 43–52 (2012)CrossRefGoogle Scholar
  143. 143.
    Y. Fujioka, J. Frantti, M. Kakihana, Raman scattering studies of the Ba2MnWO6 and Sr2MnWO6 double perovskites. J. Phys. Chem. B 110, 777–783 (2006)CrossRefGoogle Scholar
  144. 144.
    E.N. Silva, A.P. Ayala, I. Guedes, S.A. Larregola, R.M. Pinacca, M.C. del Viola, J.C. Pedregosa, J. Raman Spectrosc. 40, 1028 (2009)CrossRefGoogle Scholar
  145. 145.
    M.N. Iliev, H. Guo, A. Gupta, Raman spectroscopy evidence of strong spin-phonon coupling in epitaxial thin films of the double perovskite La2NiMnO6. Appl. Phys. Lett. 90, 151914 (2007)CrossRefGoogle Scholar
  146. 146.
    R.B.M. Filho, A.P. Ayala, W. Carlos, A. de Paschoal, Appl. Phys. Lett. 102, 192902 (2013)CrossRefGoogle Scholar
  147. 147.
    J. Gebhardt, A.M. Rappe, Adv. Mater., 1802697 (2018)Google Scholar
  148. 148.
    W.-J. Yin, J.-H. Yang, J. Kang, Y. Yan, S.-H. Wei, Halide perovskite materials for solar cells: a theoretical review. J. Mater. Chem. A 3, 8926–8942 (2015)CrossRefGoogle Scholar
  149. 149.
    Z. Fan, K. Sun, J. Wang, Perovskites for photovoltaics: a combined review of organic–inorganic halide perovskites and ferroelectric oxide perovskites. J. Mater. Chem. A 3, 18809–18828 (2015)CrossRefGoogle Scholar
  150. 150.
    C. Quarti, G. Grancini, E. Mosconi, P. Bruno, J.M. Ball, M.M. Lee, The Raman spectrum of the CH3NH3PbI3 hybrid perovskite: interplay of theory and experiment. J. Phys. Chem. Lett. 5, 279–284 (2014)CrossRefGoogle Scholar
  151. 151.
    M.A. Perez-Osorio, R.L. Milot, M.R. Filip, J.B. Patel, L.M. Herz, M.B. Johnston, F. Giustino, Vibrational properties of the organic–inorganic halide perovskite CH3NH3PbI3 from theory and experiment: factor group analysis, first-principles calculations, and low-temperature infrared spectra. J. Phys. Chem. C 119, 25703–25718 (2015)CrossRefGoogle Scholar
  152. 152.
    R.G. Niemann, A.G. Kontos, D. Palles, E.I. Kamitsos, A. Kaltzoglou, F. Brivio, P. Falaras, P.J. Cameron, Halogen effects on ordering and bonding of CH3NH3+in CH3NH3PbX3(X = Cl, Br, I) hybrid perovskites: a vibrational spectroscopic study. J. Phys. Chem. C 120, 2509–2519 (2016)CrossRefGoogle Scholar
  153. 153.
    L.-Q. Xie, T.-Y. Zhang, C. Liang, N. Guo, W. Yu, G.-K. Liu, J.-R. Wang, J.-Z. Zhou, J.-W. Yan, Y.-X. Zhao, B.-W. Mao, Z.-Q. Tia, Organic–inorganic interactions of single crystalline organolead halide perovskites studied by Raman spectroscopy. Phys. Chem. Chem. Phys. 18, 18112–18118 (2016)CrossRefGoogle Scholar
  154. 154.
    P. Pistor, A. Ruiz, A. Cabot, V.R. Izquierdo-Roca, Sci. Rep. 6, 35973 (2016)CrossRefGoogle Scholar
  155. 155.
    M. Ledinsky, P. Loper, B. Niesen, J. Holovsky, S.-J. Moon, J.-H. Yum, S. De Wolf, A. Fejfar, C. Ballif, J. Phys. Chem. Lett. 6, 401 (2015)CrossRefGoogle Scholar
  156. 156.
    C. La-o-vorakiat, H. Xia, J. Kadro, T. Salim, D. Zhao, T. Ahmed, Y.M. Lam, J.-X. Zhu, R.A. Marcus, M.-E. Michel-Beyerle, E.E.M. Chia, J. Phys. Chem. Lett. 7, 1 (2016)CrossRefGoogle Scholar
  157. 157.
    V.H. Damle, L. Gouda, S. Tirosh, Y.R. Tischler, Structural characterization and room temperature low-frequency Raman scattering from MAPbI3 halide perovskite films rigidized by cesium incorporation. ACS Appl. Energy Mater. 1, 6707–6713 (2018)CrossRefGoogle Scholar

Copyright information

© Qatar University and Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Premkumar Selvarajan
    • 1
  • Goutam Chandra
    • 1
    • 2
  • Susmita Bhattacharya
    • 3
  • Sanchita Sil
    • 4
  • Ajayan Vinu
    • 5
    Email author
  • Siva Umapathy
    • 1
    • 6
    Email author
  1. 1.Department of Inorganic & Physical ChemistryIndian Institute of ScienceBangaloreIndia
  2. 2.Department of PhysicsNational Institute of Technology CalicutCalicutIndia
  3. 3.Department of PhysicsIndian Institute of ScienceBangaloreIndia
  4. 4.Defence Bioengineering & Electromedical LaboratoryBangaloreIndia
  5. 5.Global Innovative Center for Advanced Nanomaterials (GICAN), Faculty of Engineering and Built EnvironmentThe University of NewcastleCallaghanAustralia
  6. 6.Indian Institute for Science Education & ResearchBhauriIndia

Personalised recommendations