Strong Enhancement of Raman Scattering from a Bulk-Inactive Vibrational Mode in Few-Layer MoTe<sub>2</sub>

Yamamoto, Mahito; Wang, Sheng Tsung; Ni, Meiyan; Lin, Yu‐Shan; Li, Song Lin; Aikawa, Satoru; Jian, Wen‐Bin; Ueno, Keiji; Wakabayashi, Katsunori; Tsukagoshi, Kazuhito

doi:10.1021/nn5007607

Cited by 290 publications

(336 citation statements)

References 73 publications

(109 reference statements)

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“…4b), LF modes show observable intensities. Such tendency is consistent with other vdW layered materials such as TMDs, where bulk-inactive vibrational modes become Ramanactive and observable in few-layer but they are non-detectable in very thick samples 41,61,62 . To understand the thickness dependence of B modes, we further calculated the frequencies of B modes of 2L to 8L BP using DFT PBE+optB88 method (Table 1).…”

Section: Thickness Dependence Of Lf Raman Spectrasupporting

confidence: 90%

Low-Frequency Interlayer Breathing Modes in Few-Layer Black Phosphorus

et al. 2015

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As a new two-dimensional layered material, black phosphorus (BP) is a promising material for nanoelectronics and nano-optoelectronics. We use Raman spectroscopy and first-principles theory to report our findings related to low-frequency (LF) interlayer breathing modes (<100 cm -1 ) in few-layer BP for the first time. The breathing modes are assigned to Ag symmetry by the laser polarization dependence study and group theory analysis. Compared to the high-frequency (HF) Raman modes, the LF breathing modes are much more sensitive to interlayer coupling and thus their frequencies show much stronger dependence on the number of layers. Hence, they could be used as effective means to probe both the crystalline orientation and thickness for fewlayer BP. Furthermore, the temperature dependence study shows that the breathing modes have a harmonic behavior, in contrast to HF Raman modes which are known to exhibit anharmonicity. 2 Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.3 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA. 2Orthorhombic black phosphorus (BP) is the most stable allotrope of phosphorus. It features a layered structure with puckered monolayers stacked by van der Waals (vdW) force 1 . Few-or single-layer BP can be mechanically exfoliated from bulk BP [2][3][4][5] . Due to BP's intrinsic thicknessdependent direct bandgap (ranging from 0.3 eV to 2.0 eV) and relatively high carrier mobility (up to ~1,000 cm 2 V -1 s -1 at room temperature) 2,4,[6][7][8][9] , it is expected to have promising applications in nanoelectronic devices [2][3][4]10 , and near and mid-infrared photodetector [11][12][13][14][15][16][17][18][19] . Recently, high performance thermoelectric devices were also predicted based on BP thin films [20][21][22] . With the surge of interest in two-dimensional (2D) materials (such as graphene and transition metal dichalcogenides (TMDs)) 23,24 , BP has become a new attraction since 2014 because it bridges the gap between graphene and TMDs, and offers the best trade-off between mobility and on-off ratio 3 . Moreover, the unique anisotropic puckered honeycomb lattice of BP leads to many novel in-plane anisotropic properties, which could lead to more applications based on BP 3,9,25,26 .Phonon behaviors play an important role in the diverse properties of materials 27 , which has been intensively studied in vdW layered materials, such as graphene and TMDs [28][29][30][31][32][33][34][35] . Raman spectroscopy is a powerful non-destructive tool to investigate the phonons and their coupling to electrons, and has been successfully applied to vdW layered materials [36][37][38][39][40] . Due to the lattice dynamics of vdW layered compounds, the phonon modes in these materials can be classified as high-frequency (HF) intralayer modes and low-frequency (LF) interlayer modes 27 . Intralayer modes involve vibrations from the intralayer chemical bonds (Fig. 1c), and the associated frequencies ...

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Section: Thickness Dependence Of Lf Raman Spectrasupporting

confidence: 90%

Low-Frequency Interlayer Breathing Modes in Few-Layer Black Phosphorus

et al. 2015

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“…A single vibrational mode (A 2 ), which corresponds to the B 1 2g mode in bulk, is expected in the monolayer. 25 The A 2 mode is IR-active and no peak related to this mode occurs in the Raman scattering spectrum of monolayer MoTe 2 at room temperature. As predicted by the group theory and previously observed 25 , the mode corresponding to B 1 2g in bulk becomes Raman active in few-layer MoTe 2 in the spectra for N ≥ 2 at ∼290 cm −1 (see Fig.…”

Section: Resultsmentioning

confidence: 98%

“…There are three major peaks observed in that range, which are due to first-order transitions at the Γ point of the Brillouin zone: the out-of-plane mode A 1g at ∼170 cm −1 , the in-plane mode E [25][26][27][28] In that mode, both Te atoms in each layer move at particular time in the same direction while the central Mo atom moves in the opposite direction (see Fig. 1).…”

Section: Resultsmentioning

confidence: 99%

Raman scattering of few-layers MoTe ₂

Grzeszczyk¹,

Gołasa²,

Zinkiewicz³

et al. 2016

2D Mater.

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We report on room-temperature Raman scattering measurements in few-layer crystals of exfoliated molybdenum ditelluride (MoTe2) performed with the use of 632.8 nm (1.96 eV) laser light excitation. In agreement with a recent study reported by G. Froehlicher et al 1 we observe a complex structure of the out-of-plane vibrational modes (A1g/A 1 ), which can be explained in terms of interlayer interactions between single atomic planes of MoTe2. In the case of low-energy shear and breathing modes of rigid interlayer vibrations, it is shown that their energy evolution with the number of layers can be well reproduced within a linear chain model with only the nearest neighbor interaction taken into account. Based on this model the corresponding in-plane and out-of-plane force constants are determined. We also show that the Raman scattering in MoTe2 measured using 514.5 nm (2.41 eV) laser light excitation results in much simpler spectra. We argue that the rich structure of the out-of-plane vibrational modes observed in Raman scattering spectra excited with the use of 632.8 nm laser light results from its resonance with the electronic transition at the M point of the MoTe2 first Brillouin zone.

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“…Indeed, although bulk MX 2 exhibit indirect bandgaps, monolayer MX 2 are direct bandgap semiconductors [3,4] with remarkable spin, valley [5] and optoelectronic properties [6]. More Generally, N -layer MX 2 crystals provide an ideal platform to uncover the impact of symmetry breaking and interlayer interactions on the electronic, optical and vibrational properties, from the bulk (three-dimensional) to the monolayer (quasi two-dimensional) limit.In particular, in N -layer MX 2 , interlayer interactions result in a splitting of all the monolayer phonon modes [7][8][9][10][11][12][13][14][15][16] (see Table I). The latter effect is known as the Davydov splitting [17] and is closely related to the force constants that govern the vibrational properties of MX 2 [9].…”

mentioning

confidence: 99%

Unified Description of the Optical Phonon Modes in N-Layer MoTe₂

et al. 2015

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N -layer transition metal dichalcogenides provide a unique platform to investigate the evolution of the physical properties between the bulk (three dimensional) and monolayer (quasi two-dimensional) limits. Here, using high-resolution micro-Raman spectroscopy, we report a unified experimental description of the Γ-point optical phonons in N -layer 2H-molybdenum ditelluride (MoTe2). We observe a series of N -dependent low-frequency interlayer shear and breathing modes (below 40 cm −1 , denoted LSM and LBM) and well-defined Davydov splittings of the mid-frequency modes (in the range 100 − 200 cm −1 , denoted iX and oX), which solely involve displacements of the chalcogen atoms. In contrast, the high-frequency modes (in the range 200 − 300 cm −1 , denoted iMX and oMX), arising from displacements of both the metal and chalcogen atoms, exhibit considerably reduced splittings. The manifold of phonon modes associated with the in-plane and out-of-plane displacements are quantitatively described by a force constant model, including interactions up to the second nearest neighbor and surface effects as fitting parameters. The splittings for the iX and oX modes observed in N -layer crystals are directly correlated to the corresponding bulk Davydov splittings between the E2u/E1g and B1u/A1g modes, respectively, and provide a measurement of the frequencies of the bulk silent E2u and B1u optical phonon modes. Our analysis could readily be generalized to other layered crystals.Keywords: Two-dimensional materials, layered crystals, transition metal dichalcogenides, MoTe2, Raman spectroscopy, interlayer breathing and shear modes, force constants, Davydov splitting, surface effects.Introduction In the wake of graphene, a vast family of layered materials is attracting tremendous attention [1]. Now available in the form of N -layer crystals, the latter exhibit peculiar physical properties that complement the assets of graphene and offer exciting perspectives to design van der Waals heterostructures [1]. Semiconducting transition metal dichalcogenides (MX 2 , with M = Mo, W and X = S, Se, Te) are among the most actively investigated layered crystals [2]. Indeed, although bulk MX 2 exhibit indirect bandgaps, monolayer MX 2 are direct bandgap semiconductors [3,4] with remarkable spin, valley [5] and optoelectronic properties [6]. More Generally, N -layer MX 2 crystals provide an ideal platform to uncover the impact of symmetry breaking and interlayer interactions on the electronic, optical and vibrational properties, from the bulk (three-dimensional) to the monolayer (quasi two-dimensional) limit.In particular, in N -layer MX 2 , interlayer interactions result in a splitting of all the monolayer phonon modes [7][8][9][10][11][12][13][14][15][16] (see Table I). The latter effect is known as the Davydov splitting [17] and is closely related to the force constants that govern the vibrational properties of MX 2 [9]. The Davydov splitting has been previously studied in polyaromatic molecules [18], thin films [19], and bulk layered crystals, ...

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Strong Enhancement of Raman Scattering from a Bulk-Inactive Vibrational Mode in Few-Layer MoTe₂

Cited by 290 publications

References 73 publications

Low-Frequency Interlayer Breathing Modes in Few-Layer Black Phosphorus

Low-Frequency Interlayer Breathing Modes in Few-Layer Black Phosphorus

Raman scattering of few-layers MoTe ₂

Unified Description of the Optical Phonon Modes in N-Layer MoTe₂

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Strong Enhancement of Raman Scattering from a Bulk-Inactive Vibrational Mode in Few-Layer MoTe2

Cited by 290 publications

References 73 publications

Low-Frequency Interlayer Breathing Modes in Few-Layer Black Phosphorus

Low-Frequency Interlayer Breathing Modes in Few-Layer Black Phosphorus

Raman scattering of few-layers MoTe 2

Unified Description of the Optical Phonon Modes in N-Layer MoTe2

Contact Info

Product

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Strong Enhancement of Raman Scattering from a Bulk-Inactive Vibrational Mode in Few-Layer MoTe₂

Raman scattering of few-layers MoTe ₂

Unified Description of the Optical Phonon Modes in N-Layer MoTe₂