Observation of infrared-active modes in Raman scattering from topological insulator nanoplates

He, Rui; Wang, Zhenhua; Qiu, Richard L.J.; Delaney, Conor; Beck, Ben; Kidd, Tim; Chancey, C. C.; Gao, Xuan

doi:10.1088/0957-4484/23/45/455703

Cited by 42 publications

(32 citation statements)

References 35 publications

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“…Note that similar tellurium segregation has been reported for Bi-Te films [30] and for Sb 2 Te 3 films under strong laser irradiation [31]. Previously, the two vibrational modes at 2.8 and 3.67 THz were observed in Raman scattering for Bi 2 Te 3 nanoplates, but not in bulk crystals [32]. They were ascribed to IR modes and their appearance was interpreted as evidence of a parity breakdown in thin flakes of the topological insulator.…”

Section: Resultssupporting

confidence: 78%

Polarization dependence of coherent phonon generation and detection in the three-dimensional topological insulatorBi2Te3

2015

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We have studied the polarization dependence of coherent phonons in the topological insulator Bi 2 Te 3 . Using polarization-dependent femtosecond pump-probe spectroscopy, we measured coherent phonons as a function of angle when the pump and probe polarizations were fixed, and the crystal orientation was rotated. For isotropic detection, depending on the spot position, oscillations either from only low-and high-frequency phonons of A 1g symmetry, or in addition from the mode at 3.6 THz were observed. All the modes were found to be independent of the orientation of electric field vector with respect to the crystal axes testifying to their full symmetry while no modes of lower symmetry appeared in any polarization geometry. For anisotropic detection both modes of E g symmetry could be detected, but their amplitudes were considerably smaller than those of A 1g symmetry. To clarify the coherent phonon assignment and the process of coherent phonon generation in Bi 2 Te 3 , the time-domain measurements were complemented by spontaneous Raman scattering. The comparison of frequency-and time-domain results and the polarization dependence suggest that the 3.6 THz mode belongs to crystalline Te arising due to tellurium segregation. A discrepancy between the time-and frequency-domain data is discussed.

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Section: Resultssupporting

confidence: 78%

Polarization dependence of coherent phonon generation and detection in the three-dimensional topological insulatorBi2Te3

2015

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“…The peak we attribute to a surface phonon is the weak feature which appears between the 2 and 1 2 modes at 159 cm -1 and 114 cm -1 for Bi2Se3 and Bi2Te3, respectively. This peak has been previously observed in thin films and few-monolayer samples of both compounds [16,18,31,32,33,34,35,36,37,38,39] and in single crystals of Bi2Se3 [39,40], but never 4 | P a g e before in bulk Bi2Te3. Note that these prior studies detected numerous other weak features in both compounds that were not observed in the present work.…”

supporting

confidence: 63%

“…The observation of extra Raman lines and, in particular, the lines we assign to surface phonons have been prevalently attributed in the literature to surface-induced symmetry breaking, which seemingly allows for scattering of nominally Raman forbidden, infrared-active modes [18,31,32,33,34,35,36,38,40]. For various reasons, we find such an interpretation to be incorrect.…”

Section: P a G Ementioning

confidence: 69%

“…Their origin remains controversial. Spectra of few-monolayer Bi2Te3 show lines at ~ 93 cm −1 and 114 cm −1 [18,31,32,33,34,35] and at ~ 160 cm −1 in Bi2Se3 [36,37], which were assigned to Raman-forbidden, infrared modes resulting from surface-induced symmetry breaking, while thin-film studies of Bi2Te3 reveal five additional peaks, one of which, at ~ 93 cm -1 , was assigned to a surface mode [38]. In bulk, single crystal of Bi2Se3, additional peaks at 68, 125, 129 and 160 cm -1 were observed and also assigned to Raman-forbidden polar modes [40].…”

Section: Resultsmentioning

confidence: 99%

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Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

Boulares

Shi

Kioupakis

et al. 2018

Solid State Communications

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Bi2Se3 and Bi2Te3 show features in the range ~ 50-160 cm -1 , which have been assigned alternatively to Raman-forbidden, bulk infrared modes arising from symmetry breaking at the surface or to surface phonons, which couple to the topologically protected electronic states. Here, we present temperature-and wavelength-dependent Raman studies showing additional modes we ascribe to surface phonons in both Bi2Se3 and Bi2Te3. Our assignment is supported by density functional theory calculations revealing surface phonons at frequencies close to those of the extra peaks in the Raman data. The theoretical results also indicate that these modes are not a consequence of spin-orbit coupling and, thus, that their occurrence is unrelated to the topological properties of these materials.1 | P a g e I. INTRODUCTIONTopological insulators (TIs) are a new class of materials that are insulating in the bulk but exhibit metallic surfaces, which arise from strong spin-orbit coupling and particular properties of their band structure. The electronic surface states of TIs consist of gapless bands characterized by a linear (Dirac) dispersion, which are protected from backscattering by time reversal symmetry [1,2]. In recent years, these novel materials have attracted significant interest, not only due to their unique electronic properties, but also because they hold promise for applications in quantum computing [2,3] Bi2Se3 and Bi2Te3 are layered compounds, which have been extensively studied in the past due to their exceptional thermoelectric properties [8]. They were also among the first compounds identified as three-dimensional TIs [9,10,11,12]. Because of its crucial relevance to their surface conductivity properties, the study of electron-phonon coupling [13] and, moreover, the search for vibrations localized at the surface have been the subject of many studies in recent years [14,15,16,17]. In particular, inelastic helium scattering [14,15], surface enhanced Raman scattering [16] and time-resolved photoemission measurements [17] in Bi2Se3 and Bi2Te3 show features that were attributed to surface modes as well as strong electron-phonon coupling at the surface.Also, weak features observed in Raman spectra were attributed to surface effects unrelated to the topological surface states [18].Here, we present experimental results on the temperature-and excitation-wavelength (λL−) dependence of Raman scattering, as well as first-principles phonon calculations for bulk and fewquintuple-layer Bi2Se3 and Bi2Te3. Other than the expected, and previously reported Raman-active bulk modes [19,20], we find weak peaks at low temperatures in both compounds, which we ascribe 2 | P a g e to surface vibrational modes. Density functional theory calculations, which do not consider spinorbit coupling, support such an assignment in that they reveal a pair of surface-modes, the lowerfrequency of which is very close in frequency with the peaks found in the Raman experiments.Arguments are also given suggesting that spin-orbit effects are not important in determi...

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“…Se atoms exhibit two different chemical environments. The chemical bonding between Bi and Se2 is of a pure covalent nature, while it is slightly ionic but still covalent in nature between Bi and Se1112627282930. As for the Bi 2 Se 3 compounds, O atoms preferentially replace Se at Se2 sites because O atoms at Se2 sites are more stable than the O atoms at Se1 sites, thus resulting in a measurable increase in the values of the lattice parameters of Bi 2 Se 3 .…”

Section: Discussionmentioning

confidence: 99%

Morphological evolution of self-deposition Bi2Se3 nanosheets by oxygen plasma treatment

Jia

Wang

et al. 2016

Sci Rep

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Bi2Se3 nanosheets were successfully synthesized by a microwave-assisted approach in the presence of polyvinylpyrroli done at a temperature of 180 °C for 2 h. The thin film was prepared on a silicon wafer via a self-deposition process in a Bi2Se3 nanosheet ink solution using the evaporation-induced self-assembly method. The structure and morphology of the obtained products were characterized by X-ray diffraction, scanning electron microscopy (SEM), x-ray photoelectron spectroscopy, and Raman spectroscopy. The highly uniform Bi2Se3 particles could be formed by controlling the oxygen plasma treatment time. After the plasma pretreatment from 10 to 20 s, the surface of Bi2Se3 film evolved from the worm-like structure to particles. The highly uniform thin film was formed on further increasing the plasma treatment time, which is consistent with the observed SEM results. Several important processes can result in the morphological evolution of Bi2Se3 nanosheets: (1) formation of Bi2Se3 oxide layer; (2) self-assembly of oxide nanoparticles under the action of high-energy oxygen plasma; and (3) electrostatic interaction and etching mechanism.

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Observation of infrared-active modes in Raman scattering from topological insulator nanoplates

Cited by 42 publications

References 35 publications

Polarization dependence of coherent phonon generation and detection in the three-dimensional topological insulatorBi2Te3

Polarization dependence of coherent phonon generation and detection in the three-dimensional topological insulatorBi2Te3

Surface phonons in the topological insulators Bi2Se3 and Bi2Te3

Morphological evolution of self-deposition Bi2Se3 nanosheets by oxygen plasma treatment

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