Contrast and Raman spectroscopy study of single- and few-layered charge density wave material: 2H-TaSe2

Hajiyev, Parviz; Cong, Chunxiao; Qiu, Caiyu; Yu, Ting

doi:10.1038/srep02593

Cited by 133 publications

(141 citation statements)

References 48 publications

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“…These data clearly show that the transition temperature between the C-CDW and IC-CDW phases decreases for thinner 1T-TaSe2 film. Bulk 2H-TaSe2 has a transition from the normal metal phase to the IC-CDW phase at 123 K, followed by the C-CDW phase transformation at 90 K [31,73]. From Figure 7C, the intensities of the two-phonon peak and E2g mode of 2H-TaSe2 lessen with decreasing temperature.…”

Section: Raman Spectroscopic Characterizationmentioning

confidence: 88%

“…In recent years, temperature-dependent Raman spectra of 1T-VSe 2 [71], 1T-TaS 2 [72], 1T-TaSe 2 [28], 2H-TaSe 2 [31,73], 1T-TiSe 2 [11] and 2H-NbSe 2 [10] have been reported. In addition, Raman spectroscopy has been used vastly to investigate stacking order [74,75], number of layers [76], molecular doping [77], edge orientations [78,79], strain effects [80,81] and other properties of 2D materials.…”

Section: Raman Spectroscopic Characterizationmentioning

confidence: 99%

“…However, thinner layers of 2D CDW materials, such as 1T-TaS 2 [41,42], 2H-TaS 2 [27], 1T-TaSe 2 [42], 2H-TaSe 2 [31], 2H-NbSe 2 [43] and 1T-TiSe 2 [11], have been reported recently by the mechanical exfoliation technique. Figure 3 shows the first successful exfoliation of a tantalum diselenide (2H-TaSe 2 ) monolayer and a few layers reported by P. Hyziyev et al [31]. Using the conventional scotch tape procedure, thinner layers of TaSe 2 samples were exfoliated onto 300 nm SiO 2 /Si substrates.…”

Section: Mechanical Exfoliation Of Bulk Materialsmentioning

confidence: 99%

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Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

et al. 2017

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Abstract:Recently, two-dimensional (2D) charge density wave (CDW) materials have attracted extensive interest due to potential applications as high performance functional nanomaterials. As other 2D materials, 2D CDW materials are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into layers of single unit cell thickness. Although bulk CDW materials have been studied for decades, recent developments in nanoscale characterization and device fabrication have opened up new opportunities allowing applications such as oscillators, electrodes in supercapacitors, energy storage and conversion, sensors and spinelectronic devices. In this review, we first outline the synthesis techniques of 2D CDW materials including mechanical exfoliation, liquid exfoliation, chemical vapor transport (CVT), chemical vapor deposition (CVD), molecular beam epitaxy (MBE) and electrochemical exfoliation. Then, the characterization procedure of the 2D CDW materials such as temperature-dependent Raman spectroscopy, temperature-dependent resistivity, magnetic susceptibility and scanning tunneling microscopy (STM) are reviewed. Finally, applications of 2D CDW materials are reviewed.

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Section: Raman Spectroscopic Characterizationmentioning

confidence: 88%

Section: Raman Spectroscopic Characterizationmentioning

confidence: 99%

Section: Mechanical Exfoliation Of Bulk Materialsmentioning

confidence: 99%

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Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

et al. 2017

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“…[1][2][3][4][5] CDW is a periodic modulation of conduction electron densities and is usually found in metallic TMDs. 2H-TaSe 2 in bulk has transition from normal (metallic) phase to the incommensurate charge-density-wave (ICDW) phase at 122 K, followed by the commensurate charge-density-wave (CCDW) phase transition at 90 K. [6][7][8][9] However, the question of whether the ICDW of 2H-TaSe 2 is enhanced or suppressed upon thinning the samples down to few layers thickness has not yet been resolved.…”

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confidence: 99%

Raman spectroscopy of optical phonon and charge density wave modes in 1T-TiSe2 exfoliated flakes

Cui

et al. 2017

Solid State Communications

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2H-TaSe 2 is a model transition metal dichalcogenide material that develops charge density waves (CDWs). Here we present variable-temperature Raman spectroscopy study on both incommensurate charge density waves (ICDW) and optical phonon modes of 2H-TaSe 2 thin layers exfoliated onto SiO 2 substrate. Raman scattering intensities of all modes reach a maximum when the sample thickness is about 11 nm. This phenomenon can be explained by optical interference effect between the sample and the substrate. The E 2g ICDW amplitude modes experience redshift as temperature increases. We extract ICDW transition temperature (T ICDW ) from temperature dependence of the frequency of E 2g ICDW mode. We find that T ICDW increases in thinner flakes, which could be due to a result of significantly enhanced electron-phonon interactions. Our results open up a new window for search and control of CDW of twodimensional matter. TaSe 2 single crystals used in this work were purchased from 2D Semiconductors Company.Ultrathin layers were exfoliated onto Si substrates with 80 nm SiO 2 by the standard "Scotch-tape" method. 15 Thicknesses of exfoliated TaSe 2 ultrathin layers were determined by atomic force microscopy (AFM). A representative AFM image and height profile are shown in Fig. 1b.Raman scattering was conducted on freshly cleaved samples that were mounted in a cryostat with a window for optical access. A Helium-Neon laser at 632.8 nm was used, and the laser power was kept below 0.2 mW to avoid heating effect. Two ultra-narrow band notch filters were used to suppress the Rayleigh scattered light. The scattered light was dispersed by a Horiba iHR550 spectrometer and detected by a liquid nitrogen cooled CCD detector. Temperature of the TaSe 2 samples was estimated by the ratio of Stokes and anti-Stokes Raman scattering intensities. 14,16,17 Variable temperature Raman spectra for each sample were taken during the warming process from ~10 to ~300 K. The A 1g , E 1g , and E 2g modes are Raman active. 3 In the low-temperature CCDW phase, a superlattice of 3a 0 ×3a 0 ×c 0 is formed. 18 The commensurate superlattice shown schematically in Moncton revealed the Kohn anomaly of the Ʃ 1 -symmetric LA-phonon branch on the Ʃ line by neutron scattering. 18,19 In 2H structure, the LA branch is degenerate with the Ʃ 1 rigid-layer mode in the largest part of the Ʃ line. The 12 Ʃ 1 modes reduced to 2A 1g + 2E 2g + 2B 1u +2E 2u modes in the CCDW phase and the two K 6 (E 2 ) modes, where Ta atoms are displaced in the basal plane, reduced to 2E 2g + 2E 1u . Fig. 2a shows Raman spectra of TaSe 2 flakes with different thicknesses at around 10 K, which is well below the T CCDW . These samples were exfoliated on the same Si wafer and measured under the same condition. To explore intrinsic CDW properties of real twodimensional 2H-TaSe 2 , high quality samples with thickness reaching the monolayer limit are necessary. The 1-nm-thick sample is the thinnest we have obtained so far. However, In the case of the 2-nm-thick sample, no Raman peaks are observ...

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“…5-9. Among the TMDCs, the 2H (H: hexagonal) polytype of tantalum diselenide (2H-TaSe 2 ) is considered one of the foundational materials (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18), showing a transition from a metallic phase to an incommensurate charge-density wave (ICDW) phase at 123 K, followed by a "lock-in" transition to a commensurate chargedensity wave (CCDW) phase at 90 K. It finally becomes a superconductor with a rather low transition temperature (T c ) of 0.15 K. Although detailed studies have been performed on the physics of CDWs and superconductivity in 2H-TaSe 2 (16)(17)(18), a comparative study of the superconductivity of the polytypes and polymorphs of TaSe 2 from the chemical perspective has not been done.…”

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confidence: 99%

Polytypism, polymorphism, and superconductivity in TaSe ₂ _−x Te _x

Luo¹,

Xie²,

Tao

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

105

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Polymorphism in materials often leads to significantly different physical properties-the rutile and anatase polymorphs of TiO 2 are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer-stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivity of TaSe 2 , one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access two stable polytypes and two stable polymorphs in the TaSe 2−x Te x solid solution and find that the 3R polytype shows a superconducting transition temperature that is between 6 and 17 times higher than that of the much more commonly found 2H polytype. The reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of T c on subtle differences in the characteristics of the single layers present or from a surprising effect of the layer-stacking sequence on electronic properties that are typically expected to be dominated by the properties of a single layer in materials of this kind.he MX 2 layered transition-metal dichalcogenides (TMDCs, M = Mo, W, V, Nb, Ta, Ti, Zr, Hf, or Re and X = Se, S, or Te), have long been of interest due to the rich electronic properties that emerge due to their low dimensionality (1-9). Structurally, these compounds can be regarded as having strongly bonded (2D) X-M-X layers, with M in either trigonal prismatic or octahedral coordination with X, and weak interlayer X-X bonding of the van der Waals type. Many of these materials manifest charge-density waves and competition between chargedensity waves (CDWs) and superconductivity, e.g., refs. 5-9. Among the TMDCs, the 2H (H: hexagonal) polytype of tantalum diselenide (2H-TaSe 2 ) is considered one of the foundational materials (8-18), showing a transition from a metallic phase to an incommensurate charge-density wave (ICDW) phase at 123 K, followed by a "lock-in" transition to a commensurate chargedensity wave (CCDW) phase at 90 K. It finally becomes a superconductor with a rather low transition temperature

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Contrast and Raman spectroscopy study of single- and few-layered charge density wave material: 2H-TaSe2

Cited by 133 publications

References 48 publications

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

Raman spectroscopy of optical phonon and charge density wave modes in 1T-TiSe2 exfoliated flakes

Polytypism, polymorphism, and superconductivity in TaSe ₂ _−x Te _x

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Contrast and Raman spectroscopy study of single- and few-layered charge density wave material: 2H-TaSe2

Cited by 133 publications

References 48 publications

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

Raman spectroscopy of optical phonon and charge density wave modes in 1T-TiSe2 exfoliated flakes

Polytypism, polymorphism, and superconductivity in TaSe 2 −x Te x

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Polytypism, polymorphism, and superconductivity in TaSe ₂ _−x Te _x