title: Contrast and Raman spectroscopy study of single- and few-layered charge density wave material: 2H-TaSe₂.
abstract: In this article, we report the first successful preparation of single- and few-layers of tantalum diselenide (2H-TaSe₂) by mechanical exfoliation technique. Number of layers is confirmed by white light contrast spectroscopy and atomic force microscopy (AFM). Vibrational properties of the atomically thin layers of 2H-TaSe₂ are characterized by micro-Raman spectroscopy. Room temperature Raman measurements demonstrate MoS₂-like spectral features, which are reliable for thickness determination. E₁g mode, usually forbidden in backscattering Raman configuration is observed in the supported TaSe₂ layers while disappears in the suspended layers, suggesting that this mode may be enabled because of the symmetry breaking induced by the interaction with the substrate. A systematic in-situ low temperature Raman study, for the first time, reveals the existence of incommensurate charge density wave phase transition in single and double-layered 2H-TaSe₂ as reflected by a sudden softening of the second-order broad Raman mode resulted from the strong electron-phonon coupling (Kohn anomaly).
authors.affiliation: Graphene Research Centre, National University of Singapore, 117546 Singapore.
authors.forename: Parviz
authors.initials: P
authors.lastname: Hajiyev
authors.forename: Chunxiao
authors.initials: C
authors.lastname: Cong
authors.forename: Caiyu
authors.initials: C
authors.lastname: Qiu
authors.forename: Ting
authors.initials: T
authors.lastname: Yu
mesh_terms: D003460:Crystallization / Q000379:methods*; D004579:Electron Transport; D008422:Materials Testing; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure*; D012643:Selenium / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods*; D055672:Static Electricity; D013635:Tantalum / Q000737:chemistry*
chemical_list: D013635:Tantalum; D012643:Selenium