Double-walled carbon nanotubes (DWNT) are made of two concentric and weakly van der Waals coupled single-walled carbon nanotubes (SWNT). DWNTs are the simplest systems for studying the mechanical and electronic interactions between concentric carbon layers. In this paper we review recent results concerning the intrinsic features of phonons of DWNTs obtained from Raman experiments performed on index-identified DWNTs. The effect of the interlayer distance on the strength of the mechanical and electronic coupling between the layers, and thus on the frequencies of the Raman-active modes, namely the radial breathing-like modes (RBLMs) and G-modes, are evidenced and discussed.
A comparative analysis of Raman spectra of barium titanate in various forms is performed over a broad range of temperatures (from 80 to 400 K). In particular, the evolution of A1(2TO) and E(1TO) soft‐mode components, sensitive to strain, is monitored for such materials as single crystal, ceramic, and polycrystalline film. Based on the temperature dependence of these components, a sequence of phase transitions is established for each of the aforementioned forms.
superlattices are characterized via Raman spectroscopy. Special attention is paid to a comprehensive analysis of their polarized Raman spectra, especially, within a soft mode (E(1TO)) range. The shift of E(1TO) soft mode is found to be more pronounced for BaTiO 3 /Ba 50 Sr 50 TiO 3 /SrTiO 3 sample than for BaTiO 3 /Ba 50 Sr 50 TiO 3 , presumably owing to stronger 2D compression of BT layers and abruptly increased temperature of transition from ferroelectric to paraelectric phase.
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