The preparation of highly anisotropic one-dimensional (1D) structures confined into carbon nanotubes (CNTs) in general is a key objective in CNTs research. In this work, the capillary effect was used to fill double wall carbon nanotubes with iron. The samples are characterized by Mössbauer and Raman spectroscopy, transmission electron microscopy, scanning area electron diffraction, and magnetization. In order to investigate their structural stability and compare it with that of single wall carbon nanotubes (SWNTs), elucidating the differences induced by the inner-outer tube interaction, unpolarized Raman spectra of tangential modes of double wall carbon nanotubes (DWNTs) filled with 1D nanocrystallin α-Fe excited with 514 nm were studied at room temperature and elevated pressure. Up to 16 GPa we find a pressure coefficient for the internal tube of 4.3 cm −1 GPa −1 and for the external tube of 5.5 cm −1 GPa −1 . In addition, the tangential band of the external and internal tubes broadens and decreases in amplitude. All findings lead to the conclusion that the outer tube acts as a protection shield for the inner tubes (at least up 16 GPa). Structural phase transitions were not observed in this range of pressure.
We report in this work for the first time the temperature dependence of the optical absorption of the ternary compound Ag2SnS3. The optical absorption of this compound has been investigated in three samples from room temperature to 10K. We found that the fundamental absorption edge of Ag2SnS3 is consistent with a direct energy gap by allowed transitions of 1.43(2) eV at the lowest temperature measured and of 1.26(5) eV at room temperature. In two samples, the existence of a broad peak or band between 1.24 eV to 1.28 eV for temperatures below 190K is observed. The temperature dependencies of the energy gap show a behavior typical of that found for most semiconductors, that is, the energy gap decreases monotonically with temperature. The most important models are used to explain the energy gap shift and several parameters from these models are reported.
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