This paper presents a Resonance Raman spectroscopy study of ~1 nm diameter HgTe nanowires formed inside single walled carbon nanotubes by melt infiltration. Raman spectra have been measured for ensembles of bundled filled tubes, produced using tubes from two separate sources, for excitation photon energies in the ranges 3.39 to 2.61eV and 1.82 to 1.26eV for Raman shifts down to ~25 cm -1 . We also present HRTEM characterization of the tubes and the results of DFT calculations of the phonon and electronic dispersion relations, and the optical absorption spectrum based upon the observed structure of the HgTe nanowires. All of the evidence supports
Low pressure chemical vapor deposition (LPCVD) using the single-source precursors [ n Bu 2 Ga(μ-E t Bu 2 ) 2 Ga n Bu 2 ] (E = P or As) in the temperature range 723−823 K (0.05 mmHg), gives shiny yellow or silvery gray films of GaP and GaAs, respectively, on silica. The composition and morphology of the deposited materials have been probed via X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray (SEM/EDX), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Raman spectroscopy, revealing crystalline (cubic) GaE with 1:1 Ga/E ratios. The GaP forms nanorods growing perpendicular to the substrate surface and is rougher than the GaAs, which appears to form smaller, densely packed microcrystallites. While the GaAs films produced in this way did not exhibit any significant luminescence, the reflective GaP films obtained by LPCVD were of good electronic quality, revealing photoluminescence comparable to that of a single crystalline GaP reference. LPCVD using Ga(P t Bu 2 ) 3 gives GaP, although this appears to be an inferior reagent compared to the dimer. Unlike the corresponding [ n Bu 2 In(μ-E t Bu 2 ) 2 In n Bu 2 ] dimers (see Aksomaityte et al., Chem. Mater. 2010, 22, 4246) which gave InE films and nanowires from supercritical chemical fluid deposition in sc-CO 2 /hexane, under the same conditions (773 K, 12 MPa), the gallium dimer precursors mostly failed to give GaE. Instead significant carbon deposition occurred, indicating solvent degradation.
We report time-resolved incoherent anti-Stokes Raman scattering measurements of the dynamics of the D and G' bands in single-walled carbon nanotubes at excitation energies of 1.51 and 1.63 eV over the temperature range 4-330 K. The measurements indicate that the population lifetimes (~1 ps) of the phonons responsible for the D band are dependent on nanotube type. The temperature dependencies are consistent with anharmonic decay of the phonons into one low (<190 cm(-1)) and one high energy phonon.
The paper presents time-resolved incoherent anti-Stokes Raman spectroscopy (TRIARS) measurements of the population dynamics of G-mode phonons in semiconducting single-walled carbon nanotubes (SWCNTs), in which the G + and G − dynamics are separated. The measurements were performed as a function of temperature over the full range 4−600 K, and at two laser excitation energies, 1.51 and 1.63 eV, which give TRIARS signals from SWCNTs in two different diameter distributions, 0.99 < d < 1.05 nm and 0.88 < d < 0.97 nm, respectively. The population lifetimes determined from the experiments were, to within experimental error, independent of mode type and diameter. In all cases the temperature dependence of the population lifetimes was well fitted by a model that assumes that two-phonon anharmonic decay is the dominant process and that the lower-energy daughter phonon has an energy of approximately 400 ± 100 cm −1 .
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