Surface Brillouin scattering study of tantalum nitride (TaN) thin films.

Elastic properties of TaN films on (001)Si are investigated by surface Brillouin scattering (SBS). The velocity dispersion is obtained from Brillouin frequency shifts and surface acoustic wave phase velocities derived from measured SBS spectra. The observed Rayleigh surface acoustic and Sezawa waves indicate a soft on hard configuration. The elastic stiffnesses from the best fit of the calculated and measured spectra were C11=288 and C44=80GPa. Using these elastic constants in the surface elastodynamic Green's function yielded theoretical Brillouin spectra in agreement with measured spectra. Employing a least squares fitting procedure to the elastic constants gives uncertainties in C11 and C44 as ±3.7 and ±2.5GPa, respectively.

Minimum lattice thermal conductivity of In3SbTe2 by surface Brillouin scattering.

Phase-change materials are chalcogenide alloys used for nonvolatile memory applications due to their rapid and reversible structural transformation. In3SbTe2 is a promising candidate that exhibits transitions dependent on thermal conductivity. The minimum lattice thermal conductivity of amorphous In3SbTe2 is investigated by surface acoustic propagation. In3SbTe2 thin films were deposited by radio frequency magnetron sputtering on (100) Si. Rutherford backscattering spectrometry and x-ray reflectivity were used to establish the elemental composition, deposition rate, and mass density. Using the Debye model, the thermal conductivity is extracted from fitted phase velocities measured by surface Brillouin scattering. The low thermal conductivity is revealed to be suitable for Joule heating.

Raman spectroscopic study of phosphogypsum thermal reduction with the carbonaceous material.

Elemental sulphur (S) can be produced from hydrogen sulphide (H2S) in a PiPco or Iron process. In turn H2S can be stripped with carbon dioxide (CO2) from calcium sulphide (CaS) obtained from the thermal reduction of phosphogypsum with carbon. The reaction pathway for the thermal reduction of the phosphogypsum with graphite was studied using thermogravimetric analysis and in situ Raman spectroscopy. The dehydration of the phosphogypsum to anhydrite was completed at about 142 °C. The dehydration was followed by the formation of the intermediate compound at about 860 °C which is characterised by a mass loss of about 11%. The intermediate compound, identified using the in situ Raman spectroscopy to be a dehydrated orschallite-type compound (Ca3[SO4][SO3]2), converted to CaS at about 935 °C. The presence of the metal impurities in the phosphogypsum: Ni(2+)(4 mg kg(-1)); Co(2+)(2 mg kg(-1)); Mn(2+)(5 mg kg(-1)); Cu(2+)(14 mg kg(-1)); Fe(2+)(200 mg kg(-1)) and Mg(2+)(300 mg kg(-1)) showed no influence the onset temperature for the reduction reaction.

Direct synthesis of carbon nanofibers from South African coal fly ash.

Carbon nanofibers (CNFs), cylindrical nanostructures containing graphene, were synthesized directly from South African fly ash (a waste product formed during the combustion of coal). The CNFs (as well as other carbonaceous materials like carbon nanotubes (CNTs)) were produced by the catalytic chemical vapour deposition method (CCVD) in the presence of acetylene gas at temperatures ranging from 400°C to 700°C. The fly ash and its carbonaceous products were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), laser Raman spectroscopy and Brunauer-Emmett-Teller (BET) surface area measurements. It was observed that as-received fly ash was capable of producing CNFs in high yield by CCVD, starting at a relatively low temperature of 400°C. Laser Raman spectra and TGA thermograms showed that the carbonaceous products which formed were mostly disordered. Small bundles of CNTs and CNFs observed by TEM and energy-dispersive spectroscopy (EDS) showed that the catalyst most likely responsible for CNF formation was iron in the form of cementite; X-ray diffraction (XRD) and Mössbauer spectroscopy confirmed these findings.