Influence of thermal history on the structure and properties of silicate glasses

We studied a set of float glass samples prepared with different fictive temperature by previous annealing around the glass transition temperature. We compared the results to previous measurements on a series of amorphous silica samples, also prepared with different fictive temperature. We showed that the modifications on the structure at a local scale are very small, the changes of physical properties are moderate but the changes on density fluctuations at a nanometer scale are rather large: 12 and 20% in float glass and silica, for relative changes of fictive temperature equal to 13 and 25% respectively. Local order and mechanical properties of silica vary in the opposite way compared to float glass (anomalous behavior) but the density fluctuations in both glasses increase with temperature and fictive temperature

In situ measurements of density fluctuations and compressibility in silica glass as a function of temperature and thermal history

In this paper, small-angle X-ray scattering measurements are used to determine the different compressibility contributions, as well as the isothermal compressibility, in thermal equilibrium in silica glasses having different thermal histories. Using two different methods of analysis, in the supercooled liquid and in the glassy state, we obtain respectively the temperature and fictive temperature dependences of the isotheraml compressibility. The values obtained in the glass and supercooled liquid states are very close to each other. They agree with previous determinations of the literature. The compressibility in the glass state slightly decreases with increasing fictive temperature. The relaxational part of the compressibility is also calculated and compared to previous determinations. We discussed the small differences between the different determinations

Dynamic sound attenuation at hypersonic frequencies in silica glass

In order to clarify the origin of the dominant processes responsible for the acoustic attenuation of phonons, which is a much debatted topic, we present Bril louin scattering experiments in various silica glasses of different OH impurities content. A large temperature range, from 5 to 1500 K is investigated, up to the glass transition temperature. Comparison of the hypersonic wave attenuation in various samples allows to identify two different processes. The first one induce s a low temperature peak related to relaxational processes; it is strongly sensitive to the extrinsic defects. The second, dominant in the hig h temperature range, is weakly dependent on the impurities and can be ascribed to anharmonic interactions

Raman spectroscopy of GeSe and AgGeSe thin films

The structural properties of Agy(Ge0.25Se0.75)1-y thin films (y=0, 0.07, 0.10, 0.15, 0.20 and 0.25 at. fraction) were studied. The films were prepared by pulsed laser deposition using bulk glass targets of the studied ternary system and deposited onto microscope slides. Their amorphous structures were confirmed by XRD (X-ray Diffraction). The effect of silver content on films structures was analysed by Raman spectroscopy. Typical Raman vibration modes were observed in the Ge0.25Se0.75 binary film: Ge-Se corner-sharing tetrahedra mode (CS) at 199 cm-1, edge sharing tetrahedra mode (ES) at 217 cm-1, and SeSe rings and chains mode at 255-265 cm-1 (CM). In the Agy(Ge0.25Se0.75)1-y ternary thin films, the same modes were observed but with a red shift and an intensity reduction in the ES and CM bands.Fil: Conde Garrido, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería ; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; ArgentinaFil: Piarristeguy, A.. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería ; ArgentinaFil: Le Parc, R.. Centre National de la Recherche Scientifique; Francia. Universite Montpellier II; FranciaFil: Ureña, Maria Andrea.Fil: Fontana, Marcelo.Fil: Arcondo, B..Fil: Pradel, A.. Universite Montpellier Ii; Franci

Chromophore Ordering by Confinement into Carbon Nanotubes

International audienceWe report an experimental study on the confinement of oligothiophene derivatives into single-walled carbon nanotubes over a large range of diameter (from 0.68 to 1.93 nm). We evidence by means of Raman spectroscopy and transmission electron microscopy that the supramolecular organizations of the confined oligothiophenes depend on the nanocontainer size. The Raman Radial Breathing Mode frequency is shown to be monitored by both the number of confined molecules into a nanotube section and the competition between oligothiophene/oligothiophene and oligothiophene/tube wall interactions. We finally propose simple Raman criteria to characterize oligothiophene supramolecular organization at the nanoscale

Charge transfer in conjugated oligomers encapsulated into carbon nanotubes

This study deals with a hybrid system consisting in quaterthiophene derivative encapsulated inside single-walled and multi-walled carbon nanotubes. Investigations of the encapsulation step are performed by transmission electron microscopy. Raman spectroscopy data point out different behaviors depending on the laser excitation energy with respect to the optical absorption of quaterthiophene. At low excitation energy (far from the oligomer resonance window) there is no significant modification of the Raman spectra before and after encapsulation. By contrast, at high excitation energy (close to the oligomer resonance window), Raman spectra exhibit a G-band shift together with an important RBM intensity loss, suggesting a significant charge transfer between the inserted molecule and the host nanotubes. Those results suggest a photo induced process leading to a significant charge transfer.Peer reviewe

One pot synthesis of carbon microspheres decorated with metal nanoparticles

The preparation of metal nanoparticles (nickel, cobalt, iron and silver) decorated on the shell of carbon microspheres (CMS) is reported. Through a simple one-pot hydrothermal method using a starch solution, gave MSC (diameter 1–5μm), which consist of a hydrophobic core with a hydrophilic shell due to the presence of oxygen containing functional groups. The samples were characterized with SEM, X-ray, Raman, TGA and FT-IR. The metal nanoparticles (size 20–80 nm) are decorated on the circumference of the MCS in line with its core–shell structure, the analysis with FTIR determined oxygen groups on the surface, the Raman studies showed disarrayed structures and aromatic elements, and the X-ray diffraction indicated a low degree of “graphitization” in the structures.Se sintetizaron microesferas de carbono empleando almidón como fuente de carbono decoradas con nanopartículas metálicas de níquel, cobalto, hierro y plata respectivamente, mediante una reacción de “one pot” vía carbonización hidrotérmica. Se obtuvieron microesferas de carbono con tamaño de diámetro de partículas entre 1-5 μm, los materiales obtenidos se caracterizaron por SEM, XRD,TGA y FT-IR, el análisis por FT-IR determinó grupos oxigenados en la superficie de las microesferas de carbono, las cuales están compuesta por una cascara hidrofílica y núcleo hidrófobo, el estudio por espectroscopía Raman determino desorden en la estructuras y elementos aromáticos, el estudio por difracción de rayos X indicó un bajo grado de grafitización en estas estructuras