Quantitative structural and textural assessment of laminar pyrocarbons through Raman spectroscopy, electron diffraction and few other techniques

In pyrocarbon materials, the width of the Raman D band (FWHMD) is very sensitive to low energy structural defects (e.g., disorientations of the graphene layers). The correlation between the two parameters, FWHMD and OA (as derived from selected area electron diffraction: SAED), has allowed to differentiate various pyrocarbons unambiguously. Furthermore, the optical properties of pyrocarbons, i.e., the extinction angle, the optical phase shift and the ordinary and extraordinary reflectance, have been accurately determined at 550 nm by means of the extinction curves method. These results are completed by in-plane and out-of-plane dielectric constant measurements by angular resolved EELS. Moreover, the hybridization degree of the carbon atoms has been assessed by the same technique. About 80% of the carbon atoms of the pyrocarbons have a sp2 hybridization. The lack of pure sp2 carbon atoms, as compared to graphite, might be explained by the presence of sp3-like line defects.Comment: Xavier Bourrat : Present Address = ISTO - CNRS-Universit\'e d'Orl\'ean

Nanostructural characterization of amorphous diamondlike carbon films

Nanostructural characterization of amorphous diamondlike carbon (a-C) films grown on silicon using pulsed-laser deposition (PLD) is correlated to both growth energetic and film thickness. Raman spectroscopy and x-ray reflectivity probe both the topological nature of 3- and 4-fold coordinated carbon atom bonding and the topographical clustering of their distributions within a given film. In general, increasing the energetic of PLD growth results in films becoming more ``diamondlike'', i.e. increasing mass density and decreasing optical absorbance. However, these same properties decrease appreciably with thickness. The topology of carbon atom bonding is different for material near the substrate interface compared to material within the bulk portion of an a-C film. A simple model balancing the energy of residual stress and the free energies of resulting carbon topologies is proposed to provide an explanation of the evolution of topographical bonding clusters in a growing a-C film

GaN-Epitaxie, Prozesstechnologie und Aufbautechnik : Abschlussbericht ; Wachstumskern Berlin WideBaSe, Verbundprojekt 7: Hocheffiziente Leistungs-Mikrowellenverstärker und Oszillatoren, Teilprojekt 7.3: GaN-Epitaxie, Prozesstechnologie und Aufbautechnik ; Berichtslaufzeit: 01.07.2010 bis 31.12.2013

[no abstract available

Power RF-Operation of AlGaN/GaN HEMTs Grown on Insulating Silicon Carbide Substrates

We report on the technology and microwave characterization of AlGaN/GaN power HEMTs on SiC substrate. DC and S-parameter are discussed, together with load-pull results on devices up to 4mm gate width. A power density of 5.2 W/mm is obtained for devices up to 2 mm gate width. The maximum power level achieved is 13.8 W at 2 GHz

Pollutant emission from a heat station supplied with agriculture biomass and wood pellet mixture

Tests for combustion of hay and sunflower husk pellets mixed with wood pellets were performed in a horizontal-feed as well as under-feed (retort) wood pellet furnace installed in boilers with a nominal heat output of 15 and 20 kW, located in a heat station. During the combustion a slagging phenomenon was observed in the furnaces. In order to lower the temperature in the furnace, fuel feeding rate was reduced with unaltered air stream rate. The higher the proportion of wood pellets in the mixture the lower carbon monoxide concentration. The following results of carbon monoxide concentration (in mg/m3 presented for 10% 02 content in flue gas) for different furnaces and fuel mixtures (proportion in wt%) were obtained: horizontal-feed furnace supplied with hay/wood: 0/100 - 326; 30/70 - 157; 50/50 - 301; 100/0 - 3300; horizontal-feed furnace supplied with sunflower husk/wood: 50/50 - 1062; 67/33 - 1721; 100/0 - 3775; under-feed (retort) furnace supplied with hay/wood: 0/100 - 90; 15/85 - 157; 30/70 - 135; 50/50 - 5179; under-feed furnace supplied with sunflower husk/wood: 67/33 - 2498; 100/0 - 3128. Boiler heat output and heat efficiency was low: 7 to 13 kW and about 55%, respectively, for the boiler with horizontal-feed furnace and 9 to 14 kW and 64%, respectively, for the boiler with under-feed furnace