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Ar dilution effects on the elastic properties of hydrogenated amorphous hard-carbon films grown by plasma-enhanced chemical vapor deposition (2001)

Valentini, L. ; Kenny, J. M.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 89 (2001), S. 1003-1007

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Hydrogenated amorphous carbon (a-C:H) films were deposited, at room temperature, from a CH4/Ar plasma produced by a radio frequency (rf) glow discharge system at 13.56 MHz, and different power values. X-ray reflectivity and Brillouin light scattering have been used to investigate the relationship between deposition conditions and elastic properties of hydrogenated amorphous carbon films. The composition of the initial gaseous mixture and the rf power input are shown to affect significantly both the mechanical and the microstructural properties of deposited films. As the fraction of methane in the feed gas is increased, both the film density and the phase velocity of the surface Rayleigh wave exhibit an enhancement, thus indicating the production of a harder material. On the other hand, x-ray reflectivity measurements suggest the occurrence of a higher degree of structural order in the sp2 lattice. Experimental findings are discussed in terms of the different chemical composition of the plasma. © 2001 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1330762

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Plinian fall deposits from Vulsini Volcanic District (Central Italy) (1994)

Nappi, G. ; Capaccioni, B. ; Mattioli, M. ; [et al.]

Springer

Bulletin of volcanology 56 (1994), S. 502-515

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ISSN: 1432-0819

Keywords: Vulsini volcanoes ; stratigraphy ; plinian fall deposits ; eruptive column dynamics ; clast dispersal ; tephra volumes

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Stratigraphic investigations of the Vulsini Volcanic District indicate the existence of five prominent plinian fall deposits, deposited over a period of about 0.34 Ma. The oldest deposit (‘Basal pumices’) crops out mainly in the peripheral areas and is one of the largest plinian events in the Vulsini District, with a volume of about 9 km3 and a calculated column height exceeding 30 km. Subcircular patterns of isopachs and isopleths around the Bolsena lake indicate emplacement in wind-free conditions and suggest a source vent location in the northernmost sector of the present Bolsena lake, where it is possible that an older central volcanic structure existed. The four younger plinian fall deposits are related to Bolsena activity. The oldest of these, named the ‘Ponticello’ and ‘Orvieto-Bagnoregio’ pumices, are mainly distributed on the north-eastern sector of the Vulsini District. Their volumes are an order of magnitude lower than that of the basal unit, and the estimated column heights do not exceed 20 km. The younger ‘Ospedaletto’ pumice deposit has a NE-SW dispersal axis, whereas the youngest ‘Casetta’ pumice deposit is found only in the north-eastern sector of the district. Their estimated volumes are respectively 1.2 and 0.1 km3, whereas the inferred vent areas appear to be located slightly to the east of the Ponticello and Orvieto-Bagnoregio pumice deposit source areas. The chronology of the Ospedaletto and Casetta pumices indicates that the final plinian activity from the Bolsena complex is contemporaneous with the Latera activity. The decreasing volumes from the oldest to the youngest units, together with the progressive shifting northeastwards of the source vents, may be related to the volcano-tectonic subsidence of the Bolsena area. The source vents for the post-Basal pumices events are mainly clustered just north of Bolsena village where the greatest displacement during subsidence occurred. Accordingly, source vent shifting appears to be related to the progressive opening of normal faults from the inner to the outer margin of the Bolsena depression.