We have studied the electrical conduction in nanostructured carbon (ns-C) films produced by deposition of a supersonic beam of neutral carbon clusters. The d.c. conduction properties of these films ...have been measured in situ during the deposition process and ex situ as a function of the temperature in vacuum and in ambient of different gases (H2, N2, CH4, He). The ns-C films exhibit an ohmic behavior with a room temperature resistivity in the range of 107-109 ${\rm\Omega}$ cm depending on the growth and storage conditions. Conductivity vs. temperature measured in vacuum in the range 290-400 K is characterized by activation energies in the range of 0.3-1.7 eV, the current response does not differ significantly in gas atmosphere. Nanocomposite carbon-metal films have been obtained by adding small amounts of metallorganic precursors containing molybdenum and cobalt during the formation of carbon clusters prior to deposition. The films are characterized by porous carbon networks containing small metal and metal carbide clusters. Electrical transport properties of these films have been studied as a function of temperature, gas pressure and relative humidity. In particular, the electrical conductivity of the sample produced with molybdenum showed to be much sensitive to changes in gas pressure and relative humidity, being characterised by fast and reversible responses. Copyright Springer-Verlag Berlin/Heidelberg 2003
Physical Review Letters 98, 216103 (2007) We report the production and characterization of a form of amorphous carbon
films with sp/sp2 hybridization (atomic fraction of sp hybridized species >
20%) ...where the predominant sp bonding appears to be (=C=C=)n cumulene.
Vibrational and electronic properties have been studied by in situ Raman
spectroscopy and electrical conductivity measurements. Cumulenic chains are
substantially stable for temperatures lower than 250 K and they influence the
electrical transport properties of the sp/sp2 carbon through a self-doping
mechanism by pinning the Fermi level closer to one of the mobility gap edges.
Upon heating above 250 K the cumulenic species decay to form graphitic
nanodomains embedded in the sp2 amorphous matrix thus reducing the activation
energy of the material. This is the first example of a pure carbon system where
the sp hybridization influences bulk properties.
Schottky diodes based on a 4H-SiC epitaxial n-type layer deposited onto a 4H-SiC n/sup +/ type substrate have been tested as particle detectors. The charge collection efficiency (CCE) has been tested ...by means of a 0.1mCi /sup 90/Sr /spl beta/-source and with 5.48 MeV /spl alpha/-particles from /sup 241/Am. The response of the SiC devices, investigated over a range of thickness up to /spl sim/20/spl mu/m, is characterized by a 100%CCE, the charge signal is stable and reproducible, with no evidence of priming or polarization effects.
The 'in-situ vitrification' (ISV) technology is one of the most promising alternative methods for the immobilization of hazardous wastes contained into polluted soils. It has been the object of a ...research project supported by the Italian Ministry of Industry and involving some Departments of the University of Bologna and two large regional corporations. The actual design of the supply system of this high-temperature thermal process is fundamental for the optimal control and management of this particular pollutant treatment. The paper reports in particular on the activity concerning the development of the electrical power system that have been developed for accomplishing ISV, with reference to its characteristics, realization and its application for the treatment of some polluted soils situated in the Ravenna area in Italy.
We report the production and characterization of a form of amorphous carbon films with sp/sp2 hybridization (atomic fraction of sp hybridized species > 20%) where the predominant sp bonding appears ...to be (=C=C=)n cumulene. Vibrational and electronic properties have been studied by in situ Raman spectroscopy and electrical conductivity measurements. Cumulenic chains are substantially stable for temperatures lower than 250 K and they influence the electrical transport properties of the sp/sp2 carbon through a self-doping mechanism by pinning the Fermi level closer to one of the mobility gap edges. Upon heating above 250 K the cumulenic species decay to form graphitic nanodomains embedded in the sp2 amorphous matrix thus reducing the activation energy of the material. This is the first example of a pure carbon system where the sp hybridization influences bulk properties.
The charge collection efficiency (CCE) of high resistivity silicon detectors, previously neutron irradiated up to 2/spl times/10/sup 15/ n/cm/sup 2/, was measured at different cryogenic temperatures ...and different bias voltages. In order to study reverse annealing (RA) effects, a few samples were heated to 80/spl deg/C and kept at room temperature for several months after irradiation. For comparison other samples (NRA) where kept at -10 C after irradiation. The RA and NRA samples, measured at 250 V forward and reverse bias voltage, present a common temperature threshold at 150 K. Below 120 K the CCE is constant and ranges between 55% and 65% for the RA and NRA sample respectively. Similar CCE was measured for a device processed with low resistivity contacts (OHMIC), opening the prospect for a consistent reduction of the cost of large area particle tracking.
Acetylation of benzyl α-d-xylopyranoside with 4 equivalents of acetic anhydride in the presence of anhydrous sodium acetate at room temperature gave the crystalline 2,4(1) and 3,4(2) diacetates of ...benzyl α-d-xylopyranoside together with the 2,3,4-triacetate 3. Detritylation of the crude mixture obtained by selective triphenylmethylation and subsequent acetylation of benzyl α-d-mannopyranoside afforded crystalline benzyl 2,3,4-tri-O-acetyl-α-d-mannopyranoside (4, 47%).
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