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Speranza G.,FBK IRST Sommarive Str. 18 | Torrengo S.,FBK IRST Sommarive Str. 18 | Torrengo S.,University of Trento | Miotello A.,University of Trento | And 5 more authors.
Diamond and Related Materials | Year: 2011

The chemistry of oxygen bonding on the diamond surface is a rich area of surface science research. It is well known that different surface terminations lead to strong variation of the material work function. This effect in diamond assumes peculiar consequences. In fact the oxidized diamond surface is hydrophilic, due to the high work function it shows a positive electron affinity and it is non conductive. On the contrary hydrogenation completely changes the orientation of the surface dipoles, the surface becomes hydrophobic, the work function lowers leading to a negative electron affinity. In addition hydrogen induces subsurface carriers which render the diamond surface semiconducting. These distinctive electronic properties make the diamond surface very interesting for the fabrication of surface field effect transistors just playing with the oxygen/hydrogen chemistry. Hydrogenation is generally obtained during the diamond synthesis in plasma reactors. Differently, the diamond surface oxidation may be accomplished with different processes (wet chemistry, plasma, UV irradiation).The realization of electronic devices calls for a complete understanding of the carbon-oxygen interactions, their stability and their influence on the electronic properties of diamond. Aim of this work is to explore the properties of diamond surfaces oxidized with piranha mixture, with O2 plasma and with UV irradiation in a pure O2 atmosphere. Each of these oxidized surfaces were annealed in situ at different temperatures and analyzed with photoelectron spectroscopies. Decreases of the oxygen concentration obtained via thermal desorption are then correlated with variations of the electronic properties obtained from UPS analyses. © 2011 Elsevier B.V.

Minati L.,FBK IRST Sommarive Str. 18 | Torrengo S.,FBK IRST Sommarive Str. 18 | Torrengo S.,University of Trento | Speranza G.,FBK IRST Sommarive Str. 18
Surface Science | Year: 2010

Gold nanoclusters were directly synthesized on thiol functionalized carbon nanotubes film and characterized by means of X-ray photoelectron spectroscopy. A carbon nanotube (CNT) supporting network was produced by spreading a concentrate suspension of thiol-functionalized CNT on platinum films. To synthesize gold nanoclusters, a water solution of tetrachloroauric acid was adsorbed on the CNT substrate and reduced by UV reduction in air. Detailed analysis of the Au 4f core line enabled us to follow the chemical modifications occurring on the substrate. In particular, the XPS analysis of gold features shows a progressive reduction of the gold precursor by increasing the irradiation time. Also information on the nanocluster size distribution after each reducing treatments are obtained. © 2009 Elsevier B.V. All rights reserved.

Speranza G.,FBK IRST Sommarive Str. 18 | Torrengo S.,FBK IRST Sommarive Str. 18 | Torrengo S.,University of Trento | Filippi M.,FBK IRST Sommarive Str. 18 | And 5 more authors.
Surface Science | Year: 2010

Surface properties of polycrystalline hydrogenated diamond produced by chemical vapour deposition upon oxidation under UV irradiation are studied. The diamond surfaces were cleaned in vacuum by thermal treatment. They were characterized estimating the electron affinity of the virgin surface by UV photoelectron spectroscopy and controlling the surface composition by X-ray photoelectron spectroscopy. The cleaned surfaces were then exposed to pure oxygen and UV radiation (deuterium lamp). Ozone induced surface oxidation was verified by XPS estimating the oxygen atomic concentration and the presence of specific chemical bonds. Surface oxidation was also verified analyzing the change in the diamond electron affinity. Oxygen was then removed in situ by a series of thermal treatments at increasing temperature. Already at ∼300 °C a remarkable reduction of the oxygen concentration occurs which persists increasing the annealing temperature. Contemporary, a progressive recovery of the initial electron affinity is also obtained. These effects are observed up to 970 °C, a temperature at which the electron affinity assumes a negative value. Specific chemical reactions are hypothesized to describe the oxidation process and to explain the electronic behaviour of the diamond surface. © 2010 Elsevier B.V. All rights reserved.

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