Biomedical subjects

Silvano Lizzit

Publications and source records attributed to Silvano Lizzit.

4 recordsLinked to original sources

PubMed2005

Unexpected behavior of the surface composition of PtRh alloys during chemical reaction.

The changes in the surface composition of a Pt(50)Rh(50)(100) alloy due to an ongoing 2H(2) + O(2)-->2H(2)O chemical reaction have been studied in situ. Exploiting the high-energy resolution and surface sensitivity of synchrotron radiation core-level spectroscopy it was possible to monitor the population of the two transitions metals atoms at the gas-surface interface. Sequences of fast high-resolution core-level spectra of the Rh3d(5/2), Pt4f(7/2), and O1s core levels showed a continuous exchange of atoms between the first and subsurface layers. An unexpected Pt surface enrichement was found under slightly oxidizing conditions, opposite to what found in a highly oxidizing atmosphere.

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PubMed2004

Ethanol decomposition: C--C cleavage selectivity on Rh(111).

Ethanol adsorption, desorption and decomposition on Rh(111) have been studied by X-ray photoelectron spectroscopy and tem-perature-programmed desorption experiments. The evolution of the C is and O is core level spectra was monitored as a function of ethanol exposure and surface temperature. Ethanol adsorption at 90 K results in two nonequivalent ethanol-adsorbed species at low surface coverage, while a third species--related to multilayer formation--appears after longer exposures. Upon surface annealing, ethanol undergoes both desorption and dissociation, thus creating intermediate surface species which further decompose to hydrogen, carbon monoxide and atomic carbon. Our results clearly show that C--C bond cleavage is the preferential dissociation channel, while C--O bond scission is not observed. Calculations performed within the framework of the unity bond index-quadratic exponent potential model, have been used to test and compare different competing dissociation channels, providing an estimate of adsorption energies and dissociation barriers.

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PubMed2003

Single-wall carbon nanotube interaction with gases: sample contaminants and environmental monitoring.

Here, we show that residual contaminants in purified single-wall carbon nanotube bundles may be responsible for the reported sensitivity of the electronic and transport properties to oxygen. Removal of these contaminants makes the electronic spectra insensitive to O(2), CO, H(2)O, and N(2), while a strong sensitivity to NO(2), SO(2), and NH(3) is observed, confirming the possible application of single-wall nanotubes as powerful sensors capable of measuring environmentally significant levels of toxic gases.

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PubMed2002

Impact of defects on the surface chemistry of ZnO(0001 macro)-O.

Scanning tunneling microscopy and core level photoelectron spectroscopy measurements have been used to investigate the morphology of ZnO(0001 macro)-O, and its reactivity with carbon monoxide and carbon dioxide, as a function of surface preparation. Real space images of the surface indicate that increasing the substrate anneal temperature during preparation significantly reduces the surface step density. Surface defect concentration is also monitored by employing formic acid as a chemical probe, which is shown to adsorb dissociatively (HCOOH --> [HCOO](-) + H(+)) only on zinc cations at step edges. Carbon 1s X-ray photoelectron spectra show that carbon monoxide and carbon dioxide both react to form surface carbonate species. Spectra, recorded both as a function of surface preparation and following coadsorption, demonstrate that the carbonate formed from either reactant molecule is located at oxygen vacancies at step edges, evidencing the significant role that defects can play in the surface chemistry of ZnO(0001 macro)-O.

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