Alberto Torrisi

Probing archaeological and artistic solid materials by spatially resolved analytical techniques

The study of ancient works-of-art and archaeological remains requires the use of analytical methods which minimise the impact on the integrity of the object. Spatially resolved analytical methods have significantly enhanced our capacity to study ancient material since they cause minimal and at times no damage to the studied object. They have also amplified the range of analytical information we can extract from ancient and valuable objects. Here we provide an overview of the recent achievements in the knowledge of the past obtained thanks to the use of a variety of spatially resolved analytical methods.

Testing a fluorinated compound as a protective material for calcarenite

Abstract A polyfluorinated compound was studied as a material for the specific protection of calcarenite. Water capillary absorption and vapour permeability measurements were carried out in order to evaluate efficiency as a protective agent. Particular attention was given to characterising its resistance against bio-deterioration induced by microorganisms such as blue and green algae. Chemical surface modifications were induced by UV-irradiation in a specially designed climatic chamber and were investigated through comparative tests on untreated and artificially weathered samples using X-ray photoelectron spectroscopy (XPS). This paper discusses the potential use of the compound studied as a specific coating material for the protection of calcarenite.

Na-surface segregation and oxygen depletion in particle bombardment of alkaline glasses

Abstract Alkaline glass samples were bombarded by 2 keV Ar ions and neutrals and the surface modification were followed by XPS. Two main effects have been detected after bombardment: (i) a lowering of the Na Si atomic ratio with a steady state value of about 1 2 of the initial value, and (ii) an oxygen depletion. Both effects are independent of the charge state of the projectiles. The sodium concentration profile has been studied by XPS tilting angle technique and it is concluded that bombardment-induced surface segregation occurs and that it is may be responsible for the observed sodium behaviour.

Oxygen depletion in electron beam bombarded glass surfaces studied by XPS

Abstract XPS has been utilized to study the compositional changes which occur in glass after electron beam irradiation. In the bombarded surfaces a reduction in Na and O signals is observed, while Ca signal shows negligible variations. Two O 1s signals, assigned to bridging and non-bridging oxygen were found. Irradiation causes a decrease of these two types of oxygen. This is at variance with Lineweavers mechanism which accounts for the decrease of the non-bridging oxygens only. After irradiation a second component in the Si 2p line is found. It has been attributed to the formation of SiSi bonds induced by oxygen outgassing. The formation of these bonds leads to a more compact structure and this might explain the observed density change in irradiated glass.

XPS investigation of the effects induced by the silanization on real glass surfaces

Abstract Real glass surfaces have been studied by XPS before and after silanization with dimethyldichlorosilane. Before silanization the glass surface is oxygen-rich with respect to the commonly accepted glass model. This discrepancy remains also when the lowering of the surface Na concentration, due to the leaching of the glass, is taken into account. The oxygen excess is attributed to the presence on the real surface of adsorbed water and carbonates. The silanization of these surfaces removes the oxygen excess and introduces Si(CH3)2 groups. A model is presented which accounts for the observed effects.

Radiation-enhanced diffusion of Na in alkaline glasses

Abstract The surface Na concentration of glass is found to increase under X-ray flux. The experimental data are well fitted by a first-order rate equation and are interpreted on the basis of radiation-enhanced diffusion mechanism of the Na with a coupling between material and defect fluxes. The Na concentration-versus-depth profiles show that the phenomenon also takes place at depth greater than the XPS sampling depth. Moreover, there is some evidence that in addition to diffusion from the bulk, surface segragation also occurs.

Two Calix-Crown Based Stationary Phases. Synthesis, Chromatographic Performance and X-ray Photoelectron Spectroscopy Investigation

Abstract Two chromatographic stationary phases, obtained by covalently linking two suitably derivatized calix[4]crown-6 and calix[4]crown-5 receptors onto silica gel, are described here. A study of their chromatographic behaviour as well as their surface composition is reported. The packing materials exhibit high selectivity toward alkali metal ions. Complete separations of Cs + from K + and Na + were obtained when using a water/methanol mixture (80:20) as the mobile phase. In these conditions, a selectivity factor Cs + /Na + =4.10 was achieved with the silica gel-bound calix[4]crown-6. The degree of coverage of the activated silica-gel surface following the covalent attachment of the macrocycle was estimated by mean of X-ray photoelectron spectroscopy (XPS). This technique allows the first few monolayers of the material to be analysed and thus is to be preferred to conventional Elemental Analysis for similar studies. Three methods for an adequate correction of the XP signals for the presence of organic contaminants are suggested and critically compared.

Applications of ESCA to fabrication problems in the semiconductor industry

Abstract Surface chemical states of materials involved in the fabrication of semiconductor devices can often alter device properties and performances, reducing product yield. X-ray Electron Spectroscopy has been applied to some problems of relevance in the power semiconductor industry. It was found to provide important information in areas like those of failure analysis, process improvement and technological development as well as basic research.

Segregation of gallium at SiO2/Si interfaces during sputtering with Ga+ ions: experimental and computer simulation study

Abstract The sputtering of SiO 2 /Si interfaces with gallium ions was studied both experimentally by using secondary neutral mass spectrometry (SNMS) and by computer simulations by means of a dynamic Monte Carlo code. Oscillations of the gallium signal (from implanted primary ions) at the interface between the SiO 2 and Si layers were observed. By means of computer simulations, it was shown that cascade effects alone cannot explain the experimental depth profiles. A model that includes additional defect transport phenomena such as bombardment-induced segregation is proposed and incorporated in an existing dynamic Monte Carlo computer code. The simulations with the new code give rise to profiles that are comparable with the experimental ones, confirming the correctness of the chosen approach.

Fluorinated Phosphoric Ester-Based Protective Material for Limestone-Made Ancient Monuments, Buildings, and Artifacts: An X-ray Photoelectron Spectroscopy Study

In this study, fluorinated phosphoric esters are evaluated as protective material for limestone from water-driven alteration processes. Hypotheses as to their molecular arrangement are also provided. The surface composition of limestone after treatment with a commercially available fluorinated phosphoric ester material was evaluated by X-ray photoelectron spectroscopy (XPS). Results were then compared with those obtained for the treated limestone after accelerated aging tests. In the limestone that had not been subjected to aging processes an XPS determined thickness of the protective coating equivalent to 95 ± 18 Å was observed. This fell to 49 ± 10 Å in the limestone examined after intensive aging tests. However, low surface wettability (θ = 135° ± 4) was seen to be maintained.