Anna Maria Salvi

XPS characterization of (copper-based) coloured stains formed on limestone surfaces of outdoor Roman monuments

Limestone basements holding bronzes or other copper alloys artefacts such as sculptures, decorations and dedicatory inscriptions are frequently met both in modern and ancient monuments. In outdoor conditions, such a combination implies the corrosion products of the copper based alloy, directly exposed to rainwater, will be drained off and migrate through the porous surfaces, forming stains of different colours and intensities, finally causing the limestone structures to deteriorate.In this work we have analysed samples from two modern limestone monuments in Rome, the Botticino surfaces of the ‘Vittoriano’ (by G.Sacconi, 1885-1911- Piazza Venezia) and the travertine basement of the ‘Statua dello Studente’ (by A.Cataldi, 1920- University city, La Sapienza), and focussed our investigation on the chemical composition of the copper-stained zones using XPS (X-ray Photoelectron Spectroscopy) as a surface-specific technique.Based on observations reporting on the structure and bonding at the calcite surfaces we have identified copper complexes and mixed calcium/copper carbonates associated with the stains, as well as the chemical state of other elements therein included, and related the compositional changes with differences in chromatic characteristics and sampling locations.

Peak fitting of the chromium 2p XPS spectrum

Abstract An XPS investigation of loss feature and peak shape analysis of the chromium 2p region has been performed. The approach is based on the use of a modified Shirley background model and requires the estimation of an individual background for each component of the photopeak under examination. The results obtained from the analysis of clean and oxidised chromium metal and pure Cr 2 O 3 , notwithstanding possible shortcomings in the model, give evidence for the importance of a proper consideration of satellite structures in the peak synthesis of Cr 2p XPS spectra. The results also have important ramifications in the peak fitting of the 2p spectra of other d-band transition metals such as manganese, iron and cobalt.

Nanoparticles and thin film formation in ultrashort pulsed laser deposition of vanadium oxide.

The ultrashort pulsed laser deposition of vanadium oxide thin films has been carried out by a frequency-doubled Nd:glass laser with a pulse duration of 250 fs. The characteristics of the plasma produced by the laser-target interaction have been studied by ICCD imaging and optical emission spectroscopy. The results confirm that an emitting plasma produced by ultrashort laser pulses is formed by both a primary and a secondary component. The secondary component consists of particles with a nanometric size, and their composition and spatial angular distribution influence the deposited films. In fact, these films, analyzed by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and atomic force microscopy, are formed by the aggregation of a large number of nanoparticles whose composition is explained by a model based on equilibrium thermal evaporation from particles directly ejected from the target. On these basis, the presence in the films of a mixture of V(2)O(5) and VO(2) is discussed.

Voltammetric and XPS investigations of polynuclear ruthenium-containing cyanometallate film electrodes

Abstract Glassy carbon electrodes coated with thin films of mixed valence ruthenium-oxo-species stabilized by cyanoruthenate or cyanoferrate crosslinks were investigated by cyclic voltammetry and X-ray photoelectron spectroscopy (XPS). Electrochemical deposition was accomplished in dilute mineral acid solutions (e.g. 10 mM H 2 SO 4 ) containing millimolar concentrations of RuCl 3 + K 4 Fe(CN) 6 , or RuCl 3 + K 4 Ru(CN) 6 , or OsCl 3 + K 4 Ru(CN) 6 . Film deposition is attributed to growth of compact and conducting lattices with significant oxo- (MOM) and cyano-bridging (M′CNM), in which M represents Ru, or Os, while M′ refers to Ru or Fe. Particular attention was devoted to the polynuclear ruthenium oxide microstructure (RuORu) crosslinked with cyanoruthenate and cyanoferrate, designated as RuORuCN and RuoFeCN respectively. From an electrochemical point of view, the mixed metal RuOFeCN behaves in a manner analogous to the RuORuCN film electrode, and indeed these modified electrodes are capable of catalyzing the oxidation of several substrates in acidic solutions. Depending on the applied potential, two distinct and selective reactive sites are recognizable in the electro-oxidation processes of As(III) and 2-furaldehyde at both RuOFeCN and RuORuCN film electrodes. XPS characterization of these ruthenium-containing cyanometallate films shows clear evidence of the existence of two oxidation states of ruthenium (Ru 3d region), which are respectively attributed to oxo-ruthenium(IV) and dioxo-ruthenium(VI) or Ru(V) in the oxide framework of the inorganic lattice.

X-ray photoelectron spectroscopy, X-ray excited Auger electron spectroscopy and time-of-flight secondary ion mass spectroscopy characterization of carbon fibres activated by d.c. corona discharge at ambient pressure and temperature

Abstract High modulus polyacrylonitrile-derived fibres were characterized by X-ray photoelectron spectroscopy, X-ray excited Auger electron spectroscopy and time-of-flight secondary ion mass spectroscopy after d.c. corona discharge treatments under a nitrogen atmosphere at ambient pressure and temperature. The results allow identification of the main functional groups produced by the treatment on the fibre surface and verification of a substantial equivalence of negative- and positive-corona discharge treatments.

Li+ distribution into V2O5 films resulting from electrochemical intercalation reactions

We studied interface effects of thin film V2O5 electrodes on top of indium tin oxide (ITO) glass for Li intercalation by means of a combination of methods: depth-profiling by secondary ion mass spectroscopy (SIMS), electrochemical insertion-extraction of lithium ions by slow-scan cyclic voltammetry (SSCV) and by potentiostatic intermittent titration technique (PITT). We show that the Li+ distribution inside the oxide film is always far from homogeneous, and that different diffusion paths (parallel to interfaces as well as perpendicular to them) have to be considered in experiments with electrodes having areas of few cm2. The exposed edge formed when cutting out coupons from the coated glass plate supporting the V2O5 electrode plays a significant role in the process, because it exposes the V2O5-ITO interface to the electrolyte.

Activation of carbon fibres by negative d.c. corona discharge at ambient pressure and temperature

Abstract After a suitable cleaning treatment, high modulus, unsized, polyacrylonitrile-derived carbon fibres were surface-treated by negative d.c. corona discharges under a flow of various nitrogen/oxygen mixtures at ambient pressure and temperature. The surface composition and morphology of the fibres, characterized before and after the treatment by X-ray photoelectron spectroscopy, X-ray excited Auger spectroscopy and scanning electron microscopy, were influenced by several experimental parameters (applied potential, gaseous atmosphere, time of treatment, geometry of the corona apparatus, post-treatment storage conditions, etc.). The matter is discussed in the light of previously published information.

Factors influencing charge capacity of vanadium pentoxide thin films during lithium ion intercalation/deintercalation cycles

The intercalation of vanadium pentoxide by lithium ions leads to a change in optical properties, a process that is of value in thin-film electrochromic devices. In this study, films of V2O5, deposited on indium tin oxide (ITO) glass coupons by a sol-gel process, were challenged by increasing numbers of charge-discharge cycles ranging from 72 to 589 full cycles. The samples were characterized by x-ray photoelectron spectroscopy (XPS) and then examined in the deintercalated state by time-of-flight secondary ion mass spectroscopy (SIMS). XPS enabled measurement of the thickness and composition of the solid-electrolyte interface and provided evidence of the residual V4+ concentration within the top few nanometers of the surface. The SIMS profile gave direct information on the thickness of the films and on the thickness loss caused by rinsing the samples after the electrochemical exposure. Determination, by SIMS, of the concentration of lithium ions has enabled a correction to be made for the amount of inactiv...

Comparative Spectra Illustrating Degradation of CaC2O4⋅H2O During XPS Analysis

Calcium oxalate monohydrate is found as a by-product of environmental damage to stonework of importance in preserving cultural heritage. XPS (X-ray Photoelectron Spectroscopy) was here used to characterize the standard compound, calcium oxalate monohydrate, RPE, chemically synthesized as provided by Carlo Erba Reagents - Cod. 434004. Degradation occurred during analysis and this is described. Repeat XPS acquisitions have allowed us to monitor the spectral changes of calcium oxalate during the whole process of analysis: its degradation was rationalized by considering the effect of x-ray power; UHV exposure; and thermal effects suffered by the powdered sample after its insertion into the spectrometer and, particularly, during spectra acquisition. Measurement of degradation with time enabled extrapolation to yield the primary composition. It was found that samples will completely dehydrate in ultra high vacuum, UHV. Although dehydrated samples are then stable in UHV, during XPS acquisitions degradation of ca...

In Situ Electrochemical–AFM and Cluster-Ion-Profiled XPS Characterization of an Insulating Polymeric Membrane as a Substrate for Immobilizing Biomolecules

The electrochemical oxidation of ortho-aminophenol (oAP) by cyclic voltammetry (CV), on platinum substrates in neutral solution, produces a polymeric film (PoAP) that grows to a limiting thickness of about 10 nm. The insulating film has potential use as a bioimmobilizing substrate, with its specificity depending on the orientation of its molecular chains. Prior investigations suggest that the film consists of alternating quinoneimine and oAP units, progressively filling all the platinum sites during the electrosynthesis. This work concerns the evaluation of the growth orientation of PoAP chains, which until now was deduced only from indirect evidence. Atomic force microscopy (AFM) has been used in situ with an electrochemical cell so that PoAP deposition on a specific area can be observed, thus avoiding any surface reorganization during ex situ transport. In parallel with microscopy, XPS experiments have been performed using cluster ion beams to profile this film, which is exceptionally thin, without damage while retaining molecular information.