Monica Montecchi

Formation and distribution of compounds at the Ru–Si(001) ultrathin film interface

Interface formation between Ru and Si(001) has been studied by x-ray and ultraviolet photoemissions. The film properties were investigated, for metal deposition at room temperature, as a function of the Ru film thickness and as a function of the annealing temperature of a thick grown film. From the evolution of the Ru and Si core levels, we find that alloying takes place at the interface during growth and estimate the thickness of the intermixed region to be of the order of 15–20 ML. Annealing at increasingly high temperatures causes the formation of different silicide phases, which are discussed in relation to theoretical and experimental data on related transition metal silicides.

Perfluoropolyether-based organic-inorganic hybrid coatings: Preparation and surface characterisation

SummariesHydrophobic-oleophobic coatings were prepared by using the sol-gel process with organic-inorganic hybrids based on perfluoropolyether-polycaprolactone (PFPE-PCL) copolymers. Hybrid coatings were prepared by changing the organic-inorganic ratio, the PFPE/PCL ratio in the copolymer, and the reaction conditions. A complete surface characterisation was carried out by contact angle analysis and x-ray photoemission spectroscopy (XPS). In all cases the wettability of the coatings was found to be very low. Surface composition analysis showed that the surface segregation of the fluorinated PFPE segments was always high enough to give a very high hydrophobic character to the coating surface.RésuméDes revêtements hydrophobes-oléophobes ont été préparés, grâce au procédé sol-gel, en utilisant des hybrides organiques-inorganiques basé sur les co-polymères perfluoropolyéther-polycaprolactone (PFPE-PCL). Des revêtements hybrides ont été préparés en changeant le rapport organique-inorganique, le rapport PFPE/CPL dans le co-polymère et les conditions de la réaction. On a effectué une caractérisation complète de la surface grâce à l’analyse d’angle de contact et à la spectroscopie de photoémission X (XPS). Dans tous les cas la mouillabilité des revêtements s’est révélée d’être très basse. L’analyse de la composition de la surface a montré que la ségrégation, à la surface, des segments fluorés PFPE était à tous moments assez élevée pour doter la surface du revêtement d’une hydrophobie très élevée.ZusammenfassungHydrophobisch-olephobische Anstriche wurden durch den Sol-Gel Prozeß mit organisch-anorganischen Hybriden auf Basis von Perfluoropolyether-Polycaprolakton (PFPE-PCL) Kopolymeren hergestellt. Durch Variationen im Verhältnis von organisch/anorganischen Bestandteilen, des PFPE/PCL Verhältnisses im Kopolymer und der Reaktionsbedingungen wurden verschiedene Hybridanstriche hergestellt, und eine komplette Oberflächencharakterisation durch Kontaktwinkelanalyse und Röntgen-Fotoemissionsspektroskopie (XPS) geliefert. In allen Fällen fanden wir, daß der Anstrich nur sehr bedingt benetzbar war. Eine Analyse der Oberflächenkomposition ergab, daß die Oberflächentrennung der fluorinisierten PFPE-Segmente immer ausreichend war, um der Anstrichoberfläche einen stark hydrophoben Charakter zu verleihen.

Perfluoropolyether-based organic-inorganic hybrid coatings: preparation and surface characterisation.

SummariesHydrophobic-oleophobic coatings were prepared by using the sol-gel process with organic-inorganic hybrids based on perfluoropolyether-polycaprolactone (PFPE-PCL) copolymers. Hybrid coatings were prepared by changing the organic-inorganic ratio, the PFPE/PCL ratio in the copolymer, and the reaction conditions. A complete surface characterisation was carried out by contact angle analysis and x-ray photoemission spectroscopy (XPS). In all cases the wettability of the coatings was found to be very low. Surface composition analysis showed that the surface segregation of the fluorinated PFPE segments was always high enough to give a very high hydrophobic character to the coating surface.RésuméDes revêtements hydrophobes-oléophobes ont été préparés, grâce au procédé sol-gel, en utilisant des hybrides organiques-inorganiques basé sur les co-polymères perfluoropolyéther-polycaprolactone (PFPE-PCL). Des revêtements hybrides ont été préparés en changeant le rapport organique-inorganique, le rapport PFPE/CPL dans le co-polymère et les conditions de la réaction. On a effectué une caractérisation complète de la surface grâce à l’analyse d’angle de contact et à la spectroscopie de photoémission X (XPS). Dans tous les cas la mouillabilité des revêtements s’est révélée d’être très basse. L’analyse de la composition de la surface a montré que la ségrégation, à la surface, des segments fluorés PFPE était à tous moments assez élevée pour doter la surface du revêtement d’une hydrophobie très élevée.ZusammenfassungHydrophobisch-olephobische Anstriche wurden durch den Sol-Gel Prozeß mit organisch-anorganischen Hybriden auf Basis von Perfluoropolyether-Polycaprolakton (PFPE-PCL) Kopolymeren hergestellt. Durch Variationen im Verhältnis von organisch/anorganischen Bestandteilen, des PFPE/PCL Verhältnisses im Kopolymer und der Reaktionsbedingungen wurden verschiedene Hybridanstriche hergestellt, und eine komplette Oberflächencharakterisation durch Kontaktwinkelanalyse und Röntgen-Fotoemissionsspektroskopie (XPS) geliefert. In allen Fällen fanden wir, daß der Anstrich nur sehr bedingt benetzbar war. Eine Analyse der Oberflächenkomposition ergab, daß die Oberflächentrennung der fluorinisierten PFPE-Segmente immer ausreichend war, um der Anstrichoberfläche einen stark hydrophoben Charakter zu verleihen.

CRYSTAL CHEMISTRY AND SURFACE CONFIGURATIONS OF TWO IRON-BEARING TRIOCTAHEDRAL MICA-1M POLYTYPES

The crystal chemical features of the bulk and the uppermost (001) surface layers of freshly cleaved surfaces of two trioctahedral Fe-rich mica-1M (space group C2/m) polytypes, i.e. a tetraferriphlogopite from an alkaline-carbonatitic complex near Tapira, Belo Horizonte, Minas Gerais, Brazil, and an Fe2+-bearing phlogopite containing less tetrahedral Fe3+ from the Kovdor carbonatite-bearing, alkaline-ultrabasic complex, Kola Peninsula, Russia, are explored here. Mineral-surface effects were investigated by X-ray Photoelectron Spectroscopy (XPS) and compared to the bulk structure derived from single-crystal X-ray diffraction data. Based on microprobe analysis and the X-ray study, the chemical formulae are [XII](K0.99)[VI](Fe0.082+Fe0.153+Mg2.76Ti0.01)[IV](Fe0.823+Si3.18)O10.37F0.24(OH)1.39 and [XII](K0.94Na0.06)[VI](Fe0.172+Fe0.053+Mg2.75Mn0.01Ti0.05)[IV](Fe0.163+Al0.84Si3.00)O10.21F0.35(OH)1.44 for tetraferriphlogopite and Fe-bearing phlogopite, respectively. The tetrahedrally coordinated sites of the two minerals differ, where Fe-for-Si substitution is at 20.5% in tetra-ferriphlogopite and at 4% in Fe-bearing phlogopite.The bulk study showed that Fe3+ substitution increases the tetrahedral sheet thickness and the mean tetrahedral edge lengths in tetra-ferriphlogopite compared to Fe-bearing phlogopite. The tetrahedral rotation angle (α) changes remarkably from tetra-ferriphlogopite (α = 10.5°) to the Fe-bearing phlogopite (α = 8.5°), thus indicating a significantly greater initial lateral sheet misfit (leading to a greater tetrahedral ring distortion) between the tetrahedral and the octahedral sheets in the tetra-ferriphlogopite compared to Fe-bearing phlogopite. The Fe3+ substitution for Si and the differences in lateral dimensions of the tetrahedral and octahedral sheets affect the tetrahedral flattening angle (τ), with τ = 109.9° for tetraferriphlogopite and τ = 110.7° for Fe-bearing phlogopite.The binding energy (BE) of photoelectron peaks in XPS is dependent on the chemical state of atoms and on their local environment at the near surface. The Mg in both phlogopites is bonded to F, with the BE of Mg1s increasing as coordinated oxygen atoms are substituted by fluorine. For Fe-rich phlogopite (BE = 1306.8 eV), the binding energy is greater than for tetra-ferriphlogopite (BE = 1305.9 eV), and this is consistent with the bulk composition having greater F-for-OH substitution in Fe-rich phlogopite (F0.35vs. tetra-ferriphlogopite, F0.24 atoms per formula unit).

Crystal chemistry and surface configurations of two polylithionite-1M crystals

Abstract This paper explores the crystal chemical features of the bulk and the outermost (001) surface layers of two trioctahedral Li-rich mica-1M (space group C2) polytypes, i.e., a polylithionite (MLG-114) from Li-mica granitic pegmatite at St. Austell (SW England) and a Fe2+-rich polylithionite (Ch-140) from a rhyolite at Profitis Ilias, Chios Island, Greece. Structural formulas are [xii](K0.952Na0.019Rb0.019) [vi](Al1.034 Li1.459Fe2+0.389Fe3+0.046Mn0.038Mg0.002Zn0.002Ti0.001) [iv](Al3+0.477 Si3.523)O10.081(F1.735OH0.184) and [xii](K0.992Na0.014) [vi](Al0.980Li1.028Fe2+0.787Fe3+0.022Mn0.059Mg0.052Zn0.010Ti0.024) [iv](Al3+0.857Si3.143) O10.095 (F1.617OH0.288) for MLG-114 and Ch-140, respectively. Each mineral is characterized by a high F content in the anion site and has tetrahedral and octahedral compositions related to the exchange vector [vi]Li-1[iv]Si-1[vi]Fe2+[iv]Al. Unit-cell dimensions are a = 5.251(1), b = 9.066(2), c = 10.087(2) Å; β = 100.694(5)° for polylithionite MLG- 114 and a = 5.282(1), b = 9.121(3), c = 10.080(3) Å; β = 100.764(5)° for Ch-140. Crystal structure refinements (agreement factors are R = 3.58% and 3.75% for MLG-114 and Ch-140, respectively) demonstrate that the [vi]Li-1 [vi]Fe2+[iv]Si-1[iv]Al exchange vector produces a decrease in the lateral dimensions of the tetrahedral and octahedral sheets. The decrease in basal oxygen distances results from the effect of the strain caused by the orientation of opposing tetrahedral sheets within a 2:1 layer. The decrease reduces the strain so that the basal oxygen plane can remain nearly planar. Changes in these dimensions via distortions of the tetrahedral basal-oxygen ring (α = 3.3° and 4.1° for MLG-114 and Ch-140, respectively) are limited. Octahedral M1 and M3 sites are similar in size and much larger than M2 and the mean electron count is M3 < M1 < M2 in MLG-114 and M1 ≈ M2 < M3 in Ch-140. Al preferentially occupies the M2 site, whereas Fe and Li are nearly disordered between M1 and M3 sites with a slight preference of Fe for the M1 site in MLG-114 and for M3 site in Ch-140. Element concentrations on the (001) surface, obtained through X‑ray photoelectron spectroscopy (XPS) high-resolution spectra for Si2p, Al2p, Fe2p, K2p, Li1s, and F1s core levels, indicate that a greater amount of lithium and a smaller amount of potassium characterize the surface with respect to the bulk. The decrease in K content, commonly observed in micas, is related to its location on the cleavage surface, because the cation must be distributed equally between the two (001) surfaces generated upon cleavage. The increase in Li content on or near the (001) cleavage surface suggests a preference for cleavage near lithium-enriched regions. The surface structure of the polylithionite crystals suggests that Al, Li, and Fe cations maintain coordination features at the surface similar to the bulk. Silicon, however, which is generally in fourfold coordination, shows also a small number of [1]-fold coordinated components at a binding energy of 99.85 eV.

Electrochemical method for pickling and passivation of austenitic steel welds

Abstract The aim of this work is to develop an innovative process for pickling and passivating tungsten inert gas welds on austenitic stainless steel in order to obtain complete removal of non-protective oxides and to passivate the metal surface. In particular, the treatment intends to increase both corrosion resistance and surface appearance of the steel without making use of traditional pickling solutions (which usually contain high concentrations of strong acids). The treatment, based on an electrochemical approach, uses specific electrolytes, and to evaluate their effect in terms of corrosion resistance and surface finish, different solutions were prepared and tested using low concentrations of weak organic acids, e.g. citric, oxalic, sulphamic, gluconic and lactic acids. This aspect is very important to reduce the hazardousness of the solution compared to the traditional pickling acids.

Molecular states of polyacenes grown on noble metal surfaces

Here we present a combined photoemission (UPS), metastable deexcitation (MDS) and optical absorption (NEXAFS) at C K-edge study of molecular states of polyacenes grown on Ag(111) and Au(111), from submonolayer to multilayer thicknesses. We focus on the evolution of the HOMO and LUMO molecular states induced by the adsorption from submonolayer to monolayer thickness and we find a different redistribution of these states in the various systems formed at RT: while a strong redistribution of the molecular states takes place in Pn/Ag(111) and Tc/Ag(111) interface, a weaker interaction is indicated for Tc/Au(111).

Atomic and electronic structure of ultrathin fluoride barrier layers at the oxide/Si interface.

A SrF(2) ultrathin barrier layer on Si(001) is used to form a sharp interface and block reactivity and intermixing between the semiconductor and a Yb(2)O(3) overlayer. Yb(2)O(3)/Si(001) and Yb(2)O(3)/SrF(2)/Si(001) interfaces grown in ultra high vacuum by molecular beam epitaxy are studied by photoemission and x-ray absorption fine structure. Without the fluoride interlayer, Yb(2)O(3)/Si(001) presents an interface reacted region formed by SiO(x) and/or silicate compounds, which is about 9 Å thick and increases up to 14-15 Å after annealing at 500-700 °C. A uniform single layer of SrF(2) molecules blocks intermixing and reduces the oxidized Si region to 2.4 Å after deposition and to 3.5 Å after annealing at 500 °C. In both cases we estimate a conduction band offset and a valence band offset of ∼ 1.7 eV and 2.4 eV between the oxide and Si, respectively. X-ray absorption fine structure measurements at the Yb L(III) edge suggest that the Yb oxide films exhibit a significant degree of static disorder with and without the fluoride barrier. Sr K edge measurements indicate that the ultrathin fluoride films are reacted, with the formation of bonds between Si and Sr; the Sr-Sr and Sr-F interatomic distances in the ultrathin fluoride barrier film are relaxed to the bulk value.