Chemical bonding and composition of silicon nitride films prepared by inductively coupled plasma chemical vapor deposition

Thin silicon nitride films were prepared at 350 degrees C by inductively coupled plasma chemical vapor deposition on Si(100) substrates under different NH(3)/SiH(4) or N(2)/SiH(4) gas mixture. The chemical composition and bonding structure of the deposited films were investigated as a function of the process parameters, such as the gas flow ratio NH(3)/SiH(4) or N(2)/SiH(4) and the RF power, using X-ray photoelectron spectroscopy (XPS). The gas flow ratio was 1.4, 4.3, 7.2 or 9.5 and the RF power, 50 or 100 W. Decomposition results of Si 2p XPS spectra indicated the presence of bulk Si, under-stoichiometric nitride, stoichiometric nitride Si(3)N(4), oxynitride SiN(x)O(y), and stoichiometric oxide SiO(2), and the amounts of these compounds were strongly influenced by the two process parameters. These results were consistent with those obtained from N 1s XPS spectra. The chemical composition ratio N/Si in the film increased with increasing the gas flow ratio until the gas flow ratio reached 4.3, reflecting the high reactivity of nitrogen, and stayed almost constant for further increase in gas flow ratio, the excess nitrogen being rejected from the growing film. A considerable and unexpected incorporation of contaminant oxygen and carbon into the depositing film was observed and attributed to their high chemical reactivity. (C) 2010 Elsevier B.V. All rights reserved.

Thermo-responsive microphase separated supramolecular polyurethanes

The ability to generate very stable assemblies via non-covalent interactions has enabled materials to be constructed that were not feasible via traditional covalent bond formation processes. A series of low molecular mass bisurethane and bisurea polymers have been developed that form stable self-assembled networks through hydrogen bonding interactions. Thermo-responsive polymers were generated by end-capping poly(ethylene-co-butylene) or polybutadiene chains with the bisurethane or bisurea motif. Microphase separation is observed via TEM and small-angle X-ray scattering (SAXS) for the modified pseudo polymers and significant differences in the temperature dependence of microphase separation are analysed via SAXS. The importance of the polarity of the end groups is manifested in distinct temperature-dependent microphase separation behaviour. Information on the local hydrogen bonding structure is provided by wide-angle X-ray scattering and variable temperature FTI

X-ray photoelectron spectroscopy analysis of zirconium nitride-like films prepared on Si(100) substrates by ion beam assisted deposition

Thin zirconium nitride films were prepared on Si(l 00) substrates at room temperature by ion beam assisted deposition with a 2 keV nitrogen ion beam. Arrival rate ratios ARR(N/Zr) used were 0.19, 0.39, 0.92, and 1.86. The chemical composition and bonding structure of the films were analyzed with X-ray photoelectron spectroscopy (XPS). Deconvolution results for Zr 3d, Zr 3p(3/2), N 1s, O 1s, and C 1s XPS spectra indicated self-consistently the presence of metal Zr-0, nitride ZrN, oxide ZrO2, oxymnide Zr2N2O, and carbide ZrC phases, and the amounts of these compounds were influenced by ARR(N/Zr). The chemical composition ratio N/Zr in the film increased with increasing ARR(N/Zr) until ARR(N/Zr) reached 0.92, reflecting the high reactivity of nitrogen in the ion beam, and stayed almost constant for ARR(N/Zr) >= 1, the excess nitrogen being rejected from the growing film. A considerable incorporation of contaminant oxygen and carbon into the depositing film was attributed to the getter effect of zirconium. (C) 2007 Elsevier B.V. All rights reserved.

Highly corrosion resistant siloxane-polymethyl methacrylate hybrid coatings

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Study on the initial stages of water corrosion of fluorozirconate glasses

The surface corrosion process associated with the hydrolysis of fluorozirconate glass, ZBLAN (53ZrF(4), 20BaF(2), 20NaF, 4LaF(2), 3AlF(3)) was investigated using X-ray photoelectron spectroscopy (XPS), grazing-incidence small angle X-ray scattering (GISAXS), X-ray reflectivity (XRR) and scanning electron microscopy (SEM). After a short exposure period (25 min) of the glass surface to deionized water the XPS data indicate an increase of the oxygen content accompanied by a decrease of fluorine concentration. The analysis of the chemical bonding structure identified the predominant surface reaction products as zirconium hydroxyfluoride and oxyfluoride species. The second most abundant glass component, bariumfluoride, remains almost unaffected by oxygen, while sodium fluoride is completely removed from the attacked surface region. The detected structural and compositional changes are related to the selective dissolution of the glass components leading to the formation of a new surface phase. This process is accompanied by a visible surface roughening caused by reprecipitated species, observed by SEM. The modification of the glass surface is responsible for an increase of the GISAXS intensity. The scattering was attributed to nanovoids formed at the surface region of the glass with an average size of 2.4 +/- 0.05 nm. (C) 2004 Elsevier B.V. All rights reserved.

Photo-induced effects in Ge25Ga10S65 glasses studied by XPS and XAS

The present paper focuses on the structural, electronic, and compositional properties of Ge25Ga10S65 glasses before and after UV illumination in air using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) techniques. The XPS Ge 3d spectra reveal the existence of Ge-O bonds in the surface region of illuminated glass. In the case of this sample, XAS O K-edge spectra showed the formation of an enriched region of oxygen atoms in the glass bulk, indicating a different bonding structure of oxygen at the surface and in the bulk of the glass. Moreover, the structural changes that occur after UV illumination in the glass sample are identified as the formation of a homogeneous germanium oxide surface layer followed by an intermediary Ge25Ga10S65-yOz subsurface region. (c) 2005 Elsevier B.V. All rights reserved.

XPS study on water corrosion of fluorzirconate glasses and their protection by a layer of surface modified tin dioxide nanoparticles

The surface corrosion process associated with the hydrolysis of fluorozirconate glass, Z-BLAN (53ZrF(4), 20BaF(2), 20NaF, 4LaF(2), 3AlF(3)), and the corrosion protection efficiency of a nanocrystalline transparent SnO2 layer were investigated by X-ray photoelectron spectroscopy. The tin oxide film was deposited by the sol-gel dip-coating process in the presence of Tiron(R) as particle surface modifier agent. The chemical bonding structure and composition of the surface region of coated and non-coated ZBLAN were studied before water contact and after different immersion periods (5-30 min). In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species inducing the formation of a new surface phase consisting of stable zirconium oxyfluoride, barium fluoride and lanthanum fluoride species, the results for the SnO2-coated glass showed that the hydrolytic attack induces a filling of the film nanopores by dissolved glass material and the formation of tin oxylluoride and zirconium oxyfluoride species. This process results in a modified film, which acts as a hermetic diffusion barrier protecting efficiently the glass surface. (C) 2006 Elsevier B.V. All rights reserved.

Corrosion protection of fluorzirconate glasses coated by a layer of surface modified tin oxide nanoparticles

The protection efficiency against water corrosion of fluorozirconate glass, ZBLAN, dip-coated by nanocrystalline tin oxide film containing the organic molecule Tiron® was investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The chemical bonding structure of the surface region and morphology were studied before and after two water exposure periods of 5 and 30 min. The results of the analysis for the as-grown sample revealed a SnO1.6 phase containing carbon and sulfur, related to Tiron®, and traces of elements related to ZBLAN (Zr, F, Ba). This fact and the clear evidence of the presence of tin oxifluoride specie (SnOxF y) indicates a diffusion of the glass components into the porous coating. After water exposure, the increase of the oxygen concentration accompanied by a strong increase of Zr, F, Ba and Na content is interpreted as filling of the nanopores of the film by glass compounds. The formation of a compact protective layer is supported by the morphological changes observed by AFM. © 2005 Elsevier B.V. All rights reserved.

Improvement of the photocatalytic activity of magnetite by Mn-incorporation

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Abscheidung und Charakterisierung von Plasmapolymerschichten auf Fluorkohlenstoff- und Siloxan-Basis

In dieser Arbeit wurden Fluorkohlenstoff-basierte und siliziumorganische Plasmapolymerfilme hergestellt und hinsichtlich ihrer strukturellen und funktionalen Eigenschaften untersucht. Beide untersuchten Materialsysteme sind in der Beschichtungstechnologie von großem wissenschaftlichen und anwendungstechnischen Interesse. Die Schichtabscheidung erfolgte mittels plasmachemischer Gasphasenabscheidung (PECVD) an Parallelplattenreaktoren. Bei den Untersuchungen zur Fluorkohlenstoff-Plasmapolymerisation stand die Herstellung ultra-dünner, d. h. weniger als 5 nm dicker Schichten im Vordergrund. Dies wurde durch gepulste Plasmaanregung und Verwendung eines Gasgemisches aus Trifluormethan (CHF3) und Argon realisiert. Die Bindungsstruktur der Schichten wurden in Abhängigkeit der eingespeisten Leistung, die den Fragmentationsgrad der Monomere im Plasma bestimmt, analysiert. Hierzu wurden die Röntgen-Photoelektronenspektroskopie (XPS), Rasterkraftmikroskopie (AFM), Flugzeit-Sekundärionenmassenspektrometrie (ToF-SIMS) und Röntgenreflektometrie (XRR) eingesetzt. Es zeigte sich, dass die abgeschiedenen Schichten ein homogenes Wachstumsverhalten und keine ausgeprägten Interfacebereiche zum Substrat und zur Oberfläche hin aufweisen. Die XPS-Analysen deuten darauf hin, dass Verkettungsreaktionen von CF2-Radikalen im Plasma eine wichtige Rolle für den Schichtbildungsprozess spielen. Weiterhin konnte gezeigt werden, dass der gewählte Beschichtungsprozess eine gezielte Reduzierung der Benetzbarkeit verschiedener Substrate ermöglicht. Dabei genügen Schichtdicken von weniger als 3 nm zur Erreichung eines teflonartigen Oberflächencharakters mit Oberflächenenergien um 20 mN/m. Damit erschließen sich neue Applikationsmöglichkeiten ultra-dünner Fluorkohlenstoffschichten, was anhand eines Beispiels aus dem Bereich der Nanooptik demonstriert wird. Für die siliziumorganischen Schichten unter Verwendung des Monomers Hexamethyldisiloxan (HMDSO) galt es zunächst, diejenigen Prozessparameter zu identifizieren, die ihren organischen bzw. glasartigen Charakter bestimmen. Hierzu wurde der Einfluss von Leistungseintrag und Zugabe von Sauerstoff als Reaktivgas auf die Elementzusammensetzung der Schichten untersucht. Bei niedrigen Plasmaleistungen und Sauerstoffflüssen werden vor allem kohlenstoffreiche Schichten abgeschieden, was auf eine geringere Fragmentierung der Kohlenwasserstoffgruppen zurückgeführt wurde. Es zeigte sich, dass die Variation des Sauerstoffanteils im Prozessgas eine sehr genaue Steuerbarkeit der Schichteigenschaften ermöglicht. Mittels Sekundär-Neutralteilchen-Massenspektrometrie (SNMS) konnte die prozesstechnische Realisierbarkeit und analytische Quantifizierbarkeit von Wechselschichtsystemen aus polymerartigen und glasartigen Lagen demonstriert werden. Aus dem Intensitätsverhältnis von Si:H-Molekülen zu Si-Atomen im SNMS-Spektrum ließ sich der Wasserstoffgehalt bestimmen. Weiterhin konnte gezeigt werden, dass durch Abscheidung von HMDSO-basierten Gradientenschichten eine deutliche Reduzierung von Reibung und Verschleiß bei Elastomerbauteilen erzielt werden kann.

Raman spectral evidence for hydration forces between collagen triple helices

Hydration forces are thought to result from the energetic cost of water rearrangement near macromolecular surfaces. Raman spectra, collected on the same collagen samples on which these forces were measured, reveal a continuous change in water hydrogen-bonding structure as a function of separation between collagen triple helices. The varying spectral parameters track the force-distance curve. The energetic cost of water “restructuring,” estimated from the spectra, is consistent with the measured energy of intermolecular interaction. These correlations support the idea that the change in water structure underlies the exponentially varying forces seen in this system at least over the 13–18-Å range of interaxial separations.

Anion-pi, Lone-Pair-pi, pi-pi and Hydrogen-Bonding Interactions in a Cu-II Complex of 2-Picolinate and Protonated 4,4 '-Bipyridine: Crystal Structure and Theoretical Studies

A Cu-II complex of protonated 4,4'-bipyridine (Hbyp) and 2-picolinate (pic), [Cu-2(pic)(3)(Hbyp)(H2O)(ClO4)(2)], has been synthesised and characterised by single-crystal X-ray analysis. The structure consists of two copper atoms that have different environments, bridged by a carboxylate group. The equatorial plane is formed by the two bidentate picolinate groups in one Cu-II, and one picolinate, one monodentate 4,4'-bipyridyl ligand and a water molecule in the other. Each copper atom is also weakly bonded to a perchlorate anion in an axial position. One of the coordinated perchlorate groups displays anion-pi interaction with the coordinated pyridine ring. The noncoordinated carboxylate oxygen is involved in lone-pair (l.p.)-pi interaction with the protonated pyridine ring. In addition there are pi-pi and H-bonding interactions in the structure. Bader's theory of "atoms in molecules" (AIM) is used to characterise the anion-pi and l.p.-pi interactions observed in the solid state. A high-level ab initio study (RI-MP2/aug-cc-pVTZ level of theory) has been performed to analyse the anion-pi binding affinity of the pyridine ring when it is coordinated to a transition metal and also when the other pyridine ring of the 4,4'-bipyridine moiety is protonated. Theoretical investigations support the experimental findings of an intricate network of intermolecular interactions, which is characterised in the studied complex, and also indicate that protonation as well as coordination to the transition metal have important roles in influencing the pi-binding properties of the aromatic ring. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)