Search results for "amor"
showing 10 items of 1531 documents
Amorphous TiO2 in LP-OMCVD TiNxOy thin films revealed by XPS
2001
Abstract TiN(O)–TiO 2 thin films were prepared on Si(1 0 0) by the low pressure organo metallic chemical vapor deposition (LP-OMCVD) method, using ammonia and titanium isopropoxide as precursors. In order to complete previous characterizations, an Ar + bombardment/XPS coupled study was carried out. This method is based on the fact that the behavior of a compound towards an ion bombardment is a function of its composition. In particular, Ar + bombardment of TiO 2 (whatever its form) leads to a preferential sputtering of oxygen atoms with subsequent reduction of titanium and formation of Ti 3+ and Ti 2+ easily detectable by XPS from a significant broadening of the Ti 2p lines. In the opposite…
Amorphous, nanocrystalline and crystalline calcium carbonates in biological materials
2010
Raman spectroscopy is a powerful tool in identifying different calcium carbonate polymorphs. Here, the method is applied to cultured pearls from freshwater (genus Hyriopsis) and marine bivalve species (Pinctada maxima) as well as to shells of Diplodon chilensis patagonicus bivalves. Raman spectra for vaterite, detected for the first time in an adult shell, and amorphous calcium carbonate (ACC) are discussed. Results for ACC are compared with those of synthetically produced ACC and with the Raman spectroscopic features of stable biogenic ACC from the crustacean Porcellio scaber. Decomposition of the most intense signal of all calcium carbonate polymorphs—the ν1 symmetric stretching mode of t…
Effect of the Mo atom flow on the molybdenum growth on TiO2 (110) surface
2004
Abstract Molybdenum has been deposited at room temperature on stoichiometric TiO 2 (1 1 0) surfaces with two deposition rates: 0.1 equivalent monolayer (eqML) and 1.5 eqML min −1 . X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy studies clearly reveal an effect of the deposition rate upon the growth mode and the interfacial reaction. Indeed, whereas a strong interfacial reaction between Mo and TiO 2 involves a Stranski–Krastanov growth mode with the formation of amorphous molybdenum oxide monolayers for the lowest deposition rate, no reaction can be observed for the highest deposition rate. Moreover in this latter case, the growth mode seems to be a 3D …
L’anamorphose du roman : les distorsions de la perspective dans "la Disparition" de Georges Perec
2007
L’anamorphose apparaît en application aux arts plastiques et se traduit par le bouleversement du point de vue habituel. Cette distorsion visuelle, en créant le caractère énigmatique de l’œuvre, vise à la déstabilisation du spectateur qui, sollicité par les formes, participe de la pluralité de la vision et de la démultiplication des possibles interprétatifs. Cette relativité de la place du spectateur permet la migration du concept d’anamorphose au domaine littéraire et son application en tant que pratique de création ou, plutôt, de réception : L’anamorphose […] procède par une intervention des éléments et des fonctions. Au lieu d’une réduction progressive à leurs limites visibles, c’est une …
A structural investigation of titanium dioxide photocatalysts
1991
Abstract A study of the structure and the morphology of a titanium dioxide photocatalyst (Degussa P25) reveals multiphasic material consisting of an amorphous state, together with the crystalline phases anatase and rutile in the approximate proportions 80 20 . Transmission electron microscopy provides evidence that some individual particles are a mixture of the amorphous state with either the anatase phase or with the rutile phase, and that some particles, which are mostly anatase, are covered by a thin overlayer of rutile which manifests its presence by the appearance of Moire fringes. The photocatalytic activity of this form of titanium dioxide is reported as being greater than the activi…
The influence of the anatase nanoparticles boundaries on the titania activity performance
2014
Metal oxides structures, formed by ordered self-assembling of crystalline nanoparticles aggregates, are attracting growing attention in fields such as catalysis or solar cells. The properties of these structures are influenced not only by their morphology and nanoparticles composition but also by the assembled particles boundaries. In order to determine the influence of these boundaries on the structures properties, the present investigation has been devoted to study the characteristics of anatase nanoparticles boundaries in titania aggregates prepared by TiCl4 hydrolysis at low temperature. Proton magic angle spinning nuclear magnetic resonance and high resolution transmission electron mic…
Reactive direct current magnetron sputtered TiO2 thin films with amorphous to crystalline structures.
2008
International audience; TiO2 thin films were deposited on soda–lime glass substrates by reactive direct current magnetron sputtering in a mixture of pure argon and oxygen. The influence of both the deposition time, td, and the post-annealing treatments on the films morphology, composition and structure was analyzed by scanning electron microscopy, ellipsometry, X-ray photoelectrons spectroscopy, X-ray diffraction (XRD) and Raman spectroscopy. Amorphous TiO2 was obtained for the shortest deposition time, td=15 min. Increasing td up to 30 min, poorly crystallized anatase and rutile phases were formed together with amorphous TiO2, as was revealed by complementary XRD patterns and Raman spectra…
Anatase nanoparticles boundaries resulting from titanium tetrachloride hydrolysis
2017
An important factor that governs solar energy transformation into electrical or chemical energy, when using nanoparticles-based devices, is the spatial location of traps limiting electron transport. Evidences have been presented indicating that the electron diffusion is strongly influenced by nanoparticle boundaries, whose characteristics depend on the particles preparation. In the present work we have studied the role of hydrated excess proton structures in the formation of anatase nanoparticles boundaries in samples prepared by TiCl4 hydrolysis at low temperature and strong acidic conditions. The samples, constituted by anatase nanocrystals but, mainly, by amorphous titania, are studied b…
Influence of Amorphous TiO2-x on Titania Nanoparticle Growth and Anatase-to-Rutile Transformation
2012
Amorphous TiO2-x formed together with precursors and anatase nuclei, during TiCl4 hydrolysis at soft conditions, influences both crystal growth and phase stability. The highly defective nanoparticles of anatase grow by reaction of their basic hydroxyls with acidic ones of TiO2 precursor species. The growth of anatase crystals, however, is affected by their interactions with simultaneously formed amorphous TiO2-x which increasingly covers the particles hindering the anatase-precursor contact. The interactions among anatase and amorphous and precursor components have been studied by H-1-MAS (magic angle spinning) NMR spectroscopy. The interaction between acid and basic hydroxyls favors the fo…
The effect of the surface disordered layer on the photoreactivity of titania nanoparticles
2017
It is well known that the surface of metal oxide catalysts presents, usually, non-crystalline species containing impurities and low coordinated cations, which are observed in HRTEM images as a disordered layer of amorphous phase. Despite of being these species more accessible and less stable than the crystalline catalysts components, they have been rarely considered when analysing the catalyst activity. In this work, we have studied the effect of a treatment with HCl solution at pH = 0 on the characteristics of the disordered layer in two commercial anatase TiO2 samples, using techniques such as TGA, 1H MAS-NMR and HRTEM, and by determining these sample photocatalytic activity for the 4-nit…