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We demonstrate the existence of stoichiometric variations at the nanoscale when growing nanocolumnar SiO thin films by reactive magnetron sputtering deposition at oblique angles. Results show stoichiometric variations in the range 0.3 < x < 1.3 when growing a SiO thin film. This agrees with results from a numerical growth model that obtains a shift of the stoichiometry in all nanocolumns from lower values at the side facing the Si target to higher values at the opposite side. The different momentum distribution of the gaseous reactive and sputtered species results in preferential incorporation of the latter at a particular side of the nanocolumns. The general occurrence of this mechanism during the reactive magnetron sputtering deposition of substoichiometric thin films at oblique angles is discussed.

The graphene family comprises not only single layer graphene but also graphene-based nanomaterials (GBN), with remarkably different number of layers, lateral dimension and price. In this work, two of these GBN, namely graphene nanoplatelets (GNP) with n~15–30 layers and few-layer graphene (FLG) with n < 3 layers have been evaluated as fillers in 3¿mol% yttria stabilized tetragonal zirconia (3YTZP) ceramic composites. Composites with 10 and 20¿vol% GNP or FLG have been fabricated by wet powder processing and spark plasma sintering (SPS) and the influence of the content and number of layers of the graphene-based filler has been assessed. For both graphene-based fillers, an intermediate zirconia oxycarbide has been detected in the grain boundaries. The lower stacking degree and much more homogeneous distribution of the FLG, revealed by transmission electron microscopy (TEM), can improve load transfer between the GBNs and the ceramic matrix. However, high FLG contents lower densification of the composites, due partly to the larger FLG interplanar spacing also estimated by TEM. The hardness (both Vickers and nanoindentation) and the elastic modulus decrease with increased GBN content and with improved graphene dispersion. The FLG greatly inhibit the crack propagation that occur perpendicular to their preferential orientation plane. The composites with thinner FLG have higher electrical conductivity than those with GNP. The highest electrical conductivity is achieved by composites with 20¿vol% FLG in the direction perpendicular to the compression axis during sintering, s¿¿=¿3400¿±¿500¿Sm-1., Peer Reviewed, Postprint (published version)

Lanthanide-based inorganic nanoparticles (Ln-NPs) are an excellent choice for potential use as phosphors in luminescent bioimaging and as contrast agents in X-rays computed tomography (CT). Among the different Ln salts, Ln fluorides are preferred as phosphors matrices because of the low phonon energy of the fluoride lattice, which provides improved quantum efficiency to the phosphor. Cerium fluoride (CeF3), in particular, benefits from the well-known Ce3+ capacity to absorb ultraviolet (UV) radiation and efficiently transfer it to several active lanthanide ions like Tb3+. To date, different approaches have been developed for the synthesis of Ln:CeF3 NPs (e.g. hydrothermal synthesis, microemulsion, sonochemistry, etc.), most of which produce either aggregated NPs or micrometric particles, which are useless in biotechnology. The few procedures that yield highly uniform and well dispersed Ln:CeF3 nanoparticles suffer a number of drawbacks including high temperature synthesis, need of additives, use of hydrofluoric acid or hydrophobicity of the obtained NPs. Therefore, developing an effective, commercially attractive procedure working at mild or low temperatures, in the absence of surfactants, dispersing agents or corrosive precursors, to obtain uniform, hydrophilic Ln:CeF3 NPs is still a challenge. Herein we present an effective and commercially attractive procedure that renders uniform, hydrophilic Ln3+:CeF3 (Ln=Tb, Nd) nanoparticles at room temperature. The method consists of the homogeneous precipitation, in a mixture of polyol and water, of cations and anions using precursors that allow the controlled release of the latter. Different morphologies (lentils and disks) and sizes (from 40 nm to 80 nm diameter) are obtained depending on the polyol used as reaction medium (Figure 1). The Nd3+:CeF3 NPs are good candidates for in-vivo imaging because their excitation and emission wavelengths lie in the biological windows (Figure 2a). The Tb3+:CeF3 NPs produce an intense gr

A new approach is presented to produce amorphous porous silicon coatings (a-pSi) with closed porosity by magnetron sputtering of a silicon target. It is shown how the use of He as the process gas at moderated power (50–150 W RF) promotes the formation of closed nanometric pores during the growth of the silicon films. The use of oblique-angle deposition demonstrates the possibility of aligning and orientating the pores in one direction. The control of the deposition power allows the control of the pore size distribution. The films have been characterized by a variety of techniques, including scanning and transmission electron microscopy, electron energy loss spectroscopy, Rutherford back scattering and x-ray photoelectron spectroscopy, showing the incorporation of He into the films (most probably inside the closed pores) and limited surface oxidation of the silicon coating. The ellipsometry measurements show a significant decrease in the refractive index of porous coatings (n500 nm = 3.75) in comparison to dense coatings (n500 nm = 4.75). The capability of the method to prepare coatings with a tailored refractive index is therefore demonstrated. The versatility of the methodology is shown in this paper by preparing intrinsic or doped silicon and also depositing (under DC or RF discharge) a-pSi films on a variety of substrates, including flexible materials, with good chemical and mechanical stability. The fabrication of multilayers of silicon films of controlled refractive index in a simple (one-target chamber) deposition methodology is also presented.

Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa). ©2012 Microscopy Society of America ., SCOPUS: ar.j, info:eu-repo/semantics/published

Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa). ©2012 Microscopy Society of America .

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info:eu-repo/semantics/published

info:eu-repo/semantics/nonPublished

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