This paper reports the chemical synthesis of MgO and Er-doped MgO nanoparticles (NPs) by the sol–gel method. Their microstructural, optical characterization and the evaluation of their photocatalytic activity are presented. The synthesized NPs were characterized by means of X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Environmental Scanning Electron Microscopy (ESEM), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDX), UV–Visible and Photoluminescence (PL) spectroscopy. The effective synthesis of cubic MgO compound is attested by XRD, FTIR and electron diffraction in TEM. Er2O3 cubic secondary phase is found in the 2 and 3 wt% Er-doped MgO samples. The average size of the roundish cuboid-shaped crystallites decreases from 50 to 32 nm upon the incorporation of the rare earth element (TEM, XRD). Concomitantly, the size of flakes in which the NPs do agglomerate follows the same trend (ESEM). UV–Visible results show that the calculated band-gap energy of the NPs was in the 5.23 to 5.35 eV range. PL analysis showed that all samples have visible emissions owing to the formation of defects in the MgO band-gap. The photocatalytic activity against methylene blue dye was evaluated under UV light irradiation. The photocatalytic results showed an improvement in degradation efficiency with the addition of erbium in samples, with a maximal MB dye removal for the 3 wt% Er-doped MgO sample after 90 min irradiation. The performance is ascribed to a higher separation of the photo-generated (electron–hole) and larger surface area.

Uniaxial tensile tests were carried out on nickel sheets containing only few grains across the thickness thus presenting a so-called multicrystalline state. Pristine sheets used as reference and substrates covered by a nickel layer deposited by physical vapor deposition (magnetron sputtering) were studied. Results attest that the surface treatment affects the plastic deformation mechanisms by playing the role of a blocking barrier to dislocation movement which leads to a significant improvement of mechanical performances. The surface restructuring of the nickel sheets is efficient to stop dislocation escape through free surfaces and allows a mechanical improvement of the well-known strong mechanical softening of the multicrystals.

The article deals with the effect of Mg dopant on the properties and the photocatalytic of ZnO films synthesized by the sol–gel technique onto glass substrates. It is found that Mg dopant has a strong influence on the microstructure and functional properties. The EDX analysis revealed that Mg had been incorporated into the ZnO. Structural studies through XRD have shown that the deposited films are of hexagonal structure with a preferential growth along the c-axis and nanometer crystal size. According to AFM analysis; it is found that the roughness of Mg-doped ZnO films increases with the Mg dopant. The film surface depicted wrinkles morphology as observed by ESEM. Optical investigations by spectrophotometry and photoluminescence revealed that as the Mg dopant is increased, the optical band-gap increases. Moreover, near band edge and visible emissions as probed by Photoluminescence can be manipulated by the Mg dopant, as their intensity increases and decreases, respectively. Finally, the photocatalytic activity for degradation of methylene blue is strongly improved all the more as the Mg content is increased.

This paper reports a cathodoluminescence (CL) spectroscopic study of nanogranular A1N0Er, samples with erbium content, x, in the range 0.5-3.6 at%. A wide range of erbium concentration was studied with the aim of understanding the concentration quenching of CL. The composition of thin films, deposited by radiofrequency reactive magnetron sputtering, was accurately determined by Energy Dispersive X-ray Spectroscopy (EDS). CL emission was investigated in the extended visible spectral range from 350 nm to 850 nm. The critical concentration of luminescent activator Er3+ above which CL quenching occurs is 1%; the corresponding critical distance between Er3+ ions in A1N0Er(x) is about 1.0 nm. The quenching mechanism is discussed. We discount an exchange-mediated interaction in favour of a multipole-multipole phonon-assisted interaction.

The structural properties of Er-doped AlNO epilayers grown by radio frequency magnetron sputtering were studied by Extended X-ray Absorption Fine Structure spectra recorded at the Er L3 edge. The analysis revealed that Er substitutes for Al in all the studied samples, and the increase in the Er concentration from 0.5 to 3.6 at. % is not accompanied by the formation of ErN, Er2O3, or Er clusters. Simultaneously recorded X-ray Absorption Near Edge Structure spectra verify that the bonding configuration of Er is similar in all studied samples. The Er-N distance is constant at 2.18–2.19 Å, i.e., approximately 15% larger than the Al-N bond length, revealing that the introduction of Er in the cation sublattice causes a considerable local distortion. The Debye-Waller factor, which measures the static disorder of the second nearest shell of Al neighbors, has a local minimum for the sample containing 1% Er that coincides with the highest photoluminescence efficiency of the sample set.

In the present study an ab initio investigation on the AlN:Er system for concentrations of Er ranging from 0.78 to 12.5% is presented. The crystallographic localisation of the rare earth atoms in the wurtzite lattice is determined, elucidating previously published experimental deductions, and the existence of a solid solution in the AlN:Er system in this range is confirmed. Er incorporation in the tetrahedral and octahedral insertion sites is shown to be thermodynamically metastable and is found to induce shallow states in the bandgaps. The effect of Er concentration on the lattice constants and bandgaps and bandstructures of the ErxAl1−xN ternary compound is presented. Finally, in accordance with experimental specifications, Er incorporation in the AlNO system is also examined.

This paper presents a thorough experimental investigation of erbium-doped aluminium nitride thin films prepared by R.F. magnetron sputtering, coupling Scanning Transmission Electron Microscopy X-ray-mapping imagery, conventional Transmission Electron Microscopy and X-ray diffraction. The study is an attempt of precise localisation of the rare earth atoms inside the films and in the hexagonal würtzite unit cell. The study shows that AlN:Erx is a solid solution even when x reaches 6at.%, and does not lead to the precipitation of erbium rich phases. The X-ray diffraction measurements completed by simulation show that the main location of erbium in the AlN würtzite is the metal substitution site on the whole range. They also show that octahedral and tetrahedral sites of the würtzite do welcome Er ions over the [1.6–6%] range. The XRD deductions allow some interpretations on the theoretical mechanisms of the photoluminescence mechanisms and more specifically on their concentration quenching.

Er-doped aluminum nitride films, containing different Er concentrations, were obtained at room temperature by reactive radio frequency magnetron sputtering. The prepared samples show a nano-columnar microstructure and the size of the columns is dependent on the magnetron power. The Er-related photoluminescence (PL) was studied in relation with the temperature, the Er content and the microstructure. Steady-state PL, PL excitation spectroscopy and time-resolved PL were performed. Both visible and near infrared PL were obtained at room temperature for the as-deposited samples. It is demonstrated that the PL intensity reaches a maximum for an Er concentration equal to 1 at% and that the PL efficiency is an increasing function of the magnetron power. Decay time measurements show the important role of defect related non-radiative recombination, assumed to be correlated to the presence of grain boundaries. Moreover PL excitation results demonstrate that an indirect excitation of Er3+ ions occurs for excitation wavelengths lower than 600 nm.

The effect of magnetron power on the room temperature 1.54 mu m infra-red photoluminescence intensity of erbium doped AlN films grown by r.f. magnetron sputtering, has been studied. The AlN: Er thin films were deposited on (001) Silicon substrates. The study presents relative photoluminescence intensities of nanocrystallized samples prepared with identical sputtering parameters for two erbium doping levels (0.5 and 1.5 at%). The structural evolution of the crystallites as a function of the power is followed by transmission electron microscopy. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A study of the transverse acoustic phonons on nano-structured AlN films has been carried out by using high-resolution micro-Brillouin spectroscopy. Dense films have been deposited by radio frequency (r.f.) magnetron sputtering under ultra high vacuum at room temperature. Films with different morphologies were prepared and investigated by transmission electron microscopy and Brillouin Spectroscopy (equiaxed nano-sized, nano-columnar grains and amorphous phase). Results show a dependence of the transverse modes on the nano-structure. The nano-columnar film exhibits two transversal modes as expected for the AlN würtzite while the equiaxed nano-sized and the amorphous films only exhibit one isotropic transverse mode as expected in amorphous materials. One important result is that the sound propagation velocity in the AlN amorphous phase is higher than the one in the non-textured nano-crystalline phase. This phenomenon has, however, already been observed in ferroelectric ceramics.

In the prospect of understanding the photoluminescence mechanisms of AlN films doped with erbium and targeting photonic applications we have synthesized non doped and Er-doped AlN films with different crystallized nanostructures by using PVD magnetron sputtering. Their crystalline morphology and their visible photoluminescence properties were precisely measured.Due to the weak cross-section absorption of rare earths like erbium, it is necessary to obtain an efficient energy transfer mechanism between the host matrix and the rare earth to obtain high luminescence efficiency. Our strategy is then to elaborate some nanostructures that could introduce additional intermediate electronic levels within the gap thanks to the presence of structural defects (point defects, grain boundaries{\ldots}) and could lead to energy transfer from the AlN matrix to the rare earth.Doped and non-doped AlN films were prepared by radio frequency magnetron sputtering by using different experimental conditions that will be detailed. It will notably be shown how a negative polarization of samples during deposition allows obtaining crystalline morphologies ranging from the classical columnar structure to a highly disordered polycrystalline structure with grains of several nanometers (nearly amorphous). The nanostructures of the films could be categorized in three types: 1) type 1 was nanocolumnar (width of column ~ 15 nm), 2) type 2 was made of short columns (width of column ~ 10 nm) and 3) the last type was made of equiaxed nanocrystallites (size of grains ~3-4 nm).High-resolution photoluminescence spectroscopy was performed to characterize their optical behaviour. The samples were excited by the laser wavelengths at 458, 488 or 514 nm. A broad photoluminescence band was observed centred around 520 nm in columnar samples. In the same energy range, the highly resolved spectra also showed several sharp emission peaks. This fine structure could be attributed to erbium transitions. This fine structure tended to disappear going from type 1 to type 3 samples. Indeed, the relative intensity of the peaks decreased and their full width at half maximum increased. This change could be related to the density of defects that increased when the size of the grains decreased. The photoluminescence properties of the films in the visible range will be discussed in relation with their structure.

Cr–Ni–N coatings were deposited on 304 stainless steel substrates using a conventional direct current magnetron reactive sputtering system in nitrogen–argon reactive gas mixtures. The influence of Ni content (0 ≦ x ≦ 20 at.%) on the coating composition, microstructure, and tribological properties was investigated by glow discharge optical spectroscopy, X-ray diffraction and transmission electron microscopy, scanning electron microscopy (SEM), nano-indentation, and pin-on-disk tests. The results showed that microstructure and properties of coatings changed due to the introduction of Ni. The ternary Cr–Ni–N coatings exhibited solid solution structures in spite of the different compositions. The addition of Ni strongly favoured preferred orientation growth of <200>. This preferred orientation resulted from the formed nano-columns being composed of grains with the same crystallographic orientation, as confirmed by SEM cross-sectional observations. The mechanical properties including the nano-hardness and reduced Young's modulus decreased with increasing Ni content. Pin-on-disk tests showed that low Ni content coatings presented higher abrasion resistance than high Ni content coatings.

CNx and SiCN thin films were deposited by microwave plasma assisted chemical vapour deposition on Si, Si/Si3N4 and WC-Co/Si substrates in a N-2/CH4 gas mixture. The source of silicon was the substrate itself. Its role in the growth of CNx and SiCN is not well understood yet. To better understand the surface mechanisms involved in the film growth. as well as the role played by the silicon, some films are synthesized on WC-co cermets and WC-Co recovered by a variable thickness silicon layer. Morphological analyses realized by scanning electron microscopy and transmission electron microscopy show that the obtained films are made of nano-crystal line grains with size ranging between 20 and 70 nm. The X-ray diffraction spectrum and selected area electron diffraction patterns exhibits a signature that could correspond to beta-C3N4, cubic-C3N4 and cubic-SiCN. The films deposited on WC-Co substrates are compared to those, which are synthesized on Si and Si/Si3N4 substrates. We have observed that the deposition of a continuous film was impossible on non-silicon contain (WC-Co) substrates, and only carbon balls were obtained on a such substrate. Otherwise, the deposition becomes possible if a silicon underlayer is deposited on to the WC-Co substrates. The films are close to those synthesized with Si or Si/Si3N4 Substrates. In all cases, the growth stops as soon as a thin film is deposited on the substrate and the plasma cannot access to the silicon underlayer. Finally, a growth mechanism showing that silicon takes part of the deposition and improves the nitrogen ratio in the films is proposed. Regarding the energy dispersion X-ray spectroscopy and secondary ion mass spectroscopy results, it seems that the incorporation of nitrogen is activated only by the presence of silicon, which behaves as a catalyst. (C) 2008 Elsevier B.V. All rights reserved.