Effect of the Nd content on the structural and photoluminescence properties of silicon-rich silicon dioxide thin films

In this article, the microstructure and photoluminescence (PL) properties of Nd-doped silicon-rich silicon oxide (SRSO) are reported as a function of the annealing temperature and the Nd concentration. The thin films, which were grown on Si substrates by reactive magnetron co-sputtering, contain the same Si excess as determined by Rutherford backscattering spectrometry. Fourier transform infrared (FTIR) spectra show that a phase separation occurs during the annealing because of the condensation of the Si excess resulting in the formation of silicon nanoparticles (Si-np) as detected by high-resolution transmission electron microscopy and X-ray diffraction (XRD) measurements. Under non-resonant excitation at 488 nm, our Nd-doped SRSO films simultaneously exhibited PL from Si-np and Nd3+ demonstrating the efficient energy transfer between Si-np and Nd3+ and the sensitizing effect of Si-np. Upon increasing the Nd concentration from 0.08 to 4.9 at.%, our samples revealed a progressive quenching of the Nd3+ PL which can be correlated with the concomitant increase of disorder within the host matrix as shown by FTIR experiments. Moreover, the presence of Nd-oxide nanocrystals in the highest Nd-doped sample was established by XRD. It is, therefore, suggested that the Nd clustering, as well as disorder, are responsible for the concentration quenching of the PL of Nd3+

Undoped and Nd3+ doped Si-based single layers and superlattices for photonic applications

International audienceThis work presents the benefits of the superlattice approach to control light emission properties of materials with Si nanoclusters and rare‐earth ions. The undoped and Nd3+‐doped both Si‐rich‐SiO2 single layers and Si‐rich‐SiO2/SiO2 superlattices were grown by radio frequency magnetron sputtering. Their properties were investigated by means of spectroscopic ellipsometry, Fourier infrared transmission spectroscopy, transmission electron microscopy, and photoluminescence (PL) methods versus deposition conditions, annealing treatment, and superlattice design (doping and thickness of alternated sublayers). An intense Nd3+ emission from as‐deposited single layers and superlattices was observed. The lower annealing temperature (below 900 °C) of the single layers and superlattices favors the formation of amorphous Si clusters that act as effective sensitizers of rare‐earth ions. The highest Nd3+ PL intensity was achieved after a conventional annealing at about 600–800 °C in nitrogen flow for all samples. Crystallized Si‐nanoclusters were formed in Si‐rich‐SiO2 single layers upon annealing at 1000–1100 °C, whereas their formation in the superlattices occurred at higher temperatures (1100–1150 °C). The mechanism of Nd ions' excitation via energy transfer from Si‐nanoclusters and/or matrix defects, if any, is discussed

Thickness-dependent optimization of Er3+ light emission from silicon-rich silicon oxide thin films

This study investigates the influence of the film thickness on the silicon-excess-mediated sensitization of Erbium ions in Si-rich silica. The Er3+ photoluminescence at 1.5 μm, normalized to the film thickness, was found five times larger for films 1 μm-thick than that from 50-nm-thick films intended for electrically driven devices. The origin of this difference is shared by changes in the local density of optical states and depth-dependent interferences, and by limited formation of Si-based sensitizers in "thin" films, probably because of the prevailing high stress. More Si excess has significantly increased the emission from "thin" films, up to ten times. This paves the way to the realization of highly efficient electrically excited devices

Structural and optical characterization of pure Si-rich nitride thin films

International audienceThe specific dependence of the Si content on the structural and optical properties of O-and H-free Si-rich nitride (SiN x>1.33) thin films deposited by magnetron sputtering is investigated. A semiempirical relation between the composition and the refractive index was found. In the absence of Si-H, N-H, and Si-O vibration modes in the FTIR spectra, the transverse and longitudinal optical (TO-LO) SiN stretching pair modes could be unambiguously identified using the Berreman effect. With increasing Si content, the LO and the TO bands shifted to lower wavenumbers, and the LO band intensity dropped suggesting that the films became more disordered. Besides, the LO and the TO bands shifted to higher wavenumbers with increasing annealing temperature which may result from the phase separation between Si nanoparticles (Si-np) and the host medium. Indeed, XRD and Raman measurements showed that crystalline Si-np formed upon 1100°C annealing but only for SiN x0.9 , demonstrating that this PL is not originating from confined states in crystalline Si-np. As an additional proof, the PL was quenched while crystalline Si-np could be formed by laser annealing. Besides, the PL cannot be explained neither by defect states in the bandgap nor by tail to tail recombination. The PL properties of SiN x>0.9 could be then due to a size effect of Si-np but having an amorphous phase

Microstructure and optical properties of Pr3+-doped hafnium silicate films

International audienceIn this study, we report on the evolution of the microstructure and photoluminescence properties of Pr 3+-doped hafnium silicate thin films as a function of annealing temperature (T A). The composition and microstructure of the films were characterized by means of Rutherford backscattering spectrometry, spectroscopic ellipsometry, Fourier transform infrared absorption, and X-ray diffraction, while the emission properties have been studied by means of photoluminescence (PL) and PL excitation (PLE) spectroscopies. It was observed that a post-annealing treatment favors the phase separation in hafnium silicate matrix being more evident at 950°C. The HfO 2 phase demonstrates a pronounced crystallization in tetragonal phase upon 950°C annealing. Pr 3+ emission appeared at T A = 950°C, and the highest efficiency of Pr 3+ ion emission was detected upon a thermal treatment at 1,000°C. Analysis of the PLE spectra reveals an efficient energy transfer from matrix defects towards Pr 3+ ions. It is considered that oxygen vacancies act as effective Pr 3+ sensitizer. Finally, a PL study of undoped HfO 2 and HfSiO x matrices is performed to evidence the energy transfer

Toward RGB LEDs based on rare earth-doped ZnO

By using ZnO thin films doped with Ce, Tb or Eu, deposited via radiofrequency magnetron sputtering, we have developed monochromatic (blue, green and red, respectively) light emitting devices (LEDs). The rare earth ions introduced with doping rates lower than 2% exhibit narrow and intense emission peaks due to electronic transitions in relaxation processes induced after electrical excitation. This study proves zinc oxide to be a good host for these elements, its high conductivity and optical transparency in the visible range being as well exploited as top transparent electrode. After structural characterization of the different doped layers, a device structure with intense electroluminescence is presented, modeled, and electrically and optically characterized. The different emission spectra obtained are compared in a chromatic diagram, providing a reference for future works with similar devices. The results hereby presented demonstrate three operating monochromatic LEDs, as well as a combination of the three species into another one, with a simply-designed structure compatible with current Si technology and demonstrating an integrated red-green-blue emission

Synthesis of bioorganometallic nanomolar-potent CB2agonists containing a ferrocene unit

A small library of ferrocene-containing amides has been synthesized using standard amide coupling chemistry with ferrocenylamine. Ferrocene analogues of known bioactive adamantylamides were shown to be effective cannabinoid receptor (CB1 and CB2) agonists, displaying, in many cases, single-digit nanomolar potency. Three final ferrocene-containing derivatives have been characterized in the solid state by X-ray crystallography and display intramolecular hydrogen bonding of the type NH---C═O. N-Methylation of the amide, confirmed by X-ray crystallography, leads to both loss of hydrogen bonding and biological activity

Genomic Species Are Ecological Species as Revealed by Comparative Genomics in Agrobacterium tumefaciens

The definition of bacterial species is based on genomic similarities, giving rise to the operational concept of genomic species, but the reasons of the occurrence of differentiated genomic species remain largely unknown. We used the Agrobacterium tumefaciens species complex and particularly the genomic species presently called genomovar G8, which includes the sequenced strain C58, to test the hypothesis of genomic species having specific ecological adaptations possibly involved in the speciation process. We analyzed the gene repertoire specific to G8 to identify potential adaptive genes. By hybridizing 25 strains of A. tumefaciens on DNA microarrays spanning the C58 genome, we highlighted the presence and absence of genes homologous to C58 in the taxon. We found 196 genes specific to genomovar G8 that were mostly clustered into seven genomic islands on the C58 genome—one on the circular chromosome and six on the linear chromosome—suggesting higher plasticity and a major adaptive role of the latter. Clusters encoded putative functional units, four of which had been verified experimentally. The combination of G8-specific functions defines a hypothetical species primary niche for G8 related to commensal interaction with a host plant. This supports that the G8 ancestor was able to exploit a new ecological niche, maybe initiating ecological isolation and thus speciation. Searching genomic data for synapomorphic traits is a powerful way to describe bacterial species. This procedure allowed us to find such phenotypic traits specific to genomovar G8 and thus propose a Latin binomial, Agrobacterium fabrum, for this bona fide genomic species

Lettre Du Pere Jacques-Xavier Portier, Missionnaire de la Compagnie de Jesus, au Pere Fleuriau, de la même Compagnie. In: Lettres édifiantes et curieuses, écrites des missions étrangeres. Nouvelle édition. Mémoires du Levant. Tome II. A Paris, chez J. G.

Dedication:Content description: TitlePagination: 1Text Genre:Letter

Elaboration et caractérisations de films d oxyde de gallium dopés terres rares

Parmi les oxydes transparent conducteurs (Transparent Conductive Oxides, TCO), l oxyde de gallium Ga2O3 possède une large bande interdite (environ 4,9 eV) ce qui en fait un matériau transparent dans un domaine spectral allant de l infra-rouge à l ultraviolet. Ga2O3 apparaît donc comme une matrice hôte appropriée pour mettre en évidence la luminescence d ions terres rares. Des films d oxyde de gallium dopés au néodyme, puis à l europium ont été déposés sur des substrats de silicium et de saphir par pulvérisation magnétron radiofréquence. Ces films ont ensuite subi un traitement thermique approprié afin d obtenir la phase b-monoclinique. Les caractérisations optiques ont prouvé que les films sont bien transparents. En outre, les films dopés au néodyme émettent autour de 900 nm et 1070 nm, ce qui correspond aux transitions 4F3/2 -> 4I9/2 et 4F3/2 -> 4I11/2 des ions Nd3+. Les films dopés à l europium luminescent quant à eux dans le domaine du visible, l émission la plus intense se situant autour de 615 nm, ce qui correspond à la transition 5D0 -> 7F2 des ions Eu3+. Les propriétés structurales et de photoluminescence des films ont été étudiés en fonction de la quantité de terre rare introduite dans la matrice. De plus, les mécanismes optiques impliqués dans les phénomènes d excitation-émission de la luminescence ont été exposés. Les films d oxyde de gallium dopés avec des terres rares appropriées pourraient être intégrés dans des dispositifs optoélectroniques tels que les diodes électroluminescentes blanches.Among transparent conductive oxides, gallium oxide is of particular interest because of its singular wide band gap (around 4.9 eV) which makes it optically transparent from infrared until ultraviolet light. Gallium oxide is also a good host matrix to exhibit the luminescence of rare earth ions. Neodymium and then europium doped gallium oxide thin films have been deposited on silicon and sapphire substrates by radiofrequency magnetron sputtering and submitted to an appropriate thermal treatment in order to obtain the stable monoclinic -phase. Transparent properties have been demonstrated. Neodymium doped films have shown an efficient luminescence activity at ~900 nm and ~1070 nm, corresponding to the 4F3/2 -> 4I9/2 and 4F3/2 -> 4I11/2 transitions of the Nd3+ ions, respectively. Europium doped films have exhibited a luminescence activity in the visible spectral range, the most intense emission being at about 615 nm, corresponding to the 5D0 -> 7F2 transition of the Eu3+ ions. The dependence of the neodymium and europium contents in the films on the structural and photoluminescence properties have been studied. Moreover, the optical mechanisms involved have been investigated to be explain in the neodymium as well as in the europium doped films. Gallium oxide films doped with the suitable rare earths could be used to fabricate optoelectronics devices such as white light emitting diodes (LED).CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF