CN− Secondary Ions Form by Recombination as Demonstrated Using Multi-Isotope Mass Spectrometry of 13C- and 15N-Labeled Polyglycine

We have studied the mechanism of formation CN− secondary ions under Cs+ primary ion bombardment. We have synthesized 13C and 15N labeled polyglycine samples with the distance between the two labels and the local atomic environment of the 13C label systematically varied. We have measured four masses in parallel: 12C, 13C, and two of 12C14N, 13C14N, 12C15N, and 13C15N. We have calculated the 13C/12C isotope ratio, and the different combinations of the CN isotope ratios (27CN/26CN, 28CN/27CN, and 28CN/26CN). We have measured a high 13C15N − secondary ion current from the 13C and 15N labeled polyglycines, even when the 13C and 15N labels are separated. By comparing the magnitude of the varied combinations of isotope ratios among the samples with different labeling positions, we conclude the following: CN− formation is in large fraction due to recombination of C and N; the CO double bond decreases the extent of CN− formation compared to the case where carbon is singly bonded to two hydrogen atoms; and double-labeling with 13C and 15N allows us to detect with high sensitivity the molecular ion 13C15N−

Secondary ion mass spectrometry characterization of the diffusion properties of 17 elements implanted into silicon

A systematic investigation of the diffusion of Be, B, Na, Mg, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Zn, Ge, Rb, and Mo in silicon has been carried out. The elements were implanted into silicon wafers as low dose impurities, and then postheat treatments of the ion-implanted samples were conducted at different temperatures for a specific time. Following the anneals, the depth profiles were obtained by secondary ion mass spectrometry analyses. A wide range of diffusion behavior has been observed for these elements. Based on differences in the depth profiles the diffusion mechanism was identified where possible. (C) 2001 American Vacuum Society

Variation de la composition de nanoparticules de 1-10 nm obtenues par séparation de phase dans un verre de silice

National audienceLes verres contenant des nanoparticules ont de nombreuses applications industrielles, notamment grâce à leurs excellentes propriétés thermo-mécaniques [1]. Ils présentent aussi un intérêt pour les propriétés optiques. En effet, l'encapsulation d'ions luminescents (ions de terre rare par exemple) dans des nanoparticules entraînent de nouvelles propriétés de luminescence qui n'existeraient pas dans le verre hôte (bande d'émission élargie, efficacité quantique augmentée, etc) [2]. La préparation de tels verres repose sur des mécanismes de nucléation, croissance et de démixtion dont les premières étapes sont encore assez mal connues. Mais l'avènement de nouvelles techniques de caractérisation à l'échelle nanométrique permet d'améliorer notre compréhension de ces phénomènes. Par exemple, une évolution structurelle des nanoparticules à travers des phases cristallines métastables [3] ou une transformation d'un nucléus amorphe vers une nanoparticule cristalline [4] ont été observées. Des changements de composition ont aussi été rapportés pour des particules de taille 1-10 nm dans des alliages [5] et dans des métaux [6]. Dans cette présentation, nous nous intéressons à la composition de nanoparticules amorphes obtenues par séparation de phase dans un verre de silice. De telles études ont été rendues possibles grâce au développement récent de l'APT (Atom Probe Tomography) pour l'analyse des verres [7]. Nous étudions une fibre optique à base de silice préparée par le procédé MCVD (Modified Chemical Vapor Deposition). Les nanoparticules sont obtenues en incorporant du magnésium qui déclenche une séparation de phase grâce aux traitements thermiques inhérents au procédé MCVD [8]. La composition des nanoparticules dans le verre de silice dopée avec Mg, P, Ge et Er est étudiée dans la gamme 1-10 nm. Nous montrons la partition de Mg, P et Er dans ces nanoparticules ainsi qu'une modification de la composition en fonction de la taille des particules

Diffusion of 18 elements implanted into thermally grown SiO2

Diffusion data are presented for 18 elements implanted in SiO2 layers thermally grown on silicon and annealed at temperatures ranging from 300 to 1000degreesC. Most species studied, (e.g., Be, B, Al, Sc, Ti, V, Zn, Ga, and Mo), showed negligible diffusion over the examined temperature range. In general, this study has shown that the diffusivity of dopants or impurities in SiO2 is significantly smaller than that in silicon. However we also observed that several elements (e.g., Rb and In) have a higher diffusivity in SiO2 than in Si. Because Ga and In are both used as sources for focused ion beam analyses, the lack of Ga diffusion and the movement of In in SiO2 is of interest

Fiber Optic Dielectric Nanoparticles Characterization by Atom Probe Microscopy

International audienceThe engineered processing of dielectric nanoparticles (DNPs) in optical fibers via luminescent ion-doping of silica-based glass aims at providing an enhanced spectroscopic behavior compared to pure silica. These DNPs should positively impact applications in high power fiber lasers, light sources with new wavelengths and telecommunications. The prevalence of large phase immiscibility domains in silicate systems containing divalent metal oxides (Mg for instance) promotes the formation of DNPs through phase separation since heat treatments take place during the MCVD process. Even after 60 years of glass-ceramics research, lack of experimental data concerning early nucleation stages imposes variations in composition and heat treatments as processing steps [1]. Although classical nucleation theory was the first model proposed to explain those phenomena, growth rate mismatches remain wide. According to this capillary assumption-based model, nuclei and bulk share similar structure-composition relationship. Recent articles disprove assumption of structure, pointing toward DNPs structural changes [2] and transition from amorphous nuclei to crystalline DNPs [3]. Compositional changes for small particle sizes (~1-10 nm) have been measured in alloys with Anomalous Small Angle X-Ray Scattering (ASAXS) [4] and in steels with Atom Probe Tomography (APT) [5]. Recent developments in APT has allowed the extension of such studies to glass-ceramics [6], and in the current work, we report experimental data disproving the second capillary assumption at the early stage of nucleation-growth process. The atomic distribution map of Mg DNPs in silica-based glass doped with Mg, P, Ge and Er is reported in Figure 1 after APT analysis. In addition, quantitative assessment of Mg, P and Er content levels in DNPs smaller than 10nm in diameter (Figure 2) could refine the theories behind nucleation and growth mechanisms

Photo-Thermo-Refractive Glasses For High-Efficiency Bragg Gratings In Uv, Visible, And Ir Regions

This paper describes properties and performance of inorganic glass as a medium for volume hologram recording. Among the particular aspects discussed are recent efforts focusing on the proper choice of glass processing technology and exposure and thermal development conditions to achieve greater photosensitivity

Comparative Study Of Photo-Induced Variations Of X-Ray Diffraction And Refractive Index In Photo-Thermo-Refractive Glass

Spontaneous and photo-induced crystallization have been investigated in fluorinated silicate glass by means of X-ray diffraction and optical interferometry. This glass is a photo-sensitive material for high-efficiency phase volume hologram recording. Variations of a refractive index in this glass are controlled by UV irradiation followed by a thermal development which is photo-thermo-refractive (PTR) process. A method of discrimination of weak narrow crystalline lines from a broad diffractive pattern of a vitreous material was developed, and quantitative measurements of small concentrations of crystalline phase in glass matrix were performed. The sensitivity of the method was about 0.01 wt% of crystalline phase of NaF in a silicate glass. This crystalline phase with concentration below 0.1 wt% was detected even in a highly transparent PTR glass with a modified refractive index produced by PTR processing. A correlation between the intensity of X-ray diffraction peaks of NaF and the induced refractive index was found in equally developed PTR glass samples exposed to different dosages of UV radiation. © 2003 Elsevier B.V. All rights reserved

Variation of sub-10nm nanoparticle chemical composition in glass revealed by Atom Probe Tomography

International audienceThe study of amorphous Dielectric Nano-Particles (DNPs) smaller than 10 nm is a great challenge for the materials community. In conjunction with Transmission Electron Microscopy (TEM) and Electron-Probe Micro-Analysis (EPMA), we took advantage of a recent technology, Tri-Dimensional (3D) Atom Probe Tomography (APT) to investigate the variations of the chemical composition in sub-10-nm oxide nanoparticles, grown in silicate glass through heat treatments, at their early stages of nucleation. We provide here a comprehensive set of experimental data obtained from direct measurements of the concentration for P, Mg, Ge and Er within amorphous dielectric nanoparticles (DNP) of radii ranging from 1nm to 10nm. Most importantly, we report on the first observation of a plateau at the early stage of nucleation followed by an increase of the concentration of Mg and Pwith the size of the DNPs. We also demonstrate that the environment of erbium ions embedded in DNP changes with the size of the particles. These results have a profound impact on our understanding of amorphous phase separation mechanisms as well as spectroscopic properties of the luminescent ions and the design of (DNPs)-doped materials