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Erbium Environment In Silicon Nanoparticles
No full textThe Er environment in two sets of Er-doped Si nanoparticles (np) with nominal Er concentrations of 1-2 at.% was measured by EXAFS. Set H, with a homogeneous distribution of Er atoms, consist of samples with average np diameters of 3.2, 5.9, and 6.4 nm. The np of set C consist of a Si core covered by an Er-rich shell, with average diameters of 26 and 22 nm, nearly an order of magnitude higher than those of set H. The Er atoms in the np are coordinated to oxygen, like in the Er(tmhd)3 organometallic precursor. In set H, both the Er coordination and the average Er-O separation increase as the average nanoparticle diameter increases from 3.2 to 6.4 nm. The results for small np are remarkably similar to those found for Er in a-Si:H〈Er〉, indicating that the lattice constraints in the np are very similar to a-Si:H. Efficient Er3+ luminescence is detected in as-prepared samples. As the particle size increases the Er environment becomes er2O3-like, as in bulk Czochralski silicon. In set C, the Er environment in both samples is similar to that in Er(tmhd)3 and in Er2O3, but the Er-O distances are larger. © 2002 Elsevier Science B.V. All rights reserved.299-302PART 1673677Agrawal, G.P., (1997) Fiber-Optic Communication Systems, second ed, , Wiley, New YorkCanham, L., (2000) Nature, 408, p. 411Tsybeskov, L., (1998) MRS Bull., 23 (4), p. 33Pomrenke, G.S., Klein, P.B., Langer, D.W., Rare earth doped semiconductors (1993) Mater. Res. Soc. Symp. Proc., 301. , MRS, Pittsburgh, PACoffa, S., Polman, A., Schwartz, R., Rare earth doped semiconductors II (1996) Mater. Res. Soc. Symp. Proc., 422. , MRS, Pittsburgh, PAZavada, J.M., Gregorkiewicz, T., Steckl, A.J., Rare earth doped semiconductors III (2001) Materials Science and Engineering B, 81Polman, A., (1997) J. Appl. Phys., 82, p. 1Namavar, F., Lu, F., Perry, C.H., Cremins, A., Kalkhoran, N., Soref, R., (1995) J. Appl. Phys., 77, p. 4813Tsybeskov, L., Duttagupta, S., Hirschman, K., Fauchet, P.M., Moore, K., Hall, D., (1997) Appl. Phys. Lett., 70, p. 1790Lopez, H.A., Fauchet, P.M., (2000) Appl. Phys. Lett., 77, p. 3704Markmann, M., Neufeld, E., Sticht, A., Brunner, K., Abstreiter, G., (1999) Appl. Phys. Lett., 75, p. 2584Tessler, L.R., (1999) Braz. J. Phys., 29, p. 616Michel, J., Ferrante, J.L.B.R.F., Jacobson, D.C., Eaglesham, D.J., Fitzgerald, E.A., Xie, Y.H., Poate, J.M., Kimerling, L.C., (1991) J. Appl. Phys., 70, p. 2672Adler, D.L., Jacobson, D.C., Eaglesham, D.J., Marcus, M.A., Benton, J.L., Poate, J.M., Citrin, P.H., (1992) Appl. Phys. Lett., 61, p. 2181Littau, K., Szajowski, P., Muller, A., Kortan, A., Brus, L., (1993) J. Phys. Chem., 97, p. 1224John, J.St., Coffer, J.L., Chen, Y., Pinizzotto, R.F., (1999) J. Am. Chem. Soc., 121, p. 1888Senter, R.A., Chen, Y., Coffer, J.L., Tessler, L.R., (2001) Nano Lett., 1, p. 383John, J.St., Coffer, J.L., Chen, Y., Pinizzotto, R.F., (2000) Appl. Phys. Lett., 77, p. 1635Piamonteze, C., Iñiguez, A.C., Tessler, L.R., Alves, M.C.M., Tolentino, H., (1998) Phys. Rev. Lett., 81, p. 4652Piamonteze, C., Tessler, L.R., Tolentino, H., Alves, M.C.M., Weiser, G., Terukov, E., (2000) MRS Symp. Proc., 609, pp. A112
Erbium Environment In Zno:er Polycrystalline Fibers Produced By Electrospinning
No full textErbium-doped polycrystalline ZnO fibers were prepared by electrospinning. Organometallic Zn and Er (0.5, 1.0 and 2.0 % ErZZn ratio) precursors dissolved in methanol, DI water and acetic acid were forced through a syringe needle. An electric field of 20 kV over 16 cm was used to promote the growth of fibers from the needle to a rotating drum. The resulting material consisted of entangled fibers with 0.5 to 1 μm typical diameter. The as-prepared samples present faint Er3+ luminescence at 1.5 μm when excited by the 488 nm line of an Ar+ laser. This luminescence intensity increases up to 25 times when the samples are annealed for 30 min at 500°C in air. The effect of annealing over the Er environment was determined by EXAFS measurements at the Er L3 edge. In all as-prepared samples Er is coordinated to 8.0 ± 0.5 oxygen atoms at up to 2.33 ± 0.02 Å interatomic separation. After annealing the coordination is reduced to 5.9 ± 0.5 and the atomic separation becomes 2.29 ± 0.02 Å. This is comparable to Er2O3 where the coordination is 6 and the first neighbor distance is 2.26 ± 0.02 Å. The overcoordination in the as-prepared samples is consistent with the Er L3 edge at 8361.7 ± 0.5 eV compared to 8360.4 ± 0.5 eV in the annealed samples and 8359.9 ± 0.5 eV in Er2O3. In conclusion, the annealing of electrospun ZnO:Er fibers makes the Er environment more similar to that of Er2O3 increasing the luminescence efficiency. © 2008 Materials Research Society.1035152157Li, D., Xia, Y., (2004) Adv. Mat, 16, p. 1151Viswanathamurthi, P., Bhattarai, N., Kim, H.Y., Lee, D.R., (2004) Nanotechnology, 15, p. 320Wahl, U., Rita, E., Correia, J.G., Alves, E., Araujo, J.P., (2003) Appl. Phys. Lett, 82, p. 1173Ishii, M., Komuro, S., Morikawa, T., Ayoyagi, Y., (2001) J. Appl. Phys, 89, p. 3679Mustafa, D., Biggemann, D., Wu, J., Coffer, J.L., Tessler, L.R., (2007) Superlattices and Microstructures, 42, p. 40
Probe-free semiconducting silicon nanowire platforms for biosensing
No full textThis chapter discusses implementation of silicon nanowires (SiNW) for probe-free biosensing and their integration with microfluidic chambers for small volume sample confinement and delivery to an automated biosensor platform. The SiNW biosensor platform consists of three key elements: SiNW sensors, the probe layer for specific binding to a particular target molecule and gate voltage generation, and controlled delivery of small sample volumes that enables quantitative hybridization kinetics assessment directly from the real-time measurements. Advantages and disadvantages of using the nanoscale SiNW biosensors, and approaches to reduce the limitations are discussed. The chapter concludes with future trends and overall outloo
Structural Characterization Of Zno/ Er2o3 Core/shell Nanowires
No full textZinc oxide/erbium oxide core/shell nanowires are of great potential value to optoelectronics because of the possible demonstration of laser emission in the 1.5 μm range. In this paper we present a convenient technique to obtain structures of this composition. ZnO core nanowires were first obtained by a vapor-liquid-solid (VLS) method using gold as a catalyst. ZnO nanowires ranging from 50 to 100 nm in width were grown on the substrates. Erbium was incorporated into these nanowires by their exposure to Er(tmhd)3 at elevated temperatures. After annealing at 700 {ring operator}C in air, the nanowires presented 1.54 μm emission when excited by any of the lines of an Ar+ laser. An investigation of nanowire structure by HRTEM indicates that indeed the cores consist of hexagonal ZnO grown in the 001 direction while the surface contains randomly oriented Er2O3 nanoparticles. EXAFS analysis reveals that the Er atoms possess a sixfold oxygen coordination environment, almost identical to that of Er2O3. Taken collectively, these data suggest that the overall architectures of these nanowires are discrete layered ZnO/ Er2O3 core/shell structures whereby erbium atoms are not incorporated into the ZnO core geometry. © 2007 Elsevier Ltd. All rights reserved.4201/06/15403408Wang, Z.L., (2004) Mater. Today, 7, p. 26Johnson, J.C., Yan, H., Schaller, R.D., Haber, L.H., Saykally, R.J., Yang, P., (2001) J. Phys. Chem., 105, p. 11387Sun, X.H., Lam, S., Sham, T.K., Heigl, F., Jürgensen, A., Wong, N.B., (2005) J. Phys. Chem. B, 109, p. 3120Senter, R.A., Chen, Y., Coffer, J.L., Tessler, L.R., (2001) Nano Lett., 1, p. 383Komuro, S., Katsumata, T., Morikawa, T., Zhao, X., Isshiki, H., Aoyagi, Y., (2000) J. Appl. Phys., 88, p. 7129Peres-Casero, R., Gutiérrez-Llorente, A., Pons-Y-Moll, O., Seiler, W., Defourneau, R.M., Defourneau, D., Millon, E., Viana, B., (2005) J. Appl. Phys., 97. , 054905-1Wahl, U., Rita, E., Correia, J.G., Alves, E., Araújo, J.P., (2003) Appl. Phys. Lett., 82, p. 1173. , ISOLDE CollaborationIshii, M., Komuro, S., Morikawa, T., Aoyagi, Y., (2001) J. Appl. Phys., 89, p. 367
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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