1,720,986 research outputs found
Controlling Er–Tm interaction in Er and Tm codoped silicon-rich silicon oxide using nanometer-scale spatial separation for efficient, broadband infrared luminescence
No full textThe effect of nanometer-scale spatial separation between Er3+ and Tm3+ ions in Er and Tm codoped silicon-rich silicon oxide (SRSO) films is investigated. Er and Tm codoped SRSO films, which consist of nanocluster Si (nc-Si) embedded inside SiO2 matrix, were fabricated with electron cyclotron resonance-plasma enhanced chemical vapor deposition of SiH4 and O-2 with concurrent sputtering of Er and Tm metal targets. Spatial separation between Er3+ and Tm3+ ions was achieved by depositing alternating layers of Er- and Tm-doped layers of varying thickness while keeping the total film thickness the same. The films display broadband infrared photoluminescence (PL) from 1.5 to 2.0 mum under a single source excitation due to simultaneous excitation of Er3+ and Tm3+ ions by nc-Si. Increasing the layer thickness from 0 to 72 nm increases the Er3+ PL intensity nearly 50-fold while the Tm3+ PL intensity is unaffected. The data are well-explained by a model assuming a dipole-dipole interaction between excited Er3+ and Tm3+ ions, and suggest that by nanoscale engineering, efficient, ultrabroadband infrared luminescence can be obtained in an optically homogeneous material using a single light source. (C) 2004 American Institute of Physics
Exciton–erbium coupling and the excitation dynamics of Er3+ in erbium-doped silicon-rich silicon oxide
No full textThe exciton-erbium coupling and the excitation dynamics of Er3+ in erbium-doped silicon-rich silicon oxide are investigated using time-resolved measurements of Er3+ luminescence. The dependence of the Er3+ luminescence on the pump power and duration indicates that the exciton-erbium coupling is dominant over carrier-exciton coupling. The results further support the idea that the luminescent Er3+ ions are not in the Si nanoclusters but in the interface region surrounding the nanoclusters. (C) 2001 American Institute of Physics
Excitation mechanism of visible, Tb3+ photoluminescence from Tb-doped silicon oxynitride
No full textThe excitation mechanism of visible luminescence from Tb3+-doped silicon oxynitride is investigated. Tb-doped silicon oxynitride films were deposited by inductive-coupled plasma-enhanced chemical vapor deposition of SiH4, O-2, and N-2 with concurrent sputtering of Tb. Luminescences from both the host matrix and the Tb3+ intra-4f transition are observed, but no correlation is found between them as the composition and the annealing conditions were varied. Photoluminescence excitation spectroscopy shows a strong increase in the Tb3+ luminescence intensity as the pump energy is increased above 3.5 eV while the host matrix luminescence decreases. Taken together, the results that there is little energy transfer between band-tail states of silicon oxynitride and Tb3+, and that efficient excitation of Tb3+ by carriers requires excitation of carriers into the extended states of oxynitride. (c) 2006 American Institute of Physics
Coefficient determination related to optical gain in erbium-doped silicon-rich silicon oxide waveguide amplifier
No full textGain-determining coefficients in Er-doped, nanocrystal-Si (nc-Si) sensitized silica waveguide amplifiers are investigated. Single-mode, Er-doped silica waveguides with nc-Si embedded in them were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition of Er-doped a-Si:O-x (x<2) followed by a high-temperature anneal to precipitate nc-Si. Exciting the Er ions via nc-Si by pumping the waveguide from the top with the 477 nm line of an Ar laser resulted in an enhancement of the transmitted 1535 nm signal of up to 14 dB/cm, indicating a possible net gain of up to 7 dB/cm. From the dependence of the signal enhancement upon the pump power, an emission cross section of 2x10(-19) cm(2) at 1535 nm and an effective excitation cross section of greater than or equal to10(-17) cm(2) at 477 nm is obtained. (C) 2002 American Institute of Physics
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Controlling the formation of luminescent Si nanocrystals in plasma-enhanced chemical vapor deposited silicon-rich silicon oxide through ion irradiation
No full textThe effect of ion irradiation on the formation of luminescent Si nanocrystals from silicon-rich silicon oxide (SRSO) films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (PECVD) whose Si content ranged from 33 to 50 at. % is investigated. As-deposited SRSO films contained a high density of irregular-shaped Si nanocrystals. Irradiating these films with 380 keV Si at room temperature to a dose of 5.7x10(15) cm(-2) prior to anneal at 1000 degreesC is found to increase the luminescence intensity due to Si nanocrystals over the films. Based on the x-ray photoemission spectra and the dependence of the luminescence intensity on the irradiating ion dose, anneal time, and the silicon content of the film, we propose the destruction of pre-existing Si clusters by ion irradiation to be an important factor responsible for the observed enhancement of luminescence, and suggest that preanneal irradiation may be a viable method to control the formation of luminescent Si nanocrystals in PECVD-deposited silicon-rich silicon oxide. (C) 2002 American Institute of Physics
Variations on the Author
Full text link“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
- …
