1,720,962 research outputs found
Solid state reaction in Si-C multilayers induced by ion bombardment
No full textIn order to investigate ion beam mixing and crystallization in the silicon-carbon system, Si/C multilayers were deposited on Si substrates and irradiated with Kr and Xe ions at temperatures to 873 K. The composition of the layer system as a function of depth before and after irradiation was analyzed by means of Rutherford backscattering spectroscopy (RBS). Changes in short-range order were monitored by X-ray absorption spectroscopy (XAFS). After irradiation at temperatures below 873 K, a disordered network of Si and C atoms forms, where the chemical short-range order is determined primarily by Si-Si bonds. At 873 K, the short-range order resembles that of crystalline SIC and XAFS results clearly indicate that crystallization and build-up of long-range order has initiated. Furthermore, it is demonstrated here that energy deposition by the ion beam is essential for initiating this solid state reaction, which cannot be achieved by thermal treatment only, even at higher temperatures. (C) 2000 Elsevier Science B.V. All rights reserved
Atomic mixing of Ni2O3 SiO2, NiO SiO2, and Ni SiO2 interfaces induced by swift heavy ion irradiation
No full textWe have investigated the interface mixing of Ni2O3 SiO2, NiO SiO2, and Ni SiO2 induced by the irradiation with Ar, Kr and Xe ions of energies ranging from 90 MeV to 260 MeV. Since these energies are in the electronic stopping regime, atomic transport processes will not be directly initiated by elastic ion target collisions, but need to be excited by secondary processes like electron phonon coupling or Coulomb explosion. Nevertheless, we have observed a strong mixing effect in the ceramic systems if the electronic energy loss exceeds a certain threshold value. Estimation of an effective diffusion constant indicates that diffusion takes place in the molten ion track. In contrast to the ceramics, the metallic Ni layer is still insensitive even for the highest electronic stopping power used S e 28 keV nm and does not exhibit mixing with its SiO2 substrate. In addition, NiO SiO2 and Ni SiO2 were irradiated in the nuclear stopping regime with 600 keV Kr and 900 keV Xe ions. Here the intermixing effect is in good agreement with the assumption of ballistic atomic transpor
Diffusion of hydrogen implanted in alpha-quartz during air annealing
No full textalpha-quartz samples were implanted with 20 keV H-2(+)-ions to fluences of 5 x 10(16) H/cm(2) at a target temperature of 77 K. Rutherford Backscattering in channeling geometry (RBS-C) revealed that an amorphous surface layer of 1.54 x 10(18) atoms/cm(2) forms under these conditions. Resonant nuclear reaction analysis (RNRA) utilizing the H-1(N-15, alpha gamma)-resonance at 6.385 MeV beam energy was used to measure the implanted hydrogen profile, The samples were then annealed in air for 1 h at temperatures between 300 degrees C and 950 degrees C. After annealing, RBS-C and RNRA were again employed to study the alterations of the hydrogen profile and the amorphous layer induced by the heat treatment. In contrast to the observation with alkali ions no epitaxial regrowth could be detected even after the 950 degrees C annealing. Below about 450 degrees C also no changes of the hydrogen profile were observed, while at about 600 degrees C almost all hydrogen has left the sample. This behavior fits nicely to the results obtained for other alkali implantations, Hydrogen as the lightest (and smallest) group-I atom becomes mobile at the lowest temperature and also the observed trend that the quality of the regrown layer decreases with decreasing atomic number of the implanted species has been confirmed, since no epitaxial recrystallization has taken place. (C) 2000 Elsevier Science B.V. All rights reserved
Ion beam induced solid state reaction in Si/C layer systems
No full textIon irradiation (350 keV Xe ions) of Si/C layer systems leads to atomic mixing and a solid state reaction between the two constituents. The ballistic model underestimates the ion beam mixing rate and, in contradiction to the model, a quadratic dependence between the applied fluence and the thickness of the intermixed layer was found. This is a hint that chemical driving forces have to be taken into account. For the evolution of the chemical short range order in the intermixed material two temperature regions can be distinguished. If the irradiation is carried out below 873 K an amorphous network forms which exhibits no uniform short range order. At higher temperatures (similar to 873 K) a well-defined short range order forms which compares to that of crystalline SiC. Annealing experiments indicate that the phase formation is not a simple temperature effect, but the energy deposition by the ion beam is necessary for the formation of the SIC short range order. (C) 2001 Elsevier Science B.V. All rights reserved
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
Oxygen migration during epitaxial regrowth in Cs+-irradiated α-quartz investigated by means of nuclear reaction analysis
No full textThe migration of oxygen in ion-beam-amorphized c-SiO2 (alpha-quartz) was investigated by means of nuclear reaction analysis using the resonant reaction O-18(p,alpha)N-15 for oxygen depth profiling. Only very small amounts of oxygen were observed to diffuse in crystalline or in Xe+-ion beam-amorphized alpha-quartz after high-temperature annealing. However, a dramatic migration of oxygen occurs in Cs+-implanted alpha-quartz in the same temperature range (600-900 degrees C), where Cs diffuses out of the amorphized layer and epitaxial recrystallization occurs. These results point out to a strong correlation of all these processes. A mechanism to explain the observed indiffusion of O-18 is proposed and is related to the Cs migration and the topological modification to achieve epitaxial regrowth of the SiO2 matrix. (C) 2000 American Institute of Physics. [S0003-6951(00)02325-1]
Ion beam doping and epitaxial regrowth of α-quartz
No full textThermally induced epitaxial crystallization of thin a-SiO2 films represents a promising procedure for removing the ion-beam damage induced during the fabrication of integrated optical devices. In this paper we report on the crystallization of a-SiO2 films deposited on single crystalline alpha -quartz substrates, investigated by means of Rutherford backscattering spectrometry in channeling geometry (RBS-C). The epitaxial crystallization was achieved by means of a novel three-step procedure which uses high-fluence Cs+-ion doping of the films and subsequent annealing in air at 800-900 degreesC. Similarly, amorphous SiO2 layers, created by the ion irradiation of alpha -quartz samples, were epitaxially regrown after alkali post-implantation and annealing, thus demonstrating that the regrowth is independent of the production history of the amorphous film. Optical spectroscopy in the range 300-1100 nm showed the good optical properties of the regrown layer. (C) 2001 Elsevier Science B.V. All rights reserved
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
Phase stability of decomposed Ni-Al alloys under ion irradiation
No full textThe disordering of a decomposed Ni-12 at. %-Al alloy under irradiation with 300-keV Ni+ ions is studied in direct comparison to homogeneous Ni3Al at various temperatures. For that, the degree of long-range order is quantitatively determined by electron diffractometry. Heterogeneous alloys disorder significantly faster than the homogeneous intermetallic. In addition. their disordering rate depends on the precipitate size of the microstructure. At 823 K a steady state with an intermediate degree of order is reached. The experimental results are compared with model calculation based on a Cahn-Hilliard-type continuum model. At higher temperatures the model yields a correct description of the experiments. However, discrepancies at room temperature suggest a direct coupling of local composition and degree of order during the collision cascade. This interpretation is further supported by Monte Carlo simulations of overlapping cascade events
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