1,721,026 research outputs found
Nanoscale inhomogeneity of the Schottky barrier and resistivity in MoS2 multilayers
No full textConductive atomic force microscopy (CAFM) is employed to investigate the current injection from a nanometric contact (a Pt coated tip) to the surface of MoS2 thin films. The analysis of local current-voltage characteristics on a large array of tip positions provides high spatial resolution information on the lateral homogeneity of the tip/MoS2 Schottky barrier ΦB and ideality factor n, and on the local resistivity ρloc of the MoS2 region under the tip. Here, ΦB=300±24meV, n=1.60±0.23, and ρloc=2.99±0.68Ωcm are calculated from the distributions of locally measured values. A linear correlation is found between the ρloc and ΦB values at each tip position, indicating a similar origin of the ρloc and ΦB inhomogeneities. These findings are compared with recent literature results on the role of sulfur vacancy clusters on the MoS2 surface as preferential paths for current injection from metal contacts. Furthermore, their implications on the behavior of MoS2 based transistors are discussed
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
Epitaxial crystallization of keV-ion-bombarded α quartz
No full textIn this article, our results on the epitaxial crystallization of ion-bombarded crystalline silicon dioxide (alpha quartz) are reviewed. The epitaxial recrystallization of amorphized layers was achieved after alkali irradiation and annealing in air in the temperature range 650-875 degreesC. The systematic behavior of alkali ions in enhancing the regrowth rate both with decreasing ion size and increasing concentration is shown. The role of oxygen in the recrystallization was investigated by means of nuclear reaction analysis, by performing thermal treatments of the samples in O-18. A large amount of O-18 diffuses inside the amorphous layer in the alkali-ion implanted samples at 600-800 degreesC. From the strong correlation between the migration of O-18 and implanted alkali, it was possible to gain further insights into the recrystallization mechanism. (C) 2001 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
Apparato di sintesi su letto catalitico e separazione di fasi liquido-gas
Full text linkApparato di sintesi su letto catalitico e di separazione dei prodotti di sintesi
comprendenti una fase gassosa e due fasi liquide, una fase liquida più pesante e
l’altra fase liquida più leggera, l’apparato comprendente
- un modulo di sintesi (M1) comprendente un primo tubo (1) provvisto ad una
prima estremità di un’apertura e chiuso ad una seconda estremità da una griglia
(7), il primo tubo (1) essendo atto a contenere al suo interno un letto catalitico (6);
- ed un modulo di separazione (M2) per separare le due fasi liquide e la fase
gassosa provenienti dal modulo di sintesi (M1), comprendente un secondo tubo
(1’) disposto adiacente alla seconda estremità del primo tubo (1), comunicante con
esso ad una sua prima estremità, ed avente ad una sua seconda estremità un
elemento di chiusura (13) provvisto di un foro passante
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
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]
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