1,721,032 research outputs found
Optical Activation and Excitation Mechanisms of Er Implanted In Si
No full textThe several processes required to achieve Er luminescence in Si are investigated. In particular, the role of Er-O interactions to obtain the incorporation of high Er concentrations, electrically and optically active, in crystalline Si is addressed. Multiple Er and O implants were performed on n-type (100) Si crystals to obtain flat concentrations of approximately 1 X 10(19) Er/cm3 and approximately 1 X 10(20) O/cm3 over an approximately 2-mum-thick layer. These implants produced also a 2.3-mum-thick amorphous Si (a-Si) layer. A subsequent thermal treatment at 620-degrees-C for 3 h induced the epitaxial regrowth of the whole layer and the incorporation of both Er and O in a good-quality single crystal. A further annealing at 900-degrees-C for 30 sec produced the electrical activation of the implanted Er in the presence of O, with an Er donor concentration of approximately 8 X 10(18)/cm3 over an approximately 1.8-mum-thick layer. This value is more than two orders of magnitude above the maximum Er donor concentration reported in the literature, demonstrating the crucial role of 0 in increasing the electrically active Er concentration in crystalline Si. The optical efficiency of this sample has been studied by photoluminescence. It is seen that an enhancement by a factor of approximately 6 with respect to the literature data is obtained. Moreover, studies on the photoluminescence intensity as a function of the pump power give important information on the mechanisms underlying Er luminescence in Si and its competing phenomena. These data are presented and discussed. A plausible model based on the previous results is also presented
Preliminary Observations on Matrix Metalloproteinases in Canine Oral Melanoma: Association Of MMP-9 and TIMP-2 Immunohistochemical Expression with FXR1 and Clinical Outcome,
No full textIntroduction: Feline diffuse iris melanoma (FDIM) is the most common feline primary intraocular neoplasm. It is a slowly progressive malignant tumour, representing a possiblemodel of human iris melanoma.
In cats, histological grade andmitotic index (MI) are considered predictors of survival. Matrix metalloproteinase-9 (MMP-9) is an endopeptidase able to digest the extracellular matrix and is involved in tumour invasion. Its specific inhibitor is the tissue inhibitor of metalloproteinases-2 (TIMP-2). The present study investigates the correlation between MMP-9/TIMP-2 expression and histological grade and MI.
Materials and Methods: Sixty-one FDIMs were graded on light microscopy (grade I, n 5 22; grade II, n 5 20; grade III, n 5 19) and MI was calculated. Immunohistochemistry was performed using monoclonal anti-MMP-9 and anti-TIMP-2 antibodies and scored semiquantitatively.
Results were compared by the Mann-Whitney U test.
Results: MMP-9 was expressed in 59.1% grade I FDIMs, 90.0% grade II and 80.0% grade III tumours.TIMP-2 immunolabelled 59.1% grade I, 80.0% grade II and 73.7% grade IIIFDIMs.MMP-9was expressed in 71.4% of FDIMswithMI7 and 92.3% of FDIMwithMIO7. TIMP-2 was detected in 67.3% of caseswithMI7 and 76.9% of caseswithMI O7. MMP-9 and TIMP-2 expression differed significantly between grade I and the other two grades. TIMP-2 expression was correlated withMMP-9 expression in grade I and III tumours. IntenseMMP-9, but not TIMP-2, was significantly associated with high MI.
Conclusions: In FDIM intense immunohistochemical expression of MMP-9 correlated with known histological parameters of aggressiveness, specifically histological grade and MI
Excitation and nonradiative deexcitation processes of Er3+ in crystalline Si
No full textA detailed investigation on the excitation and deexcitation processes of Er3+ in Si is reported. In particular, we explored Er pumping through electron-hole pair recombination and Er deexcitation through Auger processes transferring energy to either free or bound electrons and holes. Since Er donor behavior would result in a free-carrier concentration varying along its profile, experiments have been performed by embedding the whole Er profile within previously prepared n-doped or p-doped regions. Multiple P (B) implants were performed in n-type (p-type) Czochralski Si samples in order to realize uniform dopant concentrations from 4 x 10(16) to 1.2 x 10(18)/cm(3) at depths between 0.5 and 2.5 mu m below the surface. These samples have been subsequently implanted with 4 MeV 3.3 x 10(13) Er/cm(2) and annealed at 900 degrees C for 30 min. Free electrons or holes concentrations in the region where Er sits were measured by spreading resistance profiling. It has been found that the release of electrons or holes from shallow donors and accepters, occurring at temperatures between 15 and 100 K, produces a strong reduction of both time decay and luminescence intensity at 1.54 mu m. These phenomena are produced by Auger deexcitation of the Er3+ intra-4f electrons with energy transfer to free carriers. The Auger coefficient of this process has been measured to be C-A similar to 5 x 10(-13) cm(3) s(-1) for both free electrons and free holes. Moreover, at 15 K (when the free carriers are frozen and the donor and acceptor levels occupied) the Er3+ time decay has been found to depend on the P (or B) concentrations. This is attributed to an impurity Auger deexcitation to electrons (or holes) bound to shallow donors (accepters): the efficiency of this process has been determined to be two orders of magnitude smaller with respect to the Auger deexcitation with free carriers. Furthermore, at temperatures above 100 K a nonradiative back-transfer decay process, characterized by an activation energy of 0.15 eV, is seen to set in for both p-type and n-type samples. This suggests that the back-transfer process, which severely limits the high-temperature luminescence efficiency, is always completed by a thermalization of an electron trapped at an Er-related level to the conduction band. Finally, by analysis of the pump power dependence of time decay and luminescence yield at 15 K, we have found that excitation of Er through the recombination of an electron-hole pair is a very efficient process, characterized by an effective cross section of 3 x 10(-15) cm(2) and able to provide an internal quantum efficiency as high as 10% at low temperatures (15 K) and pump powers (below 1 mW). This efficiency is significantly reduced when, at higher temperatures and/or high pump powers, strong nonradiative decay processes set in. These phenomena are investigated in detail and their impact on device operation perspectives are analyzed and discussed. [S0163-1829(98)01008-X]
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Room-temperature Electroluminescence From Er-doped Crystalline Si
No full textWe have obtained room-temperature electroluminescence (EL) at approximately 1.54 mum from Er and O co-doped crystalline p-n Si diodes fabricated by ion implantation, under both forward and reverse bias conditions. Under forward bias, the EL intensity decreases by a factor of approximately 15 on going from 110 to 300 K, where a weak peak is still visible. In contrast, we report the first sharp luminescence peak obtained under reverse bias conditions in the breakdown regime. In this case the EL intensity decreases only by a factor of 4 on going from 110 to 300 K and the room-temperature yield is more than one order of magnitude higher than under forward bias. The data suggest that Er excitation occurs through electron-hole mediated processes under forward bias and through impact excitatio
Erbium implantation in silicon: from materials properties to light emitting devices
No full textErbium implantation in silicon has recently emerged as a promising method to tailor the optical properties of Si towards the achievement of a light emission at 1.54 mu m. In this paper we will review our recent work on this subject. In particular a detailed investigation of the nonradiative processes, competing with the radiative emission of Er in Si will be presented, Among these processes, an Auger de-excitation with the energy released to free carriers will be demonstrated to be extremely efficient, with an Auger coefficient C-A similar to 4.4 x 10(-13) cm(3) s(-1). Using the knowledge on the material properties, an efficient Er implanted light emitting diode has been fabricated. It will be shown that by exciting Er within the depletion region of reverse biased p(+)-n(+) Si diodes in the breakdown regime it is possible to avoid Auger quenching and to achieve high efficiency. Moreover, at the switch off of the diode, when the depletion region shrinks, the excited Er ions become suddenly embedded within the neutral heavily doped region of the device. In this region Auger de-excitation with free carriers sets in and quenches the luminescence rapidly. This allows modulation of the light emitting devices at frequencies as high as a few MHz. These data will be presented and discussed. (C) 1998 Elsevier Science S.A. All rights reserved
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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