1,795,793 research outputs found
On the structure of P(n)*P(n) for p=2
No full textWe show that P(n)*(P(n)) for p = 2 with its geometrically induced structure maps is not an Hopf algebroid because neither the augmentation Epsilon nor the coproduct Delta are multiplicative. As a consequence the algebra structure of P(n)*(P(n)) is slightly different from what was supposed to be the case. We give formulas for Epsilon(xy) and Delta(xy) and show that the inversion of the formal group of P(n) is induced by an antimultiplicative involution Xi : P(n) -> P(n). Some consequences for multiplicative and antimultiplicative automorphisms of K(n) for p = 2 are also discussed
p-n Junction Formation in i-Ge Crystal by Laser Radiation
No full textP-n junction is the main component of many semiconductor devices. Thermodiffusion, ion implantation and molecular beam epitaxy are only a few methods to form a p-n junction. The main drawback for these methods is high cost per p-n junction since the equipment for these methods is expensive. A possibility of p-n junction formation by laser radiation was shown in several p- and n-type semiconductors: p-Si[1,2], p-CdTe[3], p-InSb[4,5], p-InAs[6], p-PbSe[7] and p-Ge[8] due to inversion of conductivity type. Unfortunately, the mechanism of p-n junction formation by laser radiation is not clear until now.
In the present research rectification effect of current-voltage characteristic in pure intrinsic Ge crystal after irradiation by Nd:YAG laser was observed. The effect is characterised by threshold intensity of the laser radiation. Increase of rectification ratio of current-voltage characteristics and barrier height with intensity of the laser radiation, energy of laser radiation quanta and number of pulses was observed in this experiment. The mechanism of this phenomenon is explained by generation and redistribution of intrinsic point defects in temperature gradient field, which causes strongly absorbed laser radiation. The redistribution of defects takes place because interstitial atoms drift towards the irradiated surface, but vacancies drift in the opposite direction – in the bulk of semiconductor according to Thermogradient effect. Since interstitials in Ge crystal are of n-type and vacancies are known to be of p-type, a p-n junction is formed.
[1] Y. Mada et al. Appl. Phys. Lett., 48, pp. 1205 (1986).
[2] J. Blums et al. Physics Status Solidi (a), K91, (1995).
[3] A. Medvid’ et al., Radiat. Meas., 33, 725 (2001).
[4] I. Fujisawa, Jap., J. Appl. Phys, 19, 2137 (1980).
[5] A. Medvid‘ et al. Vacuum, 51, 245 (1998).
[6] L. Kurbatov et al. Reports of Acad. Sc.USSR, 268, 594 (1983)
[7] K.D. Tovstyuk et al. Ukrainian Journal of Physics, 21, 1918 (1984).
[8] S.G. Kiyak et al. Physics and Technics of Semiconductors, 18, 1958 (1984).
Acknowledgments.
The author gratefully acknowledges financial support in part by Europe Project in the Framework of MATERA+ project, European Regional Development Fund within the project “Sol-gel and laser technologies for the development of nanostructures and barrier structures”, the ESF Projects No. 1DP/1.1.1.2.0/09/ APIA/VIAA/142 and «Support for the implementation of doctoral studies at Riga Technical University»
P-n Junction in Intrinsic Semiconductor Formed by Laser Radiation
No full textP-n junction is the most important component of many semiconductor devices. Thermodiffusion, ion implantation and molecular beam epitaxy are only a few methods to form a p-n junction. The main drawback for these methods is high cost per p-n junction. A possibility of p-n junction formation by laser radiation was shown in several semiconductors: p-Si[1,2], p-CdTe[3], p-InSb[4,5], p-InAs[6], p-PbSe[7] and p-Ge[8]. Different mechanisms have been proposed to explain the nature of inversion of conductivity type: impurities’ segregation, defects’ generation, amorphization and oxygen related donor generation. However, the proposed mechanisms have many lacks and even contradictions; therefore the mechanism of p-n junction formation by laser radiation is not clear until now. For the understanding it, i-Ge crystal was irradiated by Nd:YAG laser with different energy of quantum. The crystal was used in the experiments as a model material because the concentration of impurities in this material is lower than the concentration of intrinsic point defects at RT. Increase of rectification ratio of I-V characteristics and barrier height with intensity of the laser radiation, energy of laser radiation quanta and numbers of pulses were observed in this experiment. The mechanism of this phenomenon is explained by generation and redistribution of intrinsic point defects in temperature gradient field, which causes strongly absorbed laser radiation. The redistribution of defects takes place because interstitial atoms drift towards the irradiated surface, but vacancies drift in the opposite direction – in the bulk of semiconductor according to Thermogradient effect. Since interstitials in Ge crystal are of n-type and vacancies are known to be of p-type, a p-n junction is formed.
References
1. Y. Mada et al. Appl. Phys. Lett., 48, 1205 (1986).
2. J. Blums et al. Physics Status Solidi (a), K91, (1995).
3. A. Medvid’ et al., Radiat. Meas., 33, 725 (2001).
4. I. Fujisawa, Jap., J. Appl. Phys, 19, 2137 (1980).
5. A. Medvid‘ et al. Vacuum, 51, 245 (1998).
6. L. Kurbatov et al. Reports of Acad. Sc.USSR, 268, 594 (1983)
7. K.D. Tovstyuk et al. Ukrainian Journal of Physics, 21, 1918 (1984).
8. S.G. Kiyak et al. Physics and Technics of Semiconductors, 18, 1958 (1984)
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
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
P-n Junction Formation in i-Ge Crystal by Laser Radiation
No full textIt was shown to have a possibility of p-n junction formation by laser radiation in certain semiconductors: p-Si [1], p-CdTe [2], p-InSb [3, 4] as well as others. Mechanism of p-n junction formation by laser radiation is not clear until now.
In the experiments we have used Ge single crystals of i-type at room temperature with size: 16.0 x 3.5 x 2.0 mm. Current-voltage characteristics were measured at room temperature. Samples were treated with H2O2 in order to obtain minimum surface recombination velocity (S), which can be Smin = 100 cm/s. A permanent magnet with magnetic field of Bz=0.2 T was used in the experiments. Maximum electric field applied to the samples was Ex = 100 V/cm. Current-voltage characteristics in absence of magnetic field were linear, however when magnetic field was applied to the sample current-voltage characteristics were measured to be sublinear due to Magnetoresistance effect. Current-voltage characteristic of sample with asymmetrically treated opposite surfaces was diode type, due to Welker effect [5]. Asymmetry was obtained by mechanically polishing to obtain Smax -> ∞ and opposite surface was chemically treated to provide Smin. Surface of the sample with Smin was irradiated by fourth harmonic (λ = 266 nm, τ = 3 ns) of Nd:YAG laser. After irradiation by laser current-voltage characteristic became more diodic. We explain this phenomenon by p-n junction formation at the irradiated surface of sample.
We have proposed a mechanism for this phenomenon by using Thermogradient effect [6], which causes redistribution of intrinsic defects, vacancies and interstitial atoms in temperature gradient field. Redistribution takes place because interstitial atoms’ drift towards the irradiated surface, but vacancies drift to the opposite direction – in the bulk of semiconductor. P-n junction is formed from interstitial Ge atoms being p-type and vacancies are known to be n-type
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