1,721,010 research outputs found
Dislocations, extended defects and interfaces at nanoparticles as effective sources of room temperature photo- and electro-luminescence in silicon and silicon-germanium
No full textIn view of demonstrating the technical feasibility of silicon based, high efficiency room temperature light emitting devices (LED), the primary objectives of this Project are:
1. to find practical approaches for the creation of suitable dislocation structures or of alternative structures (like misfit dislocations in Si-Ge heterostructures, dislocation loops at Si/SiO2 interfaces and Si nanocrystals in amorphous silicon) such to enhance the quantum efficiency of the dislocation-related luminescence (DRL) or of the intrinsic emission of silicon at room temperature in view of applications for silicon-based LEDs. To this purpose, several processes of dislocation generation will be employed, in addition to the conventional plastic deformation at high temperature
2. to obtain a clear understanding of the physics of the dislocation-assisted light emission, of the correlations between the dislocation structure and their emission properties, of the role of carbon, oxygen and other light impurities like hydrogen and nitrogen as well as of metallic impurities on their emission properties and of the correlation between device surface quality, configuration and luminescence yield
3. to carry out theoretical investigations on the correlation between core structure of extended defects and optical and electronic properties of dislocations
About the first topic, the photo-(PL) and electro-luminescence (EL) emission of dislocations generated by different means will be studied in clean conditions. Different dislocation structures will be generated by special deformation procedures, by ion implantation or by the injection of self-interstitials or vacancies generated in a silicon matrix during the growth process of a precipitate having a different molar volume of the matrix, as it happens with SiO2, SiC and Er-oxide in heat treated carbon loan and carbon doped Cz silicon, carbon- implanted FZ silicon and Er-implanted Cz silicon.
Also Si-Ge heterostructures, interesting because potentially compatible with conventional microelectronic processes will be studied, before and after strain relaxation.
The second topic will be treated by studying the effect of all the mentioned impurities on clean
dislocations prepared by plastic deformation of Fz or Cz silicon, whose cleanliness will be tested by photoluminescence (PL), Deep Level Transient Spectroscopy (DLTS) and lifetime mapping measurements. The effect of impurities on the light emission features of oxygen precipitates will be also studied.
Eventually, the correlation between dislocation structure and optical properties will be studied using different computational methods, as the scc-DFTB (self consistent charge functional based tight binding method) and the AIMPRO (ab initio modeling program)
http://intas.mater.unimib.it
Structural characterization of nc-Si films grown by low-energy PECVD on different substrates
No full textAdvances in structural characterization of thin film nanocrystalline silicon for photovoltaic applications
No full text
Nanocrystalline silicon films for photovoltaic and optoelectronic applications
No full textThe primary aim of this research project is to develop computational tools capable of assisting the design of a new nc-Si growth process with a Low Energy variant of a Plasma Enhanced Chemical Vapour Deposition (LEPECVD) reactor, addressed at the deposition of nc-Si films for both photovoltaic and optoelectronic applications. This objective is for many aspects really at the frontier of the today knowledge of multiphase materials, and for this reason requires the involvement of different theoretical and experimental tools and expertises. An LEPECVD reactor is actually in full use in one of the partner’s laboratories and has been already demonstrated to be a very powerful tool for high growth rate, high quality epitaxial silicon and silicon-germanium films. The modelling activities include Molecular dynamics (MD) and abinitio calculations applied to the simulation of the growth of nc-Si grains in a amorphous silicon (a- Si) matrix, to the evaluation of the best a-Si/ nc-Si ratio and the elastic/plastic effects consequent to the presence of nanocrystals of silicon in the a-Si matrix and to the presence of a grain boundary phase, which could be responsible of unwanted carrier recombination processes. The computational tools will be also used to evaluate the band offset vs microstructure and strain, in view of the fine-tuning of the optoelectronic properties. As the computer modelling could not be granted for a complete forecasting of the role of process parameters on the local nanostructural aspects and associated physical properties, additional theoretical studies on quantum confinement will be carried out. Such theoretical studies will be based on the results of systematic measurements of optoelectronic properties of nc-Si. The development of the computer modelling and of theoretical studies on quantum confinement will be paralleled, from the very early stage of the Project, by nc-Si growth experiments and by state of the art morphological, microstructural, compositional, electrical and optoelectronic characterization
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
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