1,721,076 research outputs found
Quantum confinement and light trapping effects in nanoporous Ge
No full textSemiconductors containing nanopores have gained a renewed interest as they are able to adsorb and interact with atoms and molecules and can thus be used in several interesting and emerging applications. Ge film and bulk samples, self-implanted with Ge+ ions, have shown to have a sponge-like nanoporous structure [1], as shown in fig.1. Possible applications of porous semiconductors include various novel sensors, solar cells, optoelectronic devices; they can be used for catalysis, biological molecular isolation and purification or electrodes for micro-fuel cells [2 and reference therein].
Optoelectronic characterization of the layers are carried out by Surface Photovoltage (SPV) Spectroscopy, a powerful technique which allows for obtaining detailed information on material optical properties, such as electronic transitions at gap states, and band to band transitions [2,3]. In addition, structural and microscopic analyses have been carried out in order to identify amorphous or crystalline phases and the average size of the nano- pores. Different nanoporous (np) structures have been investigated: crystalline and amorphous np-Ge obtained by implantation of bulk Ge, as well as crystalline and amorphous np-Ge obtained by ion implantation of Ge film grown on Si substrates by molecular beam epitaxy and sputtering. The effect of Au nanoparticles embedded within the nanoporous structure has been also investigated.
Changes in the SPV spectra as a function of ion implantation fluence and annealing treatments have been found and discussed on the basis of the structural properties of the samples [4]. A significant enhancement of the SPV signal in np-Ge samples decorated with Au nanoparticles has been shown, and related to enhanced light trapping effects. SPV spectra of np-Ge thin films show the main peak, which corresponds to band-to-band transitions, significantly blue shifted with respect to the same peak in bulk np-Ge (fig.2). This result has been assigned to a quantum confinement effect occurring at Ge nano- walls separating the nanopores. In addition, a strong enhancement of the SPV signal has been observed due to light confinement effects. Quantum confinement and light trapping effects demonstrated in nanoporous Ge film deposited on Si substrate can be of major interest for future photovoltaic applications of thin film solar cells.
[1] G Impellizzeri et al Nanotechnology 23, 395604 (2012)
[2] D Cavalcoli et al Microporous and Mesoporous Mat 196, 175–178 (2014)
[3] L Kronik and Y. Shapira, Surf Sci Rep. 37,1 (1999)
[4] D Cavalcoli et al, in Semiconductors and Semimetals, Elsevier, (2015
Nanopore formation induced by ion-implantation in Ge: optical properties
No full textSelf-ion implantation on bulk Ge induces the formation of nanopores,
and their growth, structure and transport properties have been recently reported
[1]. Semiconductors containing nanopores have gained a renewed interest as
they are able to adsorb and interact with atoms and molecules and can thus be
used in several interesting and emerging applications. In this contribution we
report on the influence of ion implantation and subsequent nanopore formation
on optoelectronic properties of Ge samples. The analyses are carried out by
Surface Photovoltage (SPV) Spectroscopy, a powerful technique to get detailed
information on material optical properties [2]. Different nanoporous (np)
structures have been investigated: crystalline and amorphous np-Ge obtained
by implantation of bulk Ge, as well as crystalline and amorphous np-Ge obtained
by ion implantation of Ge film grown on Si substrates by molecular beam
epitaxy and sputtering. Changes in the SPV spectra as a function of ion
implantation fluence and annealing treatments are discussed on the basis of the
structural properties of the samples. Quantum confinement effects in
nanoporous Ge film have been demonstrated, while a significant SPV
enhancement in np-Ge samples decorated with Au nanoparticles has been
shown. These results can be of major interest for future photovoltaic
applications of thin film solar cells. G Impellizzeri et al Nanotechn 23, 395604
(2012) L Kronik and Y. Shapira, Surf Sci Rep. 37,1 (1999
Copper(II) binding to the toxic fragment 180-193 of the prion
No full textCopper(II) binding to the toxic fragment 180-193 of the prio
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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