1,721,091 research outputs found
Calculations of band-filling optical nonlinearities in extrinsic semiconductors beyond the low injection limit
No full textThe calculations regarding band-filling optical nonlinearities in direct band-gap extrinsic semiconductors were carried out. The process was based on the self-consistant determination of pseudochemical potential and it improved with other calculations. These calculations also enabled direct calculation of the non-linear optical suceptibility and fixing of photogenerated electron-hole density as a parameter was not needed. The study showed that the code can easily be extended to calculate the non-linear response of multilayered structures
Nonresonant Kerr effect in microporous silicon: Nonbulk dispersive behavior of below band gap χ (3)(ω)
No full textAlthough in recent years resonant optical nonlinearities in quantum confined silicon generated significant interest, no experimental work has been dedicated to the nonresonant regime, which is the range of interest for optical switching applications. In this article we report a systematic investigation on the different types of optical nonlinearities which can be activated in quantum-sized silicon. In particular, original measurements of nonresonant nonlinear refraction (Kerr effect) are reported at different wavelengths, spanning the infrared middle-gap range. The dispersive scaling rule and values of the nonlinear refractive index are clearly incompatible with those of three-dimensional semiconductors. Hence the quantum confined density of states plays a key role in determining the frequency dispersion of the nonresonant third-order susceptivity χ (3)(ω). Also, this suggests the need of further investigation of the influence of quantum-size effects (and related density of states modifications) on below-gap χ (3). © 2002 American Institute of Physics
Non-resonant Kerr Effect in Microporous Silicon: Non-bulk Dispersive Behaviour of Below Band-gap chi(3)(w)
No full textNon-resonant Kerr Effect in Microporous Silicon: Non-bulk Dispersive Behaviour of Below Band-gap chi(3)(w)
No full textUnconventional use of mixed-phase TiO2 as optical gauge of molecular oxygen with ratiometric-enhanced responsivity
No full textWe show that mixed-phase (MP) titanium dioxide (TiO2) can be effectively employed as an unconventional, inorganic, dual-emitting and ratiometric optical sensor of O2. Thanks to the peculiar “anti-correlated” photoluminescence of the two TiO2 crystal phases, MP-TiO2 exhibits an unusual ratiometric-enhanced responsivity. Simultaneous availability of rutile and anatase TiO2 PL allows using their ratio as measurement parameter associated to O2 concentration, leading to larger experimental responsivity compared to the one obtainable for single-phase PL detection. A proof of this concept is given, showing a two-fold enhancement of the optical responsivity. Additional characteristics of mixed phase TiO2 can be envisaged as favorable for O2 optical probing, namely: (a) low production costs, (b) absence of heterogeneous components, (c) self-supporting properties. These characteristics promote testing mixed phase TiO2 use for applications requiring high indicator quantities at competitive price, possibly also tackling the need to develop supporting matrixes that carry the luminescent probes and avoiding issues related to the use of different components for ratiometric sensing
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
Second harmonic generation analysis in hydrogenated amorphous silicon nitride thin films
No full textMaterials for Chemical Sensing: A Comprehensive Review on the Recent Advances and Outlook Using Ionic Liquids, Metal–Organic Frameworks (MOFs), and MOF-Based Composites
No full textThe ability to measure and monitor the concentration of specific chemical and/or gaseous species (i.e., “analytes”) is the main requirement in many fields, including industrial processes, medical applications, and workplace safety management. As a consequence, several kinds of sensors have been developed in the modern era according to some practical guidelines that regard the characteristics of the active (sensing) materials on which the sensor devices are based. These characteristics include the cost-effectiveness of the materials’ manufacturing, the sensitivity to analytes, the material stability, and the possibility of exploiting them for low-cost and portable devices. Consequently, many gas sensors employ well-defined transduction methods, the most popular being the oxidation (or reduction) of the analyte in an electrochemical reactor, optical techniques, and chemiresistive responses to gas adsorption. In recent years, many of the efforts devoted to improving these methods have been directed towards the use of certain classes of specific materials. In particular, ionic liquids have been employed as electrolytes of exceptional properties for the preparation of amperometric gas sensors, while metal–organic frameworks (MOFs) are used as highly porous and reactive materials which can be employed, in pure form or as a component of MOF-based functional composites, as active materials of chemiresistive or optical sensors. Here, we report on the most recent developments relative to the use of these classes of materials in chemical sensing. We discuss the main features of these materials and the reasons why they are considered interesting in the field of chemical sensors. Subsequently, we review some of the technological and scientific results published in the span of the last six years that we consider among the most interesting and useful ones for expanding the awareness on future trends in chemical sensing. Finally, we discuss the prospects for the use of these materials and the factors involved in their possible use for new generations of sensor devices
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