Electroluminiscence and optical amplification in silicon nanostructures: towards the integration of electronics and photonics

This line of research of my group intends to establish a Silicon technological platform in the field of photonics allowing the development of a wide set of applications. Particularly, what is still lacking in Silicon Photonics is an efficient and integrable light source such an LED or laser. Nanocrystals in silicon oxide or nitride matrices have been recently demonstrated as competitive materials for both active components (electrically and optically driven light emitters and optical amplifiers) and passive ones (waveguides and modulators). The final goal is the achievement of a complete integration of electronic and optical functions in the same CMOS chip. The first part of this paper will introduce the structural and optical properties of LEDs fabricated from silicon nanostructures. The second will treat the interaction of such nanocrystals with rare-earth elements (Er), which lead to an efficient hybrid system emitting in the third window of optical fibers. I will present the fabrication and assessment of optical waveguide amplifiers at 1.54 ¿m for which we have been able to demonstrate recently optical gain in waveguides made from sputtered silicon suboxide materials.

Effects of prior hydrogenation on the structure and properties of thermally nanocrystallized silicon layers

Nanocrystalline silicon layers have been obtained by thermal annealing of films sputtered in various hydrogen partial pressures. The as-deposited and crystallized films were investigated by infrared, Raman, x-ray diffraction, electron microscopy, and optical absorption techniques. The obtained data show evidence of a close correlation between the microstructure and properties of the processed material, and the hydrogen content in the as-grown deposit. The minimum stress deduced from Raman was found to correspond to the widest band gap and to a maximum hydrogen content in the basic unannealed sample. Such a structure relaxation seems to originate from the so-called "chemical annealing" thought to be due to Si-H2 species, as identified by infrared spectroscopy. The variation of the band gap has been interpreted in terms of the changes in the band tails associated with the disorder which would be induced by stress. Finally, the layers originally deposited with the highest hydrogen pressure show a lowest stress-which does not correlate with the hydrogen content and the optical band gap¿and some texturing. These features are likely related to the presence in these layers of a significant crystalline fraction already before annealing.

Influence of average size and interface passivation on the spectral emission of Si nanocrystals embedded in SiO2

The correlation between the structural (average size and density) and optoelectronic properties [band gap and photoluminescence (PL)] of Si nanocrystals embedded in SiO2 is among the essential factors in understanding their emission mechanism. This correlation has been difficult to establish in the past due to the lack of reliable methods for measuring the size distribution of nanocrystals from electron microscopy, mainly because of the insufficient contrast between Si and SiO2. With this aim, we have recently developed a successful method for imaging Si nanocrystals in SiO2 matrices. This is done by using high-resolution electron microscopy in conjunction with conventional electron microscopy in dark field conditions. Then, by varying the time of annealing in a large time scale we have been able to track the nucleation, pure growth, and ripening stages of the nanocrystal population. The nucleation and pure growth stages are almost completed after a few minutes of annealing time at 1100°C in N2 and afterward the ensemble undergoes an asymptotic ripening process. In contrast, the PL intensity steadily increases and reaches saturation after 3-4 h of annealing at 1100°C. Forming gas postannealing considerably enhances the PL intensity but only for samples annealed previously in less time than that needed for PL saturation. The effects of forming gas are reversible and do not modify the spectral shape of the PL emission. The PL intensity shows at all times an inverse correlation with the amount of Pb paramagnetic centers at the Si-SiO2 nanocrystal-matrix interfaces, which have been measured by electron spin resonance. Consequently, the Pb centers or other centers associated with them are interfacial nonradiative channels for recombination and the emission yield largely depends on the interface passivation. We have correlated as well the average size of the nanocrystals with their optical band gap and PL emission energy. The band gap and emission energy shift to the blue as the nanocrystal size shrinks, in agreement with models based on quantum confinement. As a main result, we have found that the Stokes shift is independent of the average size of nanocrystals and has a constant value of 0.26±0.03 eV, which is almost twice the energy of the Si¿O vibration. This finding suggests that among the possible channels for radiative recombination, the dominant one for Si nanocrystals embedded in SiO2 is a fundamental transition spatially located at the Si¿SiO2 interface with the assistance of a local Si-O vibration.

La exposición de los menores españoles a la violencia familiar

La preocupación social por la violencia de género es una realidad, tanto en el ámbito nacional como internacional, incluyendo en la actualidad no sólo a la víctima directa sino también a los menores expuestos. La victimología del desarrollo ha contribuido a hacer visibles a estos menores y mostrarlos no como meros espectadores sino también como víctimas que se ven privadas de derechos y libertades básicos para su correcto desarrollo. Desde una perspectiva amplia es más adecua­ do hablar de exposición de los menores a la violencia familiar, incluyéndose así no sólo la dirigida hacia la mujer sino también aquélla que afecta al hombre o la que se produce de manera bidireccional entre los padres o entre uno de los padres y su pareja (Wolak y Finkelhor, 1998). A su vez, aunque menos estudiada, también de­ be considerarse dentro de esta categoría la exposición a la violencia que los padres dirigen a los hermanos del menor.Los estudios demuestran que el maltrato no siempre se extiende a toda la fratría: incluso en los casos más graves de maltrato fisico, el 18% de los hermanos estaría a salvo del trato violento dirigido a uno de ellos (Pereda y Almirall, 2004).

Prevalencia y características del abuso sexual infantil en estudiantes universitarios españoles

Objective: The purpose of this paper was to compare the prevalence rates of child sexual abuse reported by [Finkelhor, D. (1994). The international epidemiology of child sexual abuse. Child Abuse & Neglect, 18 (5), 409417] with those found in recent publications in order to confirm the widespread prevalence of child sexual abuse. Methods: Relevant articles about prevalence of child sexual abuse were identified through searches of computerized databases and a handsearch of Child Abuse & Neglect and the Journal of Child Sexual Abuse. Results: Thirty-eight independent articles were identified, corresponding to 39 prevalence studies; these articles report the prevalence of childhood sexual abuse in 21 different countries, ranging from 0 to 53% for women and 0 to 60% for men. Conclusions: Comparison of the present study with that of [Finkelhor, D. (1994). The international epidemiology of child sexual abuse. Child Abuse & Neglect, 18 (5), 409417] shows a similarity between prevalence distributions; there appears to be a general pattern that remains more or less constant over the years, especially in women. Practice implications: Twelve years after the first revision study about the international prevalence of child sexual abuse, there is still a need for new data about this topic. The present study shows child sexual abuse is still a widespread problem in the society. In this research, carried out on 38 independent studies, there is new data for 21 countries over the world, being especially relevant the results obtained from other countries different from those pertaining toNorth America or Europe. It is important to point out the high prevalence found in most of the countries, so this information could be a new warning to make society and governments aware of this problem and undertake actions to prevent sexual abuse in childhood. © 2009 Elsevier Ltd. All rights reserved.

Estudio descriptivo de víctimas de abuso sexual infantil

En este trabajo se describen las características principales que presenta la población atendida en un centro de asesoramiento y atención a menores víctimas de abusos sexuales. Este centro, con sede en Barcelona, pertenece a la asociación FADA,creada en 1997 con la finalidad de ofrecer un servicio profesional de asesoramiento, prevención y formación especializada en relación con el abuso sexual acontecido durante la infancia. El presente estudio, meramente descriptivo, muestra la frecuencia del abuso sexual, la dificultad de su descubrimiento durante la infancia, sus consecuencias más comunes, así como la reacción del entorno de la víctima ante su revelación. Para ello se han utilizado los testimonios de 385 personas víctimas de abuso sexual durante su infancia. A través del análisis de dos muestras de usuarios del centro (adultos y menores) se dan a conocer las diferencias más destacadas. Los profesionales de este centro hacen de este modo públicas sus experiencias y recalcan la urgente y necesaria atención especializada que requieren no sólo las víctimas de abuso sexual infantil, sino también sus familias y/o su entorno social.

Creation and Validation of Chronojump-Boscosystem: A Free Tool to Measure Vertical Jumps

Measuring the height of the vertical jump is an indicator of the strength and power of the lower body. The technological tools available to measure the vertical jump are black boxes and are not open to third-party verification or adaptation. We propose the creation of a measurement system called Chronojump-Boscosystem, consisting of open hardware and free software. Methods: A microcontroller was created and validated using a square wave generator and an oscilloscope. Two types of contact platforms were developed using different materials. These platforms were validated by the minimum pressure required for activation at different points by a strain gauge, together with the on/off time of our platforms in respect of the Ergojump-Boscosystem platform by a sample of 8 subjects performing submaximal jumps with one foot on each platform. Agile methodologies were used to develop and validate the software. Results: All the tools fall under the free software / open hardware guidelines and are, in that sense, free. The microcontroller margin of error is 0.1%. The validity of the fiberglass platform is 0.95 (ICC). The management software contains nearly 113.000 lines of code and is available in 7 languages.

Le bon vin d’Orleans, le punays lac de Sorbone et la mode de Bretaigne: sociocentrisme lúdic i ambivalència als blasons populars del Pantagruel de Rabelais, amb mostres de versions en diferents llengües

En aquest article es presenta una selecció d’un corpus extret del Pantagruel, en el qual els personatges de Rabelais ataquen o afalaguen, grotescament i hiperbòlica, en el més pur estil pantagruèlic, les altres nacions o viles. Per a aquests epítets ètnics, Rabelais reutilitza el blasó popular (blason populaire), en una fusió total de la lloança i la injúria. En el nostre treball comprovarem si la visió sociocèntrica que el blasonador aplica al blasonat, així com el propòsit lúdic, han aconseguit ser traslladats a les versions catalana (Miquel-Àngel Sánchez Férriz, 1985), espanyola (Alicia Yllera, 2003), italiana (Mario Bonfantini, 1953) i anglesa (Burton Raffel, 1991).

Victimització en joves de protecció a la infància i l’adolescència i de justícia juvenil

A Catalunya, un nombre significatiu d’infants i adolescents es troba sota la guarda i tutela del sistema de protecció i d’altres són atesos pel sistema de justícia juvenil. En molts casos, aquests joves han viscut experiències de maltractaments i abusos per part de les principals figures cuidadores, però també d’altres formes de violència en contextos diversos que poden incloure: el carrer, l’escola, el grup d’iguals, les noves tecnologies o els propis centres on poden residir provisionalment. Aquesta multiplicitat d’experiències de violència els converteix amb el que es coneix com a polivíctimes. Però entre l'experiència de victimització en la infància i el desenvolupament de problemes psicològics podem trobar la resiliència, la capacitat de l’ésser humà per superar o recuperar-se amb èxit de circumstàncies adverses. I aquí és on els professionals poden intervenir amb èxit. Els objectius principals d’aquest estudi són conèixer la prevalença d’experiències de victimització en aquests joves, identificar els casos de polivictimització, analitzar les característiques sociodemogràfiques, victimològiques i el nivell de desajust psicològic que presenten. Alhora, identificar perfils de resiliència i analitzar el seu efecte en el nivell de malestar psicològic del jove víctima. Els resultats ens indiquen que són els recursos personals, relatius a la confiança en un mateix, la fe en un futur millor, la capacitat d’identificació i connexió amb les pròpies emocions o les habilitats socials, els que permeten al jove fer front a les dificultats amb èxit. Aquests recursos personals són els que marcaran la diferència en la posterior reintegració social i correcte desenvolupament del jove i, per tant, els professionals els han de conèixer, enfortir i desenvolupar.

Reaction-diffusion lattice gas: Theory and computer results

We report on the study of nonequilibrium ordering in the reaction-diffusion lattice gas. It is a kinetic model that relaxes towards steady states under the simultaneous competition of a thermally activated creation-annihilation $(reaction$) process at temperature T, and a diffusion process driven by a heat bath at temperature T?T. The phase diagram as one varies T and T, the system dimension d, the relative priori probabilities for the two processes, and their dynamical rates is investigated. We compare mean-field theory, new Monte Carlo data, and known exact results for some limiting cases. In particular, no evidence of Landau critical behavior is found numerically when d=2 for Metropolis rates but Onsager critical points and a variety of first-order phase transitions.