Daño por excitación electrónica en SiO2 mediante irradiación con iones pesados de alta energía

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de Materiales. Fecha de lectura: 08-11-201

Variables contextuales en el éxito de las aplicaciones multimedia en la universidad

Use of multimedia technology in classroom is, in some contexts, highly fashionable. There are different myths about this question, like the security of these techonologies enhances learning. On the other hand, research designs used count usually on some methodological unsuitables. One neglected aspect is effect of student satisfaction from classroom process in some dependent variables. In this paper both satisfaction level or degree of pleasantness are measured as for a student group from high school. Procedured used are blackboard, video and computer images animation. Results shows that technology used has effects in pleasantness perceived in classroom. However, authors attract attention about possible temporariness of relations found: they are dependent of context

Medidas subjetivas para formatos de respuesta en encuestas informatizadas

La utilización de diferentes formatos para encuestas informatizada

Refractive index changes in amorphous SiO2 (silica) by swift ion irradiation

The refractive index changes induced by swift ion-beam irradiation in silica have been measured either by spectroscopic ellipsometry or through the effective indices of the optical modes propagating through the irradiated structure. The optical response has been analyzed by considering an effective homogeneous medium to simulate the nanostructured irradiated system consisting of cylindrical tracks, associated to the ion impacts, embedded into a virgin material. The role of both, irradiation fluence and stopping power, has been investigated. Above a certain electronic stopping power threshold (∼2.5 keV/nm), every ion impact creates an axial region around the trajectory with a fixed refractive index (around n = 1.475) corresponding to a certain structural phase that is independent of stopping power. The results have been compared with previous data measured by means of infrared spectroscopy and small-angle X-ray scattering; possible mechanisms and theoretical models are discussed

Comparative study of ion beam-irradiation effects on silica and α-quartz: evidences for excitonic mechanisms

Introduction - SiO 2 •Simple composition and structure; Crystalline and amorphous phases •Adequate for atomistic simulations •Abundant in nature. Relevant for many technologies -Irradiation with swift heavy ions: •They provide EXTREME physical conditions •Very high excitation densities similar to high power lasers •Very high local temperatures •By playing with high energy and heavy mass (SHI) : •One can go from low electronic excitations (collisions regime) to high electronic excitations (electronic regim

Kinetics of amorphization induced by swift heavy ions in α-quartz

The kinetics of amorphization in crystalline SiO2 (α-quartz) under irradiation with swift heavy ions (O+1 at 4 MeV, O+4 at 13 MeV, F+2 at 5 MeV, F+4 at 15 MeV, Cl+3 at 10 MeV, Cl+4 at 20 MeV, Br+5 at 15 and 25 MeV and Br+8 at 40 MeV) has been analyzed in this work with an Avrami-type law and also with a recently developed cumulative approach (track-overlap model). This latter model assumes a track morphology consisting of an amorphous core (area σ) and a surrounding defective halo (area h), both being axially symmetric. The parameters of the two approaches which provide the best fit to the experimental data have been obtained as a function of the electronic stopping power Se. The extrapolation of the σ(Se) dependence yields a threshold value for amorphization, Sth ≈ 2.1 keV/nm; a second threshold is also observed around 4.1 keV/nm. We believe that this double-threshold effect could be related to the appearance of discontinuous tracks in the region between 2.1 and 4.1 keV/nm. For stopping power values around or below the lower threshold, where the ratio h/σ is large, the track-overlap model provides a much better fit than the Avrami function. Therefore, the data show that a right modeling of the amorphization kinetics needs to take into account the contribution of the defective track halo. Finally, a short comparative discussion with the kinetic laws obtained for elastic collision damage is given

Ionoluminescence induced by swift heavy ions in silica and quartz: A comparative analysis

Ionoluminescence (IL) of the two SiO 2 phases, amorphous silica and crystalline quartz, has been comparatively investigated in this work, in order to learn about the structural defects generated by means of ion irradiation and the role of crystalline order on the damage processes. Irradiations have been performed with Cl at 10 MeV and Br at 15 MeV, corresponding to the electronic stopping regime (i.e., where the electronic stopping power S e is dominant) and well above the amorphization threshold. The light-emission kinetics for the two main emission bands, located at 1.9 eV (652 nm) and 2.7 eV (459 nm), has been measured under the same ion irradiation conditions as a function of fluence for both, silica and quartz. The role of electronic stopping power has been also investigated and discussed within current views for electronic damage. Our experiments provide a rich phenomenological background that should help to elucidate the mechanisms responsible for light emission and defect creationThis work has been supported by Spanish Ministry MICINN through the project MAT-2008-06794-C03-03, JCI-2009-05681, and by Madrid Community through the project TECHNOFUSION (S2009/ENE-1679). OPR is grateful to CONACyT, Mexico, for extending a postdoctoral fellowshi

Ionoluminescence induced by swift heavy ions in silica and quartz: a comparative analysis

Ionoluminescence (IL) of the two SiO2 phases, amorphous silica and crystalline quartz, has been comparatively investigated in this work, in order to learn about the structural defects generated by means of ion irradiation and the role of crystalline order on the damage processes. Irradiations have been performed with Cl at 10 MeV and Br at 15 MeV, corresponding to the electronic stopping regime (i.e., where the electronic stopping power Se is dominant) and well above the amorphization threshold. The light-emission kinetics for the two main emission bands, located at 1.9 eV (652 nm) and 2.7 eV (459 nm), has been measured under the same ion irradiation conditions as a function of fluence for both, silica and quartz. The role of electronic stopping power has been also investigated and discussed within current views for electronic damage. Our experiments provide a rich phenomenological background that should help to elucidate the mechanisms responsible for light emission and defect creation

Reverberation perception in Spanish cathedrals

Listening tests based on paired comparisons have been employed to investigate the subjective perception of the acoustic environment in highly reverberant large spaces. Seven cathedrals in the southern half of Spain have been included in the survey, thereby covering a wide range of reverberation-time values from 4.32 s in Murcia cathedral to 8.96 s in Cadiz cathedral at mid-frequencies. These cathedrals present a common architectural typology, known as the "Spanish style", which allows similar source-receiver points to be selected when comparisons are made between two different cathedrals. The tests were carried out in the listening room of the Acoustics Laboratory of the Applied Physics II Department of the School of Architecture of the University of Seville. Several types of anechoic sound signals (choral pieces, extracts of Baroque instrumental music, and a speech) were auralised with the impulse responses measured in the cathedrals to be used in the tests. Such auralisations were reproduced through headphones, thereby ensuring that all audio signals were perceived at the same level during each test. The results indicated the existence of a threshold, whose value depends on the type of stimulus, from which the objective reverberation differences are subjectively remain almost indistinguishable to the listene

In-situ optical reflectance characterization of ion beam irradiation damage on crystalline (quartz) and amorphous (silica) SiO2

Outline: • Motivation, aim • Complement waveguide data on silica • Optical data in quartz • Detailed analysis, i.e. both fluence kinetics and resolution • Efficiency of irradiation and analysis, samples, time... • Experimental set-up description • Reflectance procedure • Options: light source (lasers, white light..), detectors, configurations • Results and discussion • Comparative of amorphous and crystalline phase