Efectos de una cinética bidimensional de crecimiento sobre la incorporación de impurezas y estructura de semiconductores III-V epitaxiados por haces moleculares

Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 18-12-1992La utilización de una cinética de crecimiento bidimensional en la epitaxia por haces moleculares ha permitido la obtención de capas de gas impurificada con silicio, alcanzándose niveles de densidad de portadores de hasta 2 x 10(19) cm-3. Este límite es debido a la existencia del centro dx, que ancla el nivel de ferni. Una caracterización óptica y eléctrica de este tipo de capas muestra la existencia de defectos de alta impurificación (vacantes de galio-silicio donador, vacante de arsenico-silicio aceptor) sin embargo, la densidad de los mismos no supera 2 x 10(18) cm-3, es decir, menor de un 10% de la densidad de electrones. La aplicación de esta cinética a la obtención de capas con fuerte desajuste de red y de condiciones de crecimiento muy diferentes (inas y alas) ha sido estudiada, observándose una asimetría en el crecimiento de un semiconductor sobre el otro y viceversa. Posteriormente se han obtenido superredes con estos dos materiales.Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu

Procedimiento y dispositivo optico microfabricado para la detección de bandas de absorción/emisión en el infrarrojo

Fecha de publicación de la solicitud: 01/10/98.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Procedimiento y dispositivo óptico microfabricado para la detección de bandas de absorcion/emision en el infrarrojo. Facilita la deteccion de sustancias químicas y emisores de radiación con unos costes muy inferiores a los de los sistemas conocidos y con una precision suficiente para muchas aplicaciones tales como la detección de gases en mezclas. El procedimiento consiste en generar una radiación que sea plana en una banda característica de la sustancia o fuente a detectar y que atraviesa un ambiente en el que se encuentra dicha sustancia, efectuandose despues una modulación de la radiación y una detección de la radiación modulada que aportar a una señal directamente relacionada con la concentración de dicha sustancia en el referido ambiente. El dispositivo correspondiente incluye una lámpara (1) a la que se ajusta una guía óptica (2), de manera que se ilumine o radie el ambiente bajo estudio; disponiendose enfrentadamente a dicha guía (2) un detector (4), e intercalandose entre ambos un modulador (3).Peer reviewe

Fotopletismografía laparoscópica: Nueva técnica mínimamente invasiva y estudios experimentales iniciales

In the endoscopic procedures there is not possible to use the sense of touch for the detection of weak palpitations as in open surgery, neither to directly evaluate the oxygenation and perfusion of intra-corporeal organs and tissues. Here, we present the initial results after the application of laparoscopic photoplethysmography, a novel technique developed by our group, which allows obtaining specific clinical parameters and overcome the cited drawbacks. From the photoplethysmograpic signals of different wavelengths recorded in intra-abdominal organs and territories of animal models, their pulse values and oxygenation related quotients have been derived. © Sociedad Española de Óptica.Este trabajo ha sido financiado por el proyecto PI 04/0715 del Fondo de Investigaciones Sanitarias. Agradecemos la colaboración prestada durante el estudio experimental por Dr. José Carlos Manuel Palazuelos, Dr. Juan Carlos González Cueli y las diplomadas en Enfermería del CENDOS. Parte de los resultados aquí expuestos han sido presentados oralmente en el Congreso de la Sociedad Española de Laparoscopia (SECLA 2009) celebrado en Santander en mayo de 2009. SMLS está contratada por el Programa I3P con financiación del Fondo Social Europeo.Peer Reviewe

Optical phonons in isotope superlattices of GaAs, GaP, and GaSb studied by Raman scattering

We have investigated the LO-phonon Raman spectra of [100] oriented gallium isotope superlattices (69GaX)n(71GaX)n [X=P,As; both elements have a single stable isotope] at low temperature. When the number of monolayers 2n within one superlattice (SL) unit cell is varied, anticrossings between phonons confined in the 69GaX and 71GaX layers are observed. We have used a planar bond-charge model to calculate the frequencies and intensities of the modes as a function of layer thickness. For the GaP isotope SL’s, we find that a simulation of isotopically mixed interface layers is in good agreement with the experiment, while the assumption of ideal interfaces does not reproduce the data well. Spectra from the GaAs isotope SL’s are substantially broadened compared to the LO phonon width in bulk samples, thus allowing only a qualitative discussion of phonon-confinement effects. Predictions for GaSb isotope SL’s, in which both Ga and Sb isotopes can be substituted, are given. Raman spectra of bulk GaAs with varying gallium-isotope ratio are also discussed.Peer reviewe

High-speed 1.55 μm operation of low-temperature-grown GaAs-based resonant-cavity-enhanced p–i–n photodiodes

We report the design, growth, fabrication, and characterization of GaAs-based high-speed p–i–n photodiodes operating at 1.55 μm. A low-temperature-grown GaAs (LT-GaAs) layer was used as the absorption layer and the photoresponse was selectively enhanced at 1.55 μm using a resonant-cavity-detector structure. The bottom mirror of the resonant cavity was formed by a highly reflecting 15-pair GaAs/AlAs Bragg mirror. Molecular-beam epitaxy was used for wafer growth, where the active LT-GaAs layer was grown at a substrate temperature of 200 °C. The fabricated devices exhibited a resonance around 1548 nm. When compared to the efficiency of a conventional single-pass detector, an enhancement factor of 7.5 was achieved. Temporal pulse-response measurements were carried out at 1.55 μm. Fast pulse responses with 30 ps pulse-width and a corresponding 3 dB bandwidth of 11.2 GHz was measured.This work was supported by NATO Grant No. SfP971970, Turkish Department of Defense Grant No.KOBRA-001, Thales JP8.04, CAM 07N/0059/2002 and ‘‘NANOSELF’’ TIC2002-04096-C03-03. E.O. acknowledges partial support received from Turkish Academy of Sciences.Peer reviewe

A growth method to obtain flat and relaxed In0.2Ga0.8As on GaAs (0 0 1) developed through in situ monitoring of surface topography and stress evolution

13 páginas, 3 figuras.-- PACS: 81.15.Hi, 81.05.Ea, 78.35.+c, 68.35.Bs.-- Comunicación oral presentada en el XI Molecular Beam Epitaxy (MBE-XI), Pekín (11/09/2000).In this paper we develop a growth process for obtaining flat and relaxed In0.2Ga0.8As layers on GaAs (0 0 1). The process designed is based on the results obtained by in situ and real time characterization of surface morphology and layer relaxation. In particular, our results show that for growth temperatures Ts200°C the relaxation of In0.2Ga0.8As layers is inhibited and the morphology does not evolve to a crosshatched pattern. After growth thermal treatments of these low-temperature (LT) In0.2Ga0.8As layers induce the development of a very faint (rms=0.5 nm) crosshatched-like morphology. The relaxation process during the thermal annealing is strongly asymmetric and the layers present a high final strain state. By growing on top of the LT layer another In0.2Ga0.8As layer at higher temperature, relaxation is increased up to R≈70% and becomes symmetric. Depending on the growth process of the top layers morphology evolution differs, resulting in better morphologies for top layers grown by atomic layer molecular beam epitaxy (ALMBE) at Ts=400°C. We have obtained 400 nm In0.2Ga0.8As layers with a final degree of relaxation R=70% and very flat surfaces (rms=0.9 nm).The authors wish to acknowledge the Spanish “CICYT” for financial support under Project No. TIC99-1035-C02. M.U. González and M. Calleja thank the Consejería de Educación y Cultura de la Comunidad de Madrid for financial support.Peer reviewe

Nitrate removal in saline water by photo-reduction using natural FeTiO as catalyst

As climate change progresses, there is an increasing interest on the use of non-conventional water sources such as brackish or saline waters. Nowadays, the main threat in Europe detected in these waterbodies is nitrate contamination. Within the multiple available methods studied for nitrate reduction, photocatalysis presents promising results, but this technology has not yet been tested in saline water. This work tackles the elimination of nitrate ([NO3−] =50 mg/L) in brackish and saline water ([sea salt] = 5–33 g/L) using ilmenite as photocatalyst and oxalic acid as an environmental-friendly reducing agent. The main challenge when working in saline water is to overcome oxalic acid scavenging by Ca2+ present in the water matrix. This can be solved either working at over stoichiometric concentrations of oxalic acid (≈300% stoich. dose) or acidifying the reaction media. The addition of hydrochloric acid ensures the protonation of oxalic acid, reducing drastically its precipitation as CaC2O4. Working at [C2O42−] = 180 mg/L, [FeTiO3] = 450 mg/L and [HCl 37%] = 13 mM, 73% total nitrogen (TN) elimination was reached after 420 min. Reaction temperature was also evaluated in the range of 20–80 °C, which allowed to calculate the Ea=9.8 kJ/mol. Finally, the effect of dissolved O2 on the TN reduction was assessed. Overall, photocatalytic nitrate reduction presents itself as a feasible technology regardless of the water salinit

Mutational spectrum of GNAL, THAP1 and TOR1A genes in isolated dystonia: study in a population from Spain and systematic literature review

[Objective] We aimed to investigate the prevalence of TOR1A, GNAL and THAP1 variants as the cause of dystonia in a cohort of Spanish patients with isolated dystonia and in the literature.[Methods] A population of 2028 subjects (including 1053 patients with different subtypes of isolated dystonia and 975 healthy controls) from southern and central Spain was included. The genes TOR1A, THAP1 and GNAL were screened using a combination of high-resolution melting analysis and direct DNA resequencing. In addition, an extensive literature search to identify original articles (published before 10 August 2020) reporting mutations in TOR1A, THAP1 or GNAL associated to dystonia was performed.[Results] Pathogenic or likely pathogenic variants in TOR1A, THAP1 and GNAL were identified in 0.48%, 0.57% and 0.29% of our patients, respectively. Five patients carried the variation p.Glu303del in TOR1A. A very rare variant in GNAL (p.Ser238Asn) was found as a putative risk factor for dystonia. In the literature, variations in TOR1A, THAP1 and GNAL accounted for about 6%, 1.8% and 1.1% of published dystonia patients, respectively.[Conclusions] There is a different genetic contribution to dystonia of these three genes in our patients (about 1.3% of patients) and in the literature (about 3.6% of patients), probably due the high proportion of adult-onset cases in our cohort. As regards age at onset, site of dystonia onset, and final distribution, in our population there is a clear differentiation between DYT-TOR1A and DYT-GNAL, with DYT-THAP1 likely to be an intermediate phenotype.This work was supported by the Carlos III Health Institute-European Regional Development Fund (ISCIII-FEDER) [PI14/01823, PI16/01575, PI18/01898, PI19/01576], the Andalusian Regional Ministry of Economics, Innovation, Science and Employment [CVI-02526, CTS-7685], the Andalusian Regional Ministry of Health and Welfare [PI-0741-2010, PI-0471-2013, PE-0210-2018, PI-0459-2018, PE-0186-2019], and the Alicia Koplowitz and Mutua Madrileña Foundations. Pilar Gómez-Garre was supported by the "Miguel Servet" program [MSII14/00018] (from ISCIII-FEDER) and “Nicolás Monardes” program [C-0048-2017] (from the Andalusian Regional Ministry of Health). Silvia Jesús was supported by the "Juan Rodés" program [B-0007-2019] and Daniel Macías-García by the “Río Hortega” program [CM18/00142] (both from ISCIII-FEDER). María Teresa Periñán was supported by the Spanish Ministry of Education [FPU16/05061]. Cristina Tejera was supported by VPPI-US from the University of Seville.Peer reviewe

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