MBE growth of Quantum nanostructures for optoelectronics

Ponencia presemtada en el Workshop on Frontier Photonic and Electronic Materials and Devices - German-Japanese-Spanish Joint Workshop, celebrado en Kyoto del 11 al 14 de julio de 2015.Molecular Beam Epitaxy (MBE) is a powerful technique for the fabrication of several self-assembled III-V nanostructures such as quantum rings, quantum dots, and quantum wires that can cover a wide range of the spectrum from 0.98 μm to 1.6 μm. The possibility of performing in-situ, real-time, measurements of accumulated stress (Σσ) during growth of these nanostructures enables to achieve a deep understanding of the growth processes. For example, whereas quantum rings (QR) formation is crucially linked to the presence of liquid indium on the surface, quantum wires (QWR) are produced as an effective way of relaxing a large asymmetrical accumulated stress present on the sample. This information allows a fine-tuning of the optoelectronic properties by controlling their size and shape. Furthermore, the capability of tracking Σσ during growth is used to engineer strain compensated structures like multilayer quantum dot solar cells.CHE-0641523, CSIC-PIF200950I154,S2009ESP-1503, S2009ENE-1477 and AIC-B-2011-0806, MAT2011-26534.Peer Reviewe

Oleoylethanolamide Modulates BDNF-ERK Signaling and Neurogenesis in the Hippocampi of Rats Exposed to Δ9-THC and Ethanol Binge Drinking During Adolescence

Oleoylethanolamide is an endogenous NAE that modulates ethanol-seeking behavior and ethanol-induced neuroinflammation. In the present study we further analyze the role of OEA in hippocampal neurogenesis, BDNF-ERK signaling, and spatial memory that are affected by alcohol. Additionally, we addressed the effects of OEA on the association of alcohol and cannabis, a frequent combination in human alcohol addicts, and whose long-term effects are far from being understood. To this end, OEA (10 mg/kg/day, i.p.) was pharmacologically administered for 5 days/week in a preclinical model of adolescent rats with binge-like consumption (1 day/week) of ethanol (3 g/kg, i.g.) combined or not with acute administrations of Δ9-THC (5 mg/kg, i.p.) for 5 weeks. OEA restored ethanol/THC-related decreases in both short-term spatial memory (spontaneous alternation by Y-maze) and circulating levels of BDNF, reduced cell proliferation (Mki67 and IdU+ cells) and maturation (Dcx, Calb1), and improved cell survival (Casp3 and BrdU+ cells) in the dorsal hippocampus. Interestingly, OEA alone or combined with THC also decreased the mRNA levels of neurotrophic factors (Bdnf, Ntf3) and the NT3 receptor TrkC, but increased the BDNF receptor TrkB in the hippocampus of ethanol-exposed rats. These effects were likely associated with a OEA-specific phosphorylation of AKT and ERK1, key signaling regulators of cell proliferation and survival. These results suggest a regulatory role of OEA in short-term spatial memory and hippocampal neurogenesis through BDNF/AKT/ERK1 signaling in response to acute THC in an alcoholic context during adolescence

Impact of the first wave of the SARS-CoV-2 pandemic on the outcome of neurosurgical patients: A nationwide study in Spain

Objective To assess the effect of the first wave of the SARS-CoV-2 pandemic on the outcome of neurosurgical patients in Spain. Settings The initial flood of COVID-19 patients overwhelmed an unprepared healthcare system. Different measures were taken to deal with this overburden. The effect of these measures on neurosurgical patients, as well as the effect of COVID-19 itself, has not been thoroughly studied. Participants This was a multicentre, nationwide, observational retrospective study of patients who underwent any neurosurgical operation from March to July 2020. Interventions An exploratory factorial analysis was performed to select the most relevant variables of the sample. Primary and secondary outcome measures Univariate and multivariate analyses were performed to identify independent predictors of mortality and postoperative SARS-CoV-2 infection. Results Sixteen hospitals registered 1677 operated patients. The overall mortality was 6.4%, and 2.9% (44 patients) suffered a perioperative SARS-CoV-2 infection. Of those infections, 24 were diagnosed postoperatively. Age (OR 1.05), perioperative SARS-CoV-2 infection (OR 4.7), community COVID-19 incidence (cases/10 5 people/week) (OR 1.006), postoperative neurological worsening (OR 5.9), postoperative need for airway support (OR 5.38), ASA grade =3 (OR 2.5) and preoperative GCS 3-8 (OR 2.82) were independently associated with mortality. For SARS-CoV-2 postoperative infection, screening swab test <72 hours preoperatively (OR 0.76), community COVID-19 incidence (cases/10 5 people/week) (OR 1.011), preoperative cognitive impairment (OR 2.784), postoperative sepsis (OR 3.807) and an absence of postoperative complications (OR 0.188) were independently associated. Conclusions Perioperative SARS-CoV-2 infection in neurosurgical patients was associated with an increase in mortality by almost fivefold. Community COVID-19 incidence (cases/10 5 people/week) was a statistically independent predictor of mortality. Trial registration number CEIM 20/217

Continuum and discrete excitation spectrum of single quantum rings

Photoluminescence and excitation of the photoluminescence spectroscopy has been performed in single InGaAs self-assembled quantum rings embedded in a field effect structure device. To determine their electronic structure, bias-dependent optical transitions have been analyzed both, for individual quantum rings, and for the averaged ensemble. Our results are compared with a theoretical model, and also with results reported by other authors studying similar nanostructures.The authors would like to thank K. Karrai and R.J. Warburton for helpful discussions. This work was supported by Spanish MEC through NANOSELF Project (No. TIC2002-04096) and European Commission through SANDIE Network of Excellence (No. NMP4-CT-2004-500101).Peer reviewe

Oscillator strength reduction induced by external electric fields in self-assembled quantum dots and rings

We have carried out continuous wave and time resolved photoluminescence experiments in self-assembled In(Ga)As quantum dots and quantum rings embedded in field effect structure devices. In both kinds of nanostructures, we find a noticeable increase of the exciton radiative lifetime with the external voltage bias that must be attributed to the field-induced polarizability of the confined electron hole pair. The interplay between the exciton radiative recombination and the electronic carrier tunneling in the presence of a stationary electric field is therefore investigated and compared with a numerical calculation based on the effective mass approximation.The authors gratefully acknowledge financial support by the Spanish MEC and CAM through Projects Nos.TEC-2005-05781-C03-01/03, NAN2004-09109-C04-01/03,CSD2006-0019, and S-505/ESP/000200, and by the European Commission through the SANDIE Network of Excellence (Contract No. NMP4-CT-2004-500101).Peer reviewe

0D band gap engineering by MBE quantum rings: Fabrication and optical properties

© Springer-Verlag Berlin Heidelberg 2014. The partial capping technique has played a key role in the engineering of 0D nanostructures with tailor made properties (Michler et al. in Science 290(5500): 2282, 2000; Kiravittaya et al. in Rep. Prog. Phys. 72(4):046502, 2009). For example, it has allowed to fabricate a single-photon source that is based on a single self assembled quantum nanostructure embedded in a high-quality factor microcavity structure (Michler et al. in Science 290(5500):2282, 2000). Another example is the possibility to engineer what has been called “the smallest rings of electricity” (see Chap. 2), which unveil novel magnetic properties associated to non-trivial topologies at the nanoscale (Fomin (ed.) in J. Nanoelectron. Optoelectron., vol. 6. American Scientific, 2011) (see Chaps. 2, 4, 14, 17, and 18). In this chapter we show how it is possible to modify the shape and size of InAs on GaAs self assembled quantum dots grown by Molecular Beam Epitaxy (MBE) by introducing a pause during the capping process, also known as partial overgrowth technique (García et al. in Appl. Phys. Lett. 71:2014, 1997; Appl. Phys. Lett. 72:3172, 1998; Granados and García in Appl. Phys. Lett. 82:2401, 2003). Under certain growth-pause capping conditions it is possible to obtain self-assembled quantum rings. The changes in shape and size lead to a modification of the quantum confinement potential and enables the control over fundamental physical properties, such as the optical emission energy from ground or excited states, the magnitude of its fine structure splitting or the sign of its permanent electric dipole moment.Peer Reviewe

Elefantiasis verrucosa nostra colonizada.

Cutaneous myiasis is a rare parasitic disease in our environment. We report a case of cutaneous myiasis caused by larvae of musca domestica in a patient with predisposing factors. In this case, lack of hygiene led elephantiasis nostra verrucosa to be the ideal breeding ground for the parasites.Prevention, with proper hygiene or the use of insect repellents, is essential in patients with predisposing factors.La miasis cutánea es una parasitosis infrecuente en nuestro medio. Exponemos un caso de miasis cutánea producida por larvas de musca domestica en una paciente con condiciones basales predisponentes. En este caso la falta de higiene condujo a que la elefantiasis verrucosa nostra fuera el caldo de cultivo idóneo para la parasitación. La prevención, con una higiene adecuada o la utilización de repelentes de insectos, es fundamental en pacientes con factores predisponentes

Competition between carrier recombination and tunneling in quantum dots and rings under the action of electric fields

6 páginas, 3 figuras.-- Proceedings of the 7th International Conference on Physics of Light-Matter Coupling in Nanostructures.In the presence of a stationary electric field applied in the growth direction tunneling of electrons out of the quantum dots can take place. This mechanism competes with the quantum confined Stark effect (QCSE) that produces an increase of the exciton lifetime by increasing the electric field, mainly due to a net decrease of the electron–hole wavefunction overlap. The electric field range where QCSE dominates over tunneling will be mainly determined by the size of the nanostructure along the vertical direction (height), as demonstrated in this work.The authors gratefully acknowledge financial support by the Spanish MEC through projects TEC-2005-05781-C03-03 and NAN 2004-09109-C04-04, and by the European Commission through SANDiE Network of Excellence (Contract No. NMP4-CT-2004-500101).Peer reviewe