Kinetic study of hydrogen lateral diffusion at high temperature in a directly-bonded InP-SiO2/Si substrate

Hybrid integration of III-V materials onto silicon by direct bonding technique is a mature and promising approaches to develop advanced photonic integrated devices into the silicon photonics platform. In this approach, the III-V material stack is grown on an InP wafer in a unique epitaxial step prior to the direct bonding process onto the silicon-on-insulator wafer. Currently, no additional epitaxial regrowth steps are implemented after bonding. This can be seen as a huge limitation as compared to the III-V on III-V wafer mature technology where multi-regrowth steps are most often implemented. In this work, we have studied the material behavior of an InP membrane on silicon (InPoSi) under epitaxial regrowth conditions by metal-organic vapor phase epitaxy (MOVPE). MOVPE requires high-temperature elevation, typically above 600 °C. We show for the first time the appearance of voids at 400 °C in an InP seed (100 nm) directly-bonded onto a thermally oxidized Si substrate despite the use of a thick SiO₂ oxide (200 nm) at the bonding interface. This phenomenon is explained by a weakening of the bonding interface while high-pressurized hydrogen is present. A kinetic study of the hydrogen lateral diffusion is carried out, enabling the assessment of its lateral diffusion length. To overcome the void formation, highly efficient outgassing trenches after bonding are demonstrated. Finally, high-quality AlGaInAs-based multi-quantum well (MQW) heterostructure surrounded by two InP layers was grown by MOVPE on InPoSi template patterned with outgassing trenches. This process is not only compatible with MOVPE regrowth conditions (650 °C under PH₃) but also with conventional fabrication processes used for photonic devices.

Modification of translation factor aIF5A from Sulfolobus solfataricus

Eukaryotic eIF5A and its bacterial orthologue EF-P are translation elongation factors whose task is to rescue ribosomes from stalling during the synthesis of proteins bearing particular sequences such as polyproline stretches. Both proteins are characterized by unique post-translational modifications, hypusination and lysinylation, respectively, which are essential for their function. An orthologue is present in all Archaea but its function is poorly understood. Here, we show that aIF5A of the crenarchaeum Sulfolobus solfataricus is hypusinated and forms a stable complex with deoxyhypusine synthase, the first enzyme of the hypusination pathway. The recombinant enzyme is able to modify its substrate in vitro resulting in deoxyhypusinated aIF5A. Moreover, with the aim to identify the enzyme involved in the second modification step, i.e. hypusination, a set of proteins interacting with aIF5A was identified.

Nanoscale elemental quantification in heterostructured SiGe nanowires

The nanoscale chemical characterization of axial heterostructured Si1-xGex nanowires (NWs) has been performed using scanning Auger microscopy (SAM) through local spectroscopy, line-scan and depth profile measurements. Local Auger profiles are realized with sufficient lateral resolution to resolve individual nanowires. Axial and radial composition heterogeneities are highlighted. Our results confirm the phenomenon of Ge radial growth forming a Ge shell around the nanowire. Moreover, quantification is performed after verifying the absence of preferential sputtering of Si or Ge on a bulk SiGe sample. Hence, reliable results are obtained for heterostructured NW diameters higher than 100 nm. However, for smaller sizes, we have noticed that the sensitivity factors evaluated from bulk samples cannot be used because of edge effects occurring for highly topographical features and a modified contribution of backscattered electrons.

Superlattice Calculation in an Empirical spds* Tight-Binding Model

We propose an empirical tight-binding method for tetrahedrally coordinated cubic materials and apply it to group IV and III-V semiconductors, extending existing calculations by the inclusion of all five d-orbitals per atom in the basis set. The symmetry character of the conduction states at the surface of the Brillouin zone is considerably improved compared to calculations in smaller bases, and the corresponding band positions can be obtained within the experimental uncertainties. Because the distance dependence of the tight-binding parameters is derived from deformation potentials, the model is particularly suited for an investigation of strained superlattices where the states at direct or pseudo-direct conduction band minima are composed of wavefunctions of all the minima at Γ, X, and L of the constituents. Investigations of GaAs/AlAs and short-period superlattices indicate a strong mixing between the conduction band valleys in the miniband structure, and the results are in better agreement with experiments than state-of-the-art empirical pseudopotential calculations.

Contamination of drinking water sources during the rainy season in an urban post-conflict community in Guinea Bissau: implications for sanitation priority

Since the 1998 civil warcholera outbreaks and waterborne infections have been a major cause of morbidity and mortality during the rainy season in Guinea Bidsau. Our survey aims at: (1) describing the distribution, characteristics and use of water sources and sewage facilities in a central area of the capital city of Bissau; (2) determining the microbiological quality of drinking water during the rainy season. After mapping of the Cuntum 3 study area, water sources' and latrines' location, characteristics and use were determined by visual inspection and interviews with householders. Microbiological analyses were peformed from water sources for evaluation of total Coliforms, E. coli, Enterococcus faecalis. Twelve water sources (9 wells, 3 taps) and 15 latrines were identified and used by 444 inhabitants. Water sources and latrines were at less than 5 meters distance apart. Wells were self-built, hand-dug, shallow (4-6 meters), unprotected. Taps were located outdoor. Latrines were self-built, open air, unprotected. None of the houses had a bathroom. Maintenance of wells, taps and latrines is not performed on regular basis and well's handling habits are not safe. Well and tap water showed heavy faecal contamination with more than 1000 CFU/100 ml. The contamination of drinking water in Bissau due to poor construction, maintenance and improperuse ten years after the civil war, demonstrates the need to allocate resources after conflicts in the area of water and sanitation. Both should be included as a priority in post-conflict reconstruction programs in order to reduce cholera outbreaks and diarrhoea related mortality.

Resonantly absorbing one-dimensional photonic crystals

A compact theoretical description of the effects of dissipation on the propagation of light waves through a multilayer periodic mirror built from resonant absorbing atoms is presented. Depending on the lattice periodicity, ultranarrow photonic gaps, weak polaritonic gaps, as well as rather atypical gap structures may be observed. Because of the atom's absorption line shape Bloch gap modes may acquire quite a cumbersome structure which is thoroughly studied here or which may even disappear when dissipation becomes sufficiently strong. The same approach well applies also to resonantly absorbing photonic crystals based on excitonic resonances.

Ultrafast all optical switching via tunable Fano interference

Tunneling induced quantum interference experienced by an incident probe in asymmetric double quantum wells can easily be modulated by means of an external control light beam. This phenomenon, which is here examined within the dressed-state picture, can be exploited to devise a novel all-optical ultrafast switch. For a suitably designed semiconductor heterostructure, the switch is found to exhibit frequency bandwidths of the order of 0.1 THz and response and recovery times of about 1 ps.

Polaritonic stop-band transparency via exciton-biexciton coupling in CuCl

Radiation is almost completely reflected within the exciton-polariton stop band of a semiconductor, as in the typical case of CuCl. We predict, however, that a coherently driven exciton-biexciton transition allows for the propagation of a probe light beam within the stop band. The phenomenon is reminiscent of electromagnetically induced transparency effects occurring in three-level atomic systems, except that it here involves delocalized electronic excitations in a crystalline structure via a frequency and wave-vector selective polaritonic mechanism. A well-developed transparency, favored by the narrow linewidth of the biexciton, is established within the stop band where a probe pulse may propagate with significant delays. The transparency window can be controlled via the pump beam detuning and intensity.

Vavilov-Cherenkov effect in a driven resonant medium

The Vavilov-Cherenkov effect in a dispersive and resonant absorbing medium is substantially modified by the presence of an external electromagnetic field. Depending on the field parameters and configuration we anticipate a remarkable increase of the emission yield at resonance. Our predictions are implemented by numerical estimates for cuprous oxide (Cu2O) where the yield turns out to be one to two orders of magnitude that obtained in the absence of the field.

Slow group velocity and Cherenkov radiation

We study theoretically the effect of ultraslow group velocities on the emission of Vavilov-Cherenkov radiation in a coherently driven medium. We show that in this case the aperture of the group cone on which the intensity of the radiation peaks is much smaller than that of the usual wave cone associated with the Cherenkov coherence condition. As a specific example, we consider a coherently driven ultracold atomic gas where such singular behavior may be observed.

Preclinical Evaluation of CHF3381 as a Novel Antiepileptic Agent

CHF3381 [n-(2-indanyl)-glycinamide hydrochloride] has been selected on the basis of a screening program as the compound displaying the highest anticonvulsant activity in the maximal electroshock seizure (MES) test and the best therapeutic index with reference to the rotarod test in mice and rats. In this study, the antiepileptic activity and the behavioural toxicity of CHF3381 were characterised in multiple model systems. CHF3381 effectively prevented MES-induced convulsions when administered i.p. (ED50, 24 mg/kg and 7.5 mg/kg) or p.o. (ED50, 21 mg/kg and 21 mg/kg) in both mice and rats, respectively. The time course of oral anti-MES activity in the rat was related to the brain concentration profile of unchanged CHF3381. Interestingly, the brain drug levels were about 4-5 times higher than in plasma. CHF3381 was very effective in mice against picrotoxin-, and i.c.v. N-methyl-D-aspartate (NMDA)-induced hind limb tonic extension (ED50 Approximately/=10 mg/kg), but was a weaker antagonist of 4-amynopyridine- and bicuculline-induced tonic seizures (ED50 approximately/=100 mg/kg), and ineffective against pentylentetrazole- and picrotoxin-induced clonic seizures. CHF3381 antagonised the behavioural effects and lethality of i.p. administered NMDA (ED50 = 57 mg/kg p.o.), indicating that the compound may act as a functional NMDA antagonist. In keeping with this idea, CHF3381 weakly displaced [(3)H]-TCP from binding to NMDA receptor channels (Ki, 8.8 microM). In the rat amygdala kindling model, CHF3381 was more efficient against kindling development than against kindled seizures (minimally active dose = 80 vs. 120 mg/kg i.p). Furthermore, it significantly increased the seizure threshold in kindled rats at relatively low doses (40 mg/kg i.p.). In contrast with MK-801-induced hyperactivity, CHF3381 moderately reduced the spontaneous locomotor activity in mice at anticonvulsant doses. Toxic effects on motor performance (rotarod test) were found at high doses only (TD50 approximately/= 300 mg/kg p.o., congruent with 100 mg/kg i.p. in both mice and rats). Furthermore, CHF3381 did not impair passive avoidance and Morris water maze responding in the therapeutic range of doses. Finally, the development of tolerance after repeated doses was negligible. These data indicate that CHF3381 exerts anticonvulsant and antiepileptogenic effects in various seizure models and possesses good therapeutic window, with scarce propensity to cause neurological side-effects.

Fresnel light drag in a coherently driven moving medium

We theoretically study how the phase of a light plane wave propagating in a resonant medium under electromagnetically induced transparency (EIT) is affected by the uniform motion of the medium. For cuprous oxide (Cu2O), where EIT can be implemented through a typical pump-probe configuration, the resonant probe beam experiences a phase shift (Fresnel-Fizeau effect) that may vary over a wide range of values, positive or negative, and even vanishing, due to the combined effects of the strong frequency dispersion and anisotropy both induced by the pump. The use of such a coherently driven dragging medium may improve by at least 1 order of magnitude the sensitivity at low velocity in optical drag experiments.

The consequence of land mines on public health

An estimated 110 million land mines scattered in 64 countries continue to terrorize people and destroy human lives long after wars and fighting have ceased. Despite efforts to clear these devices, their numbers continue to increase and their presence constitutes a substantial threat to public health in affected countries. Direct consequences include both the physical and emotional injuries from the impact, flying debris, and structural collapse associated with their detonation. Indirect consequences include increases in the incidence of waterborne diseases, diarrhea, malnutrition, infectious diseases, and spread of the human immunodeficiency virus associated with the increased use of blood. Those at highest risk of these later consequences are mostly the disadvantaged poor, especially children. Psychiatric disorders, such as post-traumatic stress disorder, occur in those not directly injured as well as those physically wounded by the explosion. Besides efforts to ban production, stockpiling and export of land mines, a comprehensive and integrated health program aimed at the prevention, treatment, and rehabilitation of those injured directly or indirectly by land mines is needed urgently. Strategies should include mine-awareness programs, enhanced transport of those directly injured, training the villagers in first aid, augmenting the capacity and quality of treatment facilities, improving the psychological support and treatment capabilities, development of rehabilitation programs, and the institution and enhancement of public-health programs directed at the indirect consequences associated with the presence of land mines. Land mines constitute a major public health problem in the world that must be addressed.