Increasing the angular sensitivity of two-dimensional photonic crystal based sensors to arbitrary values.

A new design of photonic crystal (PhC) for optical sensing using guided mode resonance (GMR) is presented. We theoretically show that angular sensitivity is inversely proportional to the group velocity of the probed mode and can be made arbitrarily high in a properly designed PhC. PhCs made in polycrystalline diamond on insulator are fabricated. The angular sensitivity dependence is validated. We measured modes with group velocity of c/80 at a wavelength of 800 nm. A sensitivity in the order of 500 ° per refractive index unit is inferred, a value much larger than the one usually encountered in PhCs.

III-nitride on silicon electrically injected microrings for nanophotonic circuits.

Nanophotonic circuits using group III-nitrides on silicon are still lacking one key component: efficient electrical injection. In this paper we demonstrate an electrical injection scheme using a metal microbridge contact in thin III-nitride on silicon mushroom-type microrings that is compatible with integrated nanophotonic circuits with the goal of achieving electrically injected lasing. Using a central buried n-contact to bypass the insulating buffer layers, we are able to underetch the microring, which is essential for maintaining vertical confinement in a thin disk. We demonstrate direct current room-temperature electroluminescence with 440 mW/cm2 output power density at 20 mA from such microrings with diameters of 30 to 50 µm. The first steps towards achieving an integrated photonic circuit are demonstrated.

Solving thermal issues in tensile-strained Ge microdisks.

We propose to use Ge-dielectric-metal stacking to allow one to address both thermal management with the metal as an efficient heat sink and tensile strain engineering with the buried dielectric as a stressor layer. This scheme is particularly useful for the development of Ge-based optical sources. We demonstrate experimentally the relevance of this approach by comparing the optical response of tensile-strained Ge microdisks with an Al heat sink or an oxide pedestal. Photoluminescence indicates a much reduced temperature rise in the microdisk (16 K with Al pedestal against 200 K with SiO2 pedestal under a 9 mW continuous wave optical pumping). An excellent agreement is found with finite element modeling of the temperature rise. This original stacking combining metal and dielectrics is promising for integrated photonics where thermal management is an issue.

Near-infrared III-nitride-on-silicon nanophotonic platform with microdisk resonators.

We have developed a nanophotonic platform with microdisks using epitaxial III-nitride materials on silicon. The two-dimensional platform consists of suspended waveguides and mushroom-type microdisks as resonators side-coupled with a bus waveguide. Loaded quality factors up to 80000 have been obtained in the near-infrared spectral range for microdisk diameters between 8 and 15 µm. We analyze the dependence of the quality factors as a function of coupling efficiency. We have performed continuous-wave second harmonic generation experiments in resonance with the whispering gallery modes supported by the microdisks.

Surface-sensitive diamond photonic crystals for high-performance gas detection.

Diamond slotted photonic crystal (PhC) cavities were fabricated and used for gas detection. They exhibit wavelength sensitivity reaching a 350 nm per unit change of the refractive index of the gaseous environment of the PhC. With a simple oxidized surface termination, diamond PhCs display an ultrahigh sensitivity to the surface adsorption of polar molecules. Gaseous concentrations as low as 80 parts per million (ppm) of hexanol vapor in nitrogen are probed, and a detection limit in the ppm range is inferred, demonstrating a high interest of such devices for trace sensing.

IGF-IR: a new prognostic biomarker for human glioblastoma.

BACKGROUND: Glioblastomas (GBMs) are the most common malignant primary brain tumours in adults and are refractory to conventional therapy, including surgical resection, radiotherapy and chemotherapy. The insulin-like growth factor (IGF) system is a complex network that includes ligands (IGFI and IGFII), receptors (IGF-IR and IGF-IIR) and high-affinity binding proteins (IGFBP-1 to IGFBP-6). Many studies have reported a role for the IGF system in the regulation of tumour cell biology. However, the role of this system remains unclear in GBMs. METHODS: We investigate the prognostic value of both the IGF ligands' and receptors' expression in a cohort of human GBMs. Tissue microarray and image analysis were conducted to quantitatively analyse the immunohistochemical expression of these proteins in 218 human GBMs. RESULTS: Both IGF-IR and IGF-IIR were overexpressed in GBMs compared with normal brain (P<10(-4) and P=0.002, respectively). Moreover, with regard to standard clinical factors, IGF-IR positivity was identified as an independent prognostic factor associated with shorter survival (P=0.016) and was associated with a less favourable response to temozolomide. CONCLUSIONS: This study suggests that IGF-IR could be an interesting target for GBM therapy.

Tensile-strained germanium microdisk electroluminescence.

We report room temperature electroluminescence of tensile-strained germanium microdisks. The strain is transferred into the microdisks using silicon nitride stressors. Carrier injection is achieved with Schottky contacts on n-type doped germanium. We show that a biaxial tensile-strain up to 0.72% can be transferred by optimizing the carrier injection profile. The transferred strain is measured by the electroluminescence spectral red-shift and compared to finite element modeling. We discuss the impact of this strain level to achieve population inversion in germanium.

Effective thermal resistance of a photonic crystal microcavity.

We present a simple method to accurately measure the effective thermal resistance of a photonic crystal microcavity. The cavity is embedded between two Schottky contacts forming a metal-semiconductor-metal device. The photocarriers circulating in the device provide a local temperature rise that can be dominated by Joule effect under certain conditions. We show that the effective thermal resistance (R(th)) can be experimentally deduced from the spectral shift of the cavity resonance wavelength measured at different applied bias. We deduce a value of R(th)1.6×10(4) KW(-1) for a microcavity on silicon-on-insulator, which is in good agreement with 3D thermal modeling by finite elements.

Optical gain in single tensile-strained germanium photonic wire.

We have investigated the optical properties of tensile-strained germanium photonic wires. The photonic wires patterned by electron beam lithography (50 µm long, 1 µm wide and 500 nm thick) are obtained by growing a n-doped germanium film on a GaAs substrate. Tensile strain is transferred in the germanium layer using a Si3N4 stressor. Tensile strain around 0.4% achieved by the technique corresponds to an optical recombination of tensile-strained germanium involving light hole band around 1690 nm at room temperature. We show that the waveguided emission associated with a single tensile-strained germanium wire increases superlinearly as a function of the illuminated length. A 20% decrease of the spectral broadening is observed as the pump intensity is increased. All these features are signatures of optical gain. A 80 cm⁻¹ modal optical gain is derived from the variable strip length method. This value is accounted for by the calculated gain material value using a 30 band k · p formalism. These germanium wires represent potential building blocks for integration of nanoscale optical sources on silicon.

Water resources and nitrate discharges in relation to agricultural land uses in an intensively irrigated watershed.

Application of integrated hydrological models to manage water resources and non-point agricultural pollutants are increasingly used in decision-making processes. In this study SWAT (Soil and Water Assessment Tool) was used to simulate the water balance and nitrate pollution in an intensively irrigated agricultural catchment (Flumen River in Monegros, Aragon, NE Spain). Rainfall comprised only 45% of the inputs of water in the Flumen watershed and the rest is contributed through irrigation canals from two other rivers outside the Flumen watershed. Green water storage and green water flow are the dominant components of the water balance in the watershed, which is related to the important contribution of water for irrigation. In general, green water storage and green water flow are quite similar in the subwatersheds dominated by irrigation agriculture that are located in the central part of the watershed. A similar pattern was observed for blue water, with high amounts in the central irrigated subwatersheds compared to the non-irrigated subwatersheds. Consequently, nitrate infiltration in the aquifer was higher in the inner irrigated subwatersheds (100-250 kg N ha-1 year-1) but much lower than the lateral flow rates estimated in the non-irrigated subwatersheds (1400-2000 kg N ha-1 year-1). Two scenarios simulating the effects of expected climate change factors in this zone were performed. A reduction in the availability of water for irrigation will transform the area from irrigated crops to cereal. In this case the water flow of River Flumen at the outlet of the watershed is reduced by 15%. If a reduction of 40% nitrate fertilization is applied, the nitrate exported to Flumen River would decreased by 28%. These results suggest that dosing irrigation water and fertilizers in accordance with crop requirements would contribute to buffer peaks of water and nitrate discharges and to a more efficient agricultural use of the resources.

Assessment of sediment and organic carbon exports into the Arctic ocean: The case of the Yenisei River basin.

The export of organic carbon export by the rivers to the oceans either as particulate organic carbon (POC) or dissolved organic carbon (DOC) is very sensitive to climate change especially in permafrost affected catchments where soils are very rich in organic carbon. With global warming, organic carbon export in both forms is expected to increase in Arctic regions. It should affect contemporary biogeochemical cycles in rivers and oceans and therefore modify the whole food web. This study tries to understand complex processes involved in sediment, POC and DOC riverine transport in the Yenisei River basin and to quantify their respective fluxes at the river outlet. The SWAT (Soil and Water Assessment Tool) hydrological model is used in this study to simulate water and suspended sediment transfers in the largest Arctic river. POC and DOC export have been quantified with empirical models, adapted from literature for the study case. First, the hydrological model has been calibrated and validated at a daily time step for the 2003-2008 and the 2009-2016 periods respectively, and its output has been compared with field data for water and sediment fluxes. Based on conceptualization of transfer processes, calibration on climate and soil properties has been performed in order to correctly represent hydrology and sediment transfer in permafrost basins. Second, calibration of empirical models for DOC/POC transport have been performed by comparing their output with field data, available from 2003 to 2016. Our study reveals that SWAT is capable of correctly representing hydrology, sediment transfer, POC and DOC fluxes and their spatial distribution at a daily timescale, and outlines the links between these fluxes and permafrost features. Our simulation effort results in specific sediment, POC and DOC fluxes of 2.97 t km-2 yr-1, 0.13 t km-2 yr-1 and 1.14 t km-2 yr-1 for the period 2003-2016 which are in the range of previous estimates. About 60% of the total fluxes of sediment, DOC and POC to the Arctic Ocean are exported during the two months of the freshet. Spatial analysis show that permafrost-free areas have returned higher daily organic carbon export than permafrost affected zones, highlighting the thawing permafrost effect on carbon cycle in climate change feedback.

Effect of flood events on transport of suspended sediments, organic matter and particulate metals in a forest watershed in the Basque Country (Northern Spain).

An understanding of the processes controlling sediment, organic matter and metal export is critical to assessing and anticipating risk situations in water systems. Concentrations of suspended particulate matter (SPM), dissolved (DOC) and particulate (POC) organic carbon and metals (Cu, Ni, Pb, Cr, Zn, Mn, Fe) in dissolved and particulate phases were monitored in a forest watershed in the Basque Country (Northern Spain) (31.5km(2)) over three hydrological years (2009-2012), to evaluate the effect of flood events on the transport of these materials. Good regression was found between SPM and particulate metal concentration, making it possible to compute the load during the twenty five flood events that occurred during the study period at an annual scale. Particulate metals were exported in the following order: Fe>Mn>Zn>Cr>Pb>Cu>Ni. Annual mean loads of SPM, DOC and POC were estimated at 2267t, 104t and 57t, respectively, and the load (kg) of particulate metals at 76 (Ni), 83 (Cu), 135 (Pb), 256 (Cr), 532 (Zn), 1783 (Mn) and 95170 (Fe). Flood events constituted 91%-SPM, 65%-DOC, 71%-POC, 80%-Cu, 85%-Ni, 72%-Pb, 84%-Cr, 74%-Zn, 87%-Mn and 88%-Fe of total load exported during the three years studied. Flood events were classified into three categories according to their capacity for transporting organic carbon and particulate metals. High intensity flood events are those with high transport capacity of SPM, organic carbon and particulate metals. Most of the SPM, DOC, POC and particulate metal load was exported by this type of flood event, which contributed 59% of SPM, 45% of organic carbon and 54% of metals.

Phase-matched second harmonic generation with on-chip GaN-on-Si microdisks.

We demonstrate phase-matched second harmonic generation in gallium nitride on silicon microdisks. The microdisks are integrated with side-coupling bus waveguides in a two-dimensional photonic circuit. The second harmonic generation is excited with a continuous wave laser in the telecom band. By fabricating a series of microdisks with diameters varying by steps of 8 nm, we obtain a tuning of the whispering gallery mode resonances for the fundamental and harmonic waves. Phase matching is obtained when both resonances are matched with modes satisfying the conservation of orbital momentum, which leads to a pronounced enhancement of frequency conversion.

Speciation of non-methane hydrocarbons (NMHCs) from anthropogenic sources in Beirut, Lebanon.

The chemical composition of emissions from the different anthropogenic sources of non-methane hydrocarbons (NMHC) is essential for modeling and source apportionment studies. The speciated profiles of major NMHC sources in Lebanon, including road transport, gasoline vapor, power generation, and solvent use were established. Field sampling have been carried out by canisters in 2012. Around 67 NMHC (C2 to C9) were identified and quantified by using a gas chromatograph equipped with a flame ionization detector. Typical features of the roadway emissions included high percentages of isopentane, butane, toluene, xylenes, ethylene, and ethyne. Gasoline evaporation profiles included high percentage of the C4-C5 saturated hydrocarbons reaching 59 %. The main compounds of the power generator emissions are related to combustion. Toluene and C8-C9 aromatics were the most abundant species in emissions from paint applications. Finally, the impact of the use of region-specific source profile is tackled regarding the implication on air quality.

Long polaron lifetime in InAs/GaAs self-assembled quantum dots.

We have investigated the polaron dynamics in n-doped InAs/GaAs self-assembled quantum dots by pump-probe midinfrared spectroscopy. A long T1 polaron decay time is measured at both low temperature and room temperature, with values around 70 and 37 ps, respectively. The decay time decreases for energies closer to the optical phonon energy. The relaxation is explained by the strong coupling for the electron-phonon interaction and by the finite lifetime of the optical phonons. We show that, even for a large detuning of 19 meV from the LO photon energy in GaAs, the carrier relaxation remains phonon assisted.