The European Space Agency (ESA), in collaboration with the European Commission (EC) and EUMETSAT, is developing a space-borne observing system for quantification of anthropogenic carbon dioxide (CO 2 ) emissions. Forming part of the EC's Copernicus programme, the CO 2 monitoring (CO2M) mission will be implemented as a constellation of identical satellites, to be operated over a period of at least 7 years and measuring CO 2 concentration in terms of column-averaged mole fraction (denoted as XCO 2 ). Each satellite will continuously image XCO 2 along the satellite track on the sun-illuminated part of the orbit, with a swath width of >250 km. Observations will be provided at a spatial resolution of 2 x 2 km 2 , with high precision (<0.7 ppm) and accuracy (bias <0.5 ppm). To this end, the payload comprises a suite of instruments addressing the various aspects of the challenging observation requirements: A push-broom imaging spectrometer will perform co-located measurements of top-of-atmosphere radiances in the Near Infrared (NIR) and Short-Wave Infrared (SWIR) at high to moderate spectral resolution
We report on the fabrication of aluminum gallium nitride (AlGaN) Schottky diodes for extreme ultraviolet (EUV) detection. AlGaN layers were grown on silicon wafers by molecular beam epitaxy with the conventional and inverted Schottky structure, where the undoped, active layer was grown before or after the n-doped layer, respectively. Different current mechanisms were observed in the two structures. The inverted Schottky diode was designed for the optimized backside sensitivity in the hybrid imagers. A cut-off wavelength of 280 nm was observed with three orders of magnitude intrinsic rejection ratio of the visible radiation. Furthermore, the inverted structure was characterized using a EUV source based on helium discharge and an open electrode design was used to improve the sensitivity. The characteristic He I and He II emission lines were observed at the wavelengths of 58.4 nm and 30.4 nm, respectively, proving the feasibility of using the inverted layer stack for EUV detection.Extreme ultraviolet (EUV) detection is gaining increasing attention with recent developments in solar science and EUV lithography.
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