NO2 detection at room temperature with copper phthalocyanine thin film devices

In this work, we report the effect of post-deposition film treatment on the NO2 sensing properties of CuPc thin films for room temperature operation. The gas-sensitive response of the electrical conductivity to doping with NO2, doping with oxygen (in air) and cooling to 77 K in liquid nitrogen are reported. The pretreatment with NO2 is shown to improve the gas sensing properties by providing both an increase in the magnitude of the conductivity change for a given NO2 concentration and a significant improvement in the recovery time. Data is analysed using an Elovich model, which suggests that the cooled devices have the best fit to this model; the data for the NO2 doped devices suggest a Langmuir behaviour. For all devices, a simple time derivative of the change in current provides a measure of concentration for real time gas sensing applications

Seasonal variations of dissolved nitrogen and DOC:DON ratios in an intermittent Mediterranean stream

22 páginas, 6 figuras, 4 tablas.Seasonal variations of dissolved inorganic nitrogen (DIN) (NO3–N and NH4–N) and dissolved organic nitrogen (DON) were determined in Fuirosos, an intermittent stream draining an unpolluted Mediterranean forested catchment (10.5 km2) in Catalonia (Spain). The influence of flow on streamwater concentrations and seasonal differences in quality and origin of dissolved organic matter, inferred from dissolved organic carbon to nitrogen ratios (DOC:DON ratios), were examined. During baseflow conditions, nitrate and ammonium had opposite behaviour, probably controlled by biological processes such as vegetation uptake and mineralization activity. DON concentrations did not have a seasonal trend. During storms, nitrate and DON increased by several times but discharge was not a good predictor of nutrient concentrations. DOC:DON ratios in streamwater were around 26, except during the months following drought when DOC:DON ratios ranged between 42 and 20 during baseflow and stormflow conditions, respectively. Annual N export during 2000–2001 was 70 kg km 1 year 1, of which 75% was delivered during stormflow. The relative contribution of nitrogen forms to the total annual export was 57, 35 and 8% as NO3–N, DON and NH4–N, respectively.This study was supported by a Formacio´n de Personal Investigador (FPI) grant and funds provided by the Comisio´ n Interministerial de Ciencia y Tecnologı´a (CICT, reference REN2001-3327).Peer reviewe