[show abstract][hide abstract] ABSTRACT: As a contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia – Cooperative LBA Airborne Regional Experiment (LBA-CLAIRE-2001) field campaign in the heart of the Amazon Basin, we analyzed the temporal and spatial dynamics of the urban plume of Manaus City during the wet-to-dry season transition period in July 2001. During the flights, we performed vertical stacks of crosswind transects in the urban outflow downwind of Manaus City, measuring a comprehensive set of trace constituents including O3, NO, NO2, CO, VOC, CO2, and H2O. Aerosol loads were characterized by total aerosol number concentration (CN) and cloud condensation nuclei (CCN) concentrations, and light scattering properties. Measurements over pristine rainforest areas during the campaign showed low levels of pollution from biomass burning or industrial emissions, representative of wet season background conditions. The urban plume of Manaus City was found to be joined by plumes from power plants south of the city, all showing evidence of very strong photochemical ozone formation. One episode is discussed in detail, where a threefold increase in ozone mixing ratios in the atmospheric boundary layer occurred within a 100 km travel distance downwind of Manaus. Observation-based estimates of the ozone production rates in the plume reached 15 ppb h−1. Within the plume core, aerosol concentrations were strongly enhanced, with ΔCN/ΔCO ratios about one order of magnitude higher than observed in Amazon biomass burning plumes. ΔCN/ΔCO ratios tended to decrease with increasing transport time, indicative of a significant reduction in particle number by coagulation, and without substantial new particle nucleation occurring within the time/space observed. While in the background atmosphere a large fraction of the total particle number served as CCN (about 60–80% at 0.6% supersaturation), the CCN/CN ratios within the plume indicated that only a small fraction (16 ± 12%) of the plume particles were CCN. The fresh plume aerosols showed relatively weak light scattering efficiency. The CO-normalized CCN concentrations and light scattering coefficients increased with plume age in most cases, suggesting particle growth by condensation of soluble organic or inorganic species. We used a Single Column Chemistry and Transport Model (SCM) to infer the urban pollution emission fluxes of Manaus City, implying observed mixing ratios of CO, NOx and VOC. The model can reproduce the temporal/spatial distribution of ozone enhancements in the Manaus plume, both with and without accounting for the distinct (high NOx) contribution by the power plants; this way examining the sensitivity of ozone production to changes in the emission rates of NOx. The VOC reactivity in the Manaus region was dominated by a high burden of biogenic isoprene from the background rainforest atmosphere, and therefore NOx control is assumed to be the most effective ozone abatement strategy. Both observations and models show that the agglomeration of NOx emission sources, like power plants, in a well-arranged area can decrease the ozone production efficiency in the near field of the urban populated cores. But on the other hand remote areas downwind of the city then bear the brunt, being exposed to increased ozone production and N-deposition. The simulated maximum stomatal ozone uptake fluxes were 4 nmol m−2 s−1 close to Manaus, and decreased only to about 2 nmol m−2 s−1 within a travel distance >1500 km downwind from Manaus, clearly exceeding the critical threshold level for broadleaf trees. Likewise, the simulated N deposition close to Manaus was ~70 kg N ha−1 a−1 decreasing only to about 30 kg N ha−1 a−1 after three days of simulation.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2010; · 5.51 Impact Factor
[show abstract][hide abstract] ABSTRACT: Langmuir-Blodgett films of hemicyanine and amidonitrostilbene derivatives which are of interest for non-linear optical applications have been investigated. The optical absorption spectra of multilayers of the two dyes and of alternate-layer films are repeated. Surface plasmon resonance has also been used to study the linear and non-linear optical properties of these films.
[show abstract][hide abstract] ABSTRACT: Hexadecanoyltetrathiafulvalene (HDTTF) has been prepared by reaction of the lithium salt of TTF with hexadecanoyl chloride. Multilayers of HDTTF have been assembled on glass substrates; upon doping with iodine the films become highly insulating, but the conductivity increases with time following exposure, to reach a maximum value of 0.01 S cm−1 after a few hours. In contrast to this, films doped with bromine remain insulating.
[show abstract][hide abstract] ABSTRACT: Langmuir-Blodgett films of the 1 : 1 charge-transfer salt N-octadecylpyridinium-TCNQ have been deposited onto glass substrates. The layers exhibit significant bulk lateral conductivity without doping. The value obtained at room temperature is (2.0 ± 0.2) × 10−2 S cm−1; over the temperature range 100 – 300 K, the films show typical semiconductor behaviour with an activation energy of 0.13 ± 0.005 eV. Infrared and u.v.-visible transmission spectra of the films are characteristic of an organic conductor.
[show abstract][hide abstract] ABSTRACT: Hydrogenated amorphous silicon (a-Si:H) is an important semiconductor for solar cells and the basis of transistor structures to address electronic displays. In an insulated gate field effect transistor (FET) the quality of the insulating layer is of paramount importance. We have extended our earlier work on the LB film/a-Si:H system to the characterization of cadmium stearate films “as deposited” onto a-Si:H, with a view to device fabrication. Our experiments show that the monolayers stack reproducibly to form an ordered film of good quality. An unusual In characteristics is observed, which has previously been reported only for single- monolayer films: this may be due to the presence of an interfacial layer. We also report in this paper the electrical characteristics of an LB film/a-Si:H FRT. Moderate gate voltages (about 10V) can modulate the source-drain current by more than two orders of magnitude. The device characteristics are in general quite similar to those of the first reported a-Si:H FETs. It is suggested that the FET properties are dominated by the nature of the a-Si:H surface region.
Thin Solid Films 01/1983; 99:297-304. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper we describe the properties of MIS structures based on hydrogenated amorphous silicon (a-Si:H) and organic films deposited using the Langmuir-Blodgett technique. Results are reported for undoped a-Si:H passivated with an insulating film of cadmium stearate 80 nm thick. The deposition of the monolayers was found to be critically dependent on the surface condition of the semiconductor.The capacitance data display well-defined accumulation and depletion regions and suggest that inversion is obtained when the device is reverse biased. The conductance data are similar in shape to those observed for conventional MOS structures on crystalline silicon. However, hysteresis and frequency dispersion effects complicate their interpretation in terms of surface state densities.From this preliminary investigation we conclude that useful MOS devices incorporating both thick and thin insulating layers can be based on the a-Si:H/Langmuir-Blodgett film system.
Thin Solid Films 01/1982; 89(4):395-400. · 1.60 Impact Factor