The aerosol dynamics of H2O–H2SO4–HNO3 mixtures formed (i) by homogeneous nucleation and (ii) by adsorption on emitted soot particles in the jet regime of a B 747 airliner have been investigated by modeling studies. Emission indices of 0.05 g kg(fuel)-1 and 1.0 g kg(fuel)-1 for soot and SO2, respectively, were chosen. In addition, the influence of both chemiions (EI(HSO4-)=2.9×10-5 g kg(fuel)-1) and different initial S(VI)/(S(VI)+S(IV)) ratios (0.8–10%) have been taken into consideration. As opposed to previous studies which were restricted to the binary H2O–H2SO4 system, the presence of HNO3 in the plume has been included. Both, composition and size spectra of the H2O–H2SO4–HNO3 clusters have been investigated. It is found that, caused by the presence of HNO3 in liquid aerosols, the reduced vapour pressure of H2O leads to enhanced water uptake. In analogy to H2O–H2SO4–HNO3-coated soot particles and especially for high fuel sulfur contents, a fraction of these aerosols can then also freeze and hence contribute to visible contrails.

The formation of contrails by H2O/H2SO4 condensation on activated soot particles in the jet regime of a B 747 airliner has been investigated by modelling studies. Emission indices of 0.05gkg-1 fuel and 1.0gkg-1 fuel for soot and SO2, respectively, were chosen. No direct emission of S(VI) (SO3, H2SO4) has been assumed. The phase change of the H2O/H2SO4 coverage of the soot particles and hence its impact on particle growth has been investigated by variation of the ambient temperature (219K⩽Ta⩽233K) and the H2O content of the surrounding air (0.02mbar⩽pH2O⩽0.10mbar), corresponding to relative humidities between 0.1 and 1.8. At Ta=219K and pH2O=0.10 mbar the ice particles grown on combustion soot reach diametres of 4.5μm on the plume axis and of 5.7μm in its outer region. With increasing temperature, however, the particle diameters decrease. Moreover, above a threshold temperature which is dependent on ambient H2O vapour pressure, the modelled particle sizes drop to values below 62nm, corresponding to liquid particles grown by heterogeneous nucleation of H2O and H2SO4 on liquid H2O/H2SO4 soot surface coverages. This is caused by the fact that the freezing condition is no longer fulfilled. The simultaneous formation of H2O/H2SO4 droplets by homogeneous nucleation shows no significant dependence on pH2O and the diametres of the droplets do not exceed values of 3.5nm.

The formation of cloud condensation nuclei in the jet regime of a B-747 airliner at cruise has been investigated by modeling studies. Both the formation of H2O/H2SO4 clusters by homogeneous nucleation and the deposition of water vapor on soot particles activated by the adsorption of gaseous H2SO4, sulfuric acid hydrates, and H2O/H2SO4 clusters were taken into account. H2SO4 has been assumed to be formed only by OH oxidation of SO2 in the plume. Whereas at ambient temperatures between 219 and 224 K the heterogeneous condensation leads to ice particles with average diameters between 3.0 and 1.1 mu m for soot emission indices of EI(soot) = (0.05 - 0.5) g/kg, respectively, no heterogeneous condensation occurs at higher temperatures. Homogeneously nucleated H2O/H2SO4 clusters, on the other hand, have diameters of less than 7 nm and do not contribute to visible contrail formation. Assuming different sulfur emission indices (0.1 g/kg less than or equal to EI(SO2) less than or equal to 10 g/kg), we conclude that the contrail onset is essentially independent of this quantity and that a fractional H2SO4 surface coverage corresponding to a 0.1 monolayer (ML = 0.1) must be sufficient to activate the soot:particles for H2O uptake, at least for EI(SO2) greater than or equal to 0.5 g/kg fuel. Calculations based on higher threshold values (i.e., 0.1 < ML less than or equal to 0.3) lead to results which are in disagreement with the onset of contrail formation as deduced by visual observations. Moreover, the present modeling study provides an estimate of the effect of mutual coupling of homogeneous and heterogeneous condensation pathways.

Optoelectronic devices in the blue spectral region require doped ZnSxSe1−x layers for electrical confinement and optical waveguilding. Since ion implantation is often used to realize heavy doping in thin layers, we implanted gallium ions with different doses and energies into ZnSe and ZnSxSe1−x (x ≤ 0.4) layers, grown by metalorganic vapor phase epitaxy (MOVPE) on GaAs. Rapid thermal annealing was performed after SiO2 capping. For characterization, we used electron probe micro-analysis (EPMA), photoluminescence (PL) at 11 K, Raman spectroscopy, far infrared reflectivity (FIR) and Hall measurements. In ZnSe, the Ga depth profiles remain nearly gaussian after annealing, indicating weak diffusion. PL shows that both the overall intensity and the ratio of excitonic to deep centre emissions are maximum for annealing at 850°C (30 s), implying optimum crystalline quality and maximum carrier concentration. In addition, the conductivity is maximum (10 Ω-1 cm-1). However, FIR reveals a heavily doped layer at the GaAs interface, which is assigned to the annealing-induced Zn diffusion into the substrate. Furthermore, the PL spectra show donor-acceptor pair (DAP) transitions which can be attributed to shallow acceptors due to complexes of Ga and intrinsic defects. With increasing ion dose the free carrier concentration saturates at 4 × 1017 cm-3 probably due to self-compensation caused by zinc vacancies (VZn). For ZnS0.3Se0.7, EPMA measurements show a diffusion of the Ga towards the surface, while S- and Ga-rich surface defects appear during annealing. After implantation the PL spectra show deep level emissions at 2.08 and 2.35 eV, which were assigned to [GaZn − VZn] complexes and to ZnSe. Optimum annealing seems to occur at 850°C for 30 s, resulting in a maximum PL intensity with strong DAP and excitonic contributions. Similar behaviour was observed for ZnS0.4Se0.6. Up to now, due to the diffusion and compensation, the implanted and annealed ternary layers remain semi-insulating.

The incorporation processes and efficiencies of nitrogen doping for p-type conductivity in metalorganic vapour phase epitaxy (MOVPE) grown ZnSe/GaAs epilayers are investigated by means of time-integrated and time resolved photoluminescence (PL) spectroscopy. Two nitrogen-doping methods are compared, plasma-enhanced doping during growth, and ion implantation of nitrogen with annealing after growth. Both types of doped layers exhibit the IN1 transition from a neutral acceptor bound exciton complex (A0N, X), indicating an effective nitrogen embedding on selenium sites. With increasing nitrogen doping rates, a deeper bound exciton line IC1 appears, lowering the intensity of the IN1. An observed reduction of the IN1 and IC1 lifetimes for higher nitrogen doping concentrations results from an enhanced overlap of the bound exciton wave functions with those of other impurity centres.

In the present work EPMA combined with Monte Carlo simulation was applied to investigate implanted gallium depth distributions in ZnSxSe1−x layers. The layers of about 1 to 4 μm thickness were grown by MOVPE on (100)-GaAs substrate. The overlap of the Ga and zinc L X-ray spectra and the low gallium net count rates were overcome by stripping the spectra of non implanted layers and by applying appropriate beam currents and counting times. Capabilities and limitations of the EPMA technique as applied to depth profile analysis are demonstrated.