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Formation of new aerosol particles by nucleation and growth is a significant source of aerosols in the atmosphere. New particle formation events usually take place during daytime, but in some locations they have been observed also at night. In the present study we have combined chamber experiments, quantum chemical calculations and aerosol dynamics models to study nocturnal new particle formation. All our approaches demonstrate, in a consistent manner, that the oxidation products of monoterpenes play an important role in nocturnal nucleation events. By varying the conditions in our chamber experiments, we were able to reproduce the very different types of nocturnal events observed earlier in the atmosphere. The exact strength, duration and shape of the events appears to be sensitive to the type and concentration of reacting monoterpenes, as well as the extent to which the monoterpenes are exposed to ozone and potentially other atmospheric oxidants. [ABSTRACT FROM AUTHOR]

Formation of new aerosol particles by nucleation and growth is a significant source of aerosols in the atmosphere. New particle formation events usually take place during daytime, but in some locations they have been observed also at night. In the present study we have combined chamber experiments, quantum chemical calculations and aerosol dynamics models to study nocturnal new particle formation. All our approaches demonstrate, in a consistent manner, that the oxidation products of monoterpenes play an important role in nocturnal nucleation events. By varying the conditions in our chamber experiments, we were able to reproduce the very different types of nocturnal events observed earlier in the atmosphere. The exact strength, duration and shape of the events appears to be sensitive to the type and concentration of reacting monoterpenes, as well as the extent to which the monoterpenes are exposed to ozone and potentially other atmospheric oxidants. [ABSTRACT FROM AUTHOR]

The influence of biogenic particle formation on climate is a well recognised phenomenon. To understand the mechanisms underlying the biogenic particle formation, determining the chemical composition of the new particles and therefore the species that drive the particle production is of utmost importance. Due to the very small amount of mass involved, indirect approaches are frequently used to infer the composition. We present here the results of such an indirect approach by simultaneously measuring volatile and hygroscopic properties of newly formed particles in a forest environment. It is shown that the particles are composed of both sulphates and organics, with the amount of sulphate component strongly depending on the available gasphase sulphuric acid, and the organic components having the same volatility and hygroscopicity as photo-oxidation products of a monoterpene such as α-pinene. Our findings agree with a two-step process through nucleation and cluster formation followed by simultaneous growth by condensation of sulphates and organics that take the particles to climatically relevant sizes. [ABSTRACT FROM AUTHOR]

The world's forests produce atmospheric aerosol by emitting volatile organic compounds (VOC) which, after being oxidized in the atmosphere, readily condense on the omnipresent nanometer-sized nuclei and grow them to climatically relevant sizes. The cooling effect of aerosols is the greatest uncertainty in current climate models and estimates of radiative forcing. Therefore, identifying the environmental factors influencing the biogenic formation of aerosols is crucial. In this paper, we connected biogenic aerosol formation events observed in a Eucalypt forest in South-East Australia during July 2005-December 2006 to air mass history using 96-h back trajectories. Formation of new particles was most frequent in the dry westerly and south-westerly air masses. According to NDVI (Normalized Difference Vegetation Index) measurements, photosynthesis was not significantly higher in this direction compared to the north-east direction. It is unlikely, therefore, that differences in photosynthesis-derived organic precursor emissions would have been significant enough to lead to the clear difference in NPF frequency between these two directions. Instead, the high evaporation rates above the Pacific Ocean resulted in humid winds from the north-east that effectively suppressed new-particle formation in the forest hundreds of kilometers inland. No other factor varied as significantly in tune with new-particle formation as humidity and we concluded that, in addition to local meteorological factors in the forest, the magnitude of evaporation from oceans hundreds of kilometers upwind can effectively suppress or enhance new-particle formation. Our findings indicate that, unlike warm waters, the cold polar oceans provide excellent clean and dry background air that enhances aerosol formation above nearcoastal forests in Fennoscandia and South-East Australia. [ABSTRACT FROM AUTHOR]

A month-long intensive measurement campaign was conducted in March/April 2007 at Agnes Water, a remote coastal site just south of the Great Barrier Reef on the east coast of Australia. Particle and ion size distributions were continuously measured during the campaign. Coastal nucleation events were observed in clean, marine air masses coming from the south-east on 65% of the days. The events usually began at~10:00 local time and lasted for 1-4 h. They were characterised by the appearance of a nucleation mode with a peak diameter of ~10 nm. The freshly nucleated particles grew within 1-4 h up to sizes of 20-50 nm. The events occurred when solar intensity was high (~1000Wm-2) and RH was low (~60%). Interestingly, the events were not related to tide height. The volatile and hygroscopic properties of freshly nucleated particles (17-22.5 nm), simultaneously measured with a volatility-hygroscopicity-tandem differential mobility analyser (VH-TDMA), were used to infer chemical composition. The majority of the volume of these particles was attributed to internally mixed sulphate and organic components. After ruling out coagulation as a source of significant particle growth, we conclude that the condensation of sulphate and/or organic vapours was most likely responsible for driving particle growth at sizes greater than 10 nm during the nucleation events. Although there was a possibility that the precursor vapours responsible for particle formation and growth had continental sources, on the balance of available data we would suggest that the precursors were most likely of marine/coastal origin. Furthermore, a unique and particularly strong nucleation event was observed during northerly wind. The event began early one morning (08:00) and lasted almost the entire day resulting in the production of a large number of ~80 nm particles (average modal concentration during the event was 3200 cm-3). The Great Barrier Reef was the most likely source of precursor vapours responsible for this event. [ABSTRACT FROM AUTHOR]

The influence of biogenic particle formation on climate is a well recognized phenomenon. To understand the mechanisms underlying the biogenic particle formation, determining the chemical composition of the new particles and therefore the species that drive 5 the particle production is of utmost importance. Due to the very small amount of mass involved, indirect approaches are frequently used to infer the composition. We present here the results of such an indirect approach by simultaneously measuring volatile and hygroscopic properties of newly formed particles in a forest environment. We that the particles are composed of both sulphates and organics, with the amount of sulphate component strongly depending on the available gas-phase sulphuric acid, and the organic components being photo-oxidation products of most likely a monoterpene. Our findings confirm a two-step process through nucleation and cluster formation followed by simultaneous growth by condensation of sulphates and organics that take the particles to climatically relevant sizes. [ABSTRACT FROM AUTHOR]

Biogenic aerosol formation is likely to contribute significantly to the global aerosol load. In recent years, newparticle formation has been observed in various ecosystems around the world but hardly any measurements have taken place in the terrestrial Southern Hemisphere. Here, we report the first results of atmospheric ion and charged particle concentrations as well as of new-particle formation in a Eucalypt forest in Tumbarumba, South-East Australia, from July 2005 to October 2006. The measurements were carried out with an Air Ion Spectrometer (AIS) with a size range from 0.34 to 40 nm. The Eucalypt forest was a very strong source of new aerosol particles. Daytime aerosol formation took place on 52% of days with acceptable data, which is 2-3 times as often as in the Nordic boreal zone. Average growth rates for negative/positive 1.5-3 nm particles during these formation events were 2.89/2.68 nmh-1, respectively; for 3-7 nm particles 4.26/4.03, and for 7-20 nm particles 8.90/7.58 nmh-1, respectively. The growth rates for large ions were highest when the air was coming from the native forest which suggests that the Eucalypts were a strong source of condensable vapours. Average concentrations of cluster ions (0.34-1.8 nm) were 2400/1700 cm-3 for negative/positive ions, very high compared to most other measurements around the world. One reason behind these high concentrations could be the strong radon efflux from the soils around the Tumbarumba field site. Furthermore, comparison between night-time and daytime concentrations supported the view that cluster ions are produced close to the surface within the boundary layer also at night but that large ions are mostly produced in daytime. Finally, a previously unreported phenomenon, nocturnal aerosol formation, appeared in 32% of the analysed nights but was clustered almost entirely within six months from summer to autumn in 2006. From January to May, nocturnal formation was 2.5 times as frequent as daytime formation. Therefore, it appears that in summer and autumn, nocturnal production was the major mechanism for aerosol formation in Tumbarumba. [ABSTRACT FROM AUTHOR]

The growth rate of atmospheric CO2 exhibits large temporal variation that is largely determined by year-to-year fluctuations in land–atmosphere CO2 fluxes. This land–atmosphere CO2-flux is driven by large-scale biomass burning and variation in net ecosystem exchange (NEE). Between- and within years, NEE varies due to fluctuations in climate. Studies on climatic influences on inter- and intra-annual variability in gross photosynthesis (GPP) and net carbon uptake in terrestrial ecosystems have shown conflicting results. These conflicts are in part related to differences in methodology and in part to the limited duration of some studies. Here, we introduce an observation-driven methodology that provides insight into the dependence of anomalies in CO2 fluxes on climatic conditions. The methodology was applied on fluxes from a boreal and two temperate pine forests. Annual anomalies in NEE were dominated by anomalies in GPP, which in turn were correlated with incident radiation and vapor pressure deficit (VPD). At all three sites positive anomalies in NEE (a reduced uptake or a stronger source than the daily sites specific long-term average) were observed on summer days characterized by low incident radiation, low VPD and high precipitation. Negative anomalies in NEE occurred mainly on summer days characterized by blue skies and mild temperatures. Our study clearly highlighted the need to use weather patterns rather than single climatic variables to understand anomalous CO2 fluxes. Temperature generally showed little direct effect on anomalies in NEE but became important when the mean daily air temperature exceeded 23 °C. On such days GPP decreased likely because VPD exceeded 2.0 kPa, inhibiting photosynthetic uptake. However, while GPP decreased, the high temperature stimulated respiration, resulting in positive anomalies in NEE. Climatic extremes in summer were more frequent and severe in the South than in the North, and had larger effects in the South because the criteria to inhibit photosynthesis are more often met. [ABSTRACT FROM AUTHOR]

Biogenic aerosol formation is likely to contribute significantly to the global aerosol load. In recent years, new-particle formation (NPF) has been observed in various ecosystems around the world but hardly any measurements have taken place in the terrestrial Southern Hemisphere. Here, we report the first results of atmospheric ion and charged particle concentrations as well as of NPF in a Eucalypt forest in Tumbarumba, South-East Australia, from July 2005 to October 2006. The measurements were carried out with an Air Ion Spectrometer (AIS) with a size range from 0.34 to 40 nm. Daytime aerosol formation took place on 52% of days with acceptable data. Median growth rates (GR) for negative/positive 1.3-3nm particles were 2.29/2.02 nmh-1; for 3-7 nm particles 3.04/2.94 nmh-1; and for 7-20nm particles 7.13/5.62 nmh-1, respectively. Intermediate ion growth rates were highest when the wind was blowing from the direction of the native Eucalypt forest, suggesting that the Eucalypts were the strongest source of condensable vapours. Average cluster ion (0.34 to 1.8 nm) concentrations were very high, 2400/1700 cm-3 for negative/positive ions compared to other measurements around the world. These high concentrations are probably the result of the strong radon efflux from the soils around the Tumbarumba field site. Furthermore, comparison between nighttime and daytime concentrations supported the view that cluster ions are produced close to the surface within the boundary layer also at night but that large ions are mostly produced in daytime. Finally, a previously unreported phenomenon, nocturnal aerosol formation, appeared on 32% of the analysed nights but was clustered almost entirely within six months from summer to autumn in 2006. From January to May, nocturnal formation was 2.5 times as frequent as daytime formation. Therefore, it appears that in summer and autumn, nocturnal production was the major mechanism for aerosol formation in Tumbarumba. [ABSTRACT FROM AUTHOR]

This paper addresses the potential role of surface wetness in ozone deposition to plant foliage. We studied Scots pine foliage in field conditions at the SMEARII field measurement station in Finland. We used a combination of data from flux measurement at the shoot (enclosure) and canopy scale (eddy covariance), information from foliage surface wetness sensors, and a broad array of ancillary measurements such as radiation, precipitation, temperature, and relative humidity. Environmental conditions were defined as moist during rain or high relative humidity, and the subsequent 12 h from such events, circumstances that were frequent at this boreal site. From the measured fluxes we estimated the ozone conductance as the expression of the strength of the ozone removal surface sink or total deposition. Further, the stomatal contribution was estimated and the remaining deposition was analysed as non-stomatal sink. The combined time series of measurements showed that both shoot and canopyscale ozone total deposition were enhanced when moist conditions occurred. On average, the estimated stomatal deposition accounted for half of the measured removal at the shoot scale and one third at the canopy scale. However, during dry conditions the estimated stomatal uptake predicted the behaviour of the measured deposition, but during moist conditions there was disagreement. The estimated non-stomatal sink was analysed against several environmental factors and the clearest correspondence was found with ambient relative humidity. The relationship disappeared under 70% relative humidity, a threshold that coincides with the value at which surface moisture gathers at the foliage surface according to the leaf surface wetness measurements. This suggests the non-stomatal ozone sink on the foliage to be modulated by the surface films. We attempted to extract such potential modulation with the estimated film formation via the theoretical expression or adsorption isotherm. Whereas this procedure could predict the behaviour of the non-stomatal sink, it implied a chemical sink that was not accountable as simple ozone decomposition. We discuss the existence of other mechanisms whose relevance needs to be clarified, in particular: a significant stomatal aperture neglected in the estimations, and a potentially large chemical sink offered by reactive biogenic organic volatile compounds. [ABSTRACT FROM AUTHOR]

Thinning is a routine forest management operation that changes tree spacing, number, and size distribution and affects the material flows between vegetation and the atmosphere. Here, using direct micrometeorological ecosystem-scale measurements, we show that in a boreal pine forest, thinning decreases the deposition velocities of fine particles as expected but does not reduce the carbon sink, water vapor flux, or ozone deposition. The thinning decreased the all-sided leaf area index from 8 to 6, and we suggest that the redistribution of sources and sinks within the ecosystem compensated for this reduction in foliage area. In the case of water vapor and 03, changes in light penetration and among-free competition seem to increase individual transpiration rates and lead to larger stomatal apertures, thus enhancing also O3 deposition. In the case of CO2, increased ground vegetation assimilation and decreased autotrophic respiration seem to cancel out opposite changes in canopy assimilation and heterotrophic respiration. Current soil-vegetation-atmosphere transfer models should be able to reproduce these observations. [ABSTRACT FROM AUTHOR]

The strength of the H-implanted layer has been measured in 〈1 0 0〉, 〈1 1 1〉 and 〈1 1 0〉 oriented Si wafers using the crack opening method. The required annealing temperature for mechanical layer transfer increases in the order 〈1 0 0〉, 〈1 1 1〉 and 〈1 1 0〉. The damage induced by the implantation has been studied by Rutherford backscattering in the channeling mode (RBS/C). The same methods have been used to investigate the influence of boron and arsenic doping on the mechanical exfoliation. Boron doping reduces the strength of the H-implanted layer thereby enabling mechanical layer transfer at temperatures below 200 °C. We found that the exfoliation takes place closer to the wafer surface in highly boron doped Si as compared to the undoped Si. The RBS damage peak also appears to move closer to the surface when the boron concentration of the H-implanted layer is >1019 cm−3. No lowering of the exfoliation temperature was observed for compensated and arsenic doped Si layers. We suggest that the lowering of the exfoliation temperature with increasing boron doping is related to Si–H bonds associated with the neutralization of shallow acceptors by hydrogen. [Copyright &y& Elsevier]

In this work, we demonstrate a novel approach for the transfer of Si layers onto handle wafers, induced by plasma hydrogenation. In the conventional ion-cut process, hydrogen ion implantation is used to initiate layer delamination at a desired depth, which leads to ion damage in the transferred layer. In this study, we investigated the use of plasma hydrogenation to achieve high-quality layer transfer. To place hydrogen atoms introduced during plasma hydrogenation at a specific depth, a uniform trapping layer for H atoms must be prepared in the substrate before hydrogenation. The hydrogenated Si wafer was then bonded to another Si wafer coated with a thermal oxide, followed by thermal annealing to induce Si layer transfer. Cross-section transmission electron microscopy showed that the transferred Si layer was relatively free of lattice damage. The H trapping during plasma hydrogenation, and the subsequent layer delamination mechanism, are discussed. These results show direct evidence of the feasibility of using plasma hydrogenation to transfer relatively defect-free Si layers. [ABSTRACT FROM AUTHOR]

Single-crystalline silicon thin film on fused quartz (SOQ) was prepared using a technique based on wafer bonding and mechanically initiated exfoliation. MOSFETs fabricated on the resulting SOQ were characterized. The measured low-field electron effective mobility was ∼ 1072 cm²/V · s, which is ∼35% higher than that extracted from reported "universal curve" for electron effective mobility. Consistent with the mobility enhancement, a tensile strain of 0.25% in the SOQ was deduced from Raman spectroscopy. At ∼ 243 cm²/V · s, no enhancement in hole effective mobility was observed. [ABSTRACT FROM AUTHOR]

Single-crystalline silicon thin film on glass (cSOG) has been prepared using an "ion-cutting" based "layer-transfer" technique. Low-temperature processed thin-film transistors, fabricated both on cSOG and metal-induced laterally crystallized polycrystalline silicon, have been characterized and compared. The cSOG-based transistors performed comparatively better, exhibiting a significantly higher electron field-effect mobility (∼ 430 cm²/Vs), a steeper subthreshold slope and a lower leakage current that was also relatively insensitive to gate bias. [ABSTRACT FROM AUTHOR]

We report a simple and nondestructive photocurrent method for characterizing the bonding interface between two hydrophobically bonded Si wafers. The relationship of photocurrent versus wavelength was measured and analyzed. The direction of the photocurrent indicates the band-bending direction, and thus, the donor or acceptor nature of the interface states. The photocurrent is proportional to the electric field at the interface induced by band bending. Our results showed that the Si pairs bonded in air have much larger band bending at the interface than those bonded in dry nitrogen, and that both have donor-like interface states. [ABSTRACT FROM AUTHOR]

Abstract: Atomic layer deposition (ALD) is currently a widespread method to grow conformal thin films with a sub-nm thickness control. By using ALD for nanolaminate oxides, it is possible to fine tune the electrical, optical and mechanical properties of thin films. In this study the elemental depth profiles and surface roughnesses were determined for Al2O3 +TiO2 nanolaminates with nominal single-layer thicknesses of 1, 2, 5, 10 and 20nm and total thickness between 40nm and 60nm. The depth profiles were measured by means of a time-of-flight elastic recoil detection analysis (ToF-ERDA) spectrometer recently installed at the University of Jyväskylä. In TOF-E measurements 63Cu, 35Cl, 12C and 4He ions with energies ranging from 0.5 to 10MeV, were used and depth profiles of the whole nanolaminate film could be analyzed down to 5nm individual layer thickness. [Copyright &y& Elsevier]