Surface Organic Layer Research Articles

Structure of Cobalt Nanosphere Superlattice Films by Small Angle X-ray Scattering

AbstractCobalt nanocrystals, recently synthesized with narrow size distributions and controlled shapes, organize in a wide range of arrays as a function of shape, size and interparticle interactions. The nanocrystals (NCs) consist of a cobalt metal core with a nominal diameter of 11 nm, and an organic surfactant surface layer with a chain length of ∼1.7 nm. For the simplest case (ε-Co nanospheres, super-paramagnetic at room temperature) a hexagonal arrangement of NCs is observed in transmission electron microscope (TEM) images when precipitated from solution onto carbon films. For practical applications and for further understanding of the self-assembly process, long range order of the super lattice must be probed over regions that are greater in extent than may be examined by TEM. Hence, small angle x-ray scattering (SAXS) measurements were performed on cobalt nanospheres randomly dispersed in solution and assembled on glass substrates. Least squares fit to the intensity distribution as a function of the scattering vector q gave an average particle diameter of 11.0 ± 0.8 nm. Structure factor contribution to the intensity profile agrees well with a quasi-random model for scattering from a face centered cubic (FCC) superlattice composed of uniform radius cobalt spheres. The measured nearest neighbor interparticle spacing, 14.1 nm, agrees to within 2% of the predicted value of 14.4 nm based on a free energy model that governs the self-assembly of the nanoparticle system.

The effect of chemically bonded organic surface layers on the behaviour of fine powders

We have examined the effects of chemically bonded organic surface layers on the behaviour of a ceramic and a metal powder. The thin monomolecular layers were found to improve the corrosion resistance of the sensitive Nd–Fe–B powder and make the fine alumina powder hydrophobic and, as a result, making both coated powders significantly less sensitive to environmental humidity. Our analysis of the flowability of the noncoated and coated powders revealed that the alumina powder can be classified as very cohesive—the addition of the coating even increased its cohesivity. The Nd–Fe–B powder was determined to be easy flowing, and the effect of the coating changed with the applied normal stress. The coating does, however, improve the powder-compaction properties of both powders. In addition, the beneficial effect of the coating in terms of viscosity as well as in resistance to destabilization was also observed for suspensions in organic solvents.

Natural <sup>15</sup>N abundance in two nitrogen saturated forest ecosystems at Solling, Germany

This research deals with a comparative study of two different N-saturated forests: 1. beech forest and 2. spruce forest at the same locality of \solling, Central Germany. The present results show that <sup>15</sup>N natural occurrence in the rainfall (both above and below canopy) at Solling site is similar (δ<sup>15</sup>N = –15‰ to +19‰) to other sites of the world (such as NITREX sites, USA etc.). Furthermore, <sup>15</sup>N values in the soil water ranged from –4.32 (± 2.09) to +5‰ (± 1.47), which also corresponds to NITREX sites and other sites of Europe and USA. In both forests, δ<sup>15</sup>N enrichment of both NH<sub>4</sub>-N and NO<sub>3</sub>-N showed a decreasing trend of their values from bulk precipitation to the upper soil layer, but increasing in the deeper soil layer again. An increase in the <sup>15</sup>N enrichment of soil water from upper soil depth to lower soil depth was observed in our study and it is assumed to be due to the strong net nitrification taking place in the upper layer (organic surface layer) of soil. The soils at both sites showed characteristic low (negative) δ<sup>15</sup>N values in the upper organic layers, strongly increasing to positive δ<sup>15</sup>N values in the mineral soil. In the lower depths of mineral soil horizons of both stands, an increase in δ<sup>15</sup>N values was found to culminate at +3 to +5‰. In contrast to the mineral soil horizon, in the organic soil horizon (0 to 6 cm depth) of both sites there was almost a similar or slight decrease in δ<sup>15</sup>N values with depth. This is attributed to the high nitrification rate in the organic soil horizon, resulting in excessive seepage water NO<sub>3</sub>-output at both sites (especially at the spruce site).

Upward mobilization of 137Cs in surface soils of Chamaecyparis obtusa Sieb. et Zucc. (hinoki) plantation in Japan

The use of 137Cs has recently been adopted to estimate erosion in hinoki plantations in Japan. However, there have been several reports of the upward mobilization of 137Cs in forest humus layers. In this study, the vertical distribution of 137Cs within the soil profile was measured in a hinoki plantation. In order to confirm the upward migration of 137Cs from mineral soil to fresh surface litter and to identify mechanisms of the transfer, changes in 137Cs specific activity in the contents of litterbags were examined in a hinoki plantation. A controlled laboratory experiment was also conducted to assess the effect of microbial activity on the upward migration of 137Cs. As a result, the higher 137Cs activities in the surface organic layer of a hinoki plantation than in fresh litter and the increasing 137Cs total content of litterbags with time demonstrated the upward mobilization of 137Cs from mineral soil to the surface organic layer. Physical movement of soil particles by raindrop splash was considered an important process in 137Cs upward migration. The results of our laboratory experiment indicate an influence from soil microbial activity on the upward mobilization of 137Cs. Thus, upward migration of 137Cs and constant litter removal by runoff may induce 137Cs loss from steep forested catchments and underestimation of the 137Cs inventory leading to the overestimation of soil redistribution rates.

Rotational Diffusion in Iron Ferrofluids

The dynamic magnetic susceptibility of relatively monodisperse iron ferrofluids was measured from 1 Hz to 100 kHz for different sizes of the iron particles (all with a 7-nm-thick organic surface layer, dispersed in Decalin). In the case of particles with an iron core of 6-nm radius, the orientation of the magnetic dipole moment thermally rotated inside the particles (Néel rotation). In the case of particles with a slightly larger iron core, the orientation of the magnetic dipole moment was blocked inside the particles but could still change by rotational diffusion of the particles themselves (Brownian rotation). With even larger particles (above 7-nm iron core radius), aggregates were formed: the rotational diffusion rate was lower than that of single particles by more than 1 order of magnitude. This sudden appearance of aggregates above a certain size of the iron particles agrees with previous observations in two dimensions, by cryogenic transmission electron microscopy of ultrathin ferrofluid films. Here, it is found that the threshold for aggregation is practically the same in three dimensions. Moreover, the rotational diffusion rate of the aggregates is seen to increase upon dilution, indicating a decrease in aggregate size. This suggests that a dynamic equilibrium exists between the sticking of particles to each other and unsticking, especially when the particles are sufficiently small so that the sticking energy is not more than a few times the thermal energy.

Modeling the formation of secondary organic aerosol in coastal areas: Role of the sea‐salt aerosol organic layer

In recent models the formation of secondary organic aerosol has been described by absorption of semivolatile oxidation products to an organic aerosol mixture and/or dissolution into an aerosol aqueous phase. In coastal areas, freshly formed sea‐salt aerosol absorbs secondary semivolatile organic oxidation products into its surface organic layer, which consequently allows for the partitioning of the secondary organics to the sea‐salt aerosol brine core. This process is modeled in the present study. Equilibrium between the gas phase and a continental primary organic aerosol phase, a sea‐salt organic layer, and a continental aqueous aerosol is maintained, as is equilibrium between the organic layer and the brine core. Within aqueous phases, dissociation of acidic species is considered, and charge balance determines pH. Six semivolatile organic oxidation products that have been observed as secondary organic aerosol constituents, eight primary organic aerosol constituents representative of urban aerosols, five sea‐salt organic layer species, and four organic components of the brine core are described molecularly. Numerical iteration techniques are used to solve the relevant nonlinear governing equations for the concentrations of each product in each aerosol phase and the gas phase, as well as for the pH of the relevant aqueous phases. Variables of interest include ambient temperature and species concentrations. Results indicate that the aqueous aerosols and the sea‐salt aerosol brine core are the most efficient media for absorption under the conditions described, that organic layers enhance the partitioning to the brine core, and that secondary organic acids contribute to the acidification of the sea‐salt aerosol brine core.

Spatial Extent, Age, and Carbon Stocks in Drained Thaw Lake Basins on the Barrow Peninsula, Alaska

Thaw lakes and drained thaw lake basins are ubiquitous on the Arctic Coastal Plain of Alaska. Basins are wet depositional environments, ideally suited for the accumulation and preservation of organic material. Much of this soil organic carbon (SOC) is currently sequestered in the near-surface permafrost but, under a warming scenario, could become mobilized. The relative age of 77 basins on the Barrow Peninsula was estimated using the degree of plant community succession and verified by radiocarbon-dating material collected from the base of the organic layer in 21 basins. Using Landsat-7+ imagery of the region, a neural network classifying algorithm was developed from basin age-dependent spectra and texture. About 22% of the region is covered by 592 lakes (>1 ha), and at least 50% of the land surface is covered by 558 drained lake basins. Analysis of cores collected from basins indicates that (1) organic layer thickness and the degree of organic matter decomposition generally increases with basin age, and (2) SOC in the surface organic layer tends to increase with basin age, but the relation for the upper 100 cm of soil becomes obscured due to cryoturbation, organic matter decomposition, and processes leading to ice enrichment in the upper permafrost.

Cratering on Titan: impact melt, ejecta, and the fate of surface organics

We conduct three-dimensional hydrodynamical simulations of hypervelocity impacts into the crust of Titan to determine the fraction of liquid water generated, under the reasonable assumption that the crust is largely water ice, and to track the fate of the organic-rich layer that is thought to overlie the ice over much of the surface. Impactors larger than a kilometer in diameter are only slightly affected by the atmosphere, while those well under that size are strongly decelerated and broken up before reaching the surface. Impact of a 2 km diameter icy projectile into the crust at velocities of 7 km per second or higher, and angles of impact between 30° and 45°, generate about 2–5% melt by volume within the crater. Our results for the amount of aqueous melt generated in impacts on Titan are broadly consistent with the analytic model developed by Thompson and Sagan (1992) although our numerical model allows us to more precisely quantify the fraction of melt, and fate of the organics, as a function of the impact parameters. While much of the organic surface layer is heavily shocked and ejected from the immediate region of the crater, a significant fraction located behind the oblique impact trajectory is only lightly shocked and is deposited in the liquid water at the crater base. Simple calculations suggest that the resulting aqueous organic phase may remain liquid for hundreds of years or longer, enough time for the synthesis of simple precursor molecules to the origin of life.

Soil biochemical and chemical changes in relation to mature spruce (Picea abies) forest conversion and regeneration

AbstractTo investigate soil changes from forest conversion and regeneration, soil net N mineralization, potential nitrification, microbial biomass N, L‐asparaginase, L‐glutaminase, and other chemical and biological properties were examined in three adjacent stands: mature pure and dense Norway spruce (Picea abies (L.) Karst) (110 yr) (stand I), mature Norway spruce mixed with young beech (Fagus sylvatica) (5 yr) (stand II), and young Norway spruce (16 yr) (stand III). The latter two stands were converted or regenerated from the mature Norway spruce stand as former. The studied soils were characterized as having a very low pH value (2.9 – 3.5 in 0.01 M CaCl2), a high total N content (1.06 – 1.94 %), a high metabolic quotient (qCO2) (6.7 – 16.9 g CO2 kg–1 h–1), a low microbial biomass N (1.1 – 3.3 % of total N, except LOf1 at stand III), and a relatively high net N mineralization (175 – 1213 mg N kg–1 in LOf1 and Of2, 4 weeks incubation). In the converted forest (stand II), C : N ratio and qCO2 values in the LOf1 layer decreased significantly, and base saturation and exchangeable Ca showed a somewhat increment in mineral soil. In the regenerated forest (stand III), the total N storage in the surface layers decreased by 30 %. The surface organic layers (LOf1, Of2) possessed a very high net N mineralization (1.5 – 3 times higher than those in other two stands), high microbial biomass (C, N), and high basal respiration and qCO2 values. Meanwhile, in the Oh layer, the base saturation and the exchangeable Ca decreased. All studied substrates showed little net nitrification after the first period of incubation (2 weeks). In the later period of incubation (7 – 11 weeks), a considerable amount of NO3‐N accumulated (20 – 100 % of total cumulative mineral N) in the soils from the two pure spruce stands (I, III). In contrast, there was almost no net NO3‐N accumulation in the soils from the converted mixed stand (II) indicating that there was a difference in microorganisms in the two types of forest ecosystems. Soil microbial biomass N, mineral N, net N mineralization, L‐asparaginase, and L‐glutaminase were correlated and associated with forest management.

Effects of manganese acetate on the anodic performance of carbon nanotubes for Li ion rechargeable batteries

Effects of the addition of various manganese compounds on anodic performance of carbon nanotube were investigated. It was seen that the Li intercalation capacity decreased drastically by the addition of most manganese compounds. However, addition of Mn(CH 3COO) 2 greatly improved the capacity for Li intercalation. Li intercalation capacity increased with increasing Mn(CH 3COO) 2 concentration and the largest capacity of 360 and 330 mAh/g for the insertion and reversible Li intercalation was achieved when 1 wt.% Mn(CH 3COO) 2 was added. The increased capacity was sustained after 50 times of charge and discharge cycles. X-ray absorption near edge spectra (XANES) suggests that the state of added Mn ion is close to MnO 2 and so the added Mn(CH 3COO) 2 decomposed during preparation. The surface organic layer formed by the acetic acid appears to give a superior solid electrolyte interface (SEI). The positive effects of Mn(CH 3COO) 2 are obtained only when manganese ion and acetic acid coexist. Therefore, it is believed that the coexisting Mn ion works as a catalyst for the decomposition of acetic acid.

Removal of the organic surface layer in combined sewer sediment using a flushing gate

Recent research identified the different sources of pollution of wet weather Combined Sewers Overflows (CSOs): it appeared that the deposits in sewers, and especially an organic layer situated at the water-sediment interface, may contribute 40-70% to the total pollution load of CSOs. Using the cyclic flush Hydrass gate, we generated increased water flows during dry weather. The effects of flushing the deposits have been analysed: the eroded particles sampled during the first flush wave show pollutant characteristics similar to characteristics measured in the organic layer. The organic layer that has formed on the surface of deposits can thus be washed off before rainstorms occur using the cyclic flushing technique.

Primary succession pathway of Norway spruce communities on land-uplift seashores

The rising Gulf of Bothnia coastlines provide sequences of primary succession. This paper, based on data from transects in northeast Sweden (63º 51’ N, 20º 43’ E), elucidates the pathway of Norway spruce community succession on ground-moraine seashores. We studied spatial and temporal variation in depth of surface organic layer, cover of field layer and bottom layer, density of spruce categories from current seedlings to mature and dead spruce, and diversity changes. We found that field layer declines in cover while bottom layer increases in cover and that field and bottom layers and spruce category diversity show unimodal trends with time of succession. Modal diversity occurred after 100 to 200 years for field- and bottom-layer types and after 200 to 230 years for spruce categories. We also found that spruce seedlings are able to colonize after only 30 to 40 years of succession (25 to 35 cm above mean sea level), that spruce category size increases with time of succession, and that spruce mortality occurs both among small-sized trees at earlier stages and among larger-sized trees at later stages approaching old-growth conditions. We present successional stages of field- and bottom-layer types, and of spruce categories, developed from TWINSPAN analyses and models of organic layer depth development over time.

Liming effects on the chemical composition of the organic surface layer of a mature Norway spruce stand ( Picea abies [L.] Karst.)

The application of lime in a mature Norway spruce ( Picea abies [L.] Karst.) forest in southern Germany induced major changes in the activity of soil organisms and root growth. Since this may influence the chemical compostion of the soil organic matter (SOM) of the organic surface layer, its composition and changes due to the treatment were examined in this study. Fine roots of Norway spruce have a relatively low content of extractable lipids, a low alkyl C content ( 13C CPMAS NMR) and a high ratio of non-cellulosic to cellulosic carbohydrates (NC/CC, carbohydrate determination by MBTH and gas chromatography analyses) as compared to needles. Furthermore, they show high ratios of suberin/cutin compounds (thermally assisted hydrolysis and methylation, (THM)) and high ratios of eicosanic acid/phytadiene I in their lipid extracts (pyrolysis-GC/MS). Liming (4 t ha −1 dolomite) of a Norway spruce organic surface layer decreased the proportion of alkyl C, the alkyl C/ O-alkyl C ratio, and the content of extractable lipids. The NC/CC ratio and the abundance of suberin relative to cutin components increased. The contribution of the chlorophyll component phytadiene I decreased in relation to eicosanic acid. These changes are attributed to increased fine root formation in the organic layer after liming. Furthermore, the presence of less degraded lignin (THM, peak ratio of 3,4-dimethoxybenzoic acid, methyl ester/3,4-dimethoxy-benzaldehyde) on the limed plot is explained by the increased input of relatively fresh fine root material. On the other hand, the decrease in the carbon-to-nitrogen ratio may be attributed to the higher microbial activity after liming.

Analysis of organic and inorganic species on the surface of atmospheric aerosol using time-of-flight secondary ion mass spectrometry (TOF-SIMS)

This work explores the utility of time-of-flight static secondary-ion mass spectrometry (TOF-SIMS) for the analysis of the surface organic layer on individual atmospheric aerosol particles. The surface sensitivity and minimal fragmentation available with TOF-SIMS suggest that it can be a powerful tool for the examination of the organic and inorganic species on the surface of individual particles. Cascade impactors were used to collect aerosol from summer 2000 Montana forest fires, winter snowmobile samples in Yellowstone National Park, Hawaiian lava and sea salt, from an Asian Dust event reaching Salt Lake City, Utah in April 2001 and from Salt Lake Valley summer urban aerosol. TOF-SIMS analysis and multivariate statistical techniques combined gave chemical and morphological information about the particles. Surfaces of the aerosol from forest fires, snowmobile exhaust, and sea salt were all dominated by aliphatic hydrocarbons and their amphiphilic derivatives. Each source showed a different organic chemical signature. The extent and composition of the organics layer which typically covers the surface of atmospheric particles are expected to effect all of the surface related aerosol properties such as health effects, the ability of the particle to activate and form cloud droplets, and the aggregation of particles as well as reactions between the particle and gas phase species.

Soil degradation and overland flow as causes of gully erosion on mountain pastures and in forests

In the European Limestone Alps, “Lithic Borofolists”, i.e. soils in a thick, peat-like organic surface layer, occur widespread in the subalpine vegetation belt in northern Italy. The most important properties of the Lithic Borofolists are their field capacity of more than 600% of the dry weight and an extremely high infiltration capacity. These soils prevent any hydraulic erosion and equilibrate the water budget of forests and the discharge of mountain torrents. Forest fires, clear-cutting, or overgrazing by cattle and horses could result in the collapse of the ecosystem within a short period of time. In the study area, overgrazing and trampling by cattle lead to a rapid degradation of Lithic Borofolists to “Histic Rendzinas” on the summer pastures. This causes a serious decrease in both field and infiltration capacity. On such degraded soils, the rainfall of an average thunderstorm may cause Horton overland flow and erosional features on the slopes as well as on the valley bottoms. Overland flow from the valley heads carries enormous quantities of silt, resulting in an extensive siltation of the summer pastures on the valley bottom and thereby lead to further reduction of the infiltration capacity. On the valley floor, the overland flow will be concentrated in shallow depressions, where it causes the erosion of steep-sided gullies. Even a beaten hunter path in a wooded area led to the formation of a deep gully during a thunderstorm.

The influence of primary ion bombardment conditions on the secondary ion emission behavior of polymer additives

The secondary ion (SI) emission behavior of pure polymer systems is meanwhile well understood. However, common plastics not only consist of the polymer host material but also contain a variety of additives normally present in low concentrations only. In order to better understand the parameters governing the SI emission of these trace compounds we performed a systematic study on the influence of the analysis parameters (primary ion (PI) type, PI energy, electron bombardment for charge compensation, etc.) using model systems. Samples were prepared by spin coating (sub)monolayers of Irganox 1010 onto additive-free low density polyethylene (LDPE). The SI parameters yield, disappearance cross-section and efficiency (yield per damaged area) were determined for PI bombardment with Ga +, Cs +, and SF 5 +. Furthermore the damaging influence of electron bombardment for charge compensation on the organic surface layers was investigated.

Os solos de uma Topossequencia na ilha de Algodoal/ Maiandeua, nordeste do estado do Pará, Brasil: composição química e produção de matéria orgânica

O estudo foi realizado na Ilha de Algodoal/Maiandeua no nordeste do Estado do Pará (00° 34' 35" S, 00° 40'00" S e 47° 39'35" WGr, 47° 3Γ25" WGr). Amostraram-se o solo e a matéria orgânica leve, nas profundidades de 0-5 cm, 5-10 cm c 10-20 cm, e a manta orgânica ao longo de uma toposseqüência com solos e cobertura vegetal diversificados. Não foram verificadas diferenças estatísticas entre os componentes químicos da fração ácido fúlvico nos solos estudados.

The thermal regime of soils in the north of Western Siberia

AbstractThe results of long‐term stationary observations upon the thermal regime of soils in natural and anthropogenically‐disturbed tundra and northern taiga landscapes in the north of Western Siberia are discussed. Quantitative assessments of the heating effect of snow cover and the cooling effect of surface organic layer on soil temperatures in both winter and summer seasons are given. Spatial and temporal variations in the depth of seasonal thaw and soil temperatures in the tundra and taiga zones are outlined. Data on changes in soil temperature regimes following disturbance of surface organic layers are presented. Contemporary tendencies in permafrost degradation induced by climatic warming, changes in the snow cover depth, and anthropogenic impacts are shown. Copyright © 2002 John Wiley & Sons, Ltd.

Implications of floristic and environmental variation for carbon cycle dynamics in boreal forest ecosystems of central Canada

Abstract. Species composition, detritus, and soil data from 97 boreal forest stands along a transect in central Canada were analysed using Correspondence Analysis to determine the dominant environmental/site variables that differentiate these forest stands. Picea mariana stands were densely clustered together on the understorey DCA plot, suggesting a consistent understorey species composition (feather mosses and Ericaceae), whereas Populus tremuloides stands had the most diverse understorey species composition (ca. 30 species, mostly shrubs and herbs). Pinus banksiana stands had several characteristic species of reindeer lichens (Cladina spp.), but saplings and Pinus seedlings were rare. Although climatic variables showed large variation along the transect, the CCA results indicated that site conditions are more important in determining species composition and differentiating the stand types. Forest floor characteristics (litter and humus layer, woody debris, and drainage) appear to be among the most important site variables. Stands of Picea had significantly higher average carbon (C) densities in the combined litter and humus layer (43530 kg‐C.ha‐1) than either Populus (25 500 kg‐C.ha‐1) or Pinus (19 400 kg‐C.ha‐1). The thick surface organic layer in lowland Picea stands plays an important role in regulating soil temperature and moisture, and organic‐matter decomposition, which in turn affect the ecosystem C‐dynamics. During forest succession after a stand‐replacing disturbance (e.g. fires), tree biomass and surface organic layer thickness increase in all stand types as forests recover; however, woody biomass detritus first decreases and then increases after ca. 80 yr. Soil C densities show slight decrease with ages in Populus stands, but increase in other stand types. These results indicate the complex C‐transfer processes among different components (tree biomass, detritus, forest floor, and soil) of boreal ecosystems at various stages of succession.

Fate of POPs (DDX, HCHs, PCBs) in upper soil layers of pine forests.

Organochlorines (HCH isomers, DDX and individual PCBs) were determined in pine needle litter and upper soil layers of three forest test areas in central Germany. The contents accumulating over a number of years or even decades in the organic surface layer are compared with the levels of new inputs from needle fall as well as with the levels of older inputs in the upper mineral soil layer. Differences in behaviour between the soil horizons are discussed, especially concerning the DDX and HCH groups. With approximately comparable Corg values (approx. 21-24%) the pH value in the range of 4.24-2.90 in the O-horizon of the forest soils exerts a large influence. Hence the A-horizon represents--for p,p'-DDT and gamma-HCH in particular--at pH values of 2.90 a pollutant reservoir which should not be underestimated and which could endanger the rhizosphere and the groundwater. According to PCBs, in the more acidic soils with a pH value <4.0 the lipophilic higher polychlorinated biphenyls were found to be more highly enriched in the humus layer.