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  • 1
    Electronic Resource
    Electronic Resource
    Structure and function of the soil microbial community in microhabitats of a heavy metal polluted soil (2000)
    Springer
    Biology and fertility of soils 32 (2000), S. 390-400 
    Details
    ISSN: 1432-0789
    Keywords: Keywords Soil microbial biomass ; Soil enzymes ; Particle-size fractions ; Heavy metals ; Phospholipid fatty acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Particle-size fractionation of a heavy metal polluted soil was performed to study the influence of environmental pollution on microbial community structure, microbial biomass, microbial residues and enzyme activities in microhabitats of a Calcaric Phaeocem. In 1987, the soil was experimentally contaminated with four heavy metal loads: (1) uncontaminated controls; (2) light (300 ppm Zn, 100 ppm Cu, 50 ppm Ni, 50 ppm V and 3 ppm Cd); (3) medium; and (4) heavy pollution (two- and threefold the light load, respectively). After 10 years of exposure, the highest concentrations of microbial ninhydrin-reactive nitrogen were found in the clay (2–0.1 μm) and silt fractions (63–2 μm), and the lowest were found in the coarse sand fraction (2,000–250 μm). The phospholipid fatty acid analyses (PLFA) and denaturing gradient gel electrophoresis (DGGE) separation of 16S rRNA gene fragments revealed that the microbial biomass within the clay fraction was predominantly due to soil bacteria. In contrast, a high percentage of fungal-derived PLFA 18 : 2ω6 was found in the coarse sand fraction. Bacterial residues such as muramic acid accumulated in the finer fractions in relation to fungal residues. The fractions also differed with respect to substrate utilization: Urease was located mainly in the 〈2 μm fraction, alkaline phosphatase and arylsulfatase in the 2–63 μm fraction, and xylanase activity was equally distributed in all fractions. Heavy metal pollution significantly decreased the concentration of ninhydrin-reactive nitrogen of soil microorganisms in the silt and clay fraction and thus in the bulk soil. Soil enzyme activity was reduced significantly in all fractions subjected to heavy metal pollution in the order arylsulfatase 〉phosphatase 〉urease 〉xylanase. Heavy metal pollution did not markedly change the similarity pattern of the DGGE profiles and amino sugar concentrations. Therefore, microbial biomass and enzyme activities seem to be more sensitive than 16S rRNA gene fragments and microbial amino-sugar-N to heavy metal treatment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740000268
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  • 2
    Electronic Resource
    Electronic Resource
    Carbon mineralization and microbial activity in a field site trial used for 14C turnover experiments over a period of 30 years (2000)
    Springer
    Biology and fertility of soils 31 (2000), S. 294-302 
    Details
    ISSN: 1432-0789
    Keywords: Key words Carbon mineralization ; 14C ; Soil microbial biomass ; Manure amendment ; Long-term experiment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Long-term experiments on different crop management systems provide essential information about turnover of soil organic matter and changes in microbial properties over a period of time. A long-term field site trial, which was established in 1967 near Vienna, Austria, to document the fate of 14C-labelled manure (straw and farmyard) under different crop management systems (crop rotation, spring wheat and bare fallow), was investigated. Soil samples were taken in 1997 and separated into size fractions (〉250 μm, 250–63 μm, 63–2 μm, 2–0.1 μm and 〈0.1 μm) after aggregate dispersion using low-energy sonication. Organic C, total N and 14C content were measured in the bulk soil and the size fractions and microbial properties were analysed in the bulk soil. Additionally, C mineralization in bulk soil samples was monitored at 20 °C over a period of 28 days, and subsequently 14C-CO2 content was analysed. The distribution of organic C and N within the size fractions was similar between crop rotation and spring wheat; the highest amounts of organic C and N were found in the clay-sized fraction. The amounts of C and N were significantly smaller in the bare fallow, which was depleted of organic matter in the coarse-sized fractions. 14C distribution differed significantly from unlabelled C distribution, labelled C was accumulated in the silt-sized fraction, indicating weak humification of the applied manure C. The highest rate of C mineralization was measured in the crop rotation and spring wheat, whereas the emission rate of the bare fallow was about 40% lower. The higher 14C:C ratio of the bulk soil in comparison to the emitted CO2 indicated that labelled C compounds still remained mineralizable after a period of 30 years. Microbial properties showed a great difference between crop management systems and bare fallow, particularly regarding urease and xylanase activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050659
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  • 3
    Electronic Resource
    Electronic Resource
    Oxygen vacancy ordering in epitaxial La0.5Sr0.5CoO3−∂ thin films on (001) LaAlO3 (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3319-3324 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS), and electron diffraction were used to study the microstructure of epitaxial La0.5Sr0.5CoO3−∂ thin films grown on (001) oriented LaAlO3 substrates. Films were characterized before and after annealing treatments under different oxygen partial pressures. EELS shows that annealing reduces the valence state of cobalt due to loss of oxygen. HRTEM image simulations show that the superstructure contrast observed in HRTEM can be explained by shifts of cations in planes containing ordered oxygen vacancies. The as-deposited film showed weak, short-range ordering of oxygen vacancies within nanometer-sized domains. The annealed film showed long-range order and a strong anisotropy in ordering, with the oxygen-deficient planes aligned parallel to the film/substrate interface. We propose that the anisotropy in ordering is a mechanism of stress relief in these films. Implications of the observed microstructure on the oxygen transport and surface oxygen exchange properties are discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1401793
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  • 4
    Electronic Resource
    Electronic Resource
    Reactions of Y2O3 films with (001) Si substrates and with polycrystalline Si capping layers (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 712-714 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use electron energy-loss spectroscopy in scanning transmission electron microscopy to investigate interfacial reactions of chemical vapor deposited Y2O3 films with the Si substrate and with in situ polycrystalline Si ("poly-Si") capping layers after postdeposition annealing. We find that in situ capping layers significantly reduce the formation of SiO2 at the interface with the substrate, but silicates form at the substrate and the capping layer interfaces. Predeposition nitridation of the Si surface can impede the reaction at the substrate interface, resulting in crystallization of Y2O3 in the film interior. Possible mechanisms of the silicate formation are discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1496500
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  • 5
    Electronic Resource
    Electronic Resource
    Microstructure of epitaxial Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films grown by metalorganic chemical vapor deposition (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3526-3531 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial, perovskite Pb(Mg1/3Nb2/3)O3–PbTiO3 films were grown by metalorganic chemical vapor deposition under various deposition conditions and characterized by x-ray diffraction and transmission electron microscopy. Pyrochlore free films were obtained under all deposition conditions used in this study. Magnesium-rich growth conditions lead to the formation of a Mg-rich impurity phase in the films, embedded as coherent lamellae parallel to the growth direction. Depending on the growth conditions, a wide variation in the stoichiometry and volume fraction of this impurity phase was found between samples, whereas morphology and crystal structure were found to be very similar. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372376
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  • 6
    Electronic Resource
    Electronic Resource
    Subwavelength-sized aperture fabrication in aluminum by a self-terminated corrosion process in the evanescent field (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 3397-3399 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a simple, one-step process to fabricate apertures of high quality for scanning near-field optical microscope probes based on aluminum-coated silicon-nitride cantilevers. An evanescent optical field at the glass–water interface is used to heat up the aluminum at the tip apex due to light absorption. The heat induces breakdown of the passivating oxide layer and corrosion of the metal. Apertures with a protruding silicon-nitride tip of up to 30 nm height and minimal diameter of 38 nm are fabricated. The diameter is predefined by the lateral dimension of the silicon-nitride tip while the tip height is controlled by the penetration depth of the evanescent field. The corrosion process proves to be self-terminating, yielding highly reproducible tip heights. Near-field optical resolution in the transmission mode of 85 nm is demonstrated. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1476059
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  • 7
    Electronic Resource
    Electronic Resource
    Oxidation states of titanium in bulk barium titanates and in (100) fiber-textured (BaxSr1−x)Ti1+yO3+z thin films (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 3149-3151 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Chemical shifts of titanium L edges and oxygen K edges in electron energy-loss spectroscopy in transmission electron microscopy were used to detect valence state reduction of Ti in bulk barium titanates, used as reference materials, and in (BaxSr1−x)Ti1+yO3+z (BST) thin films grown with excess Ti. A hollandite-type Ba titanate, containing Ti with an average valence state of approximately 3.7 in octahedral coordination, showed large chemical shifts relative to rutile TiO2 and BaTiO3, containing only Ti4+. In BST, chemical shifts relative to BaTiO3 were measured from grain interiors of columnar films with different amounts of excess Ti. We found that shifts, corresponding to an average valence state of Ti smaller than nominal 4+, increase with increasing amounts of excess Ti in the films. The results show that at least some amount of excess Ti is accommodated in these films by a defect mechanism that requires a reduction of the average valence state of Ti. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1418036
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  • 8
    Electronic Resource
    Electronic Resource
    Structure and stability of La2O3/SiO2 layers on Si(001) (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 102-104 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS) were used to investigate La2O3/SiO2/Si structures. The La2O3 layers were deposited on thermal SiO2 on silicon, followed by rapid thermal annealing treatments at 600 °C and 800 °C in a nitrogen ambient. After annealing at 600 °C, the oxide layers were amorphous. After an 800 °C treatment, crystallites appeared in the original La2O3 layer, and the total oxide layer thickness increased by 17%, most likely due to the oxygen diffusion and reaction at the Si/SiO2 interface. EELS, using a 0.2 nm probe, showed that rapid thermal annealing at 600 °C did not cause significant La diffusion into the SiO2 layer, whereas some intermixing was observed at 800 °C. We use the observed microstructures to estimate equivalent oxide thicknesses. The results demonstrate that oxygen partial pressures and initial SiO2 thickness need to be carefully controlled to control SiO2 formation at the Si interface and to achieve target equivalent oxide thickness. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1383268
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  • 9
    Electronic Resource
    Electronic Resource
    Investigation of the cleaved surface of a p–i–n laser using Kelvin probe force microscopy and two-dimensional physical simulations (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2907-2909 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the cross-sectional electric field and potential distribution of a cleaved n+-InP/InGaAsP/p+-InP p–i–n laser diode using Kelvin probe force microscopy (KFM) with a lateral resolution reaching 50 nm. The powerful characterization capabilities of KFM were compared with two-dimensional (2D) physics-based simulations. The agreement between simulations and KFM measurements regarding the main features of the electric field and potential is very good. However, the KFM yields a voltage drop between n- and p-doped InP regions which is 0.4 times the one simulated. This discrepancy is explained in terms of surface traps due to the exposure of the sample to the air and in terms of incomplete ionization. This hypothesis is confirmed by the 2D simulations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126513
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  • 10
    Electronic Resource
    Electronic Resource
    Photoinduced oxide film formation on n-type GaN surfaces using alkaline solutions (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3923-3925 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on photoassisted wet chemical formation of thin oxide films on n-GaN layers in potassium hydroxide based electrolytes at room temperature. The kinetics of the oxide formation and dissolution were examined via photocurrent transients. The tendency of the photocurrent to level out during photoelectrochemical etching experiments is associated with a quasiequilibrium state at the semiconductor/electrolyte interface. Homogeneous oxide films were grown in weak alkaline solutions (11〈pH〈13) under potentionstatic control with oxidation rates of up to 250 nm/h and characterized by Auger electron spectroscopy. Consequences on wet photochemical etch strategies are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126822
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