5 research outputs found
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In-depth analysis of elements and properties of hydrated subsurface layers on optical surfaces of a SiO2-BaO-B2O3 glass with SIMS, IBSCA, RBS and NRA Part 1. Experimental procedures and results
The formation of thin subsurface layers was studied which occurred during the chemical interaction of polished and cleaned optical surfaces with different slurries before and after covering them with λ/4-MgF2 coatings. By a suitable selection of the parameters for these chemical interactions a thickness of the subsurface layers was produced which allowed to meet the requirements of the various surface analysis methods. The thicknesses and the refractive indices of the subsurface layers could be calculated from the measured spectral reflectances. Slurries with a pH value < 9 were applied so that a leaching of glass components from the subsurface layers occurred. This was indicated by the refractive indices and was studied in detail by analyzing the in-depth distributions of the glass components. Distinct matrix effects could be disclosed from the in-depth profiles for SIMS and IBSCA by a comparison with the results of the quantitative analysis with RBS and NRA. These matrix effects were different within the subsurface layers from those observed for the bulk glass. The quantitative analysis of the hydrogen in-depth distributions by NRA allows for the first time to link differences in the matrix effects with a different hydrogen content within the subsurface layers
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Excimer laser processing of BK7 and BGG31 glasses
Large-area excimer laser processing of BK7 and BGG31 glasses was investigated for laser etching and laser-assisted metallization. Laser etching experiments were performed at wavelengths of 193, 248 and 308 nm and energy densities up to 5 J/cm^2 in various inert and reactive gases. The investigations revealed a good applicability of ArF excimer lasers for nondestructive laser etching of glass. The laser etching behavior is characterized by a characteristic threshold energy density of the order of 1 J/cm^2. Below this threshold laser etching is achieved only in reactive gases and is typically of the order of 0.1 nm/pulse. Above this specific threshold energy density the etch rate rapidly increases and is practically independent of the gas nature but depends more strongly on the gas pressure. In this ablation region the etch rate is of the order of 0.1 µm/pulse. A qualitative thermal model describing laser etching of glass in the ablation region is discussed. Laser-assisted metallization of glass surfaces has been achieved upon excimer laser irradiation of thin organometallic films on the glass surface and post-processing by electroless plating. Metallic nickel deposits showed a good adhesion and structures of a size between several 10 µm and a few millimeters were produce
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In-depth analysis of elements and properties of hydrated subsurface layers on optical surfaces of a SiO2-BaO-B2O3 glass with SIMS, IBSCA, RBS and NRA Part 2. Discussion of results
In the second part of this contribution it was derived from the comparison of the sputter yields with the specific energy losses within the bulk glass and within the various subsurface layers, that the differences in the matrix effects for SIMS and IBSCA between the bulk glass and the subsurface layers are caused by a decrease of the atomic densities and of the mean atomic bond energies within the subsurface layers as well. The knowledge of the matrix effects and their origin was most important for the interpretation of the SIMS and IBSCA in-depth profiles recorded for samples prepared with variations of the production parameters. E. g., various degrees of hydration and swelling could be distinguished by the influence of the different matrix effects on the in-depth profiles of the elements. The variations in the degrees of hydration of the subsurface layers could be ascribed to the influence of the thermal treatment before coating, to the interaction with slurries of different pH values and to the duration of storage before coating with λ/4-MgF2 layers. It is of importance for the fabrication of optical surfaces that the analysis results and the optical properties of the subsurface layers could be correlated with each other and with respective changes of the production parameters.
The results illustrate that the properties of hydrated subsurface layers depend sensitively on a great variety of parameters which may be difficult to keep constant during processing. It is recommended, therefore, that such subsurface layers should be avoided whenever possible in optical fabrication to make it easier to attain the high reproducibility required for the optical properties
Consortia of low-abundance bacteria drive sulfate reduction-dependent degradation of fermentation products in peat soil microcosms
Dissimilatory sulfate reduction in peatlands is sustained by a cryptic sulfur cycle and effectively competes with methanogenic degradation pathways. In a series of peat soil microcosms incubated over 50 days, we identified bacterial consortia that responded to small, periodic additions of individual fermentation products (formate, acetate, propionate, lactate or butyrate) in the presence or absence of sulfate. Under sulfate supplementation, net sulfate turnover (ST) steadily increased to 16–174 nmol cm(–3) per day and almost completely blocked methanogenesis. 16S rRNA gene and cDNA amplicon sequencing identified microorganisms whose increases in ribosome numbers strongly correlated to ST. Natively abundant (⩾0.1% estimated genome abundance) species-level operational taxonomic units (OTUs) showed no significant response to sulfate. In contrast, low-abundance OTUs responded significantly to sulfate in incubations with propionate, lactate and butyrate. These OTUs included members of recognized sulfate-reducing taxa (Desulfosporosinus, Desulfopila, Desulfomonile, Desulfovibrio) and also members of taxa that are either yet unknown sulfate reducers or metabolic interaction partners thereof. Most responsive OTUs markedly increased their ribosome content but only weakly increased in abundance. Responsive Desulfosporosinus OTUs even maintained a constantly low population size throughout 50 days, which suggests a novel strategy of rare biosphere members to display activity. Interestingly, two OTUs of the non-sulfate-reducing genus Telmatospirillum (Alphaproteobacteria) showed strongly contrasting preferences towards sulfate in butyrate-amended microcosms, corroborating that closely related microorganisms are not necessarily ecologically coherent. We show that diverse consortia of low-abundance microorganisms can perform peat soil sulfate reduction, a process that exerts control on methane production in these climate-relevant ecosystems