To relate surface properties and surface elemental composition - Application of XPS in soil science

Soil particles always are coated by thin layers (nm to µm) of predominantly organic compounds that form the interface between particle and pore space and govern soil functioning (e.g. liquid transport, sorption, respiration). Chemical modification of the surface layer can change surface properties such as wettability (quantified in terms of contact angle CA) with implications for e.g. liquid distribution and sorption capacity. This points to the importance to specifically analyze the coating's chemical composition in order to better understand soil functioning. The shallow analysis depth (max. 10 nm) indicates X ray photoelectron spectroscopy (XPS) as a suitable tool. Here, all elements with Z ≥ 3 will be identified by the binding energy of the photoelectrons emitted after irradiation of the surface by X rays. In sensu stricto only applicable to flat and smooth surfaces our results so far prove applicability of XPS as well to rough surfaces such as soil particles. For XPS no sample pre-treatment is needed, i.e. the surfaces analyzed are those governing e.g. CA and sorption. The relation between surface elemental composition and CA could be demonstrated within a soil chronosequence where the changes of surface element contents due to an increasing coating of the particles by organic compounds and microorganisms were correlated to increasing CA. The surface O/C ratio could be identified as a general parameter linking surface chemical composition and CA for a wide range of different materials including hydrophobized glass slides while the amount of non-polar C species was indicated to define CA. Artificially induced modifications of surface properties became visible by changes in the surface elemental composition. Gentle crushing of soil microaggregates (SMA) resulted in slightly increased N contents hinting on a preferred location of N compounds within SMA. Exposition to HCl gas to decrease soil pH or cleaning of quartz sand by HCl treatment resulted in addition of Cl and removal of Fe, respectively. However, due to its high surface sensitivity XPS measures the presence of C species on all surfaces exposed to the environment (adventitious carbon AC). AC was found to complicate the verification of sorption of small amounts of organic acids to montmorillonite, pointing on the necessity to estimate the influence of AC in certain cases. On the other hand, detection of AC indicates AC as a factor to be considered when discussing surface properties

Structures and properties of bioorgano-clays

Interactions between microbial matter and clays are a common interfacial phenomenon in soil and sediment environments. However, fundamental mechanisms governing the formation and interactions of clay minerals with microbial-derived organic substances are still poorly understood. Therefore, our central aim was to study the formation of bioorgano-clay composites and their specific material properties and compare these properties with those of well-studied organo-clays. Pure organic cations (e.g., alkylammonium homologues) and complex microbial biomass (e.g., fungal biomass from Aphanocladium sp.) were used to prepare organo- and bioorgano-clays by varying the amount of clay (montmorillonite) and organic materials used. Interaction mechanisms between organic materials and clay and the resulting structure and physicochemical properties were explored by multiple experimental methods (e.g. IR spectroscopy, contact angle, zeta potential, X-ray photoelectron spectroscopy, transmission electron microscopy) in a combination with molecular modelling to determine the structure, composition, and properties of the prepared bioorgano-clays. Depending on origin, type, and size of the organic material and the clay, two basic types of bioorgano-clays were found: (i) bioorgano-clays having their clay particles coated by bioorganic matter with only limited or no penetration into interlayer galleries and (ii) bioorgano-clays having bioorganic matter distributed in the interlayer galleries and/or on the external surfaces of clay particles. Both types show heterogeneous arrangements of the amended organic matter inducing differences in shape and size of organo-clay particles. Consequently, changes in pore volumes, stability, and elemental interface properties can be verified. Compared to organo-clays, bioorgano-clays provided e.g. a higher adsorption capacity for uranyl, suggesting that modification of clays by rather unspecific microbial compounds significantly enhanced the number of exchange sites. Bioorganic-clays, although being less specific in nature, might therefore be applied more broadly in situations where a high sorption capacity, e.g., for contaminants, is required

Extended methodology for determining wetting properties of porous media

[1] Because most methods for assessing the wettability of porous materials are restricted in their applicability, we developed two new methods for measuring contact angles and particle surface energy. The proposed methods (the Wilhelmy plate method (WPM) and the modified capillary rise method (MCRM)) were tested on 24 soils. For comparison, the water drop penetration time test (WDPTT) and the sessile drop method (SDM) were also applied. It was found that advancing contact angles, measured either with WPM or MCRM, agreed well in the range of 0° to 142°. Sessile drop contact angles were within the domain enclosed by the range of advancing and receding contact angles as determined with WPM. WDPTT, however, was only sensitive in the narrow range of 85° to 115°. We conclude that both WPM and MCRM are reliable methods for determining contact angles and particle surface energy over a wide range of porous material wettabilities

Einfluss von atmosphärischer Deposition auf das räumliche Muster von Benetzungshemmungen in Ober- und Unterböden eines grundwasserfernen Buchenwaldbestands

Der verstärkte Stofftransport mit dem Stammabfluss begünstigt die Versauerung des Bodens in unmittelbarer Nähe zu Bäumen. Veränderungen chemischer Bodenparameter wie pH-Wert oder C/N Verhältnis können dabei einen Einfluss auf die Benetzbarkeit des Bodens haben. Das Ziel dieser Studie war zu untersuchen, ob sich der Stammabstand auf die Benetzbarkeit (gemessen als Kontaktwinkel, KW) und die chemischen Parameter von Ober- und Unterböden entlang zweier Transekte (Länge ca. 50 m, Probenahmetiefe 0.1-0.2 m) auswirkt. Die Untersuchungsfläche ist ein 100 Jahre alter Buchenbestand (Fagus sylvatica L.), Bodentyp ist eine gut drainierte podsolierte Braunerde. Die Transekte hatten einen mittleren Abstand von etwa 50 m zueinander, Probenahmezeitpunkte waren Juli 2013 und Juli 2015, beprobt wurde im Abstand von 1 m. Drei kürzere Transekte (Länge 3 m) wurden zusätzlich im Juni 2013 deutlich tiefer beprobt (6 Tiefen zwischen 0.1-2 m). Die Datenauswertung mit statistischen Standardverfahren ergab keine signifikante Beziehung zwischen Stammabstand und Benetzbarkeit oder chemischen Parametern. Spektralanalytische Analysen zeigten jedoch, dass der Stammabstand bei beiden Transekten oberflächennah einen starken Einfluss sowohl auf chemische Parameter (oxalatlösliches Al, pH) als auch auf den KW in Form einer periodischen Schwingung hat (2013: mittlerer KW=40°±12°; 2015: mittlerer KW=110°±14°). Bei den kürzeren (und tiefer beprobten) 3 m-Transekten war der KW direkt am Baum i.d.R < 90°, und zeigte keine deutliche Abhängigkeit zum Stammabstand mehr. Daraus lässt sich schließen, dass der Stammabfluss nur relativ oberflächennah einen Einfluss auf die Benetzbarkeit hat. Analysen der chemischen Oberflächenstruktur der Bodenpartikel mittels Röntgenphotoelektronenspektroskopie (XPS) zeigten dabei einen klaren Zusammenhang zwischen chemischer Veränderung der Partikeloberflächen und Benetzbarkeit, etwa durch Korrelation von elementarem O/C-Verhältnis und KW (r2=0.78), dem Anteil nicht-polarer Kohlenstoffspezies und KW (r2=0.77). Ebenso gab es einen Zusammenhang zwischen Alo-Gehalt und KW (r2=0.87). Für das C/N-Verhältnis und sulfat- oder oxalatlösliches Fe gab es keine entsprechenden Zusammenhänge. Die Ergebnisse weisen auf einen engen Zusammenhang zwischen chemischen und zentralen physikalischen Parametern wie Benetzungshemmung hin und haben damit einen Einfluss auf physikalische Standorteigenschaftenwie die Wasserspeicherleistung von Waldböden

The GREGOR Fabry-P\'erot Interferometer

The GREGOR Fabry-P\'erot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large-format, high-cadence CCD detectors with sophisticated computer hard- and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field-of-view (FOV) of 50" x 38" is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25" x 38". The spectral coverage in the spectroscopic mode extends from 530-860 nm with a theoretical spectral resolution R of about 250,000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580-660 nm. The combination of fast narrow-band imaging and post-factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to about 50 km on the solar surface.Comment: 14 pages, 17 figures, 4 tables; pre-print of AN 333, p.880-893, 2012 (AN special issue to GREGOR

A retrospective of the GREGOR solar telescope in scientific literature

In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the "historical" context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes.Comment: 6 pages, 2 color figures, this is the pre-peer reviewed version of Denker et al. 2012, Astron. Nachr. 333, 81

ELT-HIRES, the high resolution spectrograph for the ELT: results from the Phase A study

We present the results from the phase A study of ELT-HIRES, an optical-infrared High Resolution Spectrograph for ELT, which has just been completed by a consortium of 30 institutes from 12 countries forming a team of about 200 scientists and engineers. The top science cases of ELT-HIRES will be the detection of life signatures from exoplanet atmospheres, tests on the stability of Nature's fundamental couplings, the direct detection of the cosmic acceleration. However, the science requirements of these science cases enable many other groundbreaking science cases. The baseline design, which allows to fulfil the top science cases, consists in a modular fiber- fed cross-dispersed echelle spectrograph with two ultra-stable spectral arms providing a simultaneous spectral range of 0.4-1.8 μm at a spectral resolution of 100,000. The fiber-feeding allows ELT-HIRES to have several, interchangeable observing modes including a SCAO module and a small diffraction-limited IFU