@article{SpiekermannHarderGilmoreetal.2019, author = {Spiekermann, Georg and Harder, M. and Gilmore, Keith and Zalden, Peter and Sahle, Christoph J. and Petitgirard, Sylvain and Wilke, Max and Biedermann, Nicole and Weis, Thomas and Morgenroth, Wolfgang and Tse, John S. and Kulik, E. and Nishiyama, Norimasa and Yava{\c{s}}, Hasan and Sternemann, Christian}, title = {Persistent Octahedral Coordination in Amorphous GeO₂ Up to 100 GPa by Kβ'' X-Ray Emission Spectroscopy}, series = {Physical Review X}, volume = {9}, journal = {Physical Review X}, number = {1}, publisher = {American Physical Society by the American Institute of Physics}, address = {Melville, NY}, issn = {2469-9926}, doi = {10.1103/PhysRevX.9.011025}, pages = {10}, year = {2019}, abstract = {We measure valence-to-core x-ray emission spectra of compressed crystalline GeO₂ up to 56 GPa and of amorphous GeO₂ up to 100 GPa. In a novel approach, we extract the Ge coordination number and mean Ge-O distances from the emission energy and the intensity of the Kβ'' emission line. The spectra of high-pressure polymorphs are calculated using the Bethe-Salpeter equation. Trends observed in the experimental and calculated spectra are found to match only when utilizing an octahedral model. The results reveal persistent octahedral Ge coordination with increasing distortion, similar to the compaction mechanism in the sequence of octahedrally coordinated crystalline GeO₂ high-pressure polymorphs.}, language = {en} } @article{SchallerPuppeKaczoreketal.2021, author = {Schaller, J{\"o}rg and Puppe, Daniel and Kaczorek, Danuta and Ellerbrock, Ruth and Sommer, Michael}, title = {Silicon cycling in soils revisited}, series = {Plants : open access journal}, volume = {10}, journal = {Plants : open access journal}, number = {2}, publisher = {MDPI}, address = {Basel}, issn = {2223-7747}, doi = {10.3390/plants10020295}, pages = {33}, year = {2021}, abstract = {Silicon (Si) speciation and availability in soils is highly important for ecosystem functioning, because Si is a beneficial element for plant growth. Si chemistry is highly complex compared to other elements in soils, because Si reaction rates are relatively slow and dependent on Si species. Consequently, we review the occurrence of different Si species in soil solution and their changes by polymerization, depolymerization, and condensation in relation to important soil processes. We show that an argumentation based on thermodynamic endmembers of Si dependent processes, as currently done, is often difficult, because some reactions such as mineral crystallization require months to years (sometimes even centuries or millennia). Furthermore, we give an overview of Si reactions in soil solution and the predominance of certain solid compounds, which is a neglected but important parameter controlling the availability, reactivity, and function of Si in soils. We further discuss the drivers of soil Si cycling and how humans interfere with these processes. The soil Si cycle is of major importance for ecosystem functioning; therefore, a deeper understanding of drivers of Si cycling (e.g., predominant speciation), human disturbances and the implication for important soil properties (water storage, nutrient availability, and micro aggregate stability) is of fundamental relevance.}, language = {en} } @article{NguyenMehargCareyetal.2019, author = {Nguyen, Minh N. and Meharg, Andy A. and Carey, Manus and Dultz, Stefan and Marone, Federica and Cichy, Sarah Bettina and Tran, Chinh T. and Le, Giang H. and Mai, Nga T. and Nguyen, Thinh T. H.}, title = {Fern, Dicranopteris linearis, derived phytoliths in soil}, series = {European journal of soil science}, volume = {70}, journal = {European journal of soil science}, number = {3}, publisher = {Wiley}, address = {Hoboken}, issn = {1351-0754}, doi = {10.1111/ejss.12754}, pages = {507 -- 517}, year = {2019}, abstract = {Ferns are among the most popular groups of plants in the tropics and subtropics, and their role as carbon sequestrators has been widely recognized. However, there is little understanding of the silicaceous structures (phytoliths) of ferns, rate of phytolith turnover, the consequences for organic matter sequestered in phytoliths and consequences for other soil properties. In the study reported here, high-resolution X-ray tomographic microscopy and chemical characterization were applied to examine the traits of phytoliths of the fern Dicranopteris linearis (Burm.f.) Underw. (D. linearis), with a focus on their dissolution properties and accumulation in northern Vietnamese soils in relation to soil properties. Tomographic images revealed an inter-embedding structure of silica and organic matter, especially in leaf-derived material. We propose that organic matter and silica can preserve each other against decomposition. In batch experiments, there was a relatively small rate of dissolution of phytoliths with dry ashing and subsequent H2O2 treatment. Silicon (Si) dissolution for D. linearis phytolith samples was much less than that for rice phytoliths. Despite the fact that the aluminum (Al) content was large in D. linearis leaves, batch dissolution data did not confirm a relation between Al and the slow rate of phytolith dissolution. The soil phytolith content varied from 0.9 to 7.5 g kg(-1) in the topsoil across the mountainous areas in northern Vietnam, whereas it tended to be smaller in the subsoil. The data indicate a relation between phytolith and soil organic matter, clay content, oxalate-soluble Al and electrical conductivity, suggesting that these soil properties are among the important factors affecting the size of the soil phytolith Si pool. Highlights}, language = {en} } @article{MalyarGorinStetsyuraetal.2012, author = {Malyar, I. V. and Gorin, D. A. and Stetsyura, S. V. and Santer, Svetlana}, title = {Effect of a nanodimensional polyethylenimine layer on current-voltage characteristics of hybrid structures based on single-crystal silicon}, series = {Journal of electronic materials}, volume = {41}, journal = {Journal of electronic materials}, number = {12}, publisher = {Springer}, address = {New York}, issn = {0361-5235}, doi = {10.1007/s11664-012-2266-4}, pages = {3427 -- 3435}, year = {2012}, abstract = {In this paper the study of the tunneling current-voltage (I-V) characteristics of silicon surfaces with n- and p-type conductivity as a function of roughness in the presence of an adsorbed insulating layer of polyethylenimine (PEI) is presented. A new approach is proposed for analysis of the tunnel current-voltage characteristics of a metal-insulator-semiconductor structure based on the combination of two models (Simmons and Schottky). Such joint analysis demonstrates the effect of surface states and evaluates changes in the band bending and electron affinity after the deposition of the polyelectrolyte layer on the semiconductor surface. As a result, we are able to differentiate between the equilibrium tunnel barrier (q phi (0)) and the barrier height (q phi (B)). It is shown that the deposition of the polymer leads to an increase of the equilibrium tunnel barrier by more than 250 meV, irrespective of the roughness and the conductivity type of the silicon substrate. The PEI deposition also leads to changes in the barrier height (less than 25 meV) that are smaller than the equilibrium tunnel barrier changes, indicating pinning of the Fermi level by the electron surface states that are energetically close to it. These surface states can trap charge carriers, a process leading to the formation of a depletion region and band bending on the semiconductor surface. Moreover, the change in the barrier height q Delta phi (B) depends on the conductivity type of the semiconductor, being positive for n-type and negative for p-type, in contrast to q Delta phi (0), which is positive for all substrates. The change is explained by capture of electrons preferably from the semiconductor space-charge region in the presence of a cationic polyelectrolyte, e.g., PEI.}, language = {en} }