A microstructural zone model for the morphology of sol-gel coatings

The thickness and the morphology of dip-coated single sol-gel layers is easily controlled by varying the sol compositions and the deposition parameters. A thorough study of the microstructure of transparent conducting ZnO: Al coatings deposited on fused silica substrates using X-ray diffraction, X-ray reflectometry and transmission electron microscopy cross-sections as well as of In2O3: Sn, SnO2: Sb, ZnO and TiO2 coatings reported in the literature shows that three basic morphologies can be observed: granular, layered and columnar. In multilayer systems they were found to depend essentially on the single layer thickness (SLT) and on the crystallite size determined from the data of thick films, a parameter called the "intrinsic crystallite size (ICS)". All the results so far analysed are in agreement with a 3-zone model when ICS is plotted against SLT or in a more refined version when q = ICS/SLT is plotted against the homologous temperature T-sintering/T-melting. Comparison with the Movchan-Demchishin and Polley-Carter models proposed for PVD and CVD coatings, respectively, is presented

Atomic scale modeling of the thermodynamic and kinetic properties of dilute alloys driven by forced atomic relocations

Sustained external forces acting on a material provide additional mechanisms to evolve the state of the system, and these mechanisms do not necessarily obey the microscopic detailed balance. Therefore, standard methods to compute the thermodynamic and kinetic properties do not apply in such driven systems. The competition between these mechanisms and the standard thermally activated jumps leads to non-equilibrium steady states. We extend the Self-Consistent Mean Field theory to take into account forced atomic relocations (FARs) as a model of these additional kinetic mechanisms. The theory is applied to the atomic-scale modelling of radiation damage. Using a first-shell approximation of the theory, we highlight the violation of Onsager reciprocal relations in driven systems. An implementation of the extended theory into the KineCluE code yields calculations of the effective Onsager coefficients in agreement with Monte Carlo simulations. A systematic parametric study is performed to emphasize the effect of FAR distances and the solute-defect interaction on the diffusion properties. The effect of FAR on the vacancy-solute flux coupling and the solute tracer diffusivity is non-negligible when: (i) the solute-vacancy thermodynamic attraction is large, (ii) the magnitude of the thermal jump frequencies is lower or comparable to the frequencies of FAR, and (iii) the range of interactions between vacancies and solute atoms is close to FAR distances.Comment: typos corrected, references added, revised arguments in Introduction and Modeling section

Controlled generation of a pn-junction in a waveguide integrated graphene photodetector

With its electrically tunable light absorption and ultrafast photoresponse, graphene is a promising candidate for high-speed chip-integrated photonics. The generation mechanisms of photosignals in graphene photodetectors have been studied extensively in the past years. However, the knowledge about efficient light conversion at graphene pn-junctions has not yet been translated into high-performance devices. Here, we present a graphene photodetector integrated on a silicon slot-waveguide, acting as a dual-gate to create a pn-junction in the optical absorption region of the device. While at zero bias the photo-thermoelectric effect is the dominant conversion process, an additional photoconductive contribution is identified in a biased configuration. Extrinsic responsivities of 35 mA/W, or 3.5 V/W, at zero bias and 76 mA/W at 300 mV bias voltage are achieved. The device exhibits a 3 dB-bandwidth of 65 GHz, which is the highest value reported for a graphene-based photodetector.Comment: 19 pages, 16 figure

The impact of commercial horticulture on river water resources in the Upper Ewaso Ng'iro River Basin, Kenya

Mount Kenya serves as a natural water tower in the savanna-dominated Upper Ewaso Ng'iro River Basin in the Kenyan highlands. Major water users in the upper reaches of the river include medium- and large-scale commercial horticulture farms that produce flowers and vegetables for export using perennial irrigation schemes. These farms first appeared in the region in 1991 and gradually became powerful stakeholders that compete with small-scale farmers and urban centers over seasonally scarce water, increasing the potential for conflict. A comprehensive survey of commercial horticulture farms in the study area, including expert interviews with managers, enabled detailed analysis of the sector's development and its impact on local river water resources. Calculation of the horticulture sector's dry season water use revealed an increase from zero liters per second (L/s) in 1991 to 357 L/s in 2003 and 663 L/s in 2013, far exceeding minimum river flows. Despite this absolute increase in total water use, reliance on river water has decreased by roughly 30% since 2003, with a dramatic absolute increase in the use of alternative sources such as water stored in dams and groundwater. At the same time, the share of river water used varies greatly between specific rivers (2.2–32.5%), depending on the local availability of alternative water sources. Overall, to mitigate water conflicts, long-term monitoring and local stakeholder engagement must accompany practices and policies of efficiency

Influence of the layer morphology on the electrical properties of sol-gel transparent conducting oxide coatings

Tranparent conducting coatings have been prepared by sol gel methods either by a conventional sol-gel process (Antimony doped Tin Oxide - ATO, Aluminium doped Zinc Oxide - AZO) or a new wet chemical process using fully dispersed crystalline nanoparticles (ATO, Indium Tin Oxide - ITO). The dip coating technique has been used as deposition technique with single coating thickness varying from a few nanometer to ca. 400 nm. The layers have been fired in a furnace. Structural properties have been determined by x-ray diffraction and TEM analysis and the electrical properties by the van der Pauw/Hall measurement. Three different coating procedures have been used to investigate the effect on the structure, morphology and the electrical properties of the coatings. It is shown that the individual layer thickness in multilayer coatings influences dramatically the mentioned properties. Very thin individual layers favour a heterogeneous nucleation with dense columnar growth of the crystallites leading to low electrical resistivity (Ω ≈ 10 -³ Ω cm), while thick individual layers result in a porous morphology made of small crystallites leading to resistivities in the 10≈2 Ω cm range

Le regard d’un Alsacien sur l’élaboration de la paix

Devant la Conférence de la Paix qui s’ouvre à Paris en janvier 1919, la délégation française dévoile ses revendications : elle souhaite principalement le retour de l’Alsace-Lorraine. Ses demandes portent également sur le sort de la Rhénanie. Les représentants français espèrent voir la rive gauche du Rhin former un État indépendant de l’Allemagne, mais placé sous l’influence politique et militaire de la France afin que ce territoire constitue une zone tampon entre le Reich et l’Europe occidentale. Quelques semaines avant le début des négociations de paix, le prêtre alsacien Émile Wetterlé fonde à Colmar un journal catholique et patriotique intitulé Le Rhin français. Son objectif est d’apporter un soutien visible aux diplomates français et de convaincre ses lecteurs de la nécessité que représente selon lui cette « question rhénane » pour la paix en Europe. Toutefois, les alliés de la France rejettent cette revendication et le traité de Versailles signé le 28 juin 1919 ne prévoit qu’une occupation militaire temporaire de la Rhénanie. Il s’agit à travers cet article d’étudier le point de vue d’une personnalité alsacienne sur cette éphémère question du « Rhin français ».Während der Pariser Friedenskonferenz, die im Januar 1919 eröffnet wurde, verlangte die französische Regierung die Rückgabe von Elsass-Lothringen und die Gründung eines Pufferstaat auf dem linken Rheinufer unter dem Einfluss Frankreichs, um Deutschland zu dämpfen. Bei diesen diplomatischen Verhandlungen in Paris, gründete der elsässische Pfarrer Emil Wetterlé in Colmar die katholische und patriotische Tageszeitung Le Rhin français (Der französische Rhein), dessen Ziel die Forderungen im Rheinland zu rechtfertigen war. Allerdings waren diese Projekte allmählich aufgegeben worden und der Versailler Vertrag vom 28. Juni 1919 sah jedoch erst die vorläufige Rheinlandbesetzung vor. Es handelt sich in diesem Fachartikel um eine Analyse der Meinung eines Elsässer über die nationalistische Rheinfrage, die keine Zukunft hatte.At the Paris Peace Conference which opened in January 1919, the French delegation claimed the restitution of Alsace-Lorraine and hoped for the creation of a Rhenish buffer state under France’s influence in order to weaken Germany. During the diplomatic talks, the Alsatian priest Émile Wetterlé founded in Colmar a patriotic and Roman Catholic newspaper which was called Le Rhin français (The French Rhine). The aim of this daily paper was to convince their readership about the necessity of the French nationalist claims on the left bank of the Rhine. However, these plans were dismissed and the Treaty of Versailles of 28 June 1919 provided only temporary occupation of the Rhineland by Allied Powers. The purpose of this study is to explore the standpoint of an Alsatian personality on the short-lived Rhine question