Fraunhofer Institute For Silicatforschung

Würzburg, Germany

Fraunhofer Institute For Silicatforschung

Würzburg, Germany
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Lobmann P.,Fraunhofer Institute For Silicatforschung
Journal of Sol-Gel Science and Technology | Year: 2017

Abstract: As an extension of spectral ellipsometry, ellipsometric porosimetry has gained considerable importance for the characterization of porous thin films. The in-situ measurement of sorption facilitates the evaluation of open porosity, pore radius distribution, film backbone refractive index and even elastic properties. Multilayer assemblies and gradients within films can be characterized. These features are especially interesting for sol–gel derived thin films that are commonly composed of aggregated nanoparticles and thus may retain significant porosity after thermal treatment. In this paper the general features of Ellipsometric Porosimetry are highlighted and related to the characterization of selected sol–gel films. The examples range from simple assessments of porosity and pore radius distribution, film backbone analysis to the characterization of multilayer assemblies and systematic changes induced by thermal treatment or leaching phenomena. Graphical abstract: Besides optical properties Ellipsometric Porosimetry can reveal structural features such as open porosity and pore radius distribution of sol-gel derived thin films. [InlineMediaObject not available: see fulltext.] © 2017 Springer Science+Business Media, LLC


Lobmann P.,Fraunhofer Institute For Silicatforschung
Journal of Sol-Gel Science and Technology | Year: 2017

Abstract: Commercial antireflective coatings prepared by sol–gel processing are compared to MgF2 λ/4 thin films. Their respective optical performance is measured by UV-Vis spectroscopy. Microstructural features as characterized by Scanning Electron Microscopy are correlated to results determined by Ellipsometric Porosimetry. A modified Crockmeter testing procedure employing steel wool as abrasive was used to examine mechanical film stability. Results indicate that MgF2 films can well compete with other porous λ/4 systems, as well as with dense interference multilayer assemblies targeting at superior optical and mechanical properties. Graphical Abstract: The performance of commercially available sol–gel antireflective coatings are compared with porous MgF2 film system. Results indicate that they exhibit superior properties compared to their SiO2 counterparts under investigation. [InlineMediaObject not available: see fulltext.] © 2017 Springer Science+Business Media New York


Dieterle L.,Karlsruhe Institute of Technology | Bockstaller P.,Karlsruhe Institute of Technology | Gerthsen D.,Karlsruhe Institute of Technology | Hayd J.,Karlsruhe Institute of Technology | And 2 more authors.
Advanced Energy Materials | Year: 2011

Nanocrystalline La 1-x Sr x CoO 3-δ (LSC) thin films with a nominal Sr-content of x= 0.4 were deposited on Ce 09Gd 0.1O 1.95 electrolyte substrates using a low temperature sol-gel process. The structural and chemical properties of the LSC thin films were studied after thermal treatment, which included a calcination step and a variable, extended annealing time at 700°C or 800°C. Transmission electron microscopy combined with selected-area electron diffraction, energy-dispersive X-ray spectrometry, and scanning transmission electron microscopy tomography was applied for the investigation of grain size, porosity, microstructure, and analysis of the local chemical composition and element distribution on the nanoscale. The area specific resistance (ASR) values of the thin film LSC cathodes, which include the lowest ASR value reported so far (ASR chem = 0.023 Ωcm 2 at 600°C) can be interpreted on the basis of the structural and chemical characterization. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA.


Bose H.,Fraunhofer Institute For Silicatforschung | Uhl D.,Fraunhofer Institute For Silicatforschung
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

Beside the characteristics of the elastomer material itself, the performance of dielectric elastomers in actuator, sensor as well as generator applications depends also on the properties of the electrode material. Various electrode materials based on metallic particles dispersed in a silicone matrix were manufactured and investigated. Anisotropic particles such as silver-coated copper flakes and silver-coated glass flakes were used for the preparation of the electrodes. The concentration of the metallic particles and the thickness of the electrode layers were varied. Specific conductivities derived from resistance measurements reached about 100 S/cm and surmount those of the reference materials based on graphite and carbon black by up to three orders of magnitude. The high conductivities of the new electrode materials can be maintained even at very large stretch deformations up to 200 %. © 2013 SPIE.


Glaubitt W.,Fraunhofer Institute For Silicatforschung | Lobmann P.,Fraunhofer Institute For Silicatforschung
Journal of Sol-Gel Science and Technology | Year: 2011

Thin films being composed of a nanoporous SiO2 network and silica nanoparticles were prepared on glass substrates by sol-gel processing. The surfaces combine anti-reflective (AR) and anti-soiling properties as demonstrated in laboratory testing and long term outdoor exposure. Films were characterized by scanning electron microscopy (SEM). It is shown that both, the structure of the nanoporous matrix as well as the particle density, contribute to this effect, the influence of relative humidity (RH) during dust exposure was investigated. Due to their generally improved solar transmittance and dust-repellant properties the coatings are believed to have a vast potential for many photovoltaic and solar thermal applications. © 2011 Springer Science+Business Media, LLC.


Jahn R.,Fraunhofer Institute For Silicatforschung | Lobmann P.,Fraunhofer Institute For Silicatforschung
Journal of Sol-Gel Science and Technology | Year: 2013

Al-doped zinc oxide (AZO) films were prepared by a wet-chemical coating technique, their microstructure and crystal growth were characterized as a function of the single layer thickness. When similar final thicknesses are attained by more multiple subsequent coating-firing cycles, film porosity is reduced from over 14 to 2 %. Simultaneously the AZO crystallite size is increased from approximately 23 to 60 nm, a preferential c-axis oriented growth is observed. Different substrates (soda-lime glass, soda-lime glass with a SiO2 barrier coating, borosilicate glass and alkali-free display glass) were used and the resulting AZO films were compared. It is found that the substrate composition primarily affects grain growth and subsequently the electrical performance of the AZO films. © 2013 Springer Science+Business Media New York.


Bose H.,Fraunhofer Institute For Silicatforschung | Fuss E.,Fraunhofer Institute For Silicatforschung
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Beside their application in actuation and energy harvesting, dielectric elastomers (DE) have also strong capabilities for stretch-sensing based on capacitive measurements. However, for compression detection the simple state-of-the-art DE films are too insensitive. In order to close this gap, a novel class of DE sensors for compression measurements has been developed. The new sensor mats consist of two flexible elastomer profiles, between which an elastomer film is squeezed, converting the compression to a stretch load. With this mechanism, very high sensitivities of the capacitive measurement under compression load are achieved. Furthermore, various parameters which influence the characteristics of the sensor mat have been identified. Most relevant are the shape of the profiles, the number and design of the electrode layers as well as the hardness of the profiles and of the elastomer film. The high variability of the sensor mat design offers farreaching possibilities to tune the characteristics of the compressions sensor in terms of the dependence of capacitance on the load force. The basic principles of the design of the new compression sensor mats are outlined and various examples of such flexible sensors are introduced in this paper. © 2014 SPIE.


Gotzendorfer S.,Fraunhofer Institute For Silicatforschung | Lobmann P.,Fraunhofer Institute For Silicatforschung
Journal of Sol-Gel Science and Technology | Year: 2011

Transparent conductive thin films of copper chromium oxide were processed on borosilicate glass by sol-gel technique. The resistivity of the films was decreased by lowering the single layer thickness of multi-layer stacks deposited by dip-coating, as well as by doping with magnesium. The additional effort of increasing the number of coating cycles from four to fifteen and sintering after each coating resulted in denser films with increased crystallite size. But whereas conductivity was improved by this procedure, the transmittance of the thin films simultaneously dropped by more than 10%. The optimum values obtained for an Mg-doped sample were ρ = 0.38Ω cm at T = 26.8%. © 2010 Springer Science+Business Media, LLC.


Bywalez R.,Fraunhofer Institute For Silicatforschung | Gotzendorfer S.,Fraunhofer Institute For Silicatforschung | Gotzendorfer S.,University of Würzburg | Lobmann P.,Fraunhofer Institute For Silicatforschung
Journal of Materials Chemistry | Year: 2010

Magnesium doped thin films of CuCrO2 and CuAl 0.5Cr0.5O2, both exhibiting delafossite structure, were synthesized via sol-gel processing. The influence of the dopant on the phase development during the subsequent 2-step annealing procedure was monitored by X-ray diffraction. Systematic variation of the dopant concentration between 2.5 and 15% revealed that the Mg inhibits crystallization and stabilizes spinel phases against thermal decomposition, whereby the amount of impurities in the delafossite films is increased. Nevertheless the p-type conductivity and surprisingly the transmittance of the CuCrO2 films were improved by Mg doping by two orders of magnitude and 16%, respectively. On the contrary the performance of the CuAl0.5Cr0.5O 2 films hardly profits from Mg doping. The Seebeck-coefficients of this system even imply a decreasing charge carrier density with increasing dopant concentration, which can only be interpreted as an expulsion of the native defects acting as strong intrinsic doping. The band gap of both oxides remains constant, however. © 2010 The Royal Society of Chemistry.


Glaubitt W.,Fraunhofer Institute For Silicatforschung | Lobmann P.,Fraunhofer Institute For Silicatforschung
Journal of the European Ceramic Society | Year: 2012

Sol-gel processing is a powerful tool to prepare antireflective (AR) coatings on optical surfaces. In this paper the different strategies to obtain antireflective properties are reviewed: porous λ/4 layers, multilayer interference-type films and index-gradient materials such as "moth eye" structures. The processing of the respective films is described and evaluated; references to respective commercial products on glass substrates are given. AR coatings may have a particularly high importance for transparent ceramics as their index of refraction is significantly higher than that of common glass types. Reflective losses therefore are higher which is especially unpleasant for materials with a yet improvable intrinsic transparency. Recent studies indicate that specific porous λ/4 layers may exhibit pronounced anti-soiling features. Laboratory experiments as well as outdoor exposure tests were used to demonstrate the dust-repellant properties. © 2012 Elsevier Ltd.

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