Neu-Ulm, Germany
Neu-Ulm, Germany
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Tischer I.,University of Ulm | Tischer I.,Heubach GmbH | Hocker M.,University of Ulm | Neuschl B.,University of Ulm | And 25 more authors.
Journal of Materials Research | Year: 2015

Group III nitrides are promising materials for light emitting diodes (LEDs). The occurrence of structural defects strongly affects the efficiency of these LEDs. We investigate the optical properties of basal plane stacking faults (BFSs), and the assignment of specific spectral features to distinct defect types by direct correlation of localized emission bands measured by cathodoluminescence in a scanning electron microscope with defects found in high resolution (scanning) transmission electron microscopy and electron beam induced current at identical sample spots. Thus, we are able to model the electronic structure of BSFs addressing I1, I2, and E type BSFs in GaN and AlGaN with low Al content. We find hints that BSFs in semipolar AlGaN layers cause local changes of the Al content, which strongly affects the usability of AlGaN as an electron blocking layer in nitride based LEDs. Copyright © Materials Research Society 2015.

Hannes M.,Helmholtz Center for Environmental Research | Wollschlager U.,Helmholtz Center for Environmental Research | Schrader F.,TU Braunschweig | Schrader F.,Thunen Institute of Climate Smart Agriculture TI AK | And 6 more authors.
Hydrology and Earth System Sciences | Year: 2015

Large weighing lysimeters are currently the most precise method to directly measure all components of the terrestrial water balance in parallel via the built-in weighing system. As lysimeters are exposed to several external forces such as management practices or wind influencing the weighing data, the calculated fluxes of precipitation and evapotranspiration can be altered considerably without having applied appropriate corrections to the raw data. Therefore, adequate filtering schemes for obtaining most accurate estimates of the water balance components are required. In this study, we use data from the TERENO (TERrestrial ENvironmental Observatories) SoilCan research site in Bad Lauchstädt to develop a comprehensive filtering procedure for high-precision lysimeter data, which is designed to deal with various kinds of possible errors starting from the elimination of large disturbances in the raw data resulting e.g., from management practices all the way to the reduction of noise caused e.g., by moderate wind. Furthermore, we analyze the influence of averaging times and thresholds required by some of the filtering steps on the calculated water balance and investigate the ability of two adaptive filtering methods (the adaptive window and adaptive threshold filter (AWAT filter; Peters et al., 2014), and a new synchro filter applicable to the data from a set of several lysimeters) to further reduce the filtering error. Finally, we take advantage of the data sets of all 18 lysimeters running in parallel at the Bad Lauchstädt site to evaluate the performance and accuracy of the proposed filtering scheme. For the tested time interval of 2 months, we show that the estimation of the water balance with high temporal resolution and good accuracy is possible. The filtering code can be downloaded from the journal website as Supplement to this publication. © Author(s) 2015.

Agency: European Commission | Branch: FP7 | Program: MC-IAPP | Phase: FP7-PEOPLE-2012-IAPP | Award Amount: 1.85M | Year: 2013

The aim of the project is to develop novel systems to monitor earth structures exposed to climate hazard. Following completion of this research and concept demonstration project and subject to additional industry or commercial funding for the development of the technology, this effort is expected to eventually result in new commercial instruments and data management systems which it is in turn expected to lead to major improvement in design, maintenance, and adaptation of geotechnical infrastructure in a changing climate. The technological and scientific project will be implemented via secondments and recruitment of 182 researcher months in total including 72 months of recruitment and 110 months of secondment (51 months from Industry to Academia and 59 months from Academia to Industry). One of the major focus of the project will be the development and concept demonstration of two instruments for field measurement of pore-water tension (suction) up to 1.5 MPa, namely a high-capacity tensiometer for long-term measurement at shallow depths (<2m) and a tensiocone for rapid measurement of suction profile at great depths (up to 20m). Using proof-of-concepts prototypes developed by the academic partners in MAGIC, scientific and technological research will be carried out jointly by Industrial and Academic partners to use their respective scientific findings into a plan to assess the feasibility for the development of commercial instruments for pore-water tension measurement. MAGIC will also attempt to develop novel techniques for high-resolution imaging of water content based on Electrical Resistivity Tomography moving from proof-of-concepts prototypes already developed by academic partners. In addition, MAGIC will tackle the problem of real-time data control based on the concepts of measurement redundancy and coherence to identify faulty data due to instrument malfunctioning and/or mis-installation before these are transferred remotely. Finally, to validate and demonstrate monitoring systems, incorporating the new instruments developed by the project, MAGIC will build a unique facility consisting of a benchmark field site instrumented with a variety of sensors for monitoring the weather-related moisture regime.

Agency: European Commission | Branch: FP7 | Program: CP-FP | Phase: ENV.2007. | Award Amount: 4.23M | Year: 2008

This project is aimed at improving current methods for monitoring contaminant distribution and biodegradation in the subsurface. Currently proven methods (based on invasive sampling of soil, soil water and gaseous phase) are unable to provide sufficiently accurate data with high enough resolution. Resulting in inability to assess of bioremediation progress and quantification of the processes involved in such bioremediation at field sites. Consequently, present assessment strategies to decide on optimal remediation approach, including design of monitoring systems, and evaluation of degradation progress, are severely flawed by uncertainty. Geophysical time-lapse measurements in combination with novel ground truthing methods give the possibility to determine: absolute contamination levels, spatial spreading, and reduced concentrations of contaminants in a heterogeneous environment. Geophysical methods of data acquisition alone are presently unable to provide absolute levels of biodegradable contamination concentrations. We aim to make improvements of fundamental constitutive relations between soil physical and degradation activity parameters and geophysically measurable parameters. Despite current improvements, there is a strong need to test these theories in practical field situations. Our project is dedicated to improving both site contamination assessment and the monitoring of bioremediation processes, and changes in soil environmental conditions. We suggest combining improved conventional soil monitoring techniques with state-of-the-art geophysical approaches. Partners in the project range from microbiologists to geophysicist, all with working experience from contaminated sites. Process studies involving lysimeters, and testing of the combination of technologies at two field sites are the major aims of the project. Focus on practical field situations and strong communication with stake-holders and SMEs will ensure high relevance for society.

Schindler U.,Leibniz Center for Agricultural Landscape Research | Durner W.,TU Braunschweig | von Unold G.,UMS GmbH | Mueller L.,Leibniz Center for Agricultural Landscape Research | Wieland R.,Leibniz Center for Agricultural Landscape Research
Journal of Plant Nutrition and Soil Science | Year: 2010

Knowledge of hydraulic functions is required for various hydrological and plant-physiological studies. The evaporation method is frequently used for the simultaneous determination of hydraulic functions of unsaturated soil samples, i.e., the water-retention curve and hydraulic-conductivity function. All methodic variants of the evaporation method suffer from the limitation that the hydraulic functions can only be determined to a mean tension of ≈ 60 kPa. This is caused by the limited measurement range of the tensiometers of typically 80 kPa on the dry end. We present a new, cost- and time-saving approach which overcomes this restriction. Using the air-entry pressure of the tensiometer's porous ceramic cup as additional defined tension value allows the quantification of hydraulic functions up to close to the wilting point. The procedure is described, uncertainties are discussed, and measured as well as simulated test results are presented for soil samples of various origins, different textures (sand, loam, silt, clay, and peat) and variable dry bulk density. The experimental setup followed the system HYPROP which is a commercial device with vertically aligned tensiometers that is optimized to perform evaporation measurements. During the experiment leaked water from the tensiometer interior wets the surrounding soil of the tensiometer cup and can lead to a tension retardation as shown by simulation results. This effect is negligible when the tensiometers are embedded vertically. For coarsely textured soils and horizontal tensiometer alignment, however, the retardation must be considered for data evaluation. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Schindler U.,Leibniz Center for Agricultural Landscape Research | Durner W.,TU Braunschweig | Von Unold G.,UMS GmbH | Muller L.,Leibniz Center for Agricultural Landscape Research
Soil Science Society of America Journal | Year: 2010

The evaporation method is frequently used for simultaneous determination of soil water retention and hydraulic conductivity relationships. Tension is measured at two depths within a short soil column as water evaporates from its surface. Water content and flux are determined by weighing the column. Tensions, water contents, and fluxes are used to derive the water retention curve and the unsaturated hydraulic conductivity function. The measurement range of the conventional procedure is limited on the wet end by the inability of pressure transducers to accurately register very small tension differences. Hence, the resulting calculated hydraulic gradient in the vertical direction is associated with large uncertainties. On the dry end, water cavitation in the tensiometer, which typically occurs around 70 to 90 kPa, is the limitation. We present here a new design based on improved tensiometers that resist cavitation to much higher tensions, some reaching values as high as 435 kPa. On the wet end, data from a simple steady-state method were used to supplement the evaporation method. On the dry end, applying the new tensiometers enabled the quantification of hydraulic functions up to 293 kPa average tension. Experimental results and soil water simulation affirmed the validity of the linearization assumption, even on the dry end when nonlinear tension-depth profiles emerge. The application of evaporation functions as a supplement for frequent weighing reduces costs for the equipment and increases the effectiveness of the method. Their validity for deriving fluxes was confirmed for the extended range, too. Results are presented for soil samples of different textures (sand, loam, silt, clay, and peat), various origins, and various dry bulk densities. © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved.

Schrade-Kohn D.,University of Ulm | Leber P.,University of Ulm | Behtash R.,UMS GmbH | Blanck H.,UMS GmbH | Schumacher H.,University of Ulm
Semiconductor Science and Technology | Year: 2010

For GaN HEMTs the gate metallization is a critical element regarding leakage current, barrier height and reliability of the devices. Therefore, it is important to analyze the material properties and changes during thermal treatment. For GaN HEMTS Ni/Au and Ni/Pt/Au contacts are frequently used. Variations of different Ni, Ni/Pt, NiAu and Ni/Pt/Au layers on silicon nitride were tested under different rapid thermal annealing conditions. The metals were investigated using resistance measurements, secondary ion mass spectrometry and x-ray diffraction analysis. It was shown that Au diffusion takes place through the Ni and Ni/Pt layers already after 20 min at 400 °C. Appropriate modifications of the Ni/Pt stack processing resulted in a decreased Au diffusion to the silicon nitride. After annealing for 20 min at 400 °C the normalized resistance of the stabilized Ni/Pt stack was 30% lower than the one of the reference Ni/Pt stack. The formation of different Ni-Pt binary alloys was proven and controlled by adjusting layer thicknesses. The impact on normalized resistance was investigated for different ratios of Ni and Pt, variations in the thermal processing and the number of deposited layers per metal species. The effects are shown to be caused by self- and inter-diffusion processes. © 2010 IOP Publishing Ltd.

Schrade-Kohn D.,University of Ulm | Leber P.,University of Ulm | Behtash R.,UMS GmbH | Blanck H.,UMS GmbH | Schumacher H.,University of Ulm
2010 International Conference on Compound Semiconductor Manufacturing Technology, CS MANTECH 2010 | Year: 2010

Conventional i-line lithography was used as a basis for resist profile modification. The aim was the creation of slanted passivation openings for gate contacts with gate lengths between 0.1 and 0.5 μm. It was shown that slanted profiles are possible by applying a post development bake to the Novolac photoresist. Dimension reduction was achieved by modifying the Novolac/bottom-antireflection- coating interface. A modified approach combining plasma treatment of the photoresist lines with a bake sequence was used to create slanted features below 0.1 μm in the passivation layer.

Pedrotti M.,University of Strathclyde | Tarantino A.,University of Strathclyde | Boeck F.,UMS GmBH
Unsaturated Soils: Research and Applications - Proceedings of the 6th International Conference on Unsaturated Soils, UNSAT 2014 | Year: 2014

Measurement of negative pore-water pressure is of primary importance in the analysis and prediction of unsaturated soil behaviour. High-capacity tensiometers developed about 20 years ago have marked a turning point in experimental unsaturated soil mechanics. Nonetheless, the scientific community still hesitates to make use of these instruments. This may be due to the relatively complex experimental procedures required to prevent occurrence of cavitation during measurement. This paper presents some of the experiences gained during the commissioning of twelve new tensiometers manufactured at the University of Strathclyde. In particular, the discussion focuses on the response of the tensiometers following i) two simplified procedures for initial saturation, ii) different pre-pressurization patterns, and iii) application of cycles of ultrasonic-waves. © 2014 Taylor & Francis Group.

Floriot D.,UMS SAS | Brunel V.,UMS SAS | Camiade M.,UMS SAS | Chang C.,UMS SAS | And 8 more authors.
European Microwave Week 2014: "Connecting the Future", EuMW 2014 - Conference Proceedings; EuMIC 2014: 9th European Microwave Integrated Circuits Conference | Year: 2014

The performances and the results of the qualification plan of the new high power GaN HEMT process GH25-10 are summarized in this paper. This technology would be the first 14 gate length process qualified in Europe on 4' SiC substrate and will be fully open in foundry mode mid of 2014. It addresses applications up to 20 GHz with state of the art figure of merits in term of power density, gain, efficiency and reliability. The first part is dedicated to the description of the process and the associated spread data analysis. A second part is focused on the review of the performances, the electrical domain of validity (operating ratings) and modeling capabilities. This view is completed by some results of the qualification process. Finally, the last part will be focused on the product development based on the GH25-10 GaN technology. © 2014 European Microwave Association-EUMA.

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