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Taylor A.,University of Oregon | Mortensen C.,University of Oregon | Rostek R.,Fraunhofer Institute For Physikalische Messtechnik | Nguyen N.,University of Oregon | Johnson D.C.,University of Oregon
Journal of Electronic Materials | Year: 2010

This article demonstrates that carrier concentrations in bismuth telluride films can be controlled through annealing in controlled vapor pressures of tellurium. For the bismuth telluride source with a small excess of tellurium, all the films reached a steady state carrier concentration of 4 × 10 19 carriers/cm 3 with Seebeck coefficients of -170 μV K -1. For temperatures below 300°C and for film thicknesses of 0.4 μm or less, the rate-limiting step in reaching a steady state for the carrier concentration appeared to be the mass transport of tellurium through the gas phase. At higher temperatures, with the resulting higher pressures of tellurium or for thicker films, it was expected that mass transport through the solid would become rate limiting. The mobility also changed with annealing, but at a rate different from that of the carrier concentration, perhaps as a consequence of the non-equilibrium concentration of defects trapped in the films studied by the low temperature synthesis approach. © 2009 TMS.


Heideman C.L.,University of Oregon | Rostek R.,Fraunhofer Institute For Physikalische Messtechnik | Anderson M.D.,University of Oregon | Anderson M.D.,U.S. National Institute of Standards and Technology | And 3 more authors.
Journal of Electronic Materials | Year: 2010

An ultralow-thermal-conductivity compound with the ideal formula [(PbSe) 1.00] 1[MoSe 2] 1 has been successfully crystallized across a range of compositions. The lattice parameters varied from 1.246 nm to 1.275 nm, and the quality of the observed 00ℓ diffraction patterns varied through the composition region where the structure crystallized. Measured resistivity values ranged over an order of magnitude, from 0.03 Ω m to 0.65 Ω m, and Seebeck coefficients ranged from -181 μV K -1 to 91 μV K -1 in the samples after the initial annealing to form the basic structure. Annealing of samples under a controlled atmosphere of selenium resulted in low conductivities and large negative Seebeck coefficients, suggesting an n-doped semiconductor. Scanning transmission electron microscopy cross-sections confirmed the interleaving of bilayers of PbSe with Se-Mo-Se trilayers. High-angle annular dark-field images revealed an interesting volume defect, where PbSe grew through a region where a layer of MoSe 2 would be expected in the perfect structure. Further studies are required to correlate the density of these defects with the observed electrical properties. © 2010 TMS.


Degreif K.,Fraunhofer Institute For Physikalische Messtechnik | Pierre R.,VDEh Betriebsforschungsinstitut GmbH | Boh M.,Lech Stahlwerke GmbH | Falkenreck U.,SMS Siemag AG
Stahl und Eisen | Year: 2010

Within the research project "Stromboli", the increase of the energetic efficiency of steelmaking in the electric arc furnace using a targeted injection of post-combustion oxygen was studied. For this purpose, a prototype of a temporal high-resolution extractive gas analysis system was developed, that allowed tracking the highly varying process conditions in the furnace off-gas. Based on these investigations and with the help of a dynamic mass and energy balance model, an optimized furnace operation was derived which, in the investigated case, led to a sustainable reduction of the electrical energy consumption of about 4%.


Panzner M.J.,Fraunhofer Institute for Material and Beam Technology | Klotzbach U.,Fraunhofer Institute for Material and Beam Technology | Beyer E.,Fraunhofer Institute for Material and Beam Technology | Torosyan G.,Fraunhofer Institute For Physikalische Messtechnik | And 2 more authors.
Lasers in the Conservation of Artworks VIII - Proceedings of the International Conference on Lasers in the Conservation of Artworks VIII, LACONA VIII | Year: 2011

The analysis of artwork offers many examples, where the dream to look behind covers could reveal valuable results. We are currently engaged in experimental work using the THz-Time-Domain (TD) technology as a new tool that could realize this dream, because THz radiation can pass through many materials without substantial attenuation. Utilizing very short pulses in the THz-TDS (THz-Time-Domain Spectroscopy) allows tomographic investigations using runtime measurements. Simultaneously, they deliver a broad spectrum of electromagnetic waves with frequencies up to 5 THz for spectroscopic investigations. However, many experiments have yet to be carried out in order to establish this method for reliable artwork investigations in the future. Some of them are presented in this report. The visualization of hidden wall paintings requires some knowledge about the physical fundamentals, for example the scattering behavior of the granular structure of the wall material. Moreover, we looked for answers on questions concerning the detection of paint pigments by means of THz-TDS using the reflection mode setup. © 2011 Taylor & Francis Group, London.


Lambrecht A.,Fraunhofer Institute For Physikalische Messtechnik | Pfeifer M.,Fraunhofer Institute For Physikalische Messtechnik | Konz W.,Fraunhofer Institute For Physikalische Messtechnik | Herbst J.,Fraunhofer Institute For Physikalische Messtechnik | Axtmann F.,Fraunhofer Institute For Physikalische Messtechnik
Analyst | Year: 2014

Laser spectroscopy is a powerful tool for analyzing small molecules, i.e. in the gas phase. In the mid-infrared spectral region quantum cascade lasers (QCLs) have been established as the most frequently used laser radiation source. Spectroscopy of larger molecules in the gas phase, of complex mixtures, and analysis in the liquid phase requires a broader tuning range and is thus still the domain of Fourier transform infrared (FTIR) spectroscopy. However, the development of tunable external cavity (EC) QCLs is starting to change this situation. The main advantage of QCLs is their high spectral emission power that is enhanced by a factor of 104 compared with thermal light sources. Obviously, transmission measurements with EC-QCLs in strongly absorbing samples are feasible, which can hardly be measured by FTIR due to detector noise limitations. We show that the high power of EC-QCLs facilitates spectroscopy beyond simple absorption measurements. Starting from QCL experiments with liquid samples, we show results of fiber evanescent field analysis (FEFA) to detect pesticides in drinking water. FEFA is a special case of attenuated total reflection spectroscopy. Furthermore, powerful CW EC-QCLs enable fast vibrational circular dichroism (VCD) spectroscopy of chiral molecules in the liquid phase-a technique which is very time consuming with standard FTIR equipment. We present results obtained for the chiral compound 1,1′-bi-2-naphthol (BINOL). Finally, powerful CW EC-QCLs enable the application of laser photothermal emission spectroscopy (LPTES). We demonstrate this for a narrowband and broadband absorber in the gas phase. All three techniques have great potential for MIR process analytical applications. This journal is © the Partner Organisations 2014.


Salvador J.R.,General Motors | Cho J.Y.,Optimal Inc. | Ye Z.,Optimal Inc. | Moczygemba J.E.,Marlow Industries Inc. | And 9 more authors.
Journal of Electronic Materials | Year: 2013

The performance of thermoelectric (TE) materials has improved tremendously over the past decade. The intrinsic thermal and electrical properties of state-of-the-art TE materials demonstrate that the potential for widespread practical TE applications is very large and includes TE generators (TEGs) for automotive waste heat recovery. TE materials for automotive TEG applications must have good intrinsic performance, be thermomechanically compatible and be chemically stable in the 400 K to 850 K temperature range. Both n-type and p-type varieties must be available at low cost, easily fabricated and durable. They must also form robust junctions and develop good interfaces with other materials to permit efficient flows of electrical and thermal energy. Among the TE materials of interest for automotive waste heat recovery systems are the skutterudite compounds, which are the antimony-based transition-metal compounds RTE4Sb12, where R can be an alkali metal (e.g., Na, K), alkaline earth (e.g., Ba), or rare earth (e.g., La, Ce, Yb) and TE can be a transition metal (e.g., Co, Fe). We synthesized a considerable quantity of n-type and p-type skutterudites, fabricated TE modules, incorporated these modules into a prototype TEG and tested the TEG on a production General Motors (GM) vehicle. We discuss our progress on skutterudite TE module fabrication and present module performance data for electrical power output under simulated operating conditions for automotive waste heat recovery systems. We also present preliminary durability results on our skutterudite modules. © 2012 TMS.


PubMed | Fraunhofer Institute For Physikalische Messtechnik
Type: Journal Article | Journal: The Analyst | Year: 2014

Laser spectroscopy is a powerful tool for analyzing small molecules, i.e. in the gas phase. In the mid-infrared spectral region quantum cascade lasers (QCLs) have been established as the most frequently used laser radiation source. Spectroscopy of larger molecules in the gas phase, of complex mixtures, and analysis in the liquid phase requires a broader tuning range and is thus still the domain of Fourier transform infrared (FTIR) spectroscopy. However, the development of tunable external cavity (EC) QCLs is starting to change this situation. The main advantage of QCLs is their high spectral emission power that is enhanced by a factor of 10(4) compared with thermal light sources. Obviously, transmission measurements with EC-QCLs in strongly absorbing samples are feasible, which can hardly be measured by FTIR due to detector noise limitations. We show that the high power of EC-QCLs facilitates spectroscopy beyond simple absorption measurements. Starting from QCL experiments with liquid samples, we show results of fiber evanescent field analysis (FEFA) to detect pesticides in drinking water. FEFA is a special case of attenuated total reflection spectroscopy. Furthermore, powerful CW EC-QCLs enable fast vibrational circular dichroism (VCD) spectroscopy of chiral molecules in the liquid phase - a technique which is very time consuming with standard FTIR equipment. We present results obtained for the chiral compound 1,1-bi-2-naphthol (BINOL). Finally, powerful CW EC-QCLs enable the application of laser photothermal emission spectroscopy (LPTES). We demonstrate this for a narrowband and broadband absorber in the gas phase. All three techniques have great potential for MIR process analytical applications.

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