Janosch Kneer
University of Freiburg
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Publication
Featured researches published by Janosch Kneer.
IEEE\/ASME Journal of Microelectromechanical Systems | 2015
Paul Walden; Janosch Kneer; Stefan Knobelspies; Wolfgang Kronast; Ulrich Mescheder; Stefan Palzer
This paper describes a novel micromachined platform serving as an interface between nanosized, gas sensitive metal oxide particles, and the macroscopic world. Through a combination of ink-jet printing and microelectromechanical systems technologies, it thus becomes possible to quickly test and characterize new nanosized metal oxide particles with respect to their gas sensitivity. Within the framework of this report, we describe the design considerations, thermal finite-element method simulations, processing, characterization, and utilization of the platform. Due to the low-power consumption, the hotplate provides an experimental platform to test nanoparticle-based metal oxide gas sensors for mobile systems.
Applied Physics Letters | 2014
Janosch Kneer; Jürgen Wöllenstein; Stefan Palzer
Here, we present results on the investigation of the percolation phase transition in copper(II)oxide (CuO) and show how it may be used to determine trace gas concentrations. This approach provides a highly selective sensing mechanism for the detection of hydrogen sulfide even in oxygen depleted atmospheres. In real-world applications, this scenario is encountered in biogas plants and natural gas facilities, where reliable H2S sensing and filtering are important because of the destructive effects H2S has on machinery. As opposed to gas detection via standard metal-oxide reaction routes, the percolation dynamics are demonstrated to be independent of the surface morphology in accordance with the universality of phase transitions. The sensing behavior of ink-jet printed CuO layers was tested for a large set of parameters including layer temperature, hydrogen sulfide (H2S) and oxygen concentration, as well as the sensitivity towards other gas species. The electrical percolation of the sensing layer is heralded...
Sensors | 2016
Alvaro Ortiz Perez; Vera Kallfaß-de Frenes; Alexander Filbert; Janosch Kneer; Benedikt Bierer; Pirmin Held; Philipp Klein; Jürgen Wöllenstein; Dirk Benyoucef; Sigrid Kallfaß; Ulrich Mescheder; Stefan Palzer
This manuscript describes the design considerations, implementation, and laboratory validation of an odor sensing module whose purpose is to support people that suffer from incontinence. Because of the requirements expressed by the affected end-users the odor sensing unit is realized as a portable accessory that may be connected to any pre-existing smart device. We have opted for a low-cost, low-power consuming metal oxide based gas detection approach to highlight the viability of developing an inexpensive yet helpful odor recognition technology. The system consists of a hotplate employing, inkjet-printed p-type semiconducting layers of copper(II) oxide, and chromium titanium oxide. Both functional layers are characterized with respect to their gas-sensitive behavior towards humidity, ammonia, methylmercaptan, and dimethylsulfide and we demonstrate detection limits in the parts-per-billion range for the two latter gases. Employing a temperature variation scheme that reads out the layer’s resistivity in a steady-state, we use each sensor chip as a virtual array. With this setup, we demonstrate the feasibility of detecting odors associated with incontinence.
Scientific Reports | 2016
Katja Henzler; Axel Heilemann; Janosch Kneer; Peter Guttmann; He Jia; E. Bartsch; Yan Lu; Stefan Palzer
In order to take full advantage of novel functional materials in the next generation of sensorial devices scalable processes for their fabrication and utilization are of great importance. Also understanding the processes lending the properties to those materials is essential. Among the most sought-after sensor applications are low-cost, highly sensitive and selective metal oxide based gas sensors. Yet, the surface reactions responsible for provoking a change in the electrical behavior of gas sensitive layers are insufficiently comprehended. Here, we have used near-edge x-ray absorption fine structure spectroscopy in combination with x-ray microscopy (NEXAFS-TXM) for ex-situ measurements, in order to reveal the hydrogen sulfide induced processes at the surface of copper oxide nanoparticles, which are ultimately responsible for triggering a percolation phase transition. For the first time these measurements allow the imaging of trace gas induced reactions and the effect they have on the chemical composition of the metal oxide surface and bulk. This makes the new technique suitable for elucidating adsorption processes in-situ and under real operating conditions.
Advances in Science and Technology | 2016
Stefan Palzer; Jürgen Wöllenstein; Janosch Kneer
This contribution revisits recent results regarding the selective detection of the trace gases hydrogen sulfide, nitrogen oxide, and nitrogen dioxide using cupric oxide (CuO). It demonstrates how the variation of the surface temperature may be used to learn about basic material parameters as well as control the surface reactions. In contrast to commonly employed modulation schemes that continuously vary the temperature we use a steady-state approach in order to extract information about gas matrices. Our results highlight the potential for incorporating laboratory results regarding surface processes in pattern recognition schemes to improve the performance of these algorithms. We propose to implement the findings into temperature modulation schemes in order to allow for adding highly gas specific elements to the algorithms deployed.
Journal of Materials Chemistry C | 2018
He Jia; Haitao Gao; Shilin Mei; Janosch Kneer; Xianzhong Lin; Qidi Ran; Fuxian Wang; Stefan Palzer; Yan Lu
There has been long-standing interest in developing metal oxide-based sensors with high sensitivity, selectivity, fast response and low material consumption. Here we report for the first time the utilization of Cu2O@PNIPAM core–shell microgels with a nanocube-shaped core structure for construction of novel CuO gas sensing layers. The hybrid microgels show significant improvement in colloidal stability as compared to native Cu2O nanocubes. Consequently, a homogeneous thin film of Cu2O@PNIPAM nanoparticles can be engineered in a quite low solid content (1.5 wt%) by inkjet printing of the dispersion at an optimized viscosity and surface tension. Most importantly, thermal treatment of the Cu2O@PNIPAM microgels forms porous CuO nanocubes, which show much faster response to relevant trace NO2 gases than sensors produced from bare Cu2O nanocubes. This outcome is due to the fact that the PNIPAM shell can successfully hinder the aggregation of CuO nanoparticles during pyrolysis, which enables full utilization of the sensor layers and better access of the gas to active sites. These results point out great potential of such an innovative system as gas sensors with low cost, fast response and high sensitivity.
Smart Sensors, Actuators, and MEMS VII; and Cyber Physical Systems | 2015
Benedikt Bierer; Janosch Kneer; Jürgen Wöllenstein; Stefan Palzer
Metal oxide based gas sensors are usually read-out by measuring the overall resistivity of the gas sensitive layer. However, the reaction of the gas species with the metal oxide surface does not only change the electrical conductivity but also effects the required heating power to maintain the layer’s temperature. This change in power consumption may be disregarded when using standard bulk sensor chips due to their overall high thermal mass. Nevertheless, micromachined Si based hotplate devices offer the possibility to measure these effects. Here we present results that have been obtained by using a novel hotplate platform optimized for low power consumption and inkjet printing of nano sized gas sensitive metal oxide particles. The temperature of the gas sensitive layer is controlled via the heater resistance and the power consumption is recorded with a fully automated gas measurement system. To separate changes in the heat conductivity of the gas matrix from the heat of the surface reaction, the measurements have been performed in parallel using hotplates with and without a metal oxide layer deposited onto them. Here layers composed of copper (II) oxide (CuO) have been used to highlight the possibilities of the novel approach. Determining both, the gas dependent resistivity as well as heating power yields two independent sensing quantities from one single device and might be an important cornerstone on the way towards selective metal oxide based gas sensors.
Sensors and Actuators B-chemical | 2016
Janosch Kneer; Stefan Knobelspies; Benedikt Bierer; Jürgen Wöllenstein; Stefan Palzer
Sensors and Actuators B-chemical | 2016
Janosch Kneer; Jürgen Wöllenstein; Stefan Palzer
Sensors and Actuators B-chemical | 2016
Stefan Knobelspies; Benedikt Bierer; Alvaro Ortiz Perez; Jürgen Wöllenstein; Janosch Kneer; Stefan Palzer