• Chemical sensors science and technology, and

• Applications of chemical sensors.

In order to understand their interaction with the gases, two types of sensitive materials are investigated - semiconducting metal oxides (SMOX) and polymers. In both cases, all investigation techniques are used in sensor operation conditions (operando) meaning that the samples are fabricated in the same way in which the real sensors are (e.g. the SMOX are deposited as polycrystalline, thick, porous films onto substrates provided with electrodes and heaters) and are studied in real-life like conditions (heated between 200 and 400°C for the SMOX, at normal pressure, in the presence of humidity and of the target gases). Most of the operando experiments are performed in-house; for SMOX they include: DC resistance, AC impedance spectroscopy, work function changes (Kelvin probe), catalytic conversion, Hall Effect and Diffuse Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS) measurements. In cooperation with ETH Zuerich and Karlsruher Institut für Technologie (KIT), operando XAS studies are performed regularly at the European Synchrotron Radiation Facility (ESRF) at Grenoble. In the case of the polymers, the in-house operando techniques are: AC impedance spectroscopy, cyclic voltammetry, work function changes, mass changes by using quartz micro-balances (QMB) and transmission IR spectroscopy measurements.

On the side of technology, the group invented, developed and transferred to the industry - by spinning off a company, AppliedSensors GmbH - SMOX microsensor technology that combines thick film sensing layers with micro hotplates. To date, more than 6 million sensors were commercialized. The current development are focused on: a novel SMOX sensor fabrication technology - in cooperation with the University of Bremen - based on Flame Spray Pyrolysis (FSP) one step synthesis and layer deposition; and on integration of polymer and SMOX sensing layers onto flexible/plastic substrates - in cooperation with EPF Lausanne.

This type of activity capitalizes on the two strengths of our group: the analytical chemistry expertise and available analytical instrumentation and the deep understanding of the way in which chemical sensors work. The former allows us to first investigate the application and identify its boundary conditions: target gases, possible interferents, detection speed needs, etc. The latter makes it possible to select the most appropriate chemical sensors - if available, if not to develop them - combine those devices into arrays and, if necessary, with purging/enriching/separation elements. The collected data are used for establishing evaluation algorithms and the whole, hardware and software, are prototypes of Application Specific Chemical Sensor Systems (ASCSS) that can be transferred to the industry. There is already a very good track record in various fields: automotive, packaging, food quality, etc.

The R&D activities of the group are funded by a variety of third party projects financed by the European Commission, DFG, BMBF and directly by the industry.