* Corresponding authors

^a Centre for Surface Chemistry and Catalysis, K. U. Leuven, Kasteelpark Arenberg 23, B-3001 Heverlee, Belgium
E-mail: christine.kirschhock@biw.kuleuven.be
Fax: +32 16 32 19 98
Tel: +32 16 32 15 79

^b Institute for Microelectronics and Microsensors, Johannes Kepler University Linz, Altenberger Strasse 69, A-4040 Linz, Austria
E-mail: bernhard.jakoby@jku.at
Fax: +43 732 2468 9316
Tel: +43 732 2468 9300

^c Institute of Sensor and Actuator Systems, Vienna University of Technology, Austria

^d Department of chemical engineering, K. U. Leuven, Belgium