@article{25941, abstract = {{Ordered mesoporous In2O3 particles of variable size synthesized by the nanocasting method are used for preparation of resistive gas-sensing layers. Light activation by a LED (blue light, 460 nm) permits room-temperature ozone sensing. Apart from differences in base-line resistance in sensing layers containing small (diameter approx. 170 nm) or large particles (approx. 870 nm), differences in the response amplitude and response time constant are also observed. Signal stabilization is achieved faster for small particles. In addition, sensors show a particle size-dependent reaction threshold for low ozone concentration. Larger particles show negligible response to 50 ppb ozone whereas a significant response is observed for the small-particle sensors. A simple model based on geometrical properties and formation of depletion layers explaining the observed behavior is presented.}}, author = {{Klaus, Dominik and Klawinski, Danielle and Amrehn, Sabrina and Tiemann, Michael and Wagner, Thorsten}}, issn = {{0925-4005}}, journal = {{Sensors and Actuators B: Chemical}}, pages = {{181--185}}, title = {{{Light-activated resistive ozone sensing at room temperature utilizing nanoporous In2O3 particles: Influence of particle size}}}, doi = {{10.1016/j.snb.2014.09.021}}, year = {{2015}}, } @article{25942, abstract = {{Cobalt oxide spinel (Co3O4) with an ordered nanostructure is used as a resistive gas sensor for carbon monoxide (CO) in low ppm concentrations. The operating temperature has a strong impact on the concentration-dependent sensing behavior. At lower temperature (473 K) the sensor response is governed mainly by surface coverage with CO and/or CO2, whereas at higher temperature (563 K) oxygen diffusion in the crystal lattice of Co3O4 strongly affects the sensing behavior.}}, author = {{Vetter, S. and Haffer, S. and Wagner, T. and Tiemann, Michael}}, issn = {{0925-4005}}, journal = {{Sensors and Actuators B: Chemical}}, pages = {{133--138}}, title = {{{Nanostructured Co3O4 as a CO gas sensor: Temperature-dependent behavior}}}, doi = {{10.1016/j.snb.2014.09.025}}, year = {{2015}}, } @article{25954, abstract = {{The light-enhanced NO2 sensing behavior of mesoporous In2O3 is measured and interpreted by means of a new sensing model. The model aims at explaining (i) the drop in electronic resistance of n-type semiconducting In2O3 under UV light exposure, (ii) the light-enhanced reaction to oxidizing gases, and (iii) the faster reaction and regeneration in mesoporous In2O3 as compared to non-porous material. Contrary to the conventional double Schottky model the dominating factor for the change in resistance is a change of oxygen vacancy donor states (0.18 eV below the conduction band) in the bulk phase due to photoreduction, instead of chemisorption. For the faster reaction and regeneration we propose an explanation based on enhanced oxygen diffusion in the In2O3 crystal lattice, specifically dominant in the mesoporous structure. The response of ordered mesoporous In2O3 to NO2 is stronger than in case of unstructured bulk material (with an average grain size of ca. 40 nm). The reaction is significantly accelerated by illuminating the samples with UV light. However, the response of the mesoporous material is weaker in the illuminated case.}}, author = {{Wagner, Thorsten and Kohl, Claus-Dieter and Malagù, Cesare and Donato, Nicola and Latino, Mariangela and Neri, Giovanni and Tiemann, Michael}}, issn = {{0925-4005}}, journal = {{Sensors and Actuators B: Chemical}}, pages = {{488--494}}, title = {{{UV light-enhanced NO2 sensing by mesoporous In2O3: Interpretation of results by a new sensing model}}}, doi = {{10.1016/j.snb.2013.02.025}}, year = {{2013}}, } @article{25963, abstract = {{We report the synthesis of mesoporous tin dioxide (SnO2) materials with well-defined particle morphology. The products consist of uniform spheres with a diameter of 5 μm. The spheres are hierarchically porous with two distinct pore modes of 5.0 nm and 52 nm, respectively. This special porosity is the result of a synthesis procedure which involves a ‘hard templating’ (nanocasting) process. The product forms an approximately homogeneous monolayer of spheres on a sensor substrate and shows promising response to methane gas with low cross-sensitivity to water. The structural properties and gas-sensing performance are compared with a mesoporous SnO2 material without defined morphology, prepared by a ‘soft templating’ procedure.}}, author = {{Smått, J.-H. and Lindén, M. and Wagner, T. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0925-4005}}, journal = {{Sensors and Actuators B: Chemical}}, pages = {{483--488}}, title = {{{Micrometer-sized nanoporous tin dioxide spheres for gas sensing}}}, doi = {{10.1016/j.snb.2010.12.051}}, year = {{2011}}, } @article{25967, abstract = {{We report the structural characterization and gas sensing properties of mesoporous SnO2 synthesized by structure replication (nanocasting) from ordered mesoporous KIT-6 silica. The products show a high thermal stability with no structural loss up to 600 °C and only minor decrease in specific surface area by 18% at 800 °C, as proven by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and nitrogen physisorption. In particular, the samples turn out to be much more stable than porous SnO2 materials prepared by sol–gel-based synthesis procedures for comparison. The thermal stability facilitates the utilization of the materials as sensors for combustible gases which react at high temperatures; test measurements reveal promising responses to methane (CH4) as an example.}}, author = {{Waitz, T. and Becker, B. and Wagner, T. and Sauerwald, T. and Kohl, C.-D. and Tiemann, Michael}}, issn = {{0925-4005}}, journal = {{Sensors and Actuators B: Chemical}}, pages = {{788--793}}, title = {{{Ordered nanoporous SnO2 gas sensors with high thermal stability}}}, doi = {{10.1016/j.snb.2010.08.001}}, year = {{2010}}, }