Nanoparticle SnO 2 films as gas sensitive membranes

The Karlsruhe Microwave Plasma Process (KMPP), a versatile gas-phase process is applied to produce SnO 2 and core shell SnO 2 /SiO 2 nanoparticles which are, respectively, deposited in-situ on preheated Si-Substrates. These substrates are already equipped with an electrode microarray. The proof of sensor concept shows, that mechanically stable, nanoscaled and nanogranular gas sensing layers can be produced. In a first step synthesis and deposition parameters of SnO 2 are elaborated, and gas-sensitivity tests are performed. Additionally, annealing experiments are done. The morphology and struc-ture of nanoparticles is characterized by X-ray diffraction and TEM-methods. The layers are in-vestigated by SEM techniques and by XPS. The sensitivity of the nanogranular layer is deter-mined in comparison with a standard microarray equipped with sputtered layers. Particles crys-tallize in the tetragonal cassiterite structure. It is found that a precursor concentration of 3×10 −6 mol/l leads to particles with crystallite size in the region of 2nm, whereas a concentration of 5.5×10 −4 mol/l results in approximately 5nm particles. With the precursor concentration, columnar porous layers of 200nm thickness are obtained after a deposition time of 1min. This thickness is comparable to the one of sputtered layers. First sensor tests show 10 times higher sensitivity to isopropanol, compared to the standard array. The time of response is equivalent. The grain growth observed for bare and core/shell nanoparticles at 300°C is marginal.