Thin organic layers prepared by MAPLE for gas sensor application

The Matrix Assisted Pulse Laser Evaporation (MAPLE) is a new progressive technology which has been found as a convenient method for thin organic (polymeric) film preparation. The goal of the work is to use prepared films for gas sensor application. The deposition was carried out by KrF excimer laser (wavelength 248 nm) in a chamber at working pressure of 3 Pa. Deposited materials (polypyrrole -PPY, Cu (II) para-tetramethylphenylporphyrine -CuTTMP, Indium acetyl-acetonate -InAcAc and Nickel phtalocyanine -NiPc) are embedded in frozen matrix (water, dimethylsulphoxide or chloroform) at the temperature of liquid nitrogen. The deposition can be described as photothermal process where the matrix molecules are preferentially evaporated due to their higher absorption coefficient on the laser wavelength. The molecules of deposited materials obtain sufficient kinetic energy through collective collisions with the vaporized matrix molecules, to be transferred into the gas phase. Small molecules of matrix are pumped away from the deposition chamber, while PPY, InAcAc, NiPc and CuTTMP molecules are incident on the sensor substrate, which is placed 35 mm far from the target. Thus thin organic layer is grown. Raman spectroscopy confirmed good similarity of chemical composition between source and deposited CuTTMP when using chloroform matrix. Prepared layers can be used as an element of safety gas detection systems as well as low-cost analytical tool for different gas concentration during industrial chemical production. Sensor responses to hydrogen, nitrogen dioxide and alcohol vapours in air were also measured. The obtained results of dc sensitivity (S -i.e. ratio of resistance in "pure" air and that in analysed gas mixture): S ~ 11 to 10,000 ppm of hydrogen, S ~1.5 to 1 ppm of nitrogen dioxide, S ~ 4 to 40 ppm of methanol, S ~ 5 to 20 ppm of ethanol and S ~ 6 to 2 ppm of propanol.