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Synthesis of one-dimensional SnO2 lines by using electrohydrodynamic jet printing for a NO gas sensor

One-dimensional (1-D) SnO2 lines as a representative semiconducting oxide were formed by using electrohydrodynamic (EHD) jet-printing of a tin chloride pentahydrate and polyvinylpyrrolidone (PVP, 1,200k, Aldrich) solution ink. The 1-D polymer lines, including Sn precursors, were created by controlling the viscosity, that is, the polymer/tin precursor ratio, and by adjusting printing conditions such as the tip-to-substrate distance, the applied voltage, the flow rate of ink and its velocity. The printed lines were dried at 200 °C to get rid of solvent and were finally heat-treated at 600 °C to burn out PVP and form a tin oxide line. We found that the linearity and the shape of the aligned 1-D SnO2 could be controlled by adjusting various parameters such as the viscosity of the precursor solution, the ratio of Sn to the PVP polymer in the solution, the shape of the cone, the size of a droplet, the applied voltage, the working distance, and the flow rate on glass slides and Si wafers with a SiO2 layer. We found that the heat treatment for removal of the polymers should be tailored to produce continuous 1-D SnO2 lines due to the drastic volume reduction (> 90%) of the aligned fibers during the annealing process. The electrical and the NO-gas-sensing properties of the 1-D SnO2 aligned on Si wafers with Au electrode patterns were evaluated.