Schematic of the experimental setup for single-step fabrication of monodispersed mixed nanoparticle layer based gas sensors consisting of four main sections: (a) setup for synthesis of monodispersed nanoparticles, (b) setup for synthesis of monodispersed Pd nanoparticles, (c) deposition setup (low pressure impactor or electrostatic precipitator), and (d) SMPS for online monitoring of the size and concentration of and Pd particles before deposition.
Dark field TEM micrograph of monodispersed Pd nanoparticles . The inset shows HRTEM micrograph of a typical Pd nanoparticle. The lattice fringes have interplanar spacing corresponding to (111) planes of fcc metallic Pd.
(a) TEM and (b) HRTEM micrographs of monodispersed nanoparticles. The FFT patterns from the (1) central and the (2) surrounding regions reveal presence of (c) orthorhombic and (d) tetragonal phases, respectively.
(a) DIL-24 chip carrier with the mixed nanoparticle layer sample SP5, (b) low magnification SEM image of the deposited spot ( diameter), (c) high magnification SEM image revealing the high porosity of the deposited layers, and (d) corresponding STEM image showing clearly the and Pd nanoparticles (Pd particles are pointed to by arrows).
Variation in the sensor signal as a function of temperature and CO concentration in dry air for nanoparticle sample (a) SP0 and mixed nanoparticle samples (b) SP5 and (c) SP15. (d) Comparison of the lowest detected CO concentrations (in dry synthetic air) reported in literature and the corresponding sensor signal. (e) Variation of sensor signal for sample SP5 as a function of exposure time in four cycles in 1 ppm of ethanol (dotted curve)/CO (solid curve) and synthetic air (air) at 623 K.
Normalized core level spectra of sample SP15, pretreated in (a) synthetic air and after exposure to (b) CO (100 ppm in synthetic air). The vertical solid lines correspond to the binding energy positions for metallic Pd and the dotted lines to that of PdO.
Normalized valence band spectra of sample SP15, pretreated in synthetic and after exposure to CO and ethanol (100 ppm in synthetic air). A distinct feature (indicated by a thick arrow) appears in the valence band spectra for the sample exposed to CO, indicating the reduction of tin oxide surface. The Fermi level is marked by the dotted arrow.
Proposed energy level diagram of in (a) synthetic air, (b) CO, and (c) ethanol. Since both PdO and are reduced in CO ambient, an increase in band bending and the space charge region occurs resulting in -type behavior. The band diagram when is not reduced (c), resulting in decrease in band bending and reduction in the space charge region , gives rise to -type behavior.
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