Influence of surface oxygen vacancies on the LPG sensing response and the gas selectivity of Nd-doped SnO₂ nanoparticulate thin films

Nanostructured 0.1 to 6 wt% of Neodymium (Nd) doped SnO₂ thin films are deposited by nebulizer assisted spray pyrolysis process to investigate the gas sensing ability. X-ray diffraction analyses suggest that moderate addition of Nd facilitates the crystalline growth of films leading to lattice strain and substantial increase of the oxygen vacancies, to get modified the charge transport through the grains. The 3 wt% Nd doped films grow in (301), (200) and (110) preferred orientation, which is supported by Transmission Electron Micrograph. The Field Emission Scanning Micrographs reveal changes in film morphology comprising of differently sized agglomerated particles. The AFM images present the possibility of regulation of surface roughness via Nd doping. The 3 wt% Nd doped film shows maximum response of 99.8% in 500 ppm of LPG with remarkable response and recovery times of 5 s and 10 s respectively, at an operating temperature of 350 °C. The LPG response persists with a value of 63%, even at a reduced operating temperature of 250 °C. The Nd doped films also show acceptable selectivity in presence of Methane, CO₂, NO₂ and Ammonia, in the studied concentration. The Raman and Photoluminescence spectra show that the ratio of in-plane to bridging oxygen vacancies is highest for 3 wt% Nd doped sample, influencing the gas sensing action.