Study on the effect of the Fe doping on SnO2 nanoparticles prepared by spray pyrolysis technique for gas sensing applications

Abstract

Tin Oxide (SnO2) and Fe-doped SnO2 (SnO2:Fe) thin films have been synthesized by Spray Pyrolysis Technique (SPT) on plane glass substrates. SnO2 is doped with Fe in four different concentrations (2.0, 4.0, 6.0 and 8.0 wt.%). Tin (II) chloride dehydrate (SnCl2.2H2O) and iron (III) chloride (FeCl3.6H2O) are used as a host and dopant precursor. The Fe-doped SnO2 (SnO2: Fe) films have been deposited at a substrate temperature of 450oC. The surface morphology, structural, optical and electrical properties are characterized by FESEM, XRD, UV-vis spectroscopy and Four Point Probe Method. The results of Scanning Electron Microscopy (SEM) images of as-deposited films show uniform surface with comprised of dense nanoparticles. It is also observed that the surface morphologies of the films are strongly dependent upon the doping concentration. In the undoped SnO2 films, large polyhedron-like grains are distributed over small round grains. The polyhedron-like grains dwindled and are hardly distinguished from the small round grains, as the Fe-doping concentration increased further. From EDX data, the atomic weight percentage of tin (Sn) and oxygen (O2) in the SnO2 is found to be 66.25% and 33.75% respectively. It is observed that the SnO2 thin films are highly stoichiometric. The X-ray diffraction (XRD) analysis has revealed that the deposited films are polycrystalline nature with mixed faces of tetragonal rutile structure and the undoped SnO2 thin films have preferred (110), (200), (211) orientation, but as the Fe-doping concentration increased, only (110) orientation is observed. The crystallite size is found to decrease with increase in stacking fault density resulting from increasing Fe content in the SnO2 films. For pure SnO2 the crystallite size is found to be 47.33 nm and minimum crystallite size is found to be 23.40 nm for 8wt. % Fe doping concentration. The dislocation density is found to be 4.46× 10-4 line/nm2 for pure SnO2 and after Fe doping up to 8.0 wt. %, the dislocation density is increased to 18.26 × 10-4 line/nm2. The microstrains of the deposited films show the same nature of the dislocation density. The maximum value is found to be 0.837 for 8.0 wt. % of Fe.