Gas sensing properties of nanostructured MoO3 thin films prepared by spray pyrolysis

Abstract Thin films of molybdenum trioxide (MoO 3 ) were deposited on common glass using the chemical spray pyrolysis technique. A (NH 4 ) 6 Mo 7 O 24 4H 2 0 solution 0.1 M was used as the precursor one. The influence of substrate temperature on the crystallographic structure, surface morphology and electrical behavior of MoO 3 thin films was studied. MoO 3 can exist in two crystalline forms, the thermodynamically stable orthorhombic α-MoO 3 and the metastable monoclinic β-MoO 3 phase. XRD-spectra showed a growth of α-MoO 3 phase percentage as substrate temperature increases from 420 K up to 670 K. Films deposited in the 500–600 K range have a clearly porous surface structure of nanometer order as can be seen in SEM images. Changes up to six magnitude orders were observed in MoO 3 thin films electrical resistance when films temperature varied from 100 K up to 500 K. The sensing property of these MoO 3 films was also studied. The sensitivity was investigated in the temperature range 160 and 360 K for H 2 O and CO gases, respectively. Both of them are of reducing nature. In all studied cases sensitivity decreases slowly as film temperature is raised. At room temperature the sensitivity changes from 12 up to 75% depending on substrate temperature. The sensitivity for CO gas was found to be lower than that of H 2 O.