The Effect of Deposition Cycles on the Morphological Properties of Bismuth Ferrite Nanostructured Thin Films ^†

Bismuth ferrite (BiFeO₃, abbreviated as BFO) has great potential for environmental applications. It performs well in the remediation of pollutants from the environment, for example as a toxic gas sensor or a photocatalyst for the degradation of dyes. Moreover, it presents a strong photovoltaic effect [1,2]. The topography and surface area of a material significantly affect its properties. Thus, it is of significance to study the surface characteristics of the material.

In this work, we prepared a set of pure BFO nanostructred films deposited on glass via the spin-coating-assisted sol–gel method, using bismuth nitrate pentahydrate (Bi(NO₃)₃·5H₂O) and iron nitrate nonahydrate (Fe(NO₃)₃·9H₂O) as starting materials and ethylene glycol as solvent, with a different number of deposition cycles in order to investigate its effect on morphological properties.

The atomic force microscopy AFM confirmed this effect, and showed that the root mean square (Rq) of the surface roughness increases after increasing the number of cycles (from 3 to 10 cycles) reaching a value of ≈6 nm. Based on AFM surface topography maps, we found that the median grain sizes also increase from ≈35 nm to ≈55 nm. However, both the dislocation density and the specific surface area (SSA) decrease.

This showed that the sample with a higher number of cycles exhibits the highest median grain size and surface roughness value, as well as the lowest dislocation density and specific surface area. These results are important in order to identify the optimum layer number needed for the formation of BFO thin films exhibiting an improved SSA, which plays a key role in gas sensing.