Tuning the properties of manganese-doped zinc oxide nanostructured thin films deposited by SILAR approach

Abstract

Thin films of manganese-doped zinc oxide (Mn-ZnO) were fabricated using the successive ionic layer adsorption reaction (SILAR) technique. The deposition process involved four steps in a SILAR setup, utilizing zinc (II) acetate (0.20 ​M) and manganese (II) chloride (0.05 ​M) as zinc and manganese ion precursors, respectively. To provide a source of oxygen, the NaOH solution was heated to 60 ​°C on a hot plate. Three samples were grown with SILAR cycle counts of 5, 15, and 25 cycles. The optical, structural, morphological, and compositional properties of the resulting films were characterized. Using the gravimetric method, the thickness of the films increased from 57.96 ​nm to 177.63 ​nm as the number of SILAR cycles increased while the growth rate was found to decrease from 11.50 nm/cycle to 7.10 nm/cycle. Optical analysis revealed that the absorbance increased, whereas the transmittance decreased with an increasing number of SILAR cycles. The absorbance values of the films range from 1.72 ​% to 42.10 ​% while transmittance values ranged from 38.39 ​% to 96.12 ​%. The band gap of the films decreased from 2.75 ​eV to 3.35 ​eV as the SILAR cycle count increased from 5 to 25 cycles. Structural examination indicated that the deposited manganese-doped zinc oxide films possessed a polycrystalline nature with a hexagonal crystal phase and average grain sizes ranging from 25.35 to 32.67 ​nm. The micrographs of the films exhibited agglomerated particles, which grew in size as the number of SILAR cycles increased. Energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of zinc (Zn), manganese (Mn), and oxygen in the films; their proportions increased as the SILAR cycle count increased.