Vacuum-evaporated PbS:0.03 Zn thin films with varying thicknesses for environmental applications

Abstract

In this research, we explore how the thickness of PbS-doped Zn thin films made through thermal vacuum evaporation affects their physical properties for environmental applications. Our x-ray diffraction (XRD) examination shows that the films consist of pure crystalline cubic PbS phase. Additionally, the energy-dispersive X-ray spectroscope (EDXS) provides confirmation that the synthesized products are of high purity. PbS films doped with Zn have spherical nanocrystals ranging from 130 nm to 250 nm in size, as observed through field emission (FE)-scanning electron microscopy (FE-SEM) analysis. The thickness of the film layer was found to correlate significantly with an increase in crystallite size and grain size, as validated by both XRD and FE-SEM analyses. The optical energy gap (Eg) of the thin films under examination exhibited variations in relation to their respective thickness. Bandgap energy was found to decrease from 1.66 eV to 1.2 eV as film thickness was increased from 50 nm to 250 nm. The Arrhenius law shows that films with varying thicknesses have thermally activated electrical conductivity and exhibit two conduction mechanisms. After analyzing the photocatalytic decomposition of methylene blue, it was observed that a thicker (PbS)0.97(Zn)0.03 film with a larger grain size demonstrated superior photocatalytic efficiency (92 % after an exposure duration of 180 min). This is due to a smaller band gap and the presence of defect sites, which enhance catalytic reactions. The study presents a framework for researching the controllable structure, thickness, and composition of chalcogenide semiconductor thin films for environmental applications.