In situ kinetic studies of the chemical bath deposition of zinc sulfide from acidic solutions

Abstract

Adherent and uniform films of zinc sulfide have been deposited reproducibly by chemical bath deposition (CBD), onto low iron content microscope slides, under acidic conditions from solutions containing zinc(II) chloride, urea and thioacetamide. In situ measurements using a quartz crystal microbalance suggest that film growth occurs after a short induction period, via an initial rapid phase (deposition rate of 91 nm h⁻¹), followed by a slower process (growth rate of 52 nm h⁻¹). The ZnS films are predominantly of the hexagonal modification (wurtzite structure), as determined by X-ray powder diffraction. Scanning electron micrographs of the deposited layers, obtained on samples removed at regular intervals from the bath, suggest that as the reaction proceeds, uniform film growth is associated with increasing particle size, rather than continuous nucleation and deposition of new primary particles. EDAX spectra of the films are typical of thin CBD-deposited layers of ZnS; signals attributable to elements within the glass substrate are also detected. Grain size distributions have been investigated using computational image analysis, and an average grain growth rate of 33.7 nm h⁻¹ has been calculated.