In recent years, nanocrystalline ZnS thin films have received much attention because of their very important role in the photovoltaic technology and optoelectronic devices. They are presently used as buffer layers in several types of thin film solar cells, such as Cu(In,Ga)Se2 (CIGS) and Cu(In,Ga)(SeS)2 (CIGSS) [1]. Chemical bath deposition is a suitable method for the deposition of some metal chalcogenide thin films [2, 3]. In this work nanocrystalline ZnS thin films, with thicknesses typically 10-100 nm, have been chemically deposited on glass and silicon substrates using an ammonia free reaction solution, where ethylenediamine acts as a complexing agent for zinc ions and thioacetamide acts as a source of sulphide ions. Film elemental composition, thickness and homogeneity have been examined using Rutherford backscattering. Compositional analysis indicates that the pH of deposition solution plays a critical role in ZnS thin film growth. Films deposited in the acidic solution (4
