Thin film fabrication of CdS quantum dots on GaAs substrate by surfactant self-assembly

In this study, cadmium sulfide (CdS) quantum dots (QDs) were synthesized using a microemulsion-based synthesis method, in which two microemulsions containing precursors of Cd²⁺ and S^2-, were mixed to form CdS QDs. The time-course variation in the average particle size was measured by UV-visible absorption spectroscopy. Subsequently, a thin film of CdS QDs was fabricated using a self-assembled monolayer (SAM) technique. First, undoped GaAs (100) wafers were cleaned and etched using HCl aqueous solution, and a SAM of 1,6-hexanedithiol was formed on the etched wafer surface using a typical SAM technique. Finally, CdS-dithiol-GaAs structures were fabricated by immersing the SAM-coated wafer in dispersion solutions of CdS QDs. In the serial steps of the fabrication of CdS QD thin films, the wafer surface was analyzed, and thin film formation was confirmed by contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS).