Characterization and surface charge measurement of self-assembled CdS nanoparticle films

The self-assembly of CdS semiconductor nanocrystals (Q-CdS) as well-defined monolayer and multilayer films on glass, indium tin oxide, and gold surfaces was carried out. These were characterized by ultraviolet-visible spectroscopy, ellipsometry, and scanning tunneling microscopy, The adsorption of the polymeric anion hexametaphosphate (HMP) on the Q-CdS particle surface produced a negative surface charge. The diffuse double-layer interaction forces between a silica probe and the Q-CdS/HMP particle film-covered gold substrate immersed in aqueous solutions were measured using an atomic force microscope. The surface charge and electrostatic potential of Q-CdS particles were obtained by theoretical fits of the force data to solutions of the complete nonlinear Poisson-Boltzmann equation with a knowledge of the silica probe surface potential.