Directed Self-Assembly of Multilayer Thin Films of ZnS and Gold Nanoparticles by Modified Polyelectrolyte Deposition Technique

Fabrication strategies based on mechanisms of self-assembly are now widely being recognized as inevitable tools in nanotechnology. Self-organized construction of advanced materials and devices may be done starting with tailor made nanoparticles as building blocks. Multilayer thin films of gold, zinc sulphide and manganese doped zinc Sulfide nanoparticles were fabricated by a modified polyelectrolyte deposition process. A prerequisite to utilization of colloids for the fabrication of uniform layers is that they remain in suspension and resist unwanted agglomeration. The stability of colloids is generally achieved either by electrostatic stabilization, involving the creation of an electrical double layers arising from ions intentionally adsorbed on the surface of the particle and associated counter ions that surround the particle, or by steric hindrance that is achieved by the adsorption of macromolecules on the surface of the particles. The inherent necessity to introduce electrostatic or steric hindrance to avoid colloidal agglomeration was utilized to induce self-assembly of multilayers applying similar concept used for the layering of polyelectrolytes. Polyacrylic acid was used as the polyanion and chitosan as the polycation for the deposition process. Upto 100 layers of nanoparticles were constructed and films that were found to be stable and uniform over the substrate. The layer-by-layer deposition of multilayers of several different structures was prepared and devices showing resistive and capacitive electrical characteristics have been fabricated. The onset of electrical conduction in the resistive devices could be varied by introducing a dielectric interlayer between gold nanoparticles and by introducing a gold overlayer on the zinc sulphide nanoparticle devices.