Fabricating Non-Close Packed Colloidal Monolayers for Ion Irradiation Templates

Due to their unique electrical, mechanical and thermal properties, anisotropic nanoparticles are desirable components for next generation applications yet there are few processes capable of fabricating nanoparticle impregnated coatings suitable for the manufacturing environment. Our work seeks to use templated substrates to induce ordering nanoparticle thin films during robust and scalable coating processes. Specifically, we are developing new masking techniques for the production of the templated substrate. We are using lift-up soft lithography for fabricating non-close packed (ncp) colloidal monolayers onto silicon substrates, which then serve as the template for ion irradiation. The first steps to creating this monolayer are obtaining a spin-coated poly(vinyl alcohol) (PVA) thin film of ~200 nm and a close-packed colloidal monolayer using a peltier heater. We achieved a thin film of PVA with the desired thickness by examining the effects of the RPM and viscosity, measured by a rheometer, on the thickness of the film which was evaluated by atomic force microscopy (AFM). Results showed that as the RPM increases and the viscosity decreases, the thickness decreases. To form the colloidal monolayer, a drop of silica spheres suspended in ethanol was placed onto a silicon wafer and mounted onto a peltier element. The entire system was placed inside a closed box, controlled at room with fixed tilt, temperature, and humidity. We preferred using piranha etch to clean the substrate, allowing for minimum defects.