Optimization of the Automated Spray Layer-by-Layer Technique for Thin Film Deposition

摘要

The operational parameters of the automated Spray-LbL technique for thin film deposition have been investigated in order to identify their effects on film thickness and roughness. We use the automated Spray-LbL system developed at MIT to build 25 bilayer films of poly (ally amine hydrochloride) (PAH) and poly (acrylic acid) (PAA). Each of 10 operational parameters of this system are explored individually to isolate each parameter's effect on film thickness and roughness. The parameter effects are analyzed for apparent trends to determine the parameters best suited for adjusting film thickness and roughness. The optimal parameters for thickness adjustment are polyelectrolyte solution concentration, polyelectrolyte spray time, spraying distance, air pressure and polyelectrolyte charge density. These parameters are independent of the type of species used to construct the film. The effect of each operational parameter is examined in detail. While researching the parameter effects, polyelectrolyte interdiffusion was observed. This interdiffusion is investigated using both the conventional dipped LbL and Spray-LbL deposition techniques. Interdiffusion is observed when the PAH is partially charged, the polyelectrolytes chains have a low molecular weight, and the contact time is sufficiently long enough to allow for interdiffusion. Significantly reduced contact time during automated Spray-LbL process not only speeds up the film deposition time, but also hinders interdiffusion of PAH resulting in thinner films than possible from dipping. Films deposited on substrates greater than 1 in diameter area exhibit more than 20% variance in thickness. Adjustments were made to the setup of the system in an effort to expand this area of film thickness uniformity. However, it is determined that the design of this automated Spray-LbL system limits the film uniformity to an area of 1 in diameter.