Enhanced Control of Porous Thin Film Morphology via Ion Bombardment

Abstract

Ion bombardment was used during and after the deposition of controlled-porosity thin films produced using the Glancing Angle Deposition (GLAD) technique. Post-deposition ion bombardment was used to mill vertical-post morphology GLAD films, whose constituent columns varied in size due to competition effects. Smaller columns, although in the minority, can have a significant impact on the function of these films in a variety of optics applications, and can only be avoided by pre-selecting column location (i.e. seeding). Uniform milling eliminated smaller columns and left only remnants of the largest columns, which then acted as seeds during subsequent depositions. This simple, non-lithographic technique leads to more uniform column morphology. Column tilt angle can also be adjusted using ion bombardment. Methods to tune column tilt angle as a function of ion current using ion-assisted deposition are discussed, with an emphasis on improved square spiral photonic band gap crystal fabrication. Ion bombardment was found to increase the tilt angle of each spiral arm, moving the architecture closer to the theoretical optimum structure.