Vacuum deposited aluminum thin films in gray, black, brown, and whitish and their underlying causes

Aluminum films on plastic substrates are widely used for barrier and decorative applications. They typically display a bright metallic gray appearance. This paper compares typical films with films that look black or brown due to the intentional, or accidental, addition of small amounts of water vapor or oxygen during film growth and films that look whitish due to a structured, light scattering surface resulting from surface recrystallization at elevated substrate temperatures. A sample prepared to demonstrate all these behaviors was analyzed using transmission electron microscopy to examine the structural and chemical changes that underlie the changed appearance of these films. Micrographs and spatially resolved elemental analyses improve our understanding of these defective films.