Effect of Substrate Type on the Fractal Characteristics of AFM Images of Sputtered Aluminium Thin Films

The roughness features of aluminum thin films deposited by radio-frequency magnetron sputtering on Ti6Al4V, stainless steel, mild steel and commercially pure titanium substrates are studied via atomic force microscopy. The average roughness, interface width, skewness, kurtosis, roughness exponent, equivalent roughness, lateral correlation length, fractal dimension and Minkowski functionals have been computed for each sample. It is shown that both topology and fractal characteristics of the Al thin films are greatly influenced by the type of metallic substrate on which it is sputtered. The fractal studies reveal that the fractal dimensions range between 2 and 3, indicating that all the surfaces are self-affine. The Minkowski functionals show that the valleys and plateaus for all the surfaces are highly disconnected since very small positive values of Euler-Poincare are computed. The differences in roughness characteristics are superficial indication that substrate types affect the nucleation and growth of surface features such as grain sizes and particles during sputtering.