Fractal dimension: Measure of coating quality

Fractal analysis recognises that the concepts of length and area for irregu lar objects ale not absolute, but depend on the measurement scale. In the p resent work, three-dimensional topography of different surfaces has been me asured by scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) techniques. In particular, gold and aluminium thin films grown by eva poration techniques on silicon substrates have been studied. Fractal analys is by the frequency method was used to characterise the quality of the surf aces. The films were prepared with thickness from 30 zip to 2000 nm. It was observed that the low and high frequency components of the roughness depen d strongly on film thickness. Moreover at small thickness two different fra ctal components in the surface roughness cart be observed, which implies th at low thickness coatings follow a dynamic completely different from that f or high thickness. In conclusion, it has been established that fractal anal ysis can be used to characterise thin film surface coatings and to deter mi ne the coating type obtained.