Microstructure and mechanical characterization of aluminum thin films on steel substrates

Aluminum thin films were deposited on mild steel substrates at substrate temperatures of 80oC and 100oC at a constant sputtering power of 300 W by radio-frequency (RF) magnetron sputtering method. The films were then characterized for microstructure and mechanical properties by optical surface profiler (OSP), scanning electron microscopy (SEM), x-ray diffraction (XRD) and micro-scratch tests. The results showed that films deposited at 80oC consisted of long and layered structures with porous oxides whereas those deposited at 100oC were characterized by finer structures with porous and amorphous network of oxide-dominant structures. The XRD diffractograms revealed amorphous structures for both samples and lower roughness for samples deposited at 100oC. The behavior of the surfaces under extremely high micro-scratch loads (0-30 N) was characterized by piling up of the amorphous materials on the edges of the scratch track (100oC) and lateral and track-in cracking along the scratching direction (80oC). The results suggest the significance of substrate temperature on the adhesion characteristics of aluminum thin films.