Al-Si microparticle formation from Al thin film on Si substrate. Step 1: Al thin film deposition by RF sputtering, step 2: high-temperature annealing, and step 3: cooling down to room temperature. In step 2, compressive stress is stored in Al film due to the difference in thermal expansions of Al film and Si substrate, and interdiffusion of Al and Si atoms is accelerated to relieve this stress, leading to granulation. As a consequence of granulation, the original Al film is almost exhausted.
Noh Nanoscale Research Letters 2014 9:312 doi:10.1186/1556-276X-9-312