Laser-induced formation of intermetallics in multilayered Al/Ti nano-structures

In this study, multilayered structures consisting of eight (Al/Ti) bilayers deposited by d.c. ion sputtering onto Si (100) wafers, to a total thickness of ~300 nm were treated in air with a picosecond-pulsed Nd:YAG laser in a defocused regime. Irradiation was done with 200 successive pulses, at 1,064-nm wavelength, energy per pulse 15 mJ, the incidence angle of ~45°, covering an area of 2-mm in diameter. The samples were analyzed by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. It was found that laser irradiation-induced melting and a progressed Al–Ti nanoalloying within the top four bilayers (up to a depth of ~150 nm), while the underlying part of the multilayered structure remained intact. Another interesting result is that of a regularly rippled surface topography (~1.4-μm period and 100-nm amplitude) developed throughout the zone of the melted and reacted material.