Pulsed laser deposition using diffractively shaped excimer-laser beams

Controlling laser-pulse parameters is an important issue in pulsed laser deposition (PLD). In particular, homogenization of laser beams improves the reproducibility of the PLD process by guaranteeing a uniform intensity distribution and a well-defined energy density of the laser spot on the target. We have integrated a beam-homogenization system into our PLD setup, and here we discuss the results and advantages of using such a system. The optical setup is based on diffractive beam-splitter gratings, which produce a 2×2-mm² flat-top distribution with fluences of the order of 3 J/cm² on the target. We demonstrate the applicability of this technique by depositing thin films of ferromagnetic Ni–Mn–Ga shape-memory alloys. Magnetic and structural characterization, including secondary ion mass spectrometry (SIMS), indicate that nearly stoichiometric composition and crystallization in the desired martensitic phase is obtained for films deposited on Al₂O₃ under optimal conditions. In contrast, the formation of silicide compounds at temperatures above 500 ^∘C is detrimental in the deposition of Ni–Mn–Ga films directly on silicon.