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V. Kekkonen, A. Hakola, J. Likonen, Y. Ge, T. Kajava.
Applied Physics A, August 2012, Volume 108, Issue 2, pp 423-430.
Department of Applied Physics, Aalto University, P.O. Box 15100, 00076, Aalto, Espoo, Finland.
4. Picodeon Ltd. Oy, P.O. Box 1199, 70211, Kuopio, Finland.
VTT Technical Research Centre of Finland, P.O. Box 1000, 02044, VTT, Espoo, Finland.
Department of Materials Science and Engineering, Aalto University, P.O. Box 16200, 00076, Aalto, Espoo, Finland.
Abstract
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.
