Berlin 2012 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 1: Layer properties: electrical, optical, and mechanical properties
DS 1.4: Vortrag
Montag, 26. März 2012, 10:15–10:30, H 0111
Picosecond ultrasound spectroscopy on NiTi and NiMnGa thin film shape memory alloys — •Jan Mayer, Mike Hettich, Martin Schubert, and Thomas Dekorsy — Department of Physics, University of Konstanz, D-78457 Konstanz
Shape memory alloys are characterized by a reversible and diffusionless structural transition from a high-temperature austenitic phase to a low-temperature martensitic phase, induced by stress or temperature [1]. The material systems we investigate are NiTi and Ni2MnGa thin films of 110 nm and 150 nm thickness, respectivly. Ni2MnGa is ferromagnetic and has a great potential for applications due to the magnetic-field-induced shape memory effect with reversible strains of up to 9 % [2]. The films are investigated using asynchronous optical sampling (ASOPS). ASOPS is a novel technique for ultrafast time domain spectroscopy [3] and enables optical pump-probe measurements with femtosecond resolution. By measuring the change in reflectivity the vibrational dynamics of the samples are studied. The obtained coherent phonon spectra allow to study the structural phase transition in alloys of various stoichiometry. Due to the strong dependence of the transition temperature on composition [4], it is possible to investigate both phases at room temperature. The vicinity of the phase transition is analyzed by heating and cooling the samples.
[1] Martynov and Kokorin, J. Phys. III France 2, 739-749 (1992)
[2] Sozinov et al., Appl. Phys. Lett, 80, 1746 (2002)
[3] Bartels et al., Rew. Sci. Instr. 78, 035107 (2007)
[4] Chernenko et al., Acta Materialia 50, 53-60 (2002)