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- ItemGrowth of crystalline phase change materials by physical deposition methods(Abingdon : Taylor & Francis Group, 2017) Boschker, Jos E.; Calarco, RaffaellaPhase change materials are a technologically important materials class and are used for data storage in rewritable DVDs and in phase change random access memory. Furthermore, new applications for phase change materials are emerging. Phase change materials with a high structural quality, such as offered by epitaxial films, are needed in order to study the fundamental properties of phase change materials and to improve our understanding of this materials class. Here, we review the progress made in the growth of crystalline phase change materials by physical methods, such as molecular beam epitaxy, sputtering, and pulsed laser deposition. First, we discuss the difference and similarities between these physical deposition methods and the crystal structures of Ge2Sb2Te5, the prototype phase change material. Next, we focus on the growth of epitiaxial GST films on (0 0 1)- and (1 1 1)-oriented substrates, leading to the conclusion that (1 1 1)-oriented substrates are preferred for the growth of phase change materials. Finally, the growth of GeTe/Sb2Te3 superlattices on amorphous and single crystalline substrates is discussed.
- ItemHuge impact of compressive strain on phase transition temperatures in epitaxial ferroelectric KxNa1-xNbO3 thin films(Melville, NY : American Inst. of Physics, 2019) Von Helden, L.; Bogula, L.; Janolin, P.-E.; Hanke, M.; Breuer, T.; Schmidbauer, M.; Ganschow, S.; Schwarzkopf, J.We present a study in which ferroelectric phase transition temperatures in epitaxial KxNa1-xNbO3 films are altered systematically by choosing different (110)-oriented rare-earth scandate substrates and by variation of the potassium to sodium ratio. Our results prove the capability to continuously shift the ferroelectric-to-ferroelectric transition from the monoclinic MC to orthorhombic c-phase by about 400 °C via the application of anisotropic compressive strain. The phase transition was investigated in detail by monitoring the temperature dependence of ferroelectric domain patterns using piezoresponse force microscopy and upon analyzing structural changes by means of high resolution X-ray diffraction including X-ray reciprocal space mapping. Moreover, the temperature evolution of the effective piezoelectric coefficient d33,f was determined using double beam laser interferometry, which exhibits a significant dependence on the particular ferroelectric phase. © 2019 Author(s).