Evolution of low-frequency vibrational modes in ultrathin GeSbTe films
Phase change materials (PCM) are compounds employed in non-volatile random-access memory and rewriteable optical storage media thanks to the rapid and reversible transformation between the amorphous and crystalline states. GeSbTe alloys are the most studied PCMs and consist of lamellae separated by van der Waals gaps in the ordered crystalline phase. Here we report a methodology for the study of the two-dimensional (2D) character of epitaxial GeSbTe by looking at the weak inter-lamellae interactions. Our unique approach is the use of molecular beam epitaxy for the controlled synthesis of ultrathin films combined with Raman spectroscopy for the investigation of the PCM properties. The shift of the vibrational modes in the low-frequency range results in a direct probe of the film thickness. ... read more