Speaker
Description
The unique method of 57Fe emission Mössbauer spectroscopy (eMS), as performed at the large-scale facility of ISOLDE at CERN, was employed to reveal, at the most atomic-scale, important aspects governing the amorphous-to-crystalline phase transition in GeTe thin films, of importance for phase change memory (PCM) applications. By following dilute implantation of 57Mn (T½ = 1.5 min) decaying to 57Fe, we investigated the changes of the electronic charge distribution and local environment occurring around Fe probe substituting Ge (Fe@Ge), across the phase transition. The local structure of as-sputtered amorphous GeTe turned out to be a combination of tetrahedral and defect-octahedral sites. Upon crystallization a large conversion from tetrahedral to defect-free octahedral sites occurred. We discovered that only the tetrahedral fraction in amorphous GeTe participates to the change of the Fe@Ge-Te chemical bonds, with a net electronic charge density transfer of ~ 1.6 e/a0 between Fe@Ge and neighboring Te atoms. The observed atomic-scale chemical-structural changes resulted to be directly connected to the macroscopic phase transition and resistivity switch of GeTe thin films.
