Dynamics of GeSbTe phase-change nanoparticles deposited on graphene.

Phase-change Ge2Sb2Te5 nanoparticles (NPs), that are promising for next-generation phase-change memory and other emerging optoelectronic applications, have been deposited on graphene support layers and analyzed using advanced transmission electron microscopy techniques allowing high quality atomic resolution imaging at accelerating voltages as low as 40 kV. The deposition results in about three times higher NP coverage on suspended graphene than on graphene containing an amorphous background support. We attribute this to the variation in surface energy of suspended and supported graphene, indicating that the former harvests NPs more effectively. Hydrocarbon contamination on the graphene profoundly enhances the mobility of the NP atoms and after prolonged (weeks) exposure to air resulted in more severe oxidation and spreading of NPs on the suspended graphene than on supported graphene because the network of hydrocarbons develops more extensively on the suspended rather than on the supported graphene. Due to this oxidation, GeO x shells are formed out of NPs having a uniform composition initially. The present work provides new insights into the structure and stability of phase-change NPs, graphene and their combinations.