Effective method for preparation of oxide-free Ge2Sb2Te5 surface: An X-ray photoelectron spectroscopy study

Cleaning the surfaces of the as-deposited Ge2Sb2Te5 was studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). The mixed native oxides on the as-deposited Ge2Sb2Te5 surface can be easily removed by dipping Ge2Sb2Te5 in de-ionized water for 1 min, while the surface morphology remains unchanged after cleaning. Native oxides only re-grow after exposure to air for more than 4 min. Although dipping in water leads to a surface layer deficient in Ge and Sb, the surface composition of Ge2Sb2Te5 can recover to its stoichiometric value after annealing at 200 °C in vacuum. The phase remains amorphous at room temperature after dipping in water, and changes to fcc and hcp after annealing at 100 and 220 °C, respectively.