Low-temperature structure and phase transitions at the Au/Si (100) interface

High-resolution transmission electron microscopy coupled with a STEM nanoprobe reveals that the Au/Si (100) interface deposited at {~}80 ^∘{}C is not abrupt and contains a disordered Si-rich Au-Si alloy decorated with pure Au nanocrystallites. The presence of oxygen at the Au surface enhances the outdiffusion of Si atoms through the Au overlayer, resulting in the phase transition from a disordered interface to an ordered metastable Au₄Si phase. Instead, the Au/Si (100) capped with a Ge layer shows that the amorphous structure remains relatively stable. These results allow explanations of some unresolved experimental enigmas.