The path of mass transfer during Au thin film-assisted chemical etching by designed surface barriers

The mass transfer in metal-assisted chemical etching between the interfaces has been revealed directly by an epoxy protection method. The results show that the dissolution of Si occurs in the Au film surface instead of the Au–Si interface. A mass transfer path inside the Au film is proposed, in which the Si atoms dissolve in the Au film, and then diffuse across the Au lattice, and are oxidized and etched away at the Au film/solution interface. This model is proved by the oxidation products of Si atoms (SiO2 and SiF62−) on the surface of the Au thin film. In addition, the abnormal emission of H2 at the Au–Si interface indicates the probability of the diffusion of H atoms inside the Au film during the etching. This work provides a further insight into the mechanism of metal-assisted chemical etching.