Multilayered Thin Metal Film Deposition by Sequential Operation of Nanosilicon Electron Emitter in Metal–Salt Solutions

The use of a nanocrystalline silicon (nc-Si) ballistic electron emitter in metal–salt solutions induces the deposition of thin metal films. The nc-Si emitter is composed of a thin Au/Ti film, an anodized polycrystalline Si layer, and an n⁺-Si substrate. When the emitter is driven in NiCl₂, CoSO₄, and ZnSO₄ solutions without using any counter electrodes, thin Ni, Co, and Zn films are deposited on the emission area, respectively, as well as a thin Cu film in CuSO₄ solution. According to cyclic voltammogram measurements under a standard three-electrode configuration, the hot electron injection effect into the solution is clearly observed in all cases at potentials within the electrochemical window, in which no electrolytic reactions occur. Energetic electrons injected into the solutions cause the direct reduction of metal ions. As a possible application, the multilayered deposition of different metals is demonstrated by sequential operation in NiCl₂ and CuSO₄ solutions.