Metal Sheet of Atomic Thickness Embedded in Silicon

The controlled confinement of the metallic delta-layer to a single atomic plane has so far remained an unsolved problem. In the present study, the delta-type structure with atomic sheet of NiSi₂ silicide embedded into a crystalline Si matrix has been fabricated using room-temperature overgrowth of a Si film onto the Tl/NiSi₂/Si(111) atomic sandwich in ultrahigh vacuum. Tl atoms segregate at the growing Si film surface, and the 1.5-3.0 nm thick epitaxially crystalline Si layer forms atop the NiSi₂ sheet. Confinement of the NiSi₂ layer to a single atomic plane has been directly confirmed by transmission electron microscopy. The NiSi₂ delta-layer demonstrates a p-type conductivity associated with the electronic transport through the two hole-like and one electron-like interface-state bands. The basic structural and electronic properties of the NiSi₂ delta-layer remain after keeping the sample in air for one year.