2, Tel Aviv University, Tel Aviv, , Israel
The highly-controlled formation of radial silicon/NiSi core-shell heterostructures has been demonstrated for the first time. Here, we investigated the radial diffusion of nickel atoms into silicon nanopillar cores, followed by nickel silicide phase formation and the creation of a well-defined shell. The described approach is based on a two-step thermal process, which involves metal diffusion at low temperatures in the range of 200-400Co, followed by a thermal curing step at a higher temperature of 400Co. In-depth crystallographic analysis was obtained by nanosectioning the resulting silicide-shelled silicon nanopillar heterostructures, giving us the ability to study in detail the silicide shell structure. Interestingly, it was observed that the resulting silicide shell thickness has a self-limiting behavior, and can be tightly controlled by the modulation of the initial diffusion-step annealing temperature. In addition, electrical measurements of the core-shell structures revealed that the resulting shells can serve as an embedded conductive layer. The silicide shell phase and structure were examined under high-temperature conditions (T>600Co), where the silicide phase forms within the whole nanopillar cross-sectional area, accompanied with the appearance of an additional NiSi2 phase.