Interfacial reactions and microstructural evolution of periodic Ni nanodot arrays on N2+-implanted amorphous Si substrates

•The interfacial reactions between nanoscale Ni metal dots and N2+-implanted a-Si substrates were investigated.•Remarkable triangular ring-like and circular NiSi2 nanoring structures were produced.•The epitaxial crystallization of N2+-implanted a-Si was mediated by the lateral migration of NiSi2 nanodots.•The formation of remarkable NiSi2 nanoring structures was explained by the silicide-induced crystallization mechanism.