Diffusion of Pb in (100) Si under electron beam annealing following dual ion implantations of Pb/Ne, Pb/O and Pb/N

(100) Si was dual-implanted with the ions Pb+/22Ne+ (7 and 30 keV), Pb+/16O+ (7 and 26 keV) and Pb+/14N+ (7 and 24 keV) to peak concentrations of typically 10 at.%. The implanted samples were then electron beam annealed at 900 °C for 30 s with a temperature gradient of 5 °C s−1 under high vacuum conditions. Channelled RBS measurements performed with 1.5 MeV 4He+ ions showed that annealing of the Pb/Ne and Pb/O samples resulted in an almost complete recrystallisation of the amorphous layers caused by the ion implantations and a total loss of the implanted Pb. For the Pb/Ne samples the Ne diffused out to leave a rough surface sprinkled with deep craters; for the Pb/O samples some SiO2 formed below the surface. In contrast, for the Pb/N samples most of the amorphous layer survives annealing and almost all the Pb is retained. A striking feature is that annealing causes the Pb to diffuse away from the surface to be trapped in a deep diffusion sink provided by the implanted N. XRD analyses exhibited Pb (111) and Pb (220) reflections suggesting that Pb nanoclusters have grown in the understoichiometric silicon nitride layer. These structures offer an interesting opportunity for controlled carbon nanotube (CNT) growth on silicon nitride.