A viable and scalable route for the homo-growth of Si nanocones and Si/C nanostructures

The present paper focuses on the fabrication of polycrystalline Si nanocones, starting from hydrogen-containing gas mixtures activated in a dual-mode microwave/radio frequency plasma reactor. Taking advantage of the capacitive coupling of microwave (MW) and radio frequency (RF) plasmas, dense arrays of vertically aligned or isolated nanocones, with predetermined basal diameters, can be routinely prepared by engineering the distribution of Ni sites on lithographically patterned Si surfaces. Such elongated objects are constituted by nanocrystalline Si extruded from the negatively biased substrate. Under suitable experimental conditions, a thin surface deposit of hydrogenated amorphous C is achieved. The one-step growth of elongated three-dimensional Si/C entities is rationalized considering the Si–Ni diffusion induced by energetic H ions and the formation of Si/Ni systems with a melting temperature lower than the bulk Si. Reflection high-energy electron diffraction (RHEED) analysis and micro-Raman spectroscopy have been used to study the crystallographic features of the Si nanocones and to confirm the role played by the Ni deposits. The present methodology is proposed as a viable route for a scalable fabrication of designed Si or Si/C nanostructures to be integrated in Si devices.