Geometry and structure of sputter-induced cones on nickel-seeded silicon

Abstract

Microprotrusions, or cones, grown on monocrystalline Si obliquely sputtered with Ar+ ions, while being supplied with Ni ‘‘seeds’’ by sputtering, were observed by scanning and transmission electron microscopy. At temperatures lower than 400 °C, Ni atoms were deposited on the upper cone slope receiving the high fluxes of seeds, resulting in the development of ‘‘delta-winged’’ cones. Seed layers were Ni for substrate temperatures below 200 °C and nickel silicide for temperatures above 200 °C, and they were silicidized to NiSi2 above 300 °C, suggesting that Ar+ bombardment activated the NiSi2 formation at the growth front of seed-layer tip. Cones were grown heteroepitaxially at 400 °C, consisting of alternating NiSi2 and Si layers. We thus consider that a controlled particle supply process was involved in Ar+ bombardment at 400 °C. Evidence is also presented that impacting Ar+ ions induced an eutectic reaction between Ni and Si around 500 °C.

Self-organized textured surfaces of amorphous carbon

“…The seed layers thus formed serve to protect the cone from ion erosion, thereby sustaining the steady-state evolution of the cone. 9 Whereas cones developed from intrinsic sources ͑such as defects͒ are nonequilib-rium formations. This kind of cone or pyramid tends to be unstable in most cases; the structures will be eroded by prolonged sputtering.…”

Arrays of Si cones prepared by ion beams: growth mechanisms

“…The additional weak diffraction spots originate in the Si‐based superstructure in the central tip zone. They present one‐dimensional and two‐dimensional orderings along three zone directions of 1–10, [100] and [1‐1‐1] 17. In the real space, the superstructure can result from a commensurate modulation induced by Mo atoms periodically replacing Si atoms in the particular direction.…”

“…Morishita et al illustrated a layer of epitaxial Mo seed film deposited on the tip of Cu cones 18. Fujimoto et al reported that the tips of Si cones were composed of a heteroepitaxial structure of NiSi 2 ‐Si‐NiSi 2 at a target temperature of 400 °C 7. Besides Ar ions, incident particles in the present system should also include ions from the seed materials and the recoiled ions from the Si substrate.…”

“…For example, cone structures could be used in organic/inorganic hybrid photovoltaic devices 4, in which the inorganic array structure forms the direct paths for charge carriers to their respective electrodes and thus enhances the solar cell performance. Yet, cone structures have been fabricated by a variety of methods 5, 6, and produced by many combinations of seed and target materials, such as Ni‐Si, Mo‐Cu, Steel‐C and Fe‐Si, etc 7–9. The formation of cone structures has been accounted in terms of either the left‐standing mechanism or sputter/growth model 10–12.…”

Fabrication of zinc nanotip arrays by ion beam sputtering

“…An alternative to the approach of Dev et al is fabricating prealigned metal zinc nanostructures on zinc foils as a template for subsequent thermal oxidation producing prealigned ZnO nanostructures. It has been shown that cone-shaped nanostructures can be prepared using ion beam sputtering on Cu, 3 Ag, 4 Al, Fe, 5 Si, 6 Ge, 7 InP, 8 GaN, GaP, Al 2 O 3 , 9 and graphite. 10 Two formation mechanisms have been proposed, a whisker growth 11 and a left-standing process.…”