Atomic Layer Deposition of Iron, Cobalt, and Nickel Chalcogenides: Progress and Outlook

Abstract

Iron, cobalt, and nickel chalcogenides are a class of fascinating materials, which have many applications in cutting-edge technologies. Atomic layer deposition (ALD) is a highly useful technique to fabricate thin film materials. Over the past few years, ALD of iron, cobalt, and nickel chalcogenides has been developing very rapidly, with many new deposition processes being developed and demonstrated for promising applications. To date, a number of chalcogenides, including FeS x , CoS x , NiS x , Fe x Co 1−x S y , FeSe 2 , CoSe 2 , and NiSe 2 , have been successfully synthesized by thermal and/or plasma-assisted ALD, and studies on surface chemistry and film growth mechanisms have also been followed to understand the underlying ALD mechanisms. However, aside from numerous progresses, considerable scientific and technological gaps and challenges are still prominent in this area. In this perspective, we summarize the recent progress in the ALD of iron, cobalt, and nickel chalcogenides, from four aspects of precursors, processes and film properties, surface chemistry and growth mechanisms, and applications, and then present our perspective on the future of this ALD technology.

Metal Exchange and Diffusion during Atomic Layer Deposition of Cobalt and Nickel Sulfides

“…On a separate note, it has been known that the ion diffusivity in metal sulfides could be enhanced by the vacancies in the film, and the density of vacancies could be modulated by the H 2 S gas . Given that H 2 S has been widely used as the sulfur source in metal sulfide ALD, , the effect of H 2 S on the above diffusion process could be very important for the relevant film growth. Therefore, we further investigated the H 2 S effect, following the above Ni­(amd) 2 treatment at 100 °C.…”

“…The motivation to investigate this material system is to develop the ALD processes for synthesizing ternary cobalt nickel sulfides (Co x Ni y S). The ternary Co x Ni y S compounds, with various stoichiometries, have been considered as promising materials in many cutting-edge energy technologies, such as batteries, supercapacitors, and electrocatalytic water splitting, and the benefits of ALD, particularly in precise atomic-level material design, can offer great opportunities in controllable nanoscale synthesis and study of energy technologies. ,, However, our initial attempt to prepare ALD ternary Co x Ni y S films, by repeatedly depositing NiS x -on-CoS x bilayers, resulted in almost completely NiS x , which implied a pronounced effect of metal exchange and diffusion. To further unveil the detailed mechanism, we designed and conducted a series of ex situ and in situ experiments, where we particularly employed the technique of in situ X-ray photoelectron spectroscopy (XPS) with depth profiling to track the change in film composition.…”

Design Guidelines for Two-Dimensional Transition Metal Dichalcogenide Alloys

“…The offset energy for each TMD, E GS (M), is the minimum energy across the prototype space E GS (M) = min p E (M, p ). As the starting points are ML geometries, the present analysis is especially relevant for experimental techniques able to bias the synthesis toward atomically thin films . At the same time, the results presented here for a monolayer could, in principle, be extrapolated to bulk layered TMDs, as the binding energy between the layers (typically around 10 meV/atom for TMDs , ) does not usually affect the single layer phase behavior …”

Pettifor maps of complex ternary two-dimensional transition metal sulfides

“…1). An analysis equivalent to the one presented here but restricted to 2D geometries is reported in Section IX of the SI as it might be relevant for experimental techniques able to bias the synthesis towards atomically thin films 28 .…”