Atomic Layer Deposition of Iron Sulfide and Its Application as a Catalyst in the Hydrogenation of Azobenzenes

Abstract

The atomic layer deposition (ALD) of iron sulfide (FeS ) is reported for the first time. The deposition process employs bis(N,N'-di-tert-butylacetamidinato)iron(II) and H S as the reactants and produces fairly pure, smooth, and well-crystallized FeS thin films following an ideal self-limiting ALD growth behavior. The FeS films can be uniformly and conformally deposited into deep narrow trenches with aspect ratios as high as 10:1, which highlights the broad applicability of this ALD process for engineering the surface of complex 3D nanostructures in general. Highly uniform nanoscale FeS coatings on porous γ-Al O powder were also prepared. This compound shows excellent catalytic activity and selectivity in the hydrogenation of azo compounds under mild reaction conditions, demonstrating the promise of ALD FeS as a catalyst for organic reactions.

Synthesis of Thin‐Film Metal Pyrites by an Atomic Layer Deposition Approach

“…Af ew types of the Fe, Co, and Ni compounds, such as the metal chlorides, [31] carbonyls, [32] cyclopentadienyls, [33] acetylacetates, [34] and amidinates, [35] generally fit these criteria, and they have been successfully employed as the Fe, Co, and Ni precursors to depositt he corresponding metals [35a] and metal oxides, [33d,e, 36] nitrides, [37] carbides, [38] and sulfides. [24,25,27,39] As for the sulfur source,t he aforementioned gaseous H 2 S fits these criteria well, and it is indeed ac ommonly used sulfur precursor in many ALD processes. [19a] However,i nm olecular H 2 S, the sulfur atom is bonded to two hydrogen atoms with a nominal chemical state of À2, and thus it is very difficult to convert it to afford the dimericS ÀSbonda si nthe pyrite structure under normal (thermal) ALD conditions.…”

“…Over the decades, the ALD technique has been developing very fast, and hundreds of differentm aterials, such as metals, metal oxides, nitrides and sulfides, have been synthesized by ALD. [18] Very recently,m otivated by many novel applicationsi n low-dimensional electronics and energy technologies, the ALD synthesis of metal sulfides has aroused significant attention, [19] and many new ALD synthesis processes have been particularly developed for metal sulfides.E xamples of them etal sulfides whose ALD synthesis approaches were only recently available include GaS x (2014), [20] GeS (2014), [21] MoS 2 (2014), [19b, 22] Li 2 S (2014), [23] Co 9 S 8 (2015), [24] NiS (2016), [25] MnS (2016), [26] FeS (2017), [27] VS 4 (2017), [28] and ReS 2 (2018). [29] Despite the fast development as above, the ALD synthesisoft he pyrite-structured metal disulfides remained as ignificant challenge for quite a long period, and none of the metal pyrites had ever been synthesized by ALD before our recent work.…”

“…[19a] However,i nm olecular H 2 S, the sulfur atom is bonded to two hydrogen atoms with a nominal chemical state of À2, and thus it is very difficult to convert it to afford the dimericS ÀSbonda si nthe pyrite structure under normal (thermal) ALD conditions. For this reason, all previous ALD experimentsu sing H 2 Sg as and various Fe-, Co-, Ni-organic precursorsr esulted in metal sulfides with stoichiometries closet o1 :1 (i.e.,m etal monosulfides), [24,25,27,39] rather than affordingt he metal disulfides as the metal pyrites. To deal with problem, an instinctive idea is perhaps to use an alternative sulfur precursor that inherently contains the SÀSm oiety in its molecular structure.D ialkyl disulfides (alkyl-S-S-alkyl) such as dimethyl disulfide (H 3 C-S-S-CH 3 )f all into this category,a nd they are also readily availablef rom commercial vendors.…”

Atomic Layer Deposition of the Metal Pyrites FeS2, CoS2, and NiS2

“…[12] ALD is also renowned for exceptionally conformal film coatings on virtually any complex 3D structures, [12] and this feature has enabled ALD for ag reat number of novel nanoscale material designs and applications in cutting-edge technologies. [14] We consider the reason as the lack of the chemical driven force to form the dimeric SÀSbonds as in the pyrites when using the molecular H 2 Sasthe sulfur source. Previous ALD attempts for the iron, cobalt, and nickel sulfides,using various metal-organic precursors and H 2 Sgas,all turned out to afford the sulfides with metal-sulfur stoichiometries close to 1:1(i.e., metal monosulfides).…”

“…Previous ALD attempts for the iron, cobalt, and nickel sulfides,using various metal-organic precursors and H 2 Sgas,all turned out to afford the sulfides with metal-sulfur stoichiometries close to 1:1(i.e., metal monosulfides). [14] We consider the reason as the lack of the chemical driven force to form the dimeric SÀSbonds as in the pyrites when using the molecular H 2 Sasthe sulfur source. To address this issue,w ep ropose to use the H 2 Sp lasma instead, since the plasma contains many energetic and reactive species,s uch as electrons,ions,and radicals.…”