Atomic Layer Deposition of 2D Metal Dichalcogenides for Electronics, Catalysis, Energy Storage, and Beyond

Abstract

it was soon replaced by other materials. Research on the fundamental properties and preparation of TMDC monolayers in solution (1986), [8] on single-crystal substrates in ultrahigh vacuum (2001), [9] and in an accessible way using mechanical exfoliation [10] (2005) followed. It was the discovery of graphene in 2004 [11] with its ever expanding list of unique and exciting properties, phenomena, and potential applications [12] that amassed broad attention to 2D materials and resulted in the 2010 Nobel Prize in Physics awarded to Andre Geim and Konstantin Novoselov. Tremendous efforts have been put toward synthesis and applications of graphene, including the billion euro Graphene Flagship project funded by the European Union. [13,14] Graphene is a semimetal, however, and the need to have semiconducting materials for many crucial applications, in particular in electronics, has led researchers to search for other 2D materials. The scientific community turned to TMDCs following breakthroughs in observation of unique thickness-dependent properties, [15,16] monolayer synthesis using chemical vapor deposition (CVD), [17,18] and demonstration of high-performance semiconductor devices [19-21] in 2010-2013 (Figure 1). Indeed, in 2013 the number of scientific publications on TMDCs, in particular MoS 2 , nearly tripled over 2012, and the strong growth has continued to date, fueled by advances in synthesis, new devices, and exciting physical phenomena. The explosive growth in MoS 2 research has also expanded to other TMDCs, [22] resulting in yet new phenomena and potential applications being found. [23-26] It is now clear that TMDCs are remarkable in many ways. Their layered crystal structure gives rise to fundamental physics not seen in 3D materials, which enables novel devices and applications. [25,26,32,34-36] The layered structure also gives TMDCs their highly anisotropic properties, extremely high specific surface areas, possibility to intercalate different species between the layers, and stability as ultrathin sheets down to three atomic layers thick. The TMDC family contains dozens of different materials from semiconductors to semimetals, metals, and even superconductors. [5,22,25,34] However, TMDC research is still mostly in the early discovery stages and the investigations of TMDCs largely continue using flakes produced by mechanical exfoliation of bulk crystals. [10,26] Unfortunately, this method cannot be scaled up for practical 2D transition metal dichalcogenides (TMDCs) are among the most exciting materials of today. Their layered crystal structures result in unique and useful electronic, optical, catalytic, and quantum properties. To realize the technological potential of TMDCs, methods depositing uniform films of controlled thickness at low temperatures in a highly controllable, scalable, and repeatable manner are needed. Atomic layer deposition (ALD) is a chemical gas-phase thin film deposition method capable of meeting these challenges. In this review, the applications evaluated for ALD TMDCs are systematically...

Effects of the Structure and Temperature on the Nature of Excitons in the Mo0.6W0.4S2 Alloy

“…Indeed the grain size in ALD-grown samples is ∼10 nm, which is much smaller than that for CVD-grown crystals. 57 Interestingly, the values of the exciton–LO phonon coupling strength, Γ X,ph , reported by Ho et al 27 are a factor of 2–3 higher than ours. This could be due to the fact that their piezoreflectance measurements probe excitons near the sample surface, which would then appear to couple to surface phonons with higher strength than the bulk exciton–phonon coupling probed in our experiments.…”

Atomic Layer Deposition of Large-Area Polycrystalline Transition Metal Dichalcogenides from 100 °C through Control of Plasma Chemistry

“…Formation of out-of-plane oriented fins has been commonly observed for (PE)ALD as well as CVD grown TMDC multilayer films (see refs ( 35 ) and ( 67 ) and references therein). In the case of PEALD MoS 2 and WS 2 , the fins have been observed to be located at grain boundaries.…”

Self-Assembly of MoS2 Monolayer Sheets by Desulfurization

“…At high desulfurization contents, ranging from 70 to 100%, substrate-hosted MoS 2 monolayer sheets with the planar dimensions of 10 × 10 nm 2 are structurally dissociated to fracture amorphous clusters (Supporting Information Movie S3). Interestingly, it was demonstrated that such amorphous clusters 71 can transform into layered crystalline MoS 2 structures by annealing at high temperatures. 72 In contrast, substratehosted MoS 2 monolayer sheets with dimensions of 20 × 20 to 50 × 50 nm 2 can form quadrangle tube morphology at high desulfurization contents.…”