Atomic‐Layer‐Deposition‐Based 2D Transition Metal Chalcogenides: Synthesis, Modulation, and Applications

Abstract

V, Fe, Co, and Ni chalcogenides exhibit diverse stoichiometric phases with different electrical properties. [28][29][30] For example, TiS 3 is a semiconductor, while TiS 2 exhibits metallic properties. [30,31] Owing to their electrical conductivity, metallic TMCs can be used for energy conversion (including the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)) and energy storage (Li-ion batteries (LIBs), Na-ion batteries (NIBs), and supercapacitors). [29,32] Industrially compatible synthesis methods and applications are of key importance in the research of new materials. Therefore, atomic layer deposition (ALD)-based 2D TMC materials, which are applicable in industries, have been investigated. [33][34][35][36] Initially, 2D TMCs were mechanically exfoliated to determine their single-crystal characteristics. [11,20] However, the large-area synthesis and control of the layer number of TMCs are crucial. [2,37] ALD, which is a suitable synthesis method for 2D TMCs, is based on the surface reactions of the alternately supplied vapor-phase precursors. [38,39] Because it is one of the most powerful deposition methods for synthesizing uniform thin films on large areas, the next-generation low-power/ high-efficiency electronic and energy applications of materials synthesized/modified by ALD processes have been studied. [38,39] For industrial applications, the electrical, optical, and physical properties of 2D TMCs need to be improved. [18,[40][41][42][43] In addition to the synthesis of 2D TMCs, the ALD method can be used to modify 2D TMCs. In particular, the performance of 2D TMCs can be improved by depositing other materials on 2D TMCs via ALD. [44] By depositing metal oxide thin films or metal nanoparticles on 2D TMCs by ALD, the electrical properties of 2D TMC materials can be precisely controlled, the catalyst efficiency can be modulated, and strain can be induced to change the physical properties of the 2D TMCs. [45][46][47] However, because of their unique structures, ALD on 2D TMCs is quite challenging. For example, the film growth behavior on 2D TMCS is significantly different from the film growth behavior on 3D materials during ALD because of the absence of chemical sites on 2D TMCs. [48][49][50][51] Therefore, for thin film deposition on 2D TMCs by ALD, researchers have focused on improving the uniformity of thin films or synthesizing low-dimensional nanomaterials on 2D TMCs.Herein, the synthesis of 2D TMCs by ALD is reviewed and the synthesis methods are classified based on different types of ALD methods. The synthesis of TMCs by the ALD of transition Transition metal chalcogenides (TMCs) are a large family of 2D materials with different properties, and are promising candidates for a wide range of applications such as nanoelectronics, sensors, energy conversion, and energy storage. In the research of new materials, the development and investigation of industry-compatible synthesis techniques is of key importance. In this respect, it is important to study 2D TMC materials synthesized by th...

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

“…As for the chalcogen precursors, the reported chalcogen sources include hydrogen sulfide (H 2 S) and di- tert -butyl disulfide (TBDS) for sulfur and diethyldiselenide (DEDSe) for selenium (Figure ). The gaseous H 2 S, owing to its good ALD reactivity, has been prevalently used in the ALD of metal sulfides, for not only the above three metals but also many others. , H 2 S resembles H 2 O in molecular structure, but owing to its weaker S–H bond, H 2 S is a stronger Brønsted–Lowry acid than H 2 O. Therefore, H 2 S is presumably more reactive than H 2 O toward proton-mediated ligand-exchange reactions, which are considered as the governing mechanisms in many ALD processes.…”

“…ALD of metal chalcogenides can be dated back to the 1970s, when the first ZnS ALD process was reported using elemental Zn and S as precursors . However, in the following years, the development of chalcogenide ALD was relatively scarce, as compared to oxide ALD, until the past decade, when there has been a great resurgent interest in the ALD of metal chalcogenides. − Many new ALD processes have been recently developed for metal chalcogenides, and their applications have also been extensively explored. − Iron, cobalt, and nickel chalcogenides are among those materials that have been only recently realized by ALD. , Iron, cobalt, and nickel are neighboring elements in the periodic table, and they are similar in chemical properties but different with a progressive increase in the number of 3d electrons. The chalcogenides of iron, cobalt, and nickel often form similar crystal structures, which therefore offer a desirable platform for electronic structure engineering by alloying these elements.…”

Stepwise growth of crystalline MoS2 in atomic layer deposition

“…In the conventional ALD of TMDCs, however, the grown TMDC films are amorphous owing to the low deposition temperature and are subsequently annealed at a higher temperature for crystallization. [14][15][16][17][18] In these cases, the grain size is restricted to the range of several nanometers to a few tens of nanometers. Some studies have reported the ALD growth of crystallized TMDC films.…”

Surface Chemistry of MoS2 in Remote Oxygen Plasma

“…Atomic layer deposition and atomic layer etching (ALE) techniques in principle meet this demand . The former is a well-established technique and has been developed for bottom-up growth of conformal thin films. , The latter can provide nanosheets by means of thinning existing 2D materials layer by layer using sequential, self-limiting reactions. , The plasma ALE method, one of the ALE methods, has recently attracted the attention of this research field because of its good selectivity, scalability, and short processing duration. , A low-temperature gas plasma commonly contains several highly reactive species such as ions, free radicals, electrons, and so on . These species rapidly initiate chemical reactions that are inactive under common conditions.…”

“…14 The former is a well-established technique and has been developed for bottomup growth of conformal thin films. 15,16 The latter can provide nanosheets by means of thinning existing 2D materials layer by layer using sequential, self-limiting reactions. 17,18 The plasma ALE method, one of the ALE methods, has recently attracted the attention of this research field because of its good selectivity, scalability, and short processing duration.…”