Plasma-Enhanced Atomic Layer Deposition of Two-Dimensional WS2 from WF6, H2 Plasma, and H2S

Groven, Benjamin; Heyne, Markus; Mehta, Ankit Nalin; Bender, Hugo; Nuytten, Thomas; Meersschaut, Johan; Conard, Thierry; Verdonck, Patrick; Elshocht, Sven Van; Vandervorst, Wilfried; Gendt, Stefan De; Heyns, Marc; Radu, Iuliana; Caymax, Matty; Delabie, Annelies

doi:10.1021/acs.chemmater.6b05214

Cited by 75 publications

(111 citation statements)

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“…The WS2 is grown from a PEALD reaction cycle that consists out of a WF6, H2 plasma and H2S reaction (99.9 % pure H2S, 10 % in He) at 300 °C, with a bulk GPC of (2.2 ± 0.1) × 10 13 W atoms/cm 2 per cycle (equivalent of 0.02 ML/cycle or 0.01 nm/cycle) based on earlier work 24 . A careful control over the H2 plasma and H2S reactions, results in a well-controlled composition (i.e., S/W ratio of 1.9 ± 0.1) of the layers.…”

Section: Methodsmentioning

confidence: 99%

“…The H2 plasma reaction enables the reduction of -W 6+ Fx surface species, but needs to be mild (100 W, 10 s) to avoid sub-surface reduction of the WS2 layers. For detailed description of the PEALD reaction cycle and deposition conditions, the reader is referred to earlier published work 23,24 .…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, in this work, we investigate the nucleation mechanisms of a recently reported WS2 PEALD process based on a ternary reaction cycle of WF6, H2 plasma and H2S reactions on amorphous Al2O3 starting surface and on bulk, monocrystalline sapphire substrates 23,24 . In earlier work, we have demonstrated that WS2 layers deposited on amorphous Al2O3 starting surfaces have a polycrystalline structure, and the basal plane orientation depends on the deposition temperature 23 .…”

Section: Introductionmentioning

confidence: 99%

“…In earlier work, we have demonstrated that WS2 layers deposited on amorphous Al2O3 starting surfaces have a polycrystalline structure, and the basal plane orientation depends on the deposition temperature 23 . The reactions of WF6 and H2S are self-limiting, and the H2 plasma reaction is essential for the deposition of WS2 as it enables the reduction of W 6+ Fx surface species at low deposition temperatures (300 °C) 24 .…”

Section: Introductionmentioning

confidence: 99%

“…Cross-sectional TEM is performed using a FEI Tecnai F30 electron microscope operating at 300 kV. For plan-view observation, the WS2 layers are transferred from the growth substrate to a carbon lacey TEM grid, and analyzed using a FEI TITAN electron microscope operating at 60 kV to minimize the electron beam induced damage to the WS2 24 .…”

mentioning

confidence: 99%

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Nucleation mechanism during WS2 plasma enhanced atomic layer deposition on amorphous Al2O3 and sapphire substrates

Groven

Mehta

Bender

et al. 2017

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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The structure, crystallinity and properties of as-deposited two-dimensional (2D) transition metal dichalcogenides are determined by nucleation mechanisms in the deposition process. 2D materials grown by atomic layer deposition (ALD) in absence of a template, are polycrystalline or amorphous. Little is known about their nucleation mechanisms.Therefore, we investigate the nucleation behavior of WS2 during plasma enhanced ALD from WF6, H2 plasma and H2S at 300 °C on amorphous ALD Al2O3 starting surface and on monocrystalline, bulk sapphire. Preferential interaction of the precursors with the Al2O3 starting surface promotes fast closure of the WS2 layer. The WS2 layers are fully continuous at WS2 content corresponding to only 1.2 WS2 monolayers. On amorphous Al2O3, (0002) textured and polycrystalline WS2 layers form with grain size of 5 nm to 20 nm due to high nucleation density (~10 14 nuclei/cm 2 ). The WS2 growth mode changes from 2D (layer-by-layer) growth on the initial Al2O3 surface to threedimensional (Volmer-Weber) growth after WS2 layer closure. Further growth proceeds from both WS2 basal planes in register with the underlying WS2 grain, and from or over grain boundaries of the underlying WS2 layer with different in-plane orientation. In contrast, on monocrystalline sapphire, WS2 crystal grains can locally align along a preferred in-plane orientation. Epitaxial seeding occurs locally albeit a large portion of crystals remain randomly oriented, presumably due to the low deposition temperature.The WS2 sheet resistance is 168 MΩµm suggesting that charge transport in the WS2 layers is limited by grain boundaries.3

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Nucleation mechanism during WS2 plasma enhanced atomic layer deposition on amorphous Al2O3 and sapphire substrates

Groven

Mehta

Bender

et al. 2017

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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

et al. 2021

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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...

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Controlling Atomic Layer Deposition of 2D Semiconductor SnS₂ by the Choice of Substrate

Mattinen

King

Brüner³

et al. 2020

Adv Materials Inter

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been explored. The 2D semiconductors, such as MoS 2 , have become the topic of particularly active research due to the crucial role of semiconductors in modern microelectronics. [7-11] Tin disulfide (SnS 2) has recently emerged as a highly interesting 2D semiconductor. [12,13] It crystallizes in the CdI 2-type 2D structure (1T phase) similar to many TMDCs [12,14] and has a fairly large, indirect band gap of approximately 2.2 eV in bulk [13,15] and 2.4−2.6 eV as a monolayer. [15,16] SnS 2 has already shown performance comparable to the benchmark 2D semiconductor, MoS 2 , in applications such as FETs [9,12,17-19] and photodetectors. [12,20] Furthermore, possible reduction in shortchannel leakage [20,21] due to the larger, indirect band-gap of SnS 2 and higher predicted mobility [22] compared to MoS 2 make SnS 2 a favorable material for electronics. Other promising applications for SnS 2 include lithium and sodium-ion batteries, [23,24] gas sensing, [25] and various kinds of catalysis. [26-28] Synthesis of 2D materials including SnS 2 is, however, a major obstacle for the realization of practical applications. An ideal synthesis method should offer high material quality, monolayer-level thickness control as well as good uniformity on large areas and complex shapes-preferably all at low processing temperatures. The substrate is an integral part of the deposition process and applications, and there are great needs both for methods capable of directly synthesizing 2D materials on different substrates, as well as for methods depositing highquality materials on single-crystalline substrates. The latter route could be combined with a transfer of the deposited material onto another substrate, if needed. [29-31] High-quality, few-layer SnS 2 has been produced from bulk crystals by micromechanical exfoliation, [12,17] but this method offers very limited control over the flake size and thickness and has extremely low throughput. Vapor-phase deposition techniques, such as chemical vapor deposition (CVD) and atomic layer deposition (ALD), are promising techniques for the deposition of 2D materials. Thus far, CVD has been mostly used to produce high-quality, isolated few-layer flakes of SnS 2 at 450-700 °C. [16,18,32,33] CVD of continuous SnS 2 films was demonstrated recently, but films below 3-4 nm in thickness remained discontinuous and even 15 nm thick films contained some holes. [34,35] ALD has been used to deposit continuous SnS 2 films with thicknesses from approximately two up to tens of monolayers. [36-41] In addition to thermal ALD processes, [36-39] Semiconducting 2D materials, such as SnS 2 , hold great promise in a variety of applications including electronics, optoelectronics, and catalysis. However, their use is hindered by the scarcity of deposition methods offering necessary levels of thickness control and large-area uniformity. Herein, a low-temperature atomic layer deposition (ALD) process is used to synthesize up to 5 × 5 cm 2 continuous, few-layer SnS 2 films on a variety of substrates, including SiO 2 /Si, S...

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Plasma-Enhanced Atomic Layer Deposition of Two-Dimensional WS₂ from WF₆, H₂ Plasma, and H₂S

Cited by 75 publications

References 68 publications

Nucleation mechanism during WS2 plasma enhanced atomic layer deposition on amorphous Al2O3 and sapphire substrates

Nucleation mechanism during WS2 plasma enhanced atomic layer deposition on amorphous Al2O3 and sapphire substrates

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

Controlling Atomic Layer Deposition of 2D Semiconductor SnS₂ by the Choice of Substrate

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Plasma-Enhanced Atomic Layer Deposition of Two-Dimensional WS2 from WF6, H2 Plasma, and H2S

Cited by 75 publications

References 68 publications

Nucleation mechanism during WS2 plasma enhanced atomic layer deposition on amorphous Al2O3 and sapphire substrates

Nucleation mechanism during WS2 plasma enhanced atomic layer deposition on amorphous Al2O3 and sapphire substrates

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

Controlling Atomic Layer Deposition of 2D Semiconductor SnS2 by the Choice of Substrate

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Plasma-Enhanced Atomic Layer Deposition of Two-Dimensional WS₂ from WF₆, H₂ Plasma, and H₂S

Controlling Atomic Layer Deposition of 2D Semiconductor SnS₂ by the Choice of Substrate