Low temperature deposition of 2D WS2 layers from WF6 and H2S precursors: impact of reducing agents

Delabie, Annelies; Caymax, Matty; Groven, Benjamin; Heyne, Markus; Haesevoets, Karel; Meersschaut, Johan; Nuytten, Thomas; Bender, Hugo; Conard, Thierry; Verdonck, Patrick; Elshocht, Sven Van; Gendt, Stefan De; Heyns, Marc; Barla, K.; Radu, Iuliana; Thean, A.

doi:10.1039/c5cc05272f

Cited by 74 publications

(79 citation statements)

References 28 publications

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“…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%

“…Growth enhancement is not common in ALD processes 23 . It has been attributed to either the topography of the starting substrate, resulting in increased surface area, and/or to an increased reactivity and/or density of reactive sites at the starting surface 39 .…”

Section: A Substrate Enhanced Growth Of Ws2 Peald On Amorphous Al2o3mentioning

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%

“…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%

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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: A Substrate Enhanced Growth Of Ws2 Peald On Amorphous Al2o3mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

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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“…However, synthesis of large area, high quality TMD films using industry-compatible processes remains a major challenge and requires the development of highly controllable growth processes. Large area TMD layers can be grown using various techniques including chemical vapor deposition (CVD), [4][5][6] atomic layer deposition (ALD) 7 and molecular beam epitaxy (MBE) processes. 8 An interesting low cost approach that is capable of providing large-area sheets of TMDs with controllable thicknesses is chalcogenidation of ultrathin transition metal films.…”

mentioning

confidence: 99%

Demonstration of Direction Dependent Conduction through MoS₂Films Prepared by Tunable Mass Transport Fabrication

Chiappe

Mongillo

Asselberghs

et al. 2016

ECS J. Solid State Sci. Technol.

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This work focuses on the synthesis of MoS 2 films grown by sulfurization of pre-deposited ultra-thin Mo films in the presence of a sulfur-containing gaseous precursor. The growth of high-quality TMDs requires careful control of specific thermodynamic and kinetic parameters. A deep understanding of mass transport mechanisms is achieved through a systematic investigation of the structural properties of MoS 2 films grown using different sulfurization conditions. Mass transport smoothing is used to reduce surface roughness and fabricate MoS 2 films in conformal contact with the underlying substrate. Oriented MoS 2 films are obtained by combining kinetically controlled sulfurization conditions and the use of single crystal templates. Good uniformity and excellent conformity of layers over large area has enabled the synthesis of patterned MoS 2 films which show anisotropic conduction properties. Two dimensional (2D) TMD materials, due to their unique physical properties, represent an interesting alternative to conventional semiconductors. They consist of molecular layers stacked together via weak van der Waals (vdW) forces.1 The big interest toward 2D TMD for transistor applications arises from their ultra-thin body nature and low dielectric constants.2 As a consequence, this class of materials potentially provides a superior scalability option compared to conventional materials. Another important quality of vdW materials is that ideally their surfaces are chemically saturated and have no dangling bonds. This additional feature makes 2D TMD ideal building blocks for the realization of artificial heterojunctions with designed band alignment. 3To enable the transition from the laboratory level, where most work is done on exfoliated flakes, to the industrial full-wafer scale, a large area deposition technique becomes indispensable. However, synthesis of large area, high quality TMD films using industry-compatible processes remains a major challenge and requires the development of highly controllable growth processes. Large area TMD layers can be grown using various techniques including chemical vapor deposition (CVD), 4-6 atomic layer deposition (ALD) 7 and molecular beam epitaxy (MBE) processes. 8 An interesting low cost approach that is capable of providing large-area sheets of TMDs with controllable thicknesses is chalcogenidation of ultrathin transition metal films. 9,10This method is simple, fast, easily upscalable, and can be used to synthesize a large variety of TMDs, including TMD hetorostructures. 11,12 However, the huge potential of this versatile technique is limited by the fact that chalcogenidation processes normally result in the formation of nano-crystalline highly defective films. To significantly improve material quality it is necessary to gain a deeper understanding of mass transport effects taking place during the chemical conversion process. In this work we propose a mass transport study based on roughness analysis of MoS 2 films grown by sulfurization of pre-deposited ultrathin Mo films. The followin...

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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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Low temperature deposition of 2D WS₂ layers from WF₆ and H₂S precursors: impact of reducing agents

Cited by 74 publications

References 28 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

Demonstration of Direction Dependent Conduction through MoS₂Films Prepared by Tunable Mass Transport Fabrication

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

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Low temperature deposition of 2D WS2 layers from WF6 and H2S precursors: impact of reducing agents

Cited by 74 publications

References 28 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

Demonstration of Direction Dependent Conduction through MoS2Films Prepared by Tunable Mass Transport Fabrication

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

Contact Info

Product

Resources

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Low temperature deposition of 2D WS₂ layers from WF₆ and H₂S precursors: impact of reducing agents

Demonstration of Direction Dependent Conduction through MoS₂Films Prepared by Tunable Mass Transport Fabrication