Spiral growth of few-layer MoS2 by chemical vapor deposition

Dong, Xi; Yan, C. T.; Tomer, Dushyant; Li, C. H.; Li, L.

doi:10.1063/1.4960583

Cited by 24 publications

(34 citation statements)

References 34 publications

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“…The CBM of TMDs is dominated by d-states of the transition metal atom sandwiched between chalcogen atoms and is therefore less sensitive to number of layers than the VBM. Based on this measurement, the resulting WS 2 bandgap is approximately 1.78 eV and is in good agreement with the bandgap measured by scanning tunneling spectroscopy (STS) of 3L MoS 2 which is known to have a very similar electronic band structure 1,2,24 .…”

supporting

confidence: 79%

Synthesis and characterization of WS2/graphene/SiC van der Waals heterostructures via WO3−x thin film sulfurization

Bradford

Shafiei

MacLeod

et al. 2020

Sci Rep

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Van der Waals heterostructures of monolayer transition metal dichalcogenides (TMDs) and graphene have attracted keen scientific interest due to the complementary properties of the materials, which have wide reaching technological applications. Direct growth of uniform, large area TMDs on graphene substrates by chemical vapor deposition (CVD) is limited by slow lateral growth rates, which result in a tendency for non-uniform multilayer growth. In this work, monolayer and few-layer WS2 was grown on epitaxial graphene on SiC by sulfurization of WO3−x thin films deposited directly onto the substrate. Using this method, WS2 growth was achieved at temperatures as low as 700 °C – significantly less than the temperature required for conventional CVD. Achieving long-range uniformity remains a challenge, but this process could provide a route to synthesize a broad range of TMD/graphene van der Waals heterostructures with novel properties and functionality not accessible by conventional CVD growth.

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supporting

confidence: 79%

Synthesis and characterization of WS2/graphene/SiC van der Waals heterostructures via WO3−x thin film sulfurization

Bradford

Shafiei

MacLeod

et al. 2020

Sci Rep

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“…SDD growth mechanism is preferred at lower supersaturation where threading dislocations, such as slipped planes at the basal domain with a screw component present on the surface providing a continuous step source, can lead to a spiral-like growth. Spiral-like growth has been predicted by Burton, Cabrera, and Frank (BCF theory) in their pioneering theoretical work 38 , and has been observed for the different transition metal chalcogenide systems 30,[40][41][42] . Presence of such spiral-like growth on a triangular domain is shown in Fig.…”

mentioning

confidence: 85%

“…However, they concluded that a large variation exists between different samples of exfoliated MoS2 and that is necessary to find a synthesis route for obtaining high quality MoS2. So far, STM characterization of the defects in CVD grown MoS2 was mostly confined to the study of point defects and grain boundaries in rotationally commensurate epitaxial graphene/MoS2 system 28,29 and spiral growths 30 .…”

mentioning

confidence: 99%

Intra-domain periodic defects in monolayer MoS2

Roy

Ghosh

Rai

et al. 2017

Applied Physics Letters

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We present an ultra-high vacuum scanning tunneling microscopy (STM) study of structural defects in molybdenum disulfide thin films grown on silicon substrates by chemical vapor deposition. A distinctive type of grain boundary periodically arranged inside an isolated triangular domain, along with other inter-domain grain boundaries of various types, is observed. These periodic defects, about 50 nm apart and a few nanometers in width, remain hidden in optical or low-resolution microscopy studies. We report a complex growth mechanism that produces 2D nucleation and spiral growth features that can explain the topography in our films.The many incredible properties of graphene including high carrier mobility (200,000 cm 2 V −1 s −1 ) 1 have made it a very special material both from fundamental science and an engineering point of view. However, the lack of a band-gap in graphene causes high leakage current which makes it unsuitable for many optoelectronic purposes and logic-based devices and circuits. In contrast, transition metal dichalcogenides (TMDs) with the general chemical formula MX2 (M = Mo, W; X = S, Se, Te) provide a large family of two-dimensional (2D) crystals that vary greatly in physical and chemical properties 2 , ranging from metallic to semiconducting to insulators. Of all the TMDs, molybdenum sulfide (MoS2), with its indirect-to-direct band gap transition as a function of layer thickness, has been of particular interest for digital and optoelectronic applications. MoS2 has already been used to fabricate functional electronic circuit elements 3-6 , as well as used for optoelectronics 7-9 , valleytronics, spintronics 10, 11 and coupled electro-mechanics 12 .Most of the MoS2 material characterization and device demonstrations so far have been on exfoliated samples which suffer from low yield, and cannot be scaled up for practical applications. In order to address these problems, significant work has been done to introduce different growth techniques. Processes including liquid exfoliation 13 and direct sulfurization of molybdenum thin films 14 have been achieved to synthesize large MoS2 monolayers. However, the overall simplicity and the high quality of films obtained using the sulfurization of MoO3 has made it one of the most widely used methods of synthesizing large area monolayer MoS2 15-17 .Just like different synthesis techniques, various analytical techniques have been introduced. In addition to the commonly used techniques like scanning electron microscopy (SEM) and atomic force microscopy (AFM), techniques like Raman and photoluminescence (PL) spectroscopy have become common to ascertain the number of layers of these 2D materials. However, because of the resolution limit, these techniques only reveal a partial picture. SEM and AFM together show us the topographical and structural information. The spectroscopic techniques ascertain the energy levels to a certain degree. Recent techniques like microwave impedance microscopy (MIM) 18 have been used to map the dielectric constant of these films. Howev...

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“…At first glance, the spirals' growth behavior in Bi-based TI systems might be considered to come from misfit dislocations at the interface during epitaxial growth, as in conventional semiconductor systems [104][105][106], where the spirals are often considered to come from misfit dislocations at the interface during heteroepitaxial growth. When the dislocations have a screw component, they can emerge at the surface to form additional steps to facilitate the growth of spirals.…”

Section: Surface Passivation and Surface Morphologymentioning

confidence: 99%

Quantum Transport and Potential of Topological States for Thermoelectricity in Bi$_2$Te$_3$ Thin Films

Ngabonziza

2021

Preprint

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Although Bi 2 Te 3 has been used as a thermoelectric material for many years, it is only recently that thin films of this material have been synthesized as 3D topological insulators with interesting physics and potential applications related to topologically protected surface states. A major bottleneck in Bi 2 Te 3 thin films has been eliminating its bulk conductivity while increasing its crystal quality. The ability to grow epitaxial films with high crystal quality and to fabricate sophisticated Bi 2 Te 3 -based devices is attractive for implementing a variety of topological quantum devices and exploring the potential of topological states to improve thermoelectric properties. This paper reviews recent developments in quantum transport and investigates the contribution of topological insulator boundary states to thermoelectricity. It addresses special issues such as preparing low-defect-density Bi 2 Te 3 epitaxial films, gate-tuning of normal-state transport and Josephson supercurrent in topological insulator/superconductor hybrid devices. Prospective quantum transport experiments on Bi 2 Te 3 thin-film devices are discussed as well. Finally, an overview of current progress on the contribution of topological insulator boundary states to thermoelectricity is presented. Future explorations to reveal the potential of topological states for improving thermoelectric properties of Bi 2 Te 3 films and realizing high-performance thermoelectric devices are discussed.

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Spiral growth of few-layer MoS2 by chemical vapor deposition

Cited by 24 publications

References 34 publications

Synthesis and characterization of WS2/graphene/SiC van der Waals heterostructures via WO3−x thin film sulfurization

Synthesis and characterization of WS2/graphene/SiC van der Waals heterostructures via WO3−x thin film sulfurization

Intra-domain periodic defects in monolayer MoS2

Quantum Transport and Potential of Topological States for Thermoelectricity in Bi$_2$Te$_3$ Thin Films

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