Growth of Highly Crystalline and Large Scale Monolayer MoS<sub>2</sub> by CVD: The Role of substrate Position

Kumar, N Selva; Tomar, Ruchi; Wadehra, Neha; Devi, Manisha; Prakash, Balaji; Chakraverty, S.

doi:10.1002/crat.201800002

Cited by 35 publications

(20 citation statements)

References 49 publications

(57 reference statements)

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“…The resulting flakes show a large variation in properties depending on their position on the substrate. While this effect is in principle well-known from all CVD processes [40], we observe a strong and quite unusual difference in morphology, and related to this, unexpected changes of vibrational and optoelectronic properties. In particular, while the larger, individual flakes show only weak, trion-dominated PL and appear n-doped and strained, we identified a region with a very high (up to 73 %) coverage of nano-crystalline MoS 2 with negligible strain, p-type doping and a significant PL emission dominated by the A exciton.…”

Section: Discussionsupporting

confidence: 65%

Growth of p-doped 2D-MoS$_2$ on metal oxides from spatial atomic layer deposition

Maas¹,

Mistry²,

Sleziona³

et al. 2022

Preprint

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In this letter we report on the synthesis of monolayers of MoS 2 via chemical vapor deposition directly on thin films of Al 2 O 3 grown by spatial atomic layer deposition. The synthesized monolayers are characterized by atomic force microscopy as well as confocal Raman and photoluminescence spectroscopies. Our data reveals that the morphology and properties of the 2D material differ strongly depending on its position on the substrate. Close to the material source, we find individual flakes with an edge length of several hundred microns exhibiting a tensile strain of 0.3 %, n-doping on the order of n e =0.2 × 10 13 cm −2 , and a dominant trion contribution to the photoluminescence signal. In contrast to this, we identify a mm-sized region downstream, that is made up from densely packed, small MoS 2 crystallites with an edge length of several microns down to the nanometer regime and a coverage of more than 70 %. This nano-crystalline layer shows a significantly reduced strain of only <0.02 %, photoluminescence emission at an energy of 1.86 eV with a reduced trion contribution, and appears to be p-doped with a carrier density of n h =0.1 × 10 13 cm −2 . The unusual p-type doping achieved here in a standard CVD process without substitutional doping, post-processing, or the use of additional chemicals may prove useful for applications.

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Section: Discussionsupporting

confidence: 65%

Growth of p-doped 2D-MoS$_2$ on metal oxides from spatial atomic layer deposition

Maas¹,

Mistry²,

Sleziona³

et al. 2022

Preprint

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“…Numerical simulations performed by R. A. Vila et al [53] using finite element modelling revealed a decreasing concentration gradient on the surface of the substrate as the distance from the Mo-source increases, and that the concentration gradient pattern is characterized as distinct parabolic growth zones commonly found in experiments [24,29,36,45,49]. Moreover, the presence of such a concentration gradient means that the local Mo:S ratio varies along the length of the growth substrate, increasing the probability of morphology evolutions [53], oxysulfide formations [33,36,48,[50][51][52] and MoS2 domain-shape changes [24]. To make matters worse, experimental factors, such as precursor amount, gas flow rate, substrate position relative to the MoO3 source, growth temperature, geometrical parameters and possibly the spatial distribution of the MoO3 precursor itself, all have an impact on the Mo flux arriving at the substrate.…”

Section: Resultsmentioning

confidence: 96%

CVD Synthesis of Intermediate State-Free, Large-Area and Continuous MoS2 via Single-Step Vapor-Phase Sulfurization of MoO2 Precursor

et al. 2021

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The low evaporation temperature and carcinogen classification of commonly used molybdenum trioxide (MoO3) precursor render it unsuitable for the safe and practical synthesis of molybdenum disulfide (MoS2). Furthermore, as evidenced by several experimental findings, the associated reaction constitutes a multistep process prone to the formation of uncontrolled amounts of intermediate MoS2−yOy phase mixed with the MoS2 crystals. Here, molybdenum dioxide (MoO2), a chemically more stable and safer oxide than MoO3, was utilized to successfully grow cm-scale continuous films of monolayer MoS2. A high-resolution optical image stitching approach and Raman line mapping were used to confirm the composition and homogeneity of the material grown across the substrate. A detailed examination of the surface morphology of the continuous film revealed that, as the gas flow rate increased by an order of magnitude, the grain-boundary separation dramatically reduced, implying a transition from a kinetically to thermodynamically controlled growth. Importantly, the single-step vapor-phase sulfurization (VPS) reaction of MoO2 was shown to suppress intermediate state formations for a wide range of experimental parameters investigated and is completely absent, provided that the global S:Mo loading ratio is set higher than the stoichiometric ratio of 3:1 required by the VPS reaction.

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“…MoS 2 sheets are grown on a ∼300 nm SiO 2 /Si substrate by chemical vapor deposition method using MoO 3 and sulfur as a precursor at ∼700°C in an argon environment. 39 Raman and PL measurements are carried out with 532 nm laser line, keeping grating at 600 line mm −1 , using WITEC alpha 300 R Raman spectrometer. 40 AFM measurement on monolayer MoS 2 is conducted using a Bruker Multimode 8 AFM system in tapping mode under ambient conditions.…”

Section: Methodsmentioning

confidence: 99%

Sculpting Artificial Edges in Monolayer MoS₂ for Controlled Formation of Surface-Enhanced Raman Hotspots

Rani¹,

Yoshimura

Das

et al. 2020

ACS Nano

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Hotspot engineering has the potential to transform the field of surface-enhanced Raman spectroscopy (SERS) by enabling ultrasensitive and reproducible detection of analytes. However, the ability to controllably generate SERS hotspots, with desired location and geometry, over large-area substrates, has remained elusive. In this study, we sculpt artificial edges in monolayer molybdenum disulfide (MoS2) by low-power focused laser-cutting. We find that when gold nanoparticles (AuNPs) are deposited on MoS2 by drop-casting, the AuNPs tend to accumulate predominantly along the artificial edges. First-principles density functional theory (DFT) calculations indicate strong binding of AuNPs with the artificial edges due to dangling bonds that are ubiquitous on the unpassivated (laser-cut) edges. The dense accumulation of AuNPs along the artificial edges intensifies plasmonic effects in these regions, creating hotspots exclusively along the artificial edges. DFT further indicates that adsorption of AuNPs along the artificial edges prompts a transition from semiconducting to metallic behavior, which can further intensify the plasmonic effect along the artificial edges. These effects are observed exclusively for the sculpted (i.e., cut) edges and not observed for the MoS2 surface (away from the cut edges) or along the natural (passivated) edges of the MoS2 sheet. To demonstrate the practical utility of this concept, we use our substrate to detect Rhodamine B (RhB) with a large SERS enhancement (∼104) at the hotspots for RhB concentrations as low as ∼10–10 M. The single-step laser-etching process reported here can be used to controllably generate arrays of SERS hotspots. As such, this concept offers several advantages over previously reported SERS substrates that rely on electrochemical deposition, e-beam lithography, nanoimprinting, or photolithography. Whereas we have focused our study on MoS2, this concept could, in principle, be extended to a variety of 2D material platforms.

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Growth of Highly Crystalline and Large Scale Monolayer MoS₂ by CVD: The Role of substrate Position

Cited by 35 publications

References 49 publications

Growth of p-doped 2D-MoS$_2$ on metal oxides from spatial atomic layer deposition

Growth of p-doped 2D-MoS$_2$ on metal oxides from spatial atomic layer deposition

CVD Synthesis of Intermediate State-Free, Large-Area and Continuous MoS2 via Single-Step Vapor-Phase Sulfurization of MoO2 Precursor

Sculpting Artificial Edges in Monolayer MoS₂ for Controlled Formation of Surface-Enhanced Raman Hotspots

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Growth of Highly Crystalline and Large Scale Monolayer MoS2 by CVD: The Role of substrate Position

Cited by 35 publications

References 49 publications

Growth of p-doped 2D-MoS$_2$ on metal oxides from spatial atomic layer deposition

Growth of p-doped 2D-MoS$_2$ on metal oxides from spatial atomic layer deposition

CVD Synthesis of Intermediate State-Free, Large-Area and Continuous MoS2 via Single-Step Vapor-Phase Sulfurization of MoO2 Precursor

Sculpting Artificial Edges in Monolayer MoS2 for Controlled Formation of Surface-Enhanced Raman Hotspots

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Resources

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Growth of Highly Crystalline and Large Scale Monolayer MoS₂ by CVD: The Role of substrate Position

Sculpting Artificial Edges in Monolayer MoS₂ for Controlled Formation of Surface-Enhanced Raman Hotspots