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ABSTRACT Scalable synthesis of two-dimensional molybdenum disulfide (MoS 2 ) via chemical vapor deposition (CVD) is of considerable interests for many applications in electronics and optoelectronics. Here, we investigate the CVD growth of MoS 2 single crystals on sapphire substrates by using thermally evaporated molybdenum trioxide (MoO 3 ) thin films as molybdenum (Mo) source instead of conventionally used MoO 3 powder for co-evaporation synthesis. The MoO 3 thin film source provides uniform Mo vapor pressure in the growth chamber resulting in clean and reproducible MoS 2 triangles without any oxide or oxysulfide species. Scanning electron microscopy, Raman spectroscopy, photoluminescence spectroscopy and atomic force microscopy characterization were performed to characterize the growth results. Very high photoluminescence (PL) response was observed at 1.85 eV which is a good implication of high optical quality of these crystals directly grown on sapphire substrate.
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Elucidation of the growth mechanism of MoS2 during the CVD process
ABSTRACT Chemical vapor deposition (CVD) growth of two-dimensional molybdenum disulfide (MoS 2 ) using molybdenum trioxide (MoO 3 ) and sulfur (S) powder often results in intermediate molybdenum oxy-sulfide (MoOS 2 ) species along with MoS 2 due to a lack of control over the vapor pressure required for the clean growth. Much effort has been devoted in understanding and controlling of these intermediate MoOS 2 specifies. Here, we show that with a second step sulfurization at moderate temperatures, these MoOS 2 crystals can be transformed to monolayer MoS 2 crystals. Scanning electron microscopy, Raman and photoluminescence spectroscopy and atomic force microscopy characterization carried out before and after re-sulfurization confirm the monolayer MoS 2 growth via this route. This study shows that MoOS 2 formed at the intermediate state can be successfully recycled to MoS 2 .
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- Award ID(s):
- 1728309
- PAR ID:
- 10107188
- Date Published:
- Journal Name:
- MRS Advances
- Volume:
- 4
- Issue:
- 10
- ISSN:
- 2059-8521
- Page Range / eLocation ID:
- 581 to 586
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Monolayer molybdenum disulfide (MoS 2 ) is one of the most studied two-dimensional (2D) transition metal dichalcogenides that is being investigated for various optoelectronic properties, such as catalysis, sensors, photovoltaics, and batteries. One such property that makes this material attractive is the ease in which 2D MoS 2 can be converted between the semiconducting (2H) and metallic/semi-metallic (1T/1T′) phases or heavily n-type doped 2H phase with ion intercalation, strain, or excess negative charge. Using n -butyl lithium (BuLi) immersion treatments, we achieve 2H MoS 2 monolayers that are heavily n-type doped with shorter immersion times (10–120 mins) or conversion to the 1T/1T′ phase with longer immersion times (6–24 h); however, these doped/converted monolayers are not stable and promptly revert back to the initial 2H phase upon exposure to air. To overcome this issue and maintain the modification of the monolayer MoS 2 upon air exposure, we use BuLi treatments plus surface functionalization p-(CH 3 CH 2 ) 2 NPh-MoS 2 (Et 2 N-MoS 2 )—to maintain heavily n-type doped 2H phase or the 1T/1T′ phase, which is preserved for over two weeks when on indium tin oxide or sapphire substrates. We also determine that the low sheet resistance and metallic-like properties correlate with the BuLi immersion times. These modified MoS 2 materials are characterized with confocal Raman/photoluminescence, absorption, x-ray photoelectron spectroscopy as well as scanning Kelvin probe microscopy, scanning electrochemical microscopy, and four-point probe sheet resistance measurements to quantify the differences in the monolayer optoelectronic properties. We will demonstrate chemical methodologies to control the modified monolayer MoS 2 that likely extend to other 2D transition metal dichalcogenides, which will greatly expand the uses for these nanomaterials.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1557/adv.2018.660
