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Thermal Annealing Effects on 2D Materials

Bizhani, Maryam
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1575627966654889

Abstract Details

2019, Master of Science (MS), Ohio University, Physics and Astronomy (Arts and Sciences).
Two-dimensional semiconducting transition metal dichalcogenides (TMDs), which can be easily exfoliated into thin layers, have attracted attention because of their interesting electrical and optical properties. The band structure of TMDs change dramatically with the number of layers, going from an indirect gap in bulk materials to direct gap in monolayers. Sizable band gap makes TMDs a promising material for optical and electronic applications. Indirect to direct transition of band gaps in 2D-TMDs lead to a drastic increase in photoluminescence (PL) intensity as the number of layers decrease. However, intrinsic defects and strain within the structure of monolayer TMD crystals can affect their electronic and optical properties. In this study the reliability of PL on intrinsic defects and strain is used to study the effects of thermal annealing on monolayer and few-layer molybdenum disulphide (MoS2). Here crystalline triangular islands of monolayer MoS2 of up to 20 μm in size are created using the chemical vapor deposition (CVD) technique. Grain boundaries have formed where the triangular crystal domains are merged. We report a highly non-uniform PL map of different regions in the sample due to strong enhancement of PL intensity at the grain boundaries within monolayer MoS2. PL intensity images of monolayer MoS2 reveal PL modification after annealing the sample at different temperatures. After thermal annealing of crystalline monolayer MoS2 up to 300 ◦C, the PL intensity at the grain boundaries shows negligible enhancement when compared to the crystalline region, resulting in a more uniform PL map. However, optical image of the sample shows the creation of cracks within the monolayer MoS2 region after thermal annealing at 400 ◦C. Furthermore, PL images of the sample reveal that the PL intensity is enhanced at cracks sites. Raman spectra of the crystal structure at the cracks shows about 2 cm−1 blue shift in the A1g mode due to electron-phonon interaction when compared to Raman spectra of the structure within the monolayer. This result implies that the enhancement of the PL at the cracks is due to the absorption of impurities, therefore p-doping and the conversion from trion to exciton. In addition, increase in the PL intensity and blue shift in the PL wavelength of monolayer MoS2 were observed after annealing the sample at high temperature. Preliminary results on thermal annealing of CVD-grown MoS2 and related future work are presented.
Eric Stinaff, Associate Professor of Physics and Astronomy (Advisor)
77 p.
Condensed Matter Physics; Physics
2D materials; MoS2; Thermal Annealing; Crystallization

Recommended Citations

Citations

  • Bizhani, M. (2019). Thermal Annealing Effects on 2D Materials [Master's thesis, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1575627966654889

    APA Style (7th edition)

  • Bizhani, Maryam. Thermal Annealing Effects on 2D Materials. 2019. Ohio University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1575627966654889.

    MLA Style (8th edition)

  • Bizhani, Maryam. "Thermal Annealing Effects on 2D Materials." Master's thesis, Ohio University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1575627966654889

    Chicago Manual of Style (17th edition)

ohiou1575627966654889
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© 2019, all rights reserved.
This open access ETD is published by Ohio University and OhioLINK.