Considerations for utilizing sodium chloride in epitaxial molybdenum disulfide

• Main Authors: Zhang, Kehao, Bersch, Brian M, Zhang, Fu, Briggs, Natalie C, Subramanian, Shruti, Xu, Ke, Chubarov, Mikhail, Wang, Ke, Lerach, Jordan, Redwing, Joan M, Fullerton-Shirey, Susan K, Terrones, Mauricio, Robinson, Joshua A
• Format: Journal Article
• Language: English
• Published: 30-05-2018
• Subjects: Physics - Materials Science
• DOI: 10.48550/arxiv.1805.12264

The utilization of alkali salts, such as NaCl and KI, have enabled the
successful growth of large single domain and fully coalesced polycrystalline
two-dimensional (2D) transition metal dichalcogenide layers. However, the
impact of alkali salts on photonic and electronic properties are not fully
established. In this work, we report alkali-free epitaxy of MoS2 on sapphire
and benchmark the properties against alkali-assisted growth of MoS2. This study
demonstrates that although NaCl can dramatically increase the domain size of
monolayer MoS2 by 20 times, it can also induce strong optical and electronic
heterogeneities in as-grown large-scale films. This work elucidates that
utilization of NaCl can lead to variation in growth rates, loss of epitaxy, and
a high density of nanoscale MoS2 particles (4/{\mu}m2). Such phenomena suggest
that alkali atoms play an important role in Mo and S adatom mobility and
strongly influence the 2D/sapphire interface during growth. Compared to
alkali-free synthesis under the same growth conditions, MoS2 growth assisted by
NaCl results in >1% tensile strain in as-grown domains, which reduces
photoluminescence by ~20x and degrades transistor performance.