ACS Appl Mater Interfaces. 2018 Nov 28;10(47):40831-40837. doi: 10.1021/acsami.8b16374. Epub 2018 Nov 14.
The utilization of alkali salts, such as NaCl and KI, has 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 is not fully established. In this work, we report alkali-free epitaxy of MoS on sapphire and benchmark the properties against alkali-assisted growth of MoS. This study demonstrates that although NaCl can dramatically increase the domain size of monolayer MoS 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 high density of nanoscale MoS particles (4 ± 0.7/μm). 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, MoS growth assisted by NaCl results in >1% tensile strain in as-grown domains, which reduces photoluminescence by ∼20× and degrades transistor performance.
碱盐（如 NaCl 和 KI）的使用促进了大单晶和完全融合的二维（2D）过渡金属二硫属化物层的成功生长。然而，碱盐对光子和电子特性的影响尚未完全确定。在这项工作中，我们报告了蓝宝石上无碱的 MoS 外延，并将其性能与碱辅助的 MoS 生长进行了基准测试。本研究表明，尽管 NaCl 可以将单层 MoS 的畴尺寸提高 20 倍，但它也会在生长过程中导致大面积薄膜中强烈的光学和电子各向异性。这项工作阐明了 NaCl 的使用会导致生长速率的变化、外延的损失以及纳米级 MoS 颗粒的高密度（4±0.7/μm）。这些现象表明，碱原子在 Mo 和 S 吸附原子的迁移中起着重要作用，并在生长过程中强烈影响 2D/蓝宝石界面。与相同生长条件下无碱合成相比，在 NaCl 辅助下生长的 MoS 会导致生长域中存在超过 1%的拉伸应变，这会使光致发光降低约 20 倍，并降低晶体管性能。
