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Selective Growth and Robust Valley Polarization of Bilayer 3R-MoS2
ACS Applied Materials & Interfaces ( IF 8.3 ) Pub Date : 2021-11-19 , DOI: 10.1021/acsami.1c16889 Farman Ullah 1 , Je-Ho Lee 2 , Zeeshan Tahir 1 , Abdus Samad 1 , Chinh Tam Le 1 , Jungcheol Kim 3 , Donggyu Kim 3 , Mamoon Ur Rashid 1 , Sol Lee 4 , Kwanpyo Kim 4 , Hyeonsik Cheong 3 , Joon I Jang 3 , Maeng-Je Seong 2 , Yong Soo Kim 1
ACS Applied Materials & Interfaces ( IF 8.3 ) Pub Date : 2021-11-19 , DOI: 10.1021/acsami.1c16889 Farman Ullah 1 , Je-Ho Lee 2 , Zeeshan Tahir 1 , Abdus Samad 1 , Chinh Tam Le 1 , Jungcheol Kim 3 , Donggyu Kim 3 , Mamoon Ur Rashid 1 , Sol Lee 4 , Kwanpyo Kim 4 , Hyeonsik Cheong 3 , Joon I Jang 3 , Maeng-Je Seong 2 , Yong Soo Kim 1
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Noncentrosymmetric transition-metal dichalcogenides, particularly their 3R polymorphs, provide a robust setting for valleytronics. Here, we report on the selective growth of monolayers and bilayers of MoS2, which were acquired from two closely but differently oriented substrates in a chemical vapor deposition reactor. It turns out that as-grown bilayers are predominantly 3R-type, not more common 2H-type, as verified by microscopic and spectroscopic characterization. As expected, the 3R bilayer showed a significantly higher valley polarization compared with the centrosymmetric 2H bilayer, which undergoes efficient interlayer scattering across contrasting valleys because of their vertical alignment of the K and K′ points in momentum space. Interestingly, the 3R bilayer showed even higher valley polarization compared with the monolayer counterpart. Moreover, the 3R bilayer reasonably maintained its valley efficiency over a very wide range of excitation power density from ∼0.16 kW/cm2 to ∼0.16 MW/cm2 at both low and room temperatures. These observations are rather surprising because valley dephasing could be more efficient in the bilayer via both interlayer and intralayer scatterings, whereas only intralayer scattering is allowed in the monolayer. The improved valley polarization of the 3R bilayer can be attributed to its indirect-gap nature, where valley-polarized excitons can relax into the valley-insensitive band edge, which otherwise scatter into the contrasting valley to effectively cancel out the initial valley polarization. Our results provide a facile route for the growth of 3R-MoS2 bilayers that could be utilized as a platform for advancing valleytronics.
中文翻译：
双层 3R-MoS2 的选择性生长和鲁棒谷极化
非中心对称过渡金属二硫属化物，尤其是它们的 3 R多晶型物，为谷电子学提供了强大的环境。在这里，我们报告了 MoS 2的单层和双层的选择性生长，它们是在化学气相沉积反应器中从两个紧密但方向不同的基板中获得的。结果证明，生长的双层主要是 3 R型，而不是更常见的 2 H型，如显微镜和光谱表征所证实的。正如预期的那样，与中心对称的 2 H相比，3 R双层显示出明显更高的谷极化双层，由于它们在动量空间中K和K ' 点的垂直排列，因此在对比谷中经历了有效的层间散射。有趣的是，与单层对应物相比，3 R双层显示出更高的谷极化。此外，3 R双层在从~0.16 kW/cm 2到~0.16 MW/cm 2的非常宽的激发功率密度范围内合理地保持其谷效率在低温和室温下。这些观察结果相当令人惊讶，因为通过层间和层内散射在双层中谷相移可能更有效，而在单层中只允许层内散射。3 R双层改进的谷极化可归因于其间接间隙性质，其中谷极化激子可以弛豫到谷不敏感带边缘，否则会散射到对比谷中以有效抵消初始谷极化。我们的结果为 3 R -MoS 2双层的生长提供了一条简便的途径，可用作推进谷电子学的平台。
更新日期：2021-12-08
中文翻译：
双层 3R-MoS2 的选择性生长和鲁棒谷极化
非中心对称过渡金属二硫属化物，尤其是它们的 3 R多晶型物，为谷电子学提供了强大的环境。在这里，我们报告了 MoS 2的单层和双层的选择性生长，它们是在化学气相沉积反应器中从两个紧密但方向不同的基板中获得的。结果证明，生长的双层主要是 3 R型，而不是更常见的 2 H型，如显微镜和光谱表征所证实的。正如预期的那样，与中心对称的 2 H相比，3 R双层显示出明显更高的谷极化双层，由于它们在动量空间中K和K ' 点的垂直排列，因此在对比谷中经历了有效的层间散射。有趣的是，与单层对应物相比，3 R双层显示出更高的谷极化。此外，3 R双层在从~0.16 kW/cm 2到~0.16 MW/cm 2的非常宽的激发功率密度范围内合理地保持其谷效率在低温和室温下。这些观察结果相当令人惊讶，因为通过层间和层内散射在双层中谷相移可能更有效，而在单层中只允许层内散射。3 R双层改进的谷极化可归因于其间接间隙性质，其中谷极化激子可以弛豫到谷不敏感带边缘，否则会散射到对比谷中以有效抵消初始谷极化。我们的结果为 3 R -MoS 2双层的生长提供了一条简便的途径，可用作推进谷电子学的平台。
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