DQMP and GAP , Université de Genéve , 24 quai Ernest Ansermet , CH-1211 Geneva , Switzerland.
Institut de Physique de la Matiére Complexe , EPFL , CCH-1015 Lausanne , Switzerland.
Nano Lett. 2018 Aug 8;18(8):5146-5152. doi: 10.1021/acs.nanolett.8b02066. Epub 2018 Jul 19.
Recent technical progress demonstrates the possibility of stacking together virtually any combination of atomically thin crystals of van der Waals bonded compounds to form new types of heterostructures and interfaces. As a result, there is the need to understand at a quantitative level how the interfacial properties are determined by the properties of the constituent 2D materials. We address this problem by studying the transport and optoelectronic response of two different interfaces based on transition-metal dichalcogenide monolayers, namely WSe-MoSe and WSe-MoS. By exploiting the spectroscopic capabilities of ionic liquid gated transistors, we show how the conduction and valence bands of the individual monolayers determine the bands of the interface, and we establish quantitatively (directly from the measurements) the energetic alignment of the bands in the different materials as well as the magnitude of the interfacial band gap. Photoluminescence and photocurrent measurements allow us to conclude that the band gap of the WSe-MoSe interface is direct in k space, whereas the gap of WSe/MoS is indirect. For WSe/MoSe, we detect the light emitted from the decay of interlayer excitons and determine experimentally their binding energy using the values of the interfacial band gap extracted from transport measurements. The technique that we employed to reach this conclusion demonstrates a rather-general strategy for characterizing quantitatively the interfacial properties in terms of the properties of the constituent atomic layers. The results presented here further illustrate how van der Waals interfaces of two distinct 2D semiconducting materials are composite systems that truly behave as artificial semiconductors, the properties of which can be deterministically defined by the selection of the appropriate constituent semiconducting monolayers.
最近的技术进展表明，几乎可以将任何组合的范德华键合原子层薄晶体堆叠在一起，以形成新型的异质结构和界面。因此，需要从定量的角度了解界面性质是如何由组成二维材料的性质决定的。我们通过研究两种不同的基于过渡金属二卤化物单层的界面的输运和光电响应来解决这个问题，这两种界面分别是 WSe-MoSe 和 WSe-MoS。通过利用离子液体门控晶体管的光谱学能力，我们展示了如何通过单个单层的导带和价带来确定界面的能带，并且我们定量地（直接从测量中）建立了不同材料中能带的能量排列以及界面带隙的大小。光致发光和光电流测量使我们能够得出结论，WSe-MoSe 界面的带隙在 k 空间中是直接的，而 WSe/MoS 的带隙是间接的。对于 WSe/MoSe，我们检测到从层间激子衰减中发射的光，并使用从输运测量中提取的界面带隙值实验确定其结合能。我们采用的技术来得出这个结论，展示了一种相当普遍的策略，用于根据组成原子层的性质定量地描述界面性质。这里呈现的结果进一步说明了如何两个不同的二维半导体材料的范德华界面是复合系统，它们真正地表现为人工半导体，其性质可以通过选择适当的组成半导体单层来确定。
