Terrylene on monolayer WS2: coverage-dependent molecular re-orientation and interfacial electronic energy levels†

IF 5.2 Q2 MATERIALS SCIENCE, MULTIDISCIPLINARY
Qiang Wang, Sifan You, Björn Kobin, Patrick Amsalem, Fengshuo Zu, Rongbin Wang, Andreas Opitz, Stefan Hecht, Lifeng Chi and Norbert Koch
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Abstract

The electronic, optical, and functional properties of van der Waals heterostructures comprising organic and two-dimensional inorganic semiconductors depend on the structure of the molecular assembly at and near the interface. Despite the rising interest in such heterostructures, very little is known about the, potentially complex, interplay between the structure and resulting (opto)electronic properties. Herein, we demonstrate with photoemission spectroscopy and scanning tunneling microscopy experiments a coverage dependence of the molecular assembly of terrylene deposited onto monolayer WS2 (with sapphire serving as the substrate) and show how this impacts interfacial electronic properties. Up to monolayer coverage, terrylene molecules adapt a flat-lying orientation, which changes to an inclined orientation for higher coverages. This re-orientation is accompanied with a reduction in terrylene ionization energy by over 400 meV and an accordingly larger energy level offset of frontier energy levels of the two semiconductors and shift of the highest occupied molecular orbital energy level away from the WS2 valence band. This can, for instance, reduce the charge-separation efficiency of the heterostructure with molecular multilayer coverage compared to that with only monolayer coverage. Furthermore, the modification of monolayer WS2 excitonic features through molecular film deposition was evaluated using optical spectroscopy, yielding effective dielectric constants for a series of Rydberg excitons and exciton binding energies for bare and terrylene-covered monolayer WS2 supported by sapphire. Altogether, these findings allow a comprehensive and detailed understanding of the (opto)electronic properties of this prototypical van der Waals heterostructure.

Abstract Image

单层WS2上的涤纶:覆盖度依赖的分子重取向和界面电子能级
由有机和二维无机半导体组成的范德华异质结构的电子、光学和功能特性取决于界面上和界面附近的分子组装结构。尽管人们对这种异质结构的兴趣日益浓厚,但人们对这种结构与由此产生的光电性质之间潜在的复杂相互作用知之甚少。在此,我们通过光电发射光谱和扫描隧道显微镜实验证明了沉积在单层WS2上的涤纶分子组装的覆盖依赖性(以蓝宝石作为衬底),并展示了这如何影响界面电子性能。在单层覆盖范围内,涤纶分子采用平铺取向,而在更高的覆盖范围内则变为倾斜取向。这种重定向伴随着乙烯电离能的降低超过400 meV,两种半导体的前沿能级相应地有更大的能级偏移,并使最高已占据分子轨道能级远离WS2价带。例如,这可以降低具有分子多层覆盖的异质结构与仅单层覆盖的异质结构的电荷分离效率。此外,利用光谱学评价了分子膜沉积对WS2单层激子特性的修饰,得到了一系列Rydberg激子的有效介电常数和蓝宝石支撑的裸露和覆盖三元乙烯的WS2单层激子结合能。总之,这些发现允许对这种原型范德华异质结构的(光电)电子性质有一个全面和详细的了解。
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来源期刊
Materials Advances
Materials Advances MATERIALS SCIENCE, MULTIDISCIPLINARY-
CiteScore
7.60
自引率
2.00%
发文量
665
审稿时长
5 weeks
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