Directional ultrafast charge transfer in a WSe2/MoSe2 heterostructure selectively probed by time-resolved SHG imaging microscopy,Nanoscale Horizons

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Directional ultrafast charge transfer in a WSe2/MoSe2 heterostructure selectively probed by time-resolved SHG imaging microscopy
Nanoscale Horizons ( IF 8.0 ) Pub Date : 2020-10-21 , DOI: 10.1039/d0nh00396d
Jonas E. Zimmermann _{1,

2,

3,

4} , Young Duck Kim _{5,

6,

7,

8} , James C. Hone _{5,

6,

7,

8} , Ulrich Höfer _{1,

2,

3,

4} , Gerson Mette _{1,

2,

3,

4}

Affiliation

Heterostructures of two-dimensional transition metal dichalcogenides (TMD) have shown promise for various optoelectronic and novel valleytronic applications. Due to their type-II band alignment, photoexcited electrons and holes can separate into different layers through ultrafast charge transfer. While this charge-transfer process is critical for potential applications, the underlying mechanisms still remain elusive. Here, we demonstrate for a rotationally mismatched WSe₂/MoSe₂ heterostructure that directional ultrafast charge transfer between the layers becomes accessible by time-resolved optical second-harmonic generation. By tuning the photon energy of the pump pulse, one of the two materials is resonantly excited, whereas the polarization of the probe pulse can be optimized to selectively detect the charge transfer into the other material. This allows us to explore the interlayer hole transfer from the WSe₂ into the MoSe₂ layer and vice versa, which appears within a few hundred femtoseconds via hybridized intermediate states at the Γ-point. Our approach enables systematic investigations of the charge transfer in dependence of the rotational layer mismatch in TMD heterostructures.

中文翻译：

时间分辨SHG成像显微镜选择性探测WSe2 / MoSe2异质结构中的定向超快电荷转移

二维过渡金属二硫属化合物（TMD）的异质结构已显示出可用于各种光电和新型山谷电子应用的前景。由于它们的II型能带排列，光激发的电子和空穴可以通过超快的电荷转移而分成不同的层。尽管此电荷转移过程对于潜在的应用至关重要，但其基本机制仍然难以捉摸。在这里，我们演示了旋转不匹配的WSe ₂ / MoSe ₂通过时间分辨光学二次谐波的产生，可以实现层间定向超快电荷转移的异质结构。通过调节泵浦脉冲的光子能量，两种材料中的一种被共振激发，而探测脉冲的极化可以被优化以选择性地检测电荷转移到另一种材料中。这使我们能够探索从WSe ₂到MoSe ₂层的层间空穴传输，反之亦然，通过Γ处的杂化中间态在几百飞秒内出现-点。我们的方法能够根据TMD异质结构中旋转层不匹配对电荷转移进行系统研究。

更新日期：2020-11-03

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