Department of Physics and Astronomy, The University of Kansas , Lawrence, Kansas 66045, United States.
Department of Chemistry, University of Nebraska-Lincoln and Nebraska Center for Materials and Nanoscience , Lincoln, Nebraska 68588, United States.
Nano Lett. 2017 Mar 8;17(3):1623-1628. doi: 10.1021/acs.nanolett.6b04815. Epub 2017 Feb 22.
Two-dimensional materials, such as graphene and monolayer transition metal dichalcogenides, allow the fabrication of multilayer structures without lattice matching restriction. A central issue in developing such artificial materials is to understand and control the interlayer electron transfer process, which plays a key role in harnessing their emergent properties. Recent photoluminescence and transient absorption measurements revealed that the electron transfer in heterobilayers occurs on ultrafast time scales. However, there is still a lack of fundamental understanding on how this process can be so efficient at van der Waals interfaces. Here we show evidence suggesting the coherent nature of such interlayer electron transfer. In a trilayer of MoS-WS-MoSe, electrons excited in MoSe transfer to MoS in about one picosecond. Surprisingly, these electrons do not populate the middle WS layer during this process. Calculations showed the coherent nature of the charge transfer and reproduced the measured electron transfer time. The hole transfer from MoS to MoSe is also found to be efficient and ultrafast. The separation of electrons and holes extends their lifetimes to more than one nanosecond, suggesting potential applications of such multilayer structures in optoelectronics.
二维材料，如石墨烯和单层过渡金属二卤化物，允许在没有晶格匹配限制的情况下制造多层结构。开发这种人工材料的一个核心问题是理解和控制层间电子转移过程，这对于利用其新兴特性起着关键作用。最近的光致发光和瞬态吸收测量表明，异质双层中的电子转移发生在超快时间尺度上。然而，对于这个过程在范德华界面上如何能如此高效，我们仍然缺乏基本的理解。在这里，我们展示了表明这种层间电子转移具有相干性质的证据。在 MoS-WS-MoSe 的三层中，在 MoSe 中激发的电子在大约一个皮秒内转移到 MoS。令人惊讶的是，在这个过程中，这些电子不会填充中间的 WS 层。计算表明，电荷转移具有相干性质，并再现了测量的电子转移时间。从 MoS 到 MoSe 的空穴转移也是高效和超快的。电子和空穴的分离将它们的寿命延长到超过一纳秒，这表明这种多层结构在光电子学中有潜在的应用。
