Schwestka Janine, Inani Heena, Tripathi Mukesh, Niggas Anna, McEvoy Niall, Libisch Florian, Aumayr Friedrich, Kotakoski Jani, Wilhelm Richard A
TU Wien, Institute of Applied Physics, Vienna 1040, Austria.
University of Vienna, Faculty of Physics, Vienna 1090, Austria.
ACS Nano. 2020 Aug 25;14(8):10536-10543. doi: 10.1021/acsnano.0c04476. Epub 2020 Aug 7.
The growing family of 2D materials led not long ago to combining different 2D layers and building artificial systems in the form of van der Waals heterostructures. Tailoring of heterostructure properties postgrowth would greatly benefit from a modification technique with a monolayer precision. However, appropriate techniques for material modification with this precision are still missing. To achieve such control, slow highly charged ions appear ideal as they carry high amounts of potential energy, which is released rapidly upon ion neutralization at the position of the ion. The resulting potential energy deposition is thus limited to just a few atomic layers (in contrast to the kinetic energy deposition). Here, we irradiated a freestanding van der Waals MoS/graphene heterostructure with 1.3 keV/amu xenon ions in high charge states of 38, which led to nanometer-sized pores that appear only in the MoS facing the ion beam, but not in graphene beneath the hole. Reversing the stacking order leaves both layers undamaged, which we attribute to the high conductivity and carrier mobility in graphene acting as a shield for the MoS underneath. Our main focus is here on monolayer MoS, but we also analyzed areas with few-layer structures and observed that the perforation is limited to the two topmost MoS layers, whereas deeper layers remain intact. Our results demonstrate that in addition to already being a valuable tool for materials processing, the usability of ion irradiation can be extended to mono- (or bi)layer manipulation of van der Waals heterostructures when the localized potential energy deposition of highly charged ions is also added to the toolbox.
不久前，二维材料家族不断壮大，促使人们将不同的二维层结合起来，构建范德华异质结构形式的人工系统。生长后对异质结构特性进行定制将极大地受益于具有单层精度的改性技术。然而，目前仍缺乏具有这种精度的材料改性的合适技术。为了实现这种控制，慢速高电荷离子似乎是理想的选择，因为它们携带大量势能，在离子中和时会在离子位置迅速释放。因此，由此产生的势能沉积仅限于几个原子层（与动能沉积相反）。在这里，我们用1.3 keV/amu的38价态氙离子辐照了一个独立的范德华MoS/石墨烯异质结构，这导致了仅在面向离子束的MoS中出现纳米尺寸的孔，而在孔下方的石墨烯中没有出现。颠倒堆叠顺序会使两层都不受损伤，我们将此归因于石墨烯中的高导电性和载流子迁移率对下方的MoS起到了屏蔽作用。我们这里主要关注单层MoS，但我们也分析了少层结构的区域，观察到穿孔仅限于最上面的两层MoS，而更深的层保持完整。我们的结果表明，除了已经是材料加工的一种有价值的工具外，当高电荷离子的局部势能沉积也被添加到工具库中时，离子辐照的可用性可以扩展到范德华异质结构的单层（或双层）操纵。
