Laboratoire d'Innovation en Chimie des Surfaces et Nanosciences (LICSEN), Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Énergie, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette cedex, France.
Institut Universitaire de Technologie de Saida, Université Libanaise, Saida, Lebanon.
Sci Adv. 2017 May 12;3(5):e1601724. doi: 10.1126/sciadv.1601724. eCollection 2017 May.
The rapid rise of two-dimensional nanomaterials implies the development of new versatile, high-resolution visualization and placement techniques. For example, a single graphene layer becomes observable on Si/SiO substrates by reflected light under optical microscopy because of interference effects when the thickness of silicon oxide is optimized. However, differentiating monolayers from bilayers remains challenging, and advanced techniques, such as Raman mapping, atomic force microscopy (AFM), or scanning electron microscopy (SEM) are more suitable to observe graphene monolayers. The first two techniques are slow, and the third is operated in vacuum; hence, in all cases, real-time experiments including notably chemical modifications are not accessible. The development of optical microscopy techniques that combine the speed, large area, and high contrast of SEM with the topological information of AFM is therefore highly desirable. We introduce a new widefield optical microscopy technique based on the use of previously unknown antireflection and absorbing (ARA) layers that yield ultrahigh contrast reflection imaging of monolayers. The BALM (backside absorbing layer microscopy) technique can achieve the subnanometer-scale vertical resolution, large area, and real-time imaging. Moreover, the inverted optical microscope geometry allows its easy implementation and combination with other techniques. We notably demonstrate the potentiality of BALM by in operando imaging chemical modifications of graphene oxide. The technique can be applied to the deposition, observation, and modification of any nanometer-thick materials.
二维纳米材料的迅速崛起意味着新的多功能、高分辨率可视化和定位技术的发展。例如，通过优化氧化硅的厚度，在光学显微镜下，硅/二氧化硅衬底上的单层石墨烯由于干涉效应而变得可见。然而，单层和双层之间的区分仍然具有挑战性，更适合观察石墨烯单层的高级技术，如拉曼映射、原子力显微镜（AFM）或扫描电子显微镜（SEM）。前两种技术较慢，第三种在真空中操作；因此，在所有情况下，都无法进行实时实验，包括显著的化学修饰。因此，非常需要开发将 SEM 的速度、大面积和高对比度与 AFM 的拓扑信息相结合的光学显微镜技术。我们引入了一种新的宽场光学显微镜技术，该技术基于使用以前未知的抗反射和吸收（ARA）层，这些层可实现单层的超高对比度反射成像。BALM（背面吸收层显微镜）技术可实现亚纳米级的垂直分辨率、大面积和实时成像。此外，倒置的光学显微镜几何形状允许其易于实现并与其他技术结合。我们通过在操作中对氧化石墨烯的化学修饰进行成像，展示了 BALM 的潜力。该技术可应用于任何纳米厚度材料的沉积、观察和修饰。
