▎ 摘　　要

The rapid rise of two-dimensional nanomaterials implies the development of newversatile, high-resolution visualization and placement techniques. For example, a single graphene layer becomes observable on Si/SiO2 substrates by reflected light under opticalmicroscopy because of interference effectswhen the thickness of silicon oxide is optimized. However, differentiatingmonolayers frombilayers remains challenging, andadvanced techniques, such as Raman mapping, atomic forcemicroscopy (AFM), or scanning electronmicroscopy (SEM) are more suitable to observe graphenemonolayers. The first twotechniques are slow, and the third is operated in vacuum; hence, in all cases, real-time experiments including notably chemicalmodifications are not accessible. The development of opticalmicroscopy 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 layermicroscopy) technique can achieve the subnanometer-scale vertical resolution, large area, and real-time imaging. Moreover, the inverted opticalmicroscope 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.