Refahi Abou Khachfe

Graphical Abstract In article number 2300068, Dominique Ausserré, Fabien Vialla and co-workers combine Backside Absorbing Layer Microscopy (BALM) and an original self-calibrating image analysis procedure to achieve simple, accurate monolayer counting in exfoliated 2D material stacks. The authors demonstrate characterization of flakes from 1 to >30 monolayer thickness with the challenging case of transparent hexagonal boron nitride (hBN).

Abstract The properties of two-dimensional (2D) material stacks critically depend on the number of monolayers (m) in the stack. It is therefore important to quantify this number, which is a local quantity since 2D stacks are essentially heterogeneous. Optical interferential techniques based on contrast-enhancing surfaces may be sensitive enough to visualize m variations but the experimental determination of m requires heavy and unstable comparisons with multiparameter numerical models.

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.