Nano-“Squeegee” for the Creation of Clean 2D Material Interfaces

Abstract

Two-dimensional (2D) materials exhibit many exciting phenomena that make them promising as materials for future electronic, optoelectronic, and mechanical devices. Because of their atomic thinness, interfaces play a dominant role in determining material behavior. In order to observe and exploit the unique properties of these materials, it is therefore vital to obtain clean and repeatable interfaces. However, the conventional mechanical stacking of atomically thin layers typically leads to trapped contaminants and spatially inhomogeneous interfaces, which obscure the true intrinsic behavior. This work presents a simple and generic approach to create clean 2D material interfaces in mechanically stacked structures. The operating principle is to use an AFM tip to controllably squeeze contaminants out from between 2D layers and their substrates, similar to a "squeegee". This approach leads to drastically improved homogeneity and consistency of 2D material interfaces, as demonstrated by AFM topography and significant reduction of photoluminescence line widths. Also, this approach enables emission from interlayer excitons, demonstrating that the technique enhances interlayer coupling in van der Waals heterostructures. The technique enables repeatable observation of intrinsic 2D material properties, which is crucial for the continued development of these promising materials.

Twist Angle-Dependent Atomic Reconstruction and Moiré Patterns in Transition Metal Dichalcogenide Heterostructures

“…Second, the MoSe2-WSe2 stack was picked up and transferred onto the desired graphite flakes (mechanically exfoliated) followed by nano-squeegee. 28…”

Mechanical cleaning of graphene using in situ electron microscopy

“…Techniques such as heating 8 , plasma treatment 9 , laser cleaning 10 , chemical activation 11 , and current-driven cleaning 12 have been tried out and tested. In addition, first steps toward mechanical cleaning have been made using AFM [13][14][15] , but without achieving atomically clean membranes. While some methods (especially aging at elevated temperatures in ultra-high vacuum) have produced reasonable results, there is no control of the size and location of clean areas.…”

Valley phenomena in the candidate phase change material WSe2(1-x)Te2x

“…To guarantee clean hBN/TMD contact, the nano-squeegee method was used with a scan line density of ≥ 10 nm/line and a scan speed of ≤ 30 µm/s as suggested by Rosenberger et al to physically push contaminants out from in between heterostructure interfaces. 33 Results of this procedure can be seen in the atomic force microscope image of Supplementary Fig. S5.…”