Ultrasonic Delamination Based Adhesion Testing for High-Throughput Assembly of van der Waals Heterostructures

TL;DR

This paper introduces ultrasonic delamination threshold testing to rapidly assess and control interfacial adhesion in 2D material heterostructures, enabling high-throughput assembly of high-quality van der Waals stacks.

Contribution

It presents a novel ultrasonic testing method for quick adhesion evaluation and demonstrates its application in optimizing high-throughput 2D heterostructure fabrication.

Findings

Ultrasonic delamination testing effectively measures substrate adhesion of 2D materials.

Controlled adhesion tuning improves the assembly process of van der Waals heterostructures.

High-quality twisted bilayer graphene and WSe₂ heterostructures were successfully fabricated.

Abstract

Two-dimensional (2D) materials assembled into van der Waals (vdW) heterostructures contain unlimited combinations of mechanical, optical, and electrical properties that can be harnessed for potential device applications. Critically, these structures require control over interfacial adhesion in order for them to be constructed and to have enough integrity to survive industrial fabrication processes upon their integration. Here, we promptly determine the quality of adhesion of various exfoliated 2D materials on conventional SiO$_{2}$/Si substrates using ultrasonic delamination threshold testing. This test allows us to quickly infer relative substrate adhesion based on the percent area of 2D flakes that survive a fixed time in an ultrasonic bath, allowing for control over process parameters that yield high or poor adhesion. We leverage this control of adhesion to optimize the vdW heterostructure assembly process, where we show that samples with high or low substrate adhesion relative to each other can be used selectively to construct high-throughput vdW stacks. Instead of tuning the adhesion of polymer stamps to 2D materials with constant 2D-substrate adhesion, we tune the 2D-substrate adhesion with constant stamp adhesion to 2D materials. The polymer stamps may be reused without any polymer melting steps, thus avoiding high temperatures (<120{\deg}C) and allowing for high-throughput production. We show that this procedure can be used to create high-quality 2D twisted bilayer graphene on SiO$_{2}$/Si, characterized with atomic force microscopy and Raman spectroscopic mapping, as well as low-angle twisted bilayer WSe$_{2}$ on h-BN/SiO$_{2}$/Si, where we show direct real-space visualization of moir\'e reconstruction with tilt angle-dependent scanning electron microscopy.