The rapid development of two-dimensional (2D) materials has significantly transformed numerous research fields, creating unprecedented opportunities for advanced devices. The remarkable properties of these materials, including exceptional electrical conductivity, mechanical strength, and thermal stability, render them ideal candidates for applications in electronic and optoelectronic devices, thermal management solutions, energy storage systems, and sensors1,2,3,4,5,6,7,8. Additionally, the ability to construct van der Waals (vdW) heterostructures enhances their functionality, allowing for precise engineering of band structures and interlayer interactions9,10,11,12,13. This capability can lead to new or improved material properties tailored to specific applications.
However, the handling and manipulation of 2D materials pose considerable challenges, particularly in preserving their exceptional quality during processing. Residue contamination from conventional fabrication techniques can significantly undermine the integrity of the materials, adversely affecting their performance and reliability in devices14,15. The use of polymers in the fabrication of 2D materials often leaves unwanted residues16,17. To address this issue, several researchers have explored advanced fabrication techniques and clean transfer processes to enhance the production of high-purity 2D materials. Wang et al. introduced an innovative assembly technique that leverages vdW adhesion to achieve clean interfaces in graphene/boron nitride heterostructures18. Building on this concept, Wen et al. recently employed a vdW-assisted dry-transfer technique using h-BN as an intermediate layer, which allowed the clean detachment of single flakes by laterally peeling off the vdW layer19. In a notable prior technique, Pizzocchero et al. developed the "hot pick-up" technique for batch assembly of heterostructures, demonstrating rapid and high-yield production of blister-free interfaces by stacking at elevated temperatures20. Additionally, Wang et al. proposed a polymer-free approach using flexible silicon nitride membranes, which allows for clean assembly under ultra-high vacuum and high temperatures21. While previous studies have developed excellent methods, the ability to obtain residue-free single flakes and implement an easy processing method remains essential. Therefore, developing effective methods for residue-free processing is crucial for maximizing the potential of 2D materials in practical applications.
In the previous work by Lee et al., a novel fabrication method was developed that leverages the inherent vdW interactions between 2D materials to obtain single flakes and assemble heterostructures without using polymer support layers22. Comprehensive characterization, including atomic force microscopy (AFM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and electrical measurements, confirmed the residue-free nature of both the transferred flakes and the resulting heterostructures. Building upon this residue-free transfer platform, the current work provides a detailed and protocol-oriented guide that covers the entire process from experimental setup to the expanded assembly technique of complex heterostructures. Specifically, the setup of a dry transfer system, strategies for stamp preparation, and optimized procedures for obtaining clean and thin flakes of h-BN and MoS2 are detailed. These materials are extensively used due to their strong vdW adhesion and advantageous electronic properties13,23,24,25. Additionally, systematic techniques for sequential pick-up and residue-free release are described, along with various heterostructure assembly techniques such as top-down, bottom-up, and modular stacking processes.
The article is organized as follows: step 1 and step 2 detail the design of the dry transfer system and the fabrication of two types of stamps, which include a pre-exfoliation stamp and a tape stamp. Step 3 outlines the process for producing residue-free flakes using these stamps. Step 4 and step 5 describe the procedures for vertical stacking via residue-free stamp, enabling the construction of complex heterostructures. Finally, step 6 presents an AFM-tip squeezing technique to selectively remove interfacial blisters, thereby enhancing interfacial quality after assembly. Overall, these protocols aim to provide a versatile and reproducible methodology for fabricating clean and high-quality 2D heterostructures.