Universal transfer and stacking technique of van der Waals heterostructures for spintronics

TL;DR

This paper presents a universal, clean, and flexible transfer method using PVA film for assembling van der Waals heterostructures from various 2D materials, enhancing device quality and applicability in spintronics.

Contribution

Introduces a novel PVA-based transfer technique that improves interface cleanliness, flexibility, and spatial accuracy for 2D material stacking, applicable to diverse preparation methods.

Findings

Successful fabrication of a WSe2 spin valve device demonstrating high performance.

The method achieves contamination-free interfaces and precise stacking.

Applicable to both CVD-grown and exfoliated 2D materials.

Abstract

The key to achieving high-quality van der Waals heterostructure devices made from various two-dimensional (2D) materials lies in the control over clean and flexible interfaces. However, existing transfer methods based on different mediators possess insufficiencies including the presence of residues, the unavailability of flexible interface engineering, and the selectivity towards materials and substrates since their adhesions differ considerably with the various preparation conditions, from chemical vapor deposition (CVD) growth to mechanical exfoliation. In this paper, we introduce a more universal method using a prefabricated polyvinyl alcohol (PVA) film to transfer and stack 2D materials, whether they are prepared by CVD or exfoliation. This peel-off and drop-off technique promises an ideal interface of the materials without introducing contamination. In addition, the method exhibits a micron-scale spatial transfer accuracy and meets special experimental conditions such as the preparation of twisted graphene and the 2D/metal heterostructure construction. We illustrate the superiority of this method with a WSe2 vertical spin valve device, whose performance verifies the applicability and advantages of such a method for spintronics. Our PVA-assisted transfer process will promote the development of high-performance 2D-material-based devices.