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.
Highlights
Two-dimensional materials (2D) with their heterostructure interface manipulating bring infinite possibilities and many unprecedented devices in electronics [1], [2]
The various 2D materials have been the fertile ground of spintronics for low-power electronics [2], including efficient spin transport [3], spin relaxation [4], [5] and spin logic devices [6], [7] based on graphene and transition metal dichalcogenides (TMDs) [2], [8]–[10]
Compared with the requirement of making a hemispherical handle substrate [32] to transfer a sample with a specific area, in our method, inspired by the concept of ‘‘movable-type stencil’’, it only needs to control the edge of the polyvinyl alcohol (PVA) to overlap with a designate area, and greatly simplifies the process
Summary
Two-dimensional materials (2D) with their heterostructure interface manipulating bring infinite possibilities and many unprecedented devices in electronics [1], [2]. Another kind of transfer methods represented by pre-fabricated PDMS film has been shown to reduce the contamination [26], but it is difficult to pick up 2D atomic layers [27] to construct heterostructures, especially the stacking of more layers by a flexible and modularized way.
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