Controlled Adhesion of Ice - Towards Ultra-Clean 2D Materials.

The scalable 2D device fabrication and integration demand either the large-area synthesis or the post-synthesis transfer of 2D layers. While the direct synthesis of 2D materials on most targeted surfaces remains challenging, the transfer approach from the growth substrate onto the targeted surfaces offers alternative pathway for the applications and integrations. However, the current transfer techniques for the 2D materials predominantly involve polymers and organic solvents, which are liable to contaminate or deform the ultra-sensitive atomic layers. Here, we develop novel ice-aided transfer and ice-stamp transfer methods, in which water (ice) is the only medium in the entire process. Our atomic force microscopy studies showed the hexagonal 2D ice layer can be epitaxially formed between the substrates and 2D layers, enabling the firm attachment/facile detachment. In practice, the adhesion between various 2D materials and ice can be well controlled by temperature. Through such controlled adhesion of ice, we show our new transfer methods can yield ultra-high quality and exceptional cleanliness in transferred 2D flakes and continuous 2D films, and applicable for a wide range of substrates. Furthermore, beyond transfer, ice can also be used for cleaning the surfaces of 2D materials at higher temperatures. These novel techniques could enable the unprecedented ultra-clean 2D materials surfaces and performances, and will contribute to the upcoming technological revolutions associated with the 2D materials. This article is protected by copyright. All rights reserved.