Centimeter-scale Green Integration of Layer-by-Layer 2D TMD vdW Heterostructures on Arbitrary Substrates by Water-Assisted Layer Transfer

Abstract

Two-dimensional (2D) transition metal dichalcogenide (2D TMD) layers present an unusually ideal combination of excellent opto-electrical properties and mechanical tolerance projecting high promise for a wide range of emerging applications, particularly in flexible and stretchable devices. The prerequisite for realizing such opportunities is to reliably integrate large-area 2D TMDs of well-defined dimensions on mechanically pliable materials with targeted functionalities by transferring them from rigid growth substrates. Conventional approaches to overcome this challenge have been limited as they often suffer from the non-scalable integration of 2D TMDs whose structural and chemical integrity are altered through toxic chemicals-involved processes. Herein, we report a generic and reliable strategy to achieve the layer-by-layer integration of large-area 2D TMDs and their heterostructure variations onto a variety of unconventional substrates. This new 2D layer integration method employs water only without involving any other chemicals, thus renders distinguishable advantages over conventional approaches in terms of material property preservation and integration size scalability. We have demonstrated the generality of this method by integrating a variety of 2D TMDs and their heterogeneously-assembled vertical layers on exotic substrates such as plastics and papers. Moreover, we have verified its technological versatility by demonstrating centimeter-scale 2D TMDs-based flexible photodetectors and pressure sensors which are difficult to fabricate with conventional approaches. Fundamental principles for the water-assisted spontaneous separation of 2D TMD layers are also discussed.

Wafer‐scale vertical van der Waals heterostructures

“…The appearance of (opto)electronic devices based on wafer-scale 2D vdWHs arrays unveils their unprecedented potential for practical application. 34,65 Although remarkable progress has been made in synthesis and application of wafer-scale vdWHs, 66,70,80,100 challenges remain in this field. Firstly, in the aspect of materials synthesis, there is a lack of universe synthesis process for high-quality wafer-scale vdWHs.…”

“…30,34,65 In order to get rid of the effect of residual etchant, a water-assisted layer transfer method can be adopted. 36,66 The mechanical tension, caused by the different surface wettability of SiO 2 and MoS 2 when immersing the 2D MoS 2 grown on SiO 2 /Si substrate in water, overcame the weak vdW force between the 2D material and growth substrate. As a result, the MoS 2 thin film floating on the water surface could be transferred to a desired substrate for fabricating vdWHs.…”

“…As a result, the MoS 2 thin film floating on the water surface could be transferred to a desired substrate for fabricating vdWHs. 66 Since wet transfer method is no longer applicable when water sensitive or chemically unstable materials are involved, dry transfer method appears a more applicable approach for constructing vdWHs involving sensitive 2D materials. 67,68 This process can be achieved by using a thermal release tape (TRT) to attach the as-grown centimeter-scale 2D materials and then they were peeled off through a micromechanical stage with great care and low speed to ensure the full area adhesion.…”

“…Besides, large‐scale heterostructure arrays can be fabricated when the electron beam lithography (EBL) was used to pattern the transferred materials (Figure 2B). 30,34,65 In order to get rid of the effect of residual etchant, a water‐assisted layer transfer method can be adopted 36,66 . The mechanical tension, caused by the different surface wettability of SiO 2 and MoS 2 when immersing the 2D MoS 2 grown on SiO 2 /Si substrate in water, overcame the weak vdW force between the 2D material and growth substrate.…”

Two-Dimensional Near-Atom-Thickness Materials for Emerging Neuromorphic Devices and Applications

“…Particularly, one of the most significant challenges lies in how to retain the atomically sharp and clean interfaces among heterogeneously stacked distinct 2D layers avoiding structural and chemical inhomogeneity in between them. Various approaches have demonstrated the feasibility of the wafer-scale 2D layer transfer; these include polymer-assisted layer-by-layer transfer, strain-driven mechanical cracking, and water-assisted direct integration of 2D layers ( Han et al., 2020 ; Kang et al., 2015 ; Kim et al., 2019a ; Shim et al., 2018 ; Wang et al., 2020 ). However, it still remains technically challenging to congruently accompany wafer-level scalability and atomic-level precision in transferred 2D layers to ensure the reliable operation of complicated neural networks in a highly predictable manner.…”