Centimeter-Scale 2D van der Waals Vertical Heterostructures Integrated on Deformable Substrates Enabled by Gold Sacrificial Layer-Assisted Growth

Study Summary

Two-dimensional (2D) heterostructure layers assembled from vertically-stacked 2D transition metal dichalcogenides (TMDs) exhibit large in-plane strain limits and unusual optical/electrical properties, offering unprecednted opportunties for emerging electronics and optoelectronics in new form factors. In order for them to be technolgically viable buildingblocks for such unconventinoal technologies, it is critically demanded to grow and integrate them onto flexible or arbitrary-shaped substrates on a large scale which is demanded by current microelectronics manufacutring processes. However, conventional approaches to assemble them on such non-conventional substrates via chemical growths or mechanical exfoliations have been limited with small-area transfers and integrations of 2D layers with uncontrolled spatial homogenities. We report a novel strategy to universally combine the centimeter-scale growth of 2D heterostructure layers composed of two distinct TMDs and their direct assembly on unconventional substrates enabled by their deterministic transfer and integration. By taking an advantage of the water-assisted debonding of gold (Au) interfaced with silicon dioxide (SiO2),we demonstrate a direct growth of 2D heterostructure layers on SiO2/Au-based substrates over an area of>2x2cm2and their facile transfer and integration compatible with flexible substrates.

Expected Effects

We report a novel strategy to directly integrate centimeter-scale 2D TMD vdW heterostructure layers on flexible SiO2 substrates without using strong chemical agents. We demonstrate the CVD growth of vertically-stacked, few layers-only 2D MoS2/WS2 heterostructure layers on “transferable substrates” which are stacks of SiO2/gold(Au) layers. By taking an advantage of the enhanced debonding nature of Au interfaced with SiO2 inside water, we demonstrate are liable lift-off of the 2D MoS2/WS2 vdW heterostructure layers attached to flexible SiO2 layers and their transfer/integrationon arbitrarily-shaped substrates over an area of>2x2cm2. This study opens up a pathway to explore 2D heterostructure layers as novel buidingblocks for large-scale, emerging devices of unconventional forms.

[Figure. 1] (a) Image of as-grown 2D MoS2/WS2 heterostructure layers on a SiO2/Au/SiO2/Si substrate. (b) Raman spectrum obtained from the sample, revealing the presence of both MoS2 and WS2. (c, d) Low-magnification TEM (c) and HRTEM (d) micrographs of the 2D MoS2/WS2 heterostructure layers in plane view. (e) STEM-EDS elemental mapping images revealing the uniform spatial distribution of constituent elements. The scale bar is 50 nm. (f) Cross-section TEM characterizations of 2D MoS2/WS2 heterostructure layers on a SiO2 (left) and their detailed crystalline structures (right). (g) ADF-TEM image of the corresponding MoS2/WS2 interface, revealing a distinct image contrast. (h) STEM-EDS elemental map to show the spatial localization of Mo and W at the interface.

[Figure. 2] (a−.f) Sequential procedures for the transfer of 2D MoS2/WS2 heterostructure layers using the water assisted Au-SiO2 separation. (g) PDMS-coated 2D WS2/MoS2 heterostructure layers integrated on the surface of a cup. (h) 2D MoS2/WS2 heterostructure layers on a PDMS transferred from a thermal release tape. (i) Raman spectrum from 2D MoS2/WS2 heterostructure (j) Transport characteristics of transferred 2D MoS2/WS2 heterostructure layers.

[Figure. 3] (a) Illustration for the direct growth of 2D MoS2 layers on Au-deposited substrates and their subsequent transfers. (b) 2D MoS2-grown on Au/SiO2/Si substrates. 2D MoS2 are selectively grown with Mo of different thicknesses (left: 3 nm, right: 10 nm). (c) Raman spectrum obtained from the 2D MoS2 layers grown on in panel b. (d)ADF-TEM micrographs of 2D MoS2 grown on a Au/SiO2/Si substrate. The zoom-in image (red box) reveals the growth of continuous 2D MoS2 layers. (e) ADF-TEM micrograph revealing the sharp 2D MoS2/Au interface. (f) Plane-view HRTEM micrograph of few-layer 2D MoS2 layers revealing Moiré.patterns. (g) 2D MoS2/Au before (left) and after (right) integration to a supporting tape. (h) Large-area 2D MoS2 layers attached to a supporting tape. (i) Patterned 2D MoS2 layers attached to a supporting tape.