Capillary-Force-Assisted Clean-PDMS Transfer 2D Materials for Heterostructures and Nano-Devices*

Transferring 2D materials flakes for heterostructures fabrication or simply for characterization plays an essential role. A popular method for 2D material transfer is PMMA transfer. The problem comes from the PMMA residue, which cannot be fully removed from the material surface and may result in poor performance. Another alternative method is the h-BN-flake transfer, but releasing the adhered 2D materials to expose their surfaces is impossible.
Here, we develop a capillary-force-assisted clean-PDMS technique that uses a thin layer of evaporative liquid (e.g., water, ethanol, and acetone) as an instant glue to increase the adhesion energy between 2D materials and PDMS for the pick-up step. After the liquid evaporates, the adhesion energy decreases, and the 2D materials can be released onto the target substrate easily. Using this method, a monolayer graphene FET was fabricated on SiO₂ with the low charge-neutral concentration of 3 × 10¹⁰ cm⁻² and the high carrier mobility of 48,820 cm²V^-1s^-1 at room temperature. A Gr-MoS₂-Gr heterostructure photodetector was built-up with high operation speed. Finally, a capillary-force model is developed to explain the experiment.