Minimizing Residues and Strain in 2D Materials Transferred from PDMS

TL;DR

This paper presents methods to reduce residues and strain in 2D materials transferred from PDMS, improving the quality and reliability of 2D heterostructures for electronic and photonic applications.

Contribution

It introduces a UV-ozone pre-cleaning and high-temperature vacuum annealing process to minimize residues and strain in transferred 2D materials.

Findings

UV-ozone cleaning reduces organic residues

Vacuum annealing removes interfacial bubbles and wrinkles

Restores native surface morphology of 2D flakes

Abstract

Integrating layered two-dimensional (2D) materials into 3D heterostructures offers opportunities for novel material functionalities and applications in electronics and photonics. In order to build the highest quality heterostructures, it is crucial to preserve the cleanliness and morphology of 2D material surfaces that come in contact with polymers such as PDMS during transfer. Here we report that substantial residues and up to ~0.22% compressive strain can be present in monolayer MoS$_{2}$ flakes transferred using PDMS. We show that a UV-ozone pre-cleaning of the PDMS surface before exfoliation significantly reduces organic residues on transferred MoS$_{2}$ flakes. An additional 200$^{\circ}$C vacuum anneal after transfer efficiently removes interfacial bubbles and wrinkles as well as accumulated strain, thereby restoring the surface morphology of transferred flakes to their native state. Our recipe is important for building clean heterostructures of 2D materials and increasing the reproducibility and reliability of devices based on them.