Transfer of monolayer TMD WS2 and Raman study of substrate effects

Abstract

A facile transfer process for transition metal dichalcogenide WS2 flakes is reported and the effect of the underlying substrate on the flake properties is investigated using Raman spectroscopy. The flakes are transferred from their growth substrate using polymethyl methacrylate (PMMA) and a wet etch to allow the user to transfer the flakes to a final substrate using a microscope and micromanipulator combined with semi-transparent Kapton tape. The substrates used range from insulators such as industry standard high-k dielectric HfO2 and “green polymer” parylene-C, to conducting chemical vapor deposition (CVD) grown graphene. Raman spectroscopy is used first to confirm the material quality of the transferred flakes to the substrates and subsequently to analyze and separate the effects arising from material transfer from those arising from interactions with the substrate. We observe changes in the Raman spectra associated with the interactions between the substrates in the flakes. These interactions affect both in-plane and out-of-plane modes in different ways depending on their sources, for example strain or surface charge. These changes vary with final substrate, with the strongest effects being observed for WS2 transferred onto graphene and HfO2, demonstrating the importance of understanding substrate interaction for fabrication of future devices.

Crystalline tungsten sulfide thin films by atomic layer deposition and mild annealing

“…Studies of WS2 monolayers on different substrates have also shown changes in frequencies of up to 5 cm -1 for both the A1g and the E 1 2g modes depending on the substrate, at least partly due to strain. 71,76 The observed redshifts especially in our thicker films would imply a tensile strain. Regarding doping, a redshift of the A1g, and to a smaller degree of the E 1 2g mode, has been observed with increasing carrier concentration.…”

Materials analysis and focused ion beam nanofabrication of topological insulator Bi2Se3

“…For Bi 2 Se 3 samples on SiO 2 , they were directly exfoliated onto the substrate. For samples on silicon nitride membranes, the Bi 2 Se 3 was exfoliated onto PMMA, then positioned and transferred onto a 100 nm thick membrane substrate using a micromanipulator and microscope method outlined in Mlack et al 30 . After positioning, acetone was used to remove the PMMA and complete the transfer of the Bi 2 Se 3 to the membrane.…”

Photoluminescence and Raman Spectra Oscillations Induced by Laser Interference in Annealing‐Created Monolayer WS2 Bubbles

“…Like graphene, atomically thin WS 2 crystal is also a mechanically exceptional material, which can be grown or transferred on various substrates . On top of that, it is semiconductor, undergoing a transition from indirect to direct bandgap after thinning to monolayer .…”