Thickness determination of MoS2, MoSe2, WS2 and WSe2 on transparent stamps used for deterministic transfer of 2D materials

TL;DR

This paper introduces an optical microscopy-based method to accurately determine the thickness of common TMDCs on transparent stamps, facilitating easier identification of layer number for 2D material transfer processes.

Contribution

The study presents a simple, robust optical transmittance technique focusing on the blue channel to determine TMDC thickness on transparent substrates, applicable to MoS2, MoSe2, WS2, and WSe2.

Findings

Blue channel transmittance correlates monotonically with thickness.

Method is insensitive to doping variations.

Applicable to multiple TMDC materials.

Abstract

Here, we propose a method to determine the thickness of the most common transition metal dichalcogenides (TMDCs) placed on the surface of transparent stamps, used for the deterministic placement of two-dimensional materials, by analyzing the red, green and blue channels of transmission-mode optical microscopy images of the samples. In particular, the blue channel transmittance shows a large and monotonic thickness dependence, making it a very convenient probe of the flake thickness. The method proved to be robust given the small flake-to-flake variation and the insensitivity to doping changes of MoS2. We also tested the method for MoSe2, WS2 and WSe2. These results provide a reference guide to identify the number of layers of this family of materials on transparent substrates only using optical microscopy.