Thickness identification of thin InSe by optical microscopy methods

TL;DR

This paper evaluates four optical microscopy techniques for accurately determining the thickness of thin InSe flakes on various substrates, enhancing non-destructive characterization methods for this promising 2D material.

Contribution

It introduces and compares four optical methods, including transmittance, color assessment, Fresnel-law fitting, and photoluminescence analysis, for precise InSe thickness identification.

Findings

Transmittance in the blue spectrum estimates thickness on transparent substrates.

Color and optical contrast spectra can determine thickness on SiO2/Si substrates.

Photoluminescence energy shifts correlate with InSe thickness.

Abstract

Indium selenide (InSe), as a novel van der Waals layered semiconductor, has attracted a large research interest thanks to its excellent optical and electrical properties in the ultra-thin limit. Here, we discuss four different optical methods to quantitatively identify the thickness of thin InSe flakes on various substrates, such as SiO2/Si or transparent polymeric substrates. In the case of thin InSe deposited on a transparent substrate, the transmittance of the flake in the blue region of the visible spectrum can be used to estimate the thickness. For InSe supported by SiO2/Si, the thickness of the flakes can be estimated either by assessing their apparent colors or accurately analyzed using a Fresnel-law based fitting model of the optical contrast spectra. Finally, we also studied the thickness dependency of the InSe photoluminescence emission energy, which provides an additional tool to estimate the InSe thickness and it works both for InSe deposited on SiO2/Si and on a transparent polymeric substrate.