Optical-Based Thickness Measurement of MoO3 Nanosheets

Abstract

Considering that two-dimensional (2D) molybdenum trioxide has acquired more attention in the last few years, it is relevant to speed up thickness identification of this material. We provide two fast and non-destructive methods to evaluate the thickness of MoO3 flakes on SiO2/Si substrates. First, by means of quantitative analysis of the apparent color of the flakes in optical microscopy images, one can make a first approximation of the thickness with an uncertainty of ±3 nm. The second method is based on the fit of optical contrast spectra, acquired with micro-reflectance measurements, to a Fresnel law-based model that provides an accurate measurement of the flake thickness with ±2 nm of uncertainty.

In-plane anisotropic optical and mechanical properties of two-dimensional MoO3

“…We have carried out angle-resolved polarized Raman measurements in a MoO3 flake of 28 nm of thickness from 0º to 360º, with a step of 4º. The thickness has been determined by combination of atomic force microscopy with recently developed optical microscopy based techniques 64 . In Fig.…”

“…where Ifl and Isub are the intensity measured on the MoO3 flake and on the bare substrate, respectively. Interestingly, it has been demonstrated how one can use a simple Fresnel law-based model to accurately reproduce the measured optical contrast spectra 64 . Moreover, given the known refractive indexes of air, SiO2 and Si and the known thickness of the SiO2 film and MoO3 flake one can determine the refractive index of the MoO3 flake for different alignment between the incident linearly polarized light and the crystal directions by using the refractive index as a fitting parameter to achieve the best fit of the Fresnel law-based model to the experimental data.…”

Tapered Optical Fiber for Hydrogen Sensing Application Based on Molybdenum Trioxide (MoO3)

“…The average surface roughness values were 44.98 nm. Such low roughness levels indicate that light scattering has no significant effect on sensing performance [21].…”

Optical microscopy–based thickness estimation in thin GaSe flakes

“…[13][14][15][16] Since then, the isolation of a new 2D material is always followed by experimental efforts to develop optical microscopy-based recipes to identify and determine the number of layers of that novel 2D material. [17][18][19][20][21][22][23][24][25] In this work, we provide a set of simple optical microscopy methods to assess the thickness of GaSe flakes. GaSe is a material of the layered metal-monochalcogenide III-VI semiconductor family and it holds the great possibilities in optoelectronics and nonlinear optics because of the fast photoresponsivity, high carrier mobility and nonlinear optical properties.…”

“…[48,49] The optical contrast of this kind of multilayer system can be calculated by accounting for the light reflected and transmitted at each different interface with a Fresnel law based model. [4,13] The reflection coefficient in a Fresnel model with four media can be expressed as: [4,13] 𝑟 GaSe = 𝑟 01 𝑒 𝑖(Φ 1 +Φ 2 ) +𝑟 12 𝑒 −𝑖(Φ 1 −Φ 2 ) +𝑟 23 𝑒 −𝑖(Φ 1 +Φ 2 ) +𝑟 01 𝑟 12 𝑟 23 𝑒 𝑖(Φ 1 −Φ 2 ) 𝑒 𝑖(Φ 1 +Φ 2 ) +𝑟 01 𝑟 12 𝑒 −𝑖(Φ 1 −Φ 2 ) +𝑟 01 𝑟 23…”