All-Optical Characterization of the Mechanical Properties of 2D Materials

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Abstract

Two-dimensional materials have attracted scientific interest due to their exceptional chemical, optical, electronic, and mechanical properties. In particular, their Young’s modulus plays a crucial role in applications such as sensors, flexible electronics, and composite reinforcement. However, material defects, which are inevitable during fabrication and device operation, can significantly impact mechanical properties. The influence of defects on the Young’s modulus remains a topic of debate, with contradictory experimental and theoretical findings presented in literature. The most widely used method for measuring Young’s modulus is atomic force microscopy (AFM) nanoindentation. However, it suffers from tip-sample interactions, high stress concentrations, and significant variability in reported values. To address these limitations, this thesis presents a novel, all-optical method for measuring the Young’s modulus of monolayer membranes, eliminating physical contact with the sample and requiring no preliminary material assumptions. The proposed method provides Young’s modulus values by measuring nonlinear membrane dynamics together with higher harmonics and Brownian motion. Although the results exceed values reported in literature, it is noteworthy that this method yielded results for the modulus, despite inherent challenges associated with the measurement of 2D material monolayers. Various potential error sources have been identified and discussed, including measurement sensitivity, mode shape variations, and contamination effects. Recommendations for future research are provided to refine the approach and improve accuracy. With the right experimental advancements, this contactless optical technique could serve as a viable alternative to AFM nanoindentation, offering a non-invasive way to study the mechanical properties of 2D materials with greater precision and reproducibility.

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File under embargo until 28-02-2026