*Henna Khosla, Bo Li, Dong Zhou, Gang Feng, Villanova University, Philadelphia, PA
Freestanding thin coatings (FTCs) are building blocks for many devices. Determining their mechanical properties is essential for device-design with high reliability. However, it is challenging to measure FTC’s mechanical properties. A common method is probing FTCs using atomic force microscope (AFM). However, the AFM technique often suffers from (1) load-displacement coupling, (2) load-capacity limitation, and (3) inelasticity. In this work, a new methodology based on nanoindentation with continuous stiffness measurement (CSM) is developed. We show that the CSM-nanoindentation (CSMN) technique eliminates the issues from the AFM technique, enabling precise characterization. The CSMN technique is used to probe 2-dimensional (2D) materials and composite FTCs. Chemical vapor deposition (CVD) was used to deposit large single-crystal MoSe₂ monolayer. 12-nm-thick Polyethylene (PE) single crystals were deposited on the MoSe₂ monolayers to form 12.7-nm-thick PE-MoSe₂ composite layers. The MoSe₂ and PE-MoSe₂ FTCs were suspended on 5-micron holes on silicon substrate, which were probed using CSMN. While the load shows inelasticity, like in the AFM method, the stiffness shows purely elasticity and were modeled to determine the mechanical properties of the FTCs. This new CSMN methodology will enable accurate mechanical characterization of FTCs and provide insights on designing more reliable thin-coating-based devices.