Measurement of Thin Layers of Liquid and Ice on Silicon Nitride Membranes using Impedance Spectroscopy

Abstract

Cryo-Electron Microscopy (Cryo-EM) enables high-resolution bio-molecular imaging but is limited by inconsistent vitrified ice thickness and quality during sample preparation. This thesis develops MEMS-based Electrical Impedance Spectroscopy (EIS) as a rapid, non-destructive method to extract quantitative thickness information from thin liquid and ice layers prior to vitrification. Numerical simulations in COMSOL Multiphysics, supported by analytical parallel-plate and equivalent-circuit models, demonstrate that measurable impedance variations emerge for dielectric layers in the 50–500 nm range under idealized conditions, with monotonic and near-linear relationships between impedance-derived metrics and layer thickness over selected frequency windows. Experimental validation using fabricated MEMS sensor chips by DENSsolutions and white-light interferometry for ground-truth thickness confirm that EIS measurements demonstrate qualitative agreement in impedance–thickness correlation for liquid water, as impedance measurements can be reliably calibrated to thickness with repeatable trends and nanometer-scale sensitivity. Overall, this study demonstrates that MEMS-based EIS is a feasible and scalable approach for quantitative pre-vitrification thickness monitoring in cryo-EM workflows, offering a pathway toward reduced trial-and error grid screening and improved reproducibility, while clearly identifying the remaining experimental and calibration challenges required for practical deployment.