A universal FIB approach for contamination- and damage-free plan-view TEM lamellae using NaCl sacrificial layers

The preparation of high-quality plan-view transmission electron microscopy (TEM) lamellae is essential for investigating the in-plane properties of thin films. However, current focused ion beam (FIB) techniques are limited by ion-beam damage, surface contamination, and time-consuming workflows. Here, we introduce NaCl microcrystals as a sacrificial protective layer, which effectively shields the surface from ion irradiation and can be completely removed by simple dissolution in water, leaving a pristine surface. Building on this, we established a universal and streamlined FIB workflow for plan-view lamellae fabrication from thin films that eliminates the need for conventional Pt/C deposition and avoids custom hardware, relying solely on standard commercial components. Using a classic metal multilayer and an ultrathin epitaxial oxide film as representative model systems, we demonstrate that the prepared plan-view lamellae exhibit large uniform areas, preserved film structures, and contamination-free surfaces, enabling reliable surface-sensitive TEM analyses. This time-efficient and user-friendly approach offers a powerful solution for the contamination- and damage-free preparation of plan-view TEM lamellae across diverse thin-film systems, paving the way for in-depth investigations of their in-plane properties.