Sample preparation for atomic-resolution STEM at low voltages by FIB

While FIB sample preparation for transmission electron microscopy is a well established technique, few examples exist of samples of sufficient quality for atomic resolution imaging by aberration corrected (scanning) transmission electron microscopy (STEM). In this work we demonstrate the successful preparation of such samples from five different materials and present the refined lift-out preparation technique, which was applied here. Samples with parallel surfaces and a general thickness between 20 and 40 nm over a range of several μm were repeatedly prepared and analyzed by Cs-corrected STEM at 60 and 100 kV. Here, a novel ‘wedge pre-milling’ step helps to keep the protective surface layers intact during the whole milling process, allowing features close to or at the sample surface to be analyzed without preparation damage. Another example shows the cross-sectional preparation of a working thin film solar cell device to a final thickness of 10 to 20 nm over μm sized areas in the region of interest, enabling atomic resolution imaging and elemental mapping across general grain boundaries without projection artefacts. All sample preparation has been carried out in modern Dual-Beam FIB microscopes capable of low-kV Ga+ ion milling, but without additional preparation steps after the FIB lift-out procedure.

► Suitability of stand-alone FIB preparation for atomic resolution STEM is shown.
► Reproducible preparation of 10–40 nm thick samples from 5 different materials.
► Low-kV milling and adjusted procedure for crystalline, homogeneously thin specimen.
► Wedge pre-milling to protect surface-near features.