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

Area of Science:

• Materials Science
• Electron Microscopy
• Nanotechnology

Background:

• Focused Ion Beam (FIB) is a standard technique for transmission electron microscopy (TEM) sample preparation.
• Achieving atomic resolution with aberration-corrected scanning transmission electron microscopy (STEM) requires exceptionally high-quality samples, which are rarely produced by conventional FIB methods.

Purpose of the Study:

• To demonstrate a refined FIB lift-out technique for preparing samples suitable for atomic resolution aberration-corrected STEM.
• To showcase the versatility of the technique across multiple material types and device structures.

Main Methods:

• A novel 'wedge pre-milling' step was incorporated into the FIB lift-out process to preserve surface layers.
• Samples were milled to thicknesses of 10-40 nm over micrometer areas using low-kV Ga(+) ion milling in Dual-Beam FIB systems.
• Prepared samples were analyzed using Cs-corrected STEM at 60 and 100 kV.

Main Results:

• Successfully prepared high-quality samples from five different materials, enabling atomic resolution imaging.
• Demonstrated preservation of surface layers and underlying features without preparation-induced damage.
• Achieved atomic resolution imaging and elemental mapping across grain boundaries in a thin film solar cell device without projection artifacts.

Conclusions:

• The refined FIB lift-out technique, including wedge pre-milling, significantly enhances sample quality for aberration-corrected STEM.
• This method allows for detailed nanoscale analysis of sensitive materials and devices, overcoming previous limitations in sample preparation.
• The technique is effective for cross-sectional preparation of complex devices like solar cells, facilitating in-depth characterization.