An optimized sample preparation approach for atomic resolution in situ studies of thin films

Adele Moatti, Ritesh Sachan, John Prater, Jagdish Narayan, 2018
Fusion TEM holder tip
Image courtesy of Microscopy Research & Technique

Abstract

This work provides the details of a simple and reliable method with less damage to prepare electron transparent samples for in situ studies in scanning/transmission electron microscopy. In this study, we use epitaxial VO2 thin films grown on c‐Al2O3 by pulsed laser deposition, which have a monoclinic–rutile transition at ~68°C. We employ an approach combining conventional mechanical wedge‐polishing and Focused Ion beam to prepare the electron transparent samples of epitaxial VO2 thin films. The samples are first mechanically wedge‐polished and ion‐milled to be electron transparent. Subsequently, the thin region of VO2 films are separated from the rest of the polished sample using a focused ion beam and transferred to the in situ electron microscopy test stage. As a critical step, carbon nanotubes are used as connectors to the manipulator needle for a soft transfer process. This is done to avoid shattering of the brittle substrate film on the in situ sample support stage during the transfer process. We finally present the atomically resolved structural transition in VO2 films using this technique. This approach significantly increases the success rate of high‐quality sample preparation with less damage for in situ studies of thin films and reduces the cost and instrumental/user errors associated with other techniques.

Impact Statement

The authors demonstrate a sample preparation method for atomic resolution in situ studies of thin film heterostructures for electrical characterization, by combining mechanical wedge polishing and FIB lift-out approaches.