Atomic layer deposited Al2O3 as a protective overlayer for focused ion beam preparation of plan-view STEM samples

• Published in: Ultramicroscopy 2022-09, Vol.239, p.113562-113562, Article 113562
• Main Authors: Gurrentz, Joseph M., Jarvis, Karalee A., Gearba-Dolocan, Ioana R., Rose, Michael J
• Format: Article
• Language: English
• Subjects: Atomic layer deposition (ALD); Focused ion beam (FIB); High angle annular dark field (HAADF); Plan-view; Scanning tunneling electron microscopy (STEM); Thin film
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2022.113562

•An ALD aluminum oxide overlayer can protect surface-bound analytes from FIB damage•Nanostructures of embedded Pt nanoparticles were unchanged by sample preparation•ALD protective overlayers may be broadly used in plan-view STEM lamella preparation Preservation of analyte integrity during focused ion beam (FIB) sample preparation is a significant challenge in the scanning transmission electron microscopy (STEM) characterization of plan-view samples with sensitive surface chemistries. This can preclude the characterization of atomic arrangements, nanoscale surface coverages, and distributions and morphologies of functional molecular materials composed of surface-immobilized metal nanoparticles, clusters or coordination complexes. This work demonstrates effective protection of Pt nanoparticle (NP) morphology through a plan-view FIB lift-out and thinning procedure by encapsulating the sample surface in an Al2O3 overlayer grown by atomic layer deposition (ALD). High-angle annular dark field (HAADF)-STEM analysis was used in concert with energy dispersive X-ray spectroscopy (EDS) to identify and image sub-10 nm features attributed to Pt and to evaluate the distribution of implanted Ga+ (derived from the FIB milling beam). ALD is a mild chemical vapor deposition (CVD) technique that has the capability to generate dense, pinhole-free films with tunable compositions and properties, making this ALD-FIB procedure applicable to many sample architectures for plan-view lamella preparation and STEM analysis.