View article

DOI: 10.1002/adma. 201402028 oxides (TMOs),[2–9] whose properties are highly sensitive to chemical composition and stoichiometry.[3, 10–12] For instance, accurate information about the dopant-atom distribution is required to optimize the electron mobility in delta-doped TMO devices.[15, 16] The current debate about the roles of chemical intermixing in driving metal-insulator transitions in TMO heterostructures further illustrates the need for diagnosis tools on the atomic scale.[3, 10, 11]

Established chemical profiling techniques satisfy some, but not all of the mentioned requirements. For example, X-ray absorption spectroscopy (XAS),[17] hard X-ray photoemission spectroscopy (HAXPES)[14] and ion-beam analysis [18](SIMS and RBS) are element-specific but lack atomic-scale resolution. Scanning transmission electron microscopy in conjunction with electron energy loss spectroscopy (STEM-EELS)[13, 19, 20] does not have these limitations. However, the preparation procedure of the necessary thin cross-sectional slices is timeconsuming, and (like SIMS) usually leads to destruction of the sample.