Journal of Electron Spectroscopy and Related Phenomena 143 (2005) 105–115 Atomic resolution electron energy-loss spectroscopy R.F. Klie a,∗ , I. Arslan b,1 , N.D. Browning c a Brookhaven National Laboratory, Center for Functional Nanomaterials, Upton, NY 11973, USA b Department of Physics, University of California, Davis, CA 95616, USA c Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616, USA Received 12 November 2003; received in revised form 11 May 2004; accepted 11 May 2004 Available online 8 December 2004 Abstract Electron energy-loss spectroscopy (EELS) has been successfully used to measure the electronic structure of materials with atomic (i.e. sub-nanometer) spatial resolution. Furthermore, the combination of incoherent Z-contrast imaging and EELS allows us to correlate structural features, such as defects or interfaces directly with the changes in the local electronic structure. In this review, we will discuss the theoretical aspects and experimental procedures for achieving atomic-resolution EELS. In particular, we will describe the practicalities of the combination of Z-contrast imaging and EELS, used in the scanning transmission electron microscopy mode and also describe some of our recent results where column-by-column EELS has helped solve important material science problems. © 2004 Elsevier B.V. All rights reserved. Keywords: STEM; EELS; HAADF; SrTiO 3 ; MgB 2 ; GaN; Al 2 O 3 1. Introduction In recent years, the electronic structure and chemical com- position of ceramic materials has attracted increasingly more interest because of the use of such materials in electronic, op- tical and structural applications. Many analyses have tried to determine the structure–property relationship of a given ma- terial by either experiment or ab-initio/empirical calculations. In the case of the experimental analyses, it has been shown that the electronic structure of ceramic materials can be mea- sured by X-ray absorption spectroscopy (XAS) [1], angular resolved photoemission spectroscopy (ARPES) [2] or elec- tron energy-loss spectroscopy (EELS) [3,4], to name a few. However, although accurate information on the electronic structure can be obtained from bulk techniques such as XAS, they lack the ability to define the exact spatial location from which the information is obtained. As it has become increas- ∗ Corresponding author. Tel.: +1 631 344 7709; fax: +1 631 344 4071. E-mail address: klie@bnl.gov (R.F. Klie). 1 Present address: Department of Materials Science and Metallurgy, Uni- versity of Cambridge, Cambridge, UK. ingly clear that in many cases the core phenomena in ceramic materials occur at point defects, grain boundaries and hetero- interfaces, the need for spatially resolved spectroscopy has risen significantly. The combination of high-angle annular dark-field imaging (HAADF) or Z-contrast imaging, with EELS provides this high degree of spatial resolution for both imaging and analytical microscopy [3–6]. The development of high brightness field-emission guns (FEGs), highly effi- cient parallel-collection electron energy-loss spectrometers (PEELS) and more stable electron optical and beam scan- ning systems, has made direct imaging and measurements of chemical bonding effects at a sub-nanometer level possible. More than a decade ago, sub-nanometer spatial res- olution for imaging and spectroscopy was demonstrated in a dedicated STEM (DSTEM) instrument study- ing hetero-interfaces, such as CoSi 2 –Si interfaces [3,5], Si–SiO 2 interfaces [6] and diamond–silicon interfaces [4]. The electron probe diameter (i.e. spatial resolution) was re- ported to be of the order of ∼2.2 ˚ A, whereas the energy resolu- tion for spectroscopy was ∼1 eV. Although atomic resolution was not exactly achieved in these early experiments, the probe-size and energy resolution were sufficient to directly 0368-2048/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2004.05.009