Abstract
With techniques such as scanning transmission electron microscopy (STEM) and Electron energy-loss spectroscopy (EELS), TEM opens the path to study of chemical composition and bonding information coupled with the atomic level images, and thus becomes an indispensable tool to study oxide surfaces and implanted dopants in order to fully understand their defective structures and non-stoichiometric complexities. EELS has been limited in its use for such study due to the dominant bulk signal in thin samples. However, since an EELS core-loss spectrum in a very thin sample consists of a linear superposition of all components of the sample (e.g. surface and bulk) as the incident beam passes through the specimen, these components can be numerically extracted based on a series of EELS measurements. Here, we report a new simple but effective method to extract the weak surface signals from a ‘thickness’ series, in which each EELS spectrum has a fixed surface contribution but varying bulk contributions. The surface and bulk Ti L-edge and O K-edge EELS spectra from a reconstructed SrTiO3 were successfully obtained from our approach. We additionally suggest that it is possible to provide a comprehensive understanding of the reconstructed surface by combining this method with high-resolution profile images and electron diffraction. We have extended the same approach to investigate the implanted dopants and clusters inside SrTiO3 and evaluate the practical limitations of this technique.

CV
Guo-zhen Zhu attended Tsinghua University for her undergraduate studies in Materials Science and Engineering (2007) department and followed her interest in Materials Science to McMaster University at Canada, where she completed her Master in 2009 under Prof. David S. Wilkinson and her Ph.D. in 2012 under Prof. Gianluigi A.Botton. After that, she became a post-doc in the Canadian Centre for Electron Microscopy. In 2014, She joined the faculty of Shanghai Jiao Tong University as associate research professor in Schools of Materials Science and Engineering. Her research is about advanced characterization of surfaces and interfaces using scanning transmission electron microscopy. During her Ph.D., she developed a simple and accessible approach to obtain the surface electron energy-loss spectra, and gained her first Ph.D. publication in Nature. She won national and international awards such as Gerard T. Simon awards from Microscopical Society of Canada and awards from European Microscopy Congress for her research.