Crystal Interface Lab. Seminar SeriesInstitute of Engineering Innovation
The University of Tokyo

New solutions to the energy crisis throughaberration-corrected STEMbyDr. S.J. Pennycook
Materials Science and Technology Division, Oak Ridge National Laboratory, U.S.A.
Aberration-corrected STEM has improved lateral resolution by more than a factor of two, giving single atom
semsitivity for both imaging and EELS. In addition, it is possible to obtain simultaneous, aberration-corrected
phase contrast and Z-contrast images, so the complementary characteristics of each can be combined.
Aberration-correction allows much larger probe-forming apertures to be used, which results in a much decreased
depth of field. Structural information can now be extracted in three dimensions by optical sectioning, withsub-Ångström lateral resolution and a depth resolution of a few nanometers. These same advantages apply toEELS, limited somewhat by delocalization of the inelastic interaction, but primarily by the lower signal.
These benefits will be illustrated by several case studies in different areas of materials, with emphasis on energy
applications. In catalysis, single atom sensitivity in 3D enables a link to catalytic activity through density
functional calculations. The high activity of nanophase gold clusters on titania can be quantitatively explained. In
semiconductors, individual Hf atoms have been located within a Si/SiO2/HfO2 gate dielectric structure to a
precision of 0.1 x 0.1 x 1 nm, and the perturbed electronic structure linked by density functional theory tomacroscopic device properties. Column-by-column compositional mapping of InAsP quantum wires coupled toelasticity calculations explains their growth morphology and optical properties. In Si nanowires individual gold
atoms have been imaged inside the wire in several substitutional and interstitial configurations, with number
densities that are in order of calculated formation energies.
In future, new probes of materials functionality could be added to the aberration-corrected STEM, allowing direct
mapping of properties while maintaing the unprecedented capability for atomic and electronic structure
determination. Addition of a cathodoluminescence detector would allow light emission to be mapped in materials
for solid state lighting, providing direct correlation to local defects such as dislocations or interface steps. In solarcells, electron beam induced current could provide maps of charge collection efficiency, locating andcharacterizing poorly functioning interfaces. Addition of a scanning tunnelling microscope inside the STEM
would allow bias to be applied to interfaces, band bending effects to be introduced, and the effect on local
functionality to be explored. In catalysis, thin window, in-situ cells could maintain atomic resolution in highpressure or corrosive environments. All of these new probes would greatly extend our ability to probe energy
conversion processes in materials, and through theory, understand the limitations and overcome them at thefundamental quantum level.
This research was sponsored by the Office of Basic Energy Sciences, Division of Materials Sciences andEngineering, US Department of Energy. Collaborations with M. F. Chisholm, M. Varela, A. R. Lupini, A. Y.
Borisevich, W. Luo, M. P. Oxley, S-H. Oh, D. Kumar, S. N. Rashkeev, P. Werner, N. D. Zakharov, S. Molina, S.
H. Overbury, K. van Benthem, P. D. Nellist, O. L. Krivanek, N. Dellby, M. F. Murfitt, Z. S. Szilagyi, H. M.
Christen, S. F. Findlay, L. J. Allen, T. Ben, D. L. Sales, J. Pizarro, P. L. Galindo, D. Fuster, Y. Gonzalez, L.
Gonzalez, K. Sohlberg, A. Marinopoulos and S. T. Pantelides are gratefully acknowledged.

June 25 (Wed), 2008

16:30 -18:00

Main meeting room at Institute of Engineering Innovation, UT(工学部総合研究機構 9 号館 1 階 大会議室)
Organizer: Prof. Yuichi Ikuhara
TEL: 03-5841-7688
E-mail: ikuhara@sigma.t.u-tokyo.ac.jp