Imaging Oxygen with HAADF-STEM

oxygen imaging STEM 30831f1_online

 

High-angle annular dark field scanning transmission electron microscopy (HAADFSTEM) hasbeen established as a direct and robust imaging mode for determining the location of heavy atom columns within grain boundaries [1,2]. However,light elements are usually not visible in HAADFSTEM.  Structural analysis using the observed positions of only the heavy elements as reference points to compare with candidate structure models, perhaps determined by molecular dynamics or first principles calculations, has had some success. For instance, simulations in an aAl2O3 S13  grain boundary show an oxygen terminated trial structure to be consistent with the experimental HAADF image while analuminum-terminated structure is not, even though the oxygen itself was not imaged [3].
High voltage electron microscopy [4], negative Cs imagingconventional TEM [5] and exit surface wavefunction reconstruction [6] have all been used to image oxygen within grain boundaries and defect structures. However,these approaches arenot yet routine, requiring very thin specimens and detailed  simulation for intepretation and analysis [7]. Bycontrast,forbulkcrystals,annular
brightfield (ABF) STEM imaging allows for direct image interpretation with both light and heavy atom columns simultaneously visible over a wide range of thicknesses [8–10].

[1] G.Duscher,M.F.Chisholm,U.Alber,M.R¨ uhle, Nat.Mater.3(2004)621.
[2] J.P.Buban,K.Matsunaga,J.Chen,N.Shibata,W.Y.Ching,T.Yamamoto,
Y. Ikuhara,Science311(2006)212.
[3] S.Azuma,N.Shibata,S.D.Findlay,T.Mizoguchi,T.Yamamoto,Y.Ikuhara,
Philos. Mag.Lett.90(2010)539.
[4] Z.Zhang,W.Sigle,F.Phillipp,M.R¨ uhle, Science302(2003)846.
[5] C.L.Jia,K.Urban,Science303(2004)2001.
[6] C.L.Jia,A.Thust,K.Urban,Phys.Rev.Lett.95(2005)225506.
[7] K.Urban,Nat.Mater.8(2009)260.
[8] E.Okunishi,I.Ishikawa,H.Sawada,F.Hosokawa,M.Hori,Y.Kondo,Microsc.
Microanal. 15(Suppl.2)(2009)164.
[9] S.D.Findlay,N.Shibata,H.Sawada,E.Okunishi

JEOL, 15 May 2012: http://www.materialstoday.com/download/801

Direct oxygen imaging in titania nanocrystals.

Recently, rutile nanotwins were synthesized using high temperature organic solvent methods, yielding two kinds of common high-quality rutile twinned nanocrystals, (101) and (301) twins, accompanied by minor rutile nanorods (Lu et al 2012 CrystEngComm 14 3120-4). In this report, the atomic structures of the rutile and anatase nanocrystals are directly resolved with no need for calculation or image simulation using atomic resolution STEM techniques. The locations of the oxygen rows in the rutile twins’ boundaries are directly determined from both HAADF images and ABF images. To the best of our knowledge, this is the first time oxygen columns have been distinguished in rutile twin boundaries using HAADF and BF imaging………..

source: http://www.ncbi.nlm.nih.gov/pubmed/22863879

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