Oxide Surfaces: Opening the Pandora's Box for SrTi03
Oxide surfaces are an important frontier. with numerous applications in areas ranging from catalysis to oxide electronics. Despite this. our understanding of oxide surfaces is relatively primitive. There is a large body of evidence indicating that many oxide smfaces reconstruct with large unit cells, making elemental metals or semiconductors look simple. Indeed, the simplest perovskitc SrTi03 has many more reconstructions than sil.icon. Oddly many (arguably most) papers still consider SrTiO, surfaces to be simple truncations of the bulk or have unreasonable terminations dominated by oxygen vacancies or Sr adatoms, despite overwhelming evidence that this is bad science.
Using techniques based upon careful collection of diffraction datn coupled with detailed DfT analyses we have made substantial progress in understanding these surfaces over the last decade. For instance, we have solved many of the key structures on the (001) surface [1-5] (but not all). used a multi-technique solution for a series of nxl reconstmctions on the SrTiO, (110) smiace [6 as well as more recently two additional families of structures, the nxn on (111)  and the 2xn on the (110)  surfaces. In this presentation I will give an overview of these surfaces, as well as the many unknowns that remain and some recent new tools that offer new strategies to obtain infonnation ranging ii·om atomic-resolution SEM to direct HREM imaging in plan or profile  imaging modes
1. The structure and chemistry of the Ti02-rich swface of SrTiO,, (001 ). Erdman, N ., K.R. Poeppelmeier. M. Asta, 0. Warschkow. D.E. Ellis, and L.D. Marks, Nature, 2002. 419(6902). 55-58.
2. Swface structures of SrTiO, (001 ): 1l Ti02-rich reconstruction with a c(4 x 2) unit cell. Erdman, N., 0. Warschkow, M. Asta, K.R. Poeppelmeier, D.E. Ellis, and L.D. Marks, Journal of the American Chemical Society, 2003. 125(33), 10050-10056.
3. Ti02-rich reconstructions of SrTi01 (00 1 ): a theoretical study of structural pattems. Warschkow. 0., M. Asta, N. Erdman, K.R. Poeppelmeier, D.E. Ellis. and L.D. Marks, Surface Science, 2004. 573(3), 446-456.
4. Vacant-Site Octahedral Tilings on SrTi03 (001 ), the (root 13 x root J3)R33 .7 degrees Sut:fcrce, and Related Stmctures. Kienzle, D.M .. A.E. Becerra-Toledo. and L.D. Marks, Physical Review Letters. 2011. 106( 17), 176102.
5. Surface and Defect Srructure of Oxide Nanowires on SrTi0(3). Marshall, M.S.J., A.E. Becerra-Toledo, L.D. Marks, and M.R. Castell, Physical Review Letters, 2011. 107(8), 086102.
6. A homologous series of structures on the swjace ofSrTiOJl 10). Enterkin, J.A., A.K. Subramanian, B.C. Russell, M.R. Castell, K.R. Poeppelmeier, and L.D. Marks, Nature Materials, 20 l 0. 9(3), 245-248.
7. The 2xnfamily of octahedral structures 011 SrTiO, ( 1 10). Zheng. Z., A. Loon. M. Hierkel, D. U., and L.D. Marks, In Preparation, 2013.
8. Combined octahedral and tetrahedral filings on the SrTi03 ( 111) surface. Marks, L.D., A. Chiaramonti, and M. Castell, In Preparation. 2013.
9. Synthesis-dependem atomic surfaces s1ructures on oxide nanoparlicles. Lin, Y., J. \Ven. L Hu. R.M. Kennedy, P.C. Stair, K.R. Poeppehneier, and L.D. Marks, Physical Review letters, 2013.111, 156101.