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B ogdan Palosz

Institute of High Pressure Physics Polish Academy of Sciences Warsaw, Poland. B ogdan Palosz. diffraction studies of nano - crystalline diamond in real and spaces. reciprocal. American Crystallograhic Association, Honolulu, Hawaii , July 22-26 2006.

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B ogdan Palosz

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  1. Institute of High Pressure Physics Polish Academy of Sciences Warsaw, Poland Bogdan Palosz diffraction studiesof nano-crystalline diamond in realand spaces reciprocal American Crystallograhic Association, Honolulu, Hawaii, July 22-26 2006. Session: PDF Analysis of Industrially Relevant Materials

  2. Diffraction studies of nanocrystalline diamond and SiC in real and reciprocal spaces B.Palosz*, E.Grzanka*, S.Stelmakh*, W.Zerda, C.Pantea, Th.Proffen, W.Palosz* Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw, Poland Nanocrystals have a non-uniform structure, where the arrangement of atoms in the grain interior (the core) is different than that at the surface (the surface shell). This difference may be very small and missed in a conventional diffraction experiment. We show that the key in a quantitative characterization of the atomic structure of nanocrystals is acquiring a diffraction data in a very large range of the reciprocal space (>Q = 20-30 Å-1), what requires high energy X-rays or hot neutrons. Only such data can provide the accuracy needed for a meaningful description of the atomic structure of nano-grains. It concerns the analysis in real (Bragg) as well as in reciprocal spaces (PDF). With application of very large-Q neutron diffraction at LANSCE (HIPPO and NPDF stations, Q up to 50Å-1) we were able to examine distribution of strains in nano- diamond and SiC as a function of the grain size, and trace their evolution in nano-ceramics sintered under high pressures. Also, using the Wilson method, different atomic thermal vibrations of the inner and surface atoms were evaluated. We thank LANSCE for access to beamlines HIPPO and NPDF. This research is supported by the Polish Ministry of Education and Science, grant 3 T08A 020 29, and NSF grant DMR 0502136.

  3. reciprocal „versus” realspace analysis (PDF) do we see the same ? application to nano-crystallinediamond

  4. PDF Bragg „Bragg” ? „Bragg” ?!

  5. relationship between & reciprocal space real space ? ? ? unit cell inter-atomic distances coherent scattering ONLY ! information on long-range atomic order total scattering = „total” structural information

  6. crystal structures ofdiamondand graphite reciprocal space real space ao = 3.5667 Å ao = 2.456 Å co = 6.696 Å unit cell diagonal cross-section

  7. tentative model of nano-diamond, UDD

  8. specific how much of crystalline diamond is in nano-diamond ? 1 questions what is the specific atomic structure of the diamond lattice in nano-diamond ? 2 4 in which form is non-diamond carbon present in nano-diamond ? what are the characteristic dimensions of nano-diamond ? 3

  9. outline • Experimental method: large-Q powder neutron diffraction, NPDF • The examined materials: nano-diamond UD90 & UD96 • annealed up to 1200oC • Bragg scattering: reciprocal space • - phase composition • lattice parameters • PDF analysis: real space • - phase composition • interatomic bonds • Result: a tentative model of a nano-diamond – NEW !

  10. the experimental method: neutron powder diffraction (NPDF and HIPPO, LANL at LANSCE, Los Alamos) reciprocal versus realspace analysis

  11. structural information contained in a diffraction pattern

  12. ? ? the effect of annealing of nano-crystalline diamond on its atomic structure 300, 600, 800, 1000, 1200oC UD90 UD96 ?

  13. TEMs of nano-diamond UD90

  14. TEMs of nano-diamond UD96

  15. reciprocal space phase analysis phase composition of nano-diamond the diamondbut also non-diamond carbon: graphite-like ? gas-like ? other ?

  16. neutron powder diffraction patterns of nano-diamond UD90 NPDF, LANSCE, Los Alamos calculated pattern graphite does not appear even at 1200oC

  17. neutron powder diffraction patterns of nano-diamond UD96 NPDF, LANSCE, Los Alamos calculated pattern graphite appears as a phase only at 1200oC

  18. non-diamond carbon after annealing at 1200oC there is an increase of Bragg-to-diffuse scattering ratio; the difference corresponds to approximately 3 wt.% of non-diamond non-crystalline carbon in the sample

  19. non-diamond carbon after annealing at 1200oC there is an increase of Bragg-to-diffuse scattering ratio; the difference corresponds to approximately 8 wt.% of non-diamond non-crystalline carbon in the sample

  20. ? the atomic structure of the core of nano-diamond is it a small single crystal ? ?

  21. the dimension of a diamond nano-crystal is only several times larger than that of the unit cell

  22. limitations of the Bragg equation for nanocrystalline materials

  23. experimental apparent lattice parameters alp-Q dependencies of nano-diamond powders annealed up to 1200oC UD90 UD96 Q < 15Å

  24. diamond

  25. theoretical alp-Q dependencies of 5 nm nano-diamond crystals with a tensile strain in the surface shell a0T = 2.5183 Å (0.9985 a0D) c0T = 2.0644 Å (1.0040 c0D) c0 : a0 = 1.004 Q < 15Å ~30 vol. % = atoms in the surface shell !

  26. theoretical alp-Q dependencies of 5 nm nano-diamond crystals with a compressive strain in the surface shell Q > 15Å alp „refined”

  27. evolution of nano-diamond lattice in the grain core upon annealing c/a c/a c c a a

  28. experimental alp-Q dependencies of 5 nm nano-diamond powders Q > 15Å UD90 ~4 GPa Cu Mo at very large Q the measured alp values tend to match the lattice parameter in the core of the nano-diamond particle

  29. experimental alp-Q dependencies of 5 nm nano-diamond powders Q > 15Å UD96 ~1 GPa Cu Mo at very large Q the measured alp values tend to match the lattice parameter in the core of the nano-diamond particle

  30. lattice parameter of the core of nano-diamond crystal (model) c/a cT Q<15Å-1 aT Q>15Å-1 acubic

  31. ? ? real space phase analysis inter-atomic distances ? (sp3andsp2bonds) ?

  32. sp2 real-space phase analysis of nano-diamond r4 r5 inter-plane, graphite 8% UD90 15% UD96 no indication of presence of sp2 bonds in the samples annealed below 1200oC

  33. ? the atomic structure of nano-diamond how does it look like in real space ? ?

  34. Experimental: evolution of inter-atomic distances in nano-diamond upon annealing inter-lattice intra-lattice inter-lattice intra-lattice

  35. (no direct) correlation between description of nano-diamond in reciprocal and real spaces

  36. ? atomic model of nano-diamond ? ?

  37. core-shell model of nano-diamond the outer shell: non-diamond, non-graphite; transforms from sp3 to sp2 at about 1200oC the shell: with compressve strain the core: either under compressive or a tensile strain

  38. specific how much of crystalline diamond is in nano-diamond ? 1 questions ~90%: inner core diamond : strained surface shell (1 : 3) what is the specific atomic structure of the diamond lattice in nano-diamond ? 2 4 core – shell structure with compressed (3%) surface & deformed cubic lattice what are the characteristic dimensions of nano-diamond ? in which form is non-diamond carbon present in nano-diamond ? 3 core ( 4 nm) and surface shell (0.3 nm) gas-like carbon with sp3 bonds; sp2- bonds at 1200oC (graphite?)

  39. Collaboration E. Grzanka1, S. Stelmakh1, S.Gierlotka1 C. Pantea2, Th. Proffen2, T.W. Zerda3, W. Palosz4 1Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw, Poland 2LANSCE at LANL, Los Alamos, USA 3TCU, Physics Department, Forth Worth, Texas, USA 4BAE Systems, NASA/MSFC, Huntsville, Alabama, USA

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