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Spatially Resolved and Atom Specific Microscopy and Spectroscopy “New Characterization Tools” What can we do now that we could not do before and how will it change the world
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Complementarity of techniques Broad beam: good statistics average over sites Local probe: poor statistics probes individual sites Time resolutionSpatial resolution Species specificSite specific Insight N N where N = number of tools We want everything at once!
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“Real-time” surface imaging methods Nanoscale [“atomic” resolution] –Fast Scanning Tunneling Microscopy (STM) –Field Ion Microscopy (FIM/FEM) Mesoscale [chemically sensitive] –Low Energy Electron Microscopy (LEEM) –Photoemission Electron Microscopy (PEEM) –Ellipsomicroscopy for Surface Imaging (EMSI) –Imaging FT-IR spectroscopy
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Pattern formation on catalysts J. Lauterbach, et al., Surface Science 294 (1993) 116
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Ellipsomicroscopy for Surface Imaging (EMSI)
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P > 10 -3 mbar -> EMSI T = 540 K, CO/O 2 = 0.11. Image size:1mm x 1.25 mm, dt = 0.33 s Lele, T. and J. Lauterbach, Chaos 12(1) (2002) 164-171. Video
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Low Energy Electron Microscopy & Synchrotron-based Photoemission Electron Microscopy Sample -20 keV Image Electron emitter Photons (uv, x-rays) 777°C 761°C 755°C 0.5 m 755°C Dark field TiO2 surface structure - LEEM RuO 2 growth
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Probing of Valence Electrons with X-rays Atom specific Orbital symmetry selective Experiment--Theory
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Catalytic Chemistry with Orbitals Theoretical simulations, Mats Nyberg, Stockholm University Probe pulse at different delay time t Both N atoms New Ru Catalyst Active site at steps Hansen et.al. Science 294, 1508 (2001) Haber-Bosch N 2 + 3H 2 2NH 3
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XASpectroelectrochemistry Element specific Resolves multiple redox sites Perfect for fuel cells
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New Tools for Neutron Scattering: Determination of Chloroform Adsorption site in Faujasite From H pair distribution function. (J. Eckert, C. Mellot-Draznieks and A. K. Cheetham, J. Am. Chem. Soc. 2002, 124, 170 ) Parallel detectors offer more sensitivity Vibrational spectroscopy without selection rules
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Paraboloid: Height h 0 = 3.1 nm ± 0.1 nm radius r 0 = 24 nm +2 nm(tip) Volume V = pi/2 h 0 r 0 2 = 2800 nm 3 density [PE] = 25 molecules/nm 3 TOF = 19 ± 2 molecules / s AFM image 100 x 100 nm heigth 3 nm AFM image of polyethylene formed by a single catalytic site: Cr on SiO 2 / Si(100) Peter Thüne, Joachim Loos, Piet Lemstra, Hans Niemantsverdriet, Macromol Symposia 2001
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Laegsgaard, Osterlund, Thostrup, Rasmussen, Stensgaard and Besenbacher, Rev. Sci. Instrum. 72 (2001), 3537-3542. Pressure-induced reconstructions on Cu(110) exposed to H 2 10 -13 bar (before) 1 bar H 2 (during) 10 -9 bar (after) Atomic Resolution Images Under High Pressure Conditions In-situ HRTEM offers defect analysis - identification of active sites in vanadyl pyrophosphate catalysts
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Ga EELS 1.4Å As Z-contrast STEM Z=31 Z=33
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EELS profile across a single particle 2nm 760800840880 Co L 2,3 -edges Ni L 2,3 -edges Energy Loss (eV) Intensity (a.u.) 0 20 40 60 80 100 1234567 Co Ni Co/Ni Concentration profile
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Pt on -alumina 1.3 Å probe Pt on -alumina 0.5 Å probe Imaging of Active Catalyst Atom Configurations Pt atoms sit in surface vacancies [001] [110]
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