Spatially Resolved and Atom Specific Microscopy and Spectroscopy “New Characterization Tools”...
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![Page 1: 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.](https://reader035.fdocuments.in/reader035/viewer/2022062517/56649f385503460f94c548df/html5/thumbnails/1.jpg)
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 statisticsaverage over sites
Local probe:poor statisticsprobes individual sites
Time resolution Spatial resolution
Species specific Site specific
Insight NN 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
200µm
J. Lauterbach, et al., Surface Science 294 (1993) 116
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Ellipsomicroscopy for Surface Ellipsomicroscopy for Surface Imaging (EMSI)Imaging (EMSI)
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P > 10-3 mbar -> EMSI
T = 540 K, CO/O2 = 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
ImageElectron emitter
Photons (uv, x-rays)
777°C 761°C
755°C
0.5 m
755°C
Dark field
TiO2 surface structure - LEEM
QuickTime™ and aDV - NTSC decompressor
are needed to see this picture.
RuO2 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 tBoth N atoms
New Ru Catalyst
Active site at steps
Hansen et.al. Science 294, 1508 (2001)
Haber-Bosch
N2 + 3H2 2NH3
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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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-40 -20 0 20 40
-4
-2
0
2
4
Paraboloid:Height h0 = 3.1 nm ± 0.1 nmradius r0 = 24 nm +2 nm(tip)Volume V = pi/2 h0 r0
2 = 2800 nm3
density [PE] = 25 molecules/nm3
TOF = 19 ± 2 molecules / s
AFM image100 x 100 nmheigth 3 nm
AFM image of polyethylene
formed by a single catalytic site:
Cr on SiO2 / 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 H2
10-13 bar (before) 1 bar H2 (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
2nm760 800 840 880
Co L2,3-edges
Ni L2,3-edges
Energy Loss (eV)
Inte
nsi
ty (
a.u.
)
0
20
40
60
80
100
1 2 3 4 5 6 7
Co
Ni
Co/Ni Concentration profile
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Pt on -alumina1.3 Å probe
Pt on -alumina0.5 Å probe
Imaging of Active Catalyst Atom Configurations
Pt atoms sit in surface vacancies
[001]
[110]