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

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!

“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

Pattern formation on catalysts

200µm

J. Lauterbach, et al., Surface Science 294 (1993) 116

Ellipsomicroscopy for Surface Ellipsomicroscopy for Surface Imaging (EMSI)Imaging (EMSI)

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

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

Probing of Valence Electrons with X-rays

Atom specific

Orbital symmetry selective

Experiment--Theory

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

XASpectroelectrochemistry

• Element specific• Resolves multiple redox sites• Perfect for fuel cells

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

-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

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

Ga

EELS

1.4Å As

Z-contrast STEM

Z=31 Z=33

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

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]